HK1122905B - Fuel battery unit cell, fuel battery unit cell array, fuel battery module, and fuel battery system - Google Patents

Description

Fuel cell unit cell, fuel cell unit cell array, fuel cell module, and fuel cell system

Technical Field

The present invention relates to a fuel cell having a pin structure or a pn structure, a fuel cell module, and a fuel cell system, and more particularly, to a fuel cell, a fuel cell array, a fuel cell module, and a fuel cell system that can effectively exhibit a catalytic action of a metal-based catalyst or an oxide-based catalyst including platinum and ruthenium and are suitable for a small-sized fuel cell.

Background

The fuel cell mainly uses a fuel gas as a fuel, and uses a hydrogen-containing gas such as hydrogen gas or methane gas, or a liquid such as methanol to react the fuel gas or the liquid fuel with oxygen in the air, or the like, thereby generating electric energy. In this case, the discharged materials are mainly water, and harmful materials such as carbon dioxide and carbon monoxide gas are extremely little discharged, and therefore, attention has been particularly paid in recent years as an environmentally friendly energy generation mechanism. Further, unlike engines and turbines, fuel cells have the advantage of generating less noise and being efficient, and therefore, active research and development is being conducted in the direction of practical use as one of promising energy generation mechanisms in the future. Further, instead of the fuel gas, a liquid fuel such as methanol may be used, and instead of the oxidizing gas such as air, a liquid oxidizing agent containing hydrogen peroxide may be used.

Fuel cells are used in a wide range of applications, and fuel cell vehicles and the like have reached a practical range. In addition, energy systems applied to facilities requiring a large amount of heat sources and electric power, such as air conditioners and hot water supplies, are being considered, and energy systems applied to general household use, use as power sources for portable terminals such as mobile phones and notebook computers, and the like are being considered.

Fig. 14 is a diagram for explaining the principle of power generation by a fuel cell, schematically showing the basic structure of a unit cell and electrochemical reactions. Fig. 14 shows an example in which methanol is used as the fuel. As shown in fig. 14, in the fuel cell, a fuel electrode (anode) 101 and an oxygen electrode (cathode) 103 are disposed to face each other, and an electrolyte layer 102 is present between the fuel electrode 101 and the oxygen electrode 103.

Methanol (CH) is supplied to the fuel electrode 101 as shown in the following formula (1)₃OH) and water (H)₂O) reaction, dissociation into hydrogen ions (H)⁺) And electron (e)^-) With the CO-production of carbon dioxide (CO)₂)。

CH₃OH+H₂O→6H⁺+6e^-+CO₂ (1)

In the electrolyte layer 102, hydrogen ions can move, but electrons cannot move. Therefore, the hydrogen ions diffuse in the electrolyte layer 102 and move to the oxygen electrode 103, and electrons move to the oxygen electrode 103 through the electric circuit 104 that connects the fuel electrode 101 and the oxygen electrode 103 to each other outside.

Oxygen (O) is supplied to the oxygen electrode 103₂) Reacts with hydrogen ions transferred from the electrolyte layer and electrons flowing from the fuel electrode as shown in the following formula (2) to generate water (H)₂O)。

6H⁺+6e^-+3/2O₂→H₂O (2)

If methanol and oxygen are continuously supplied, the reactions of the above formulas (1) and (2) continue to occur, and electrons continue to flow in the circuit 104. I.e. by continuously supplying fuel fluid (CH)₃OH、H₂Etc.) and oxidizing fluid (O)₂Etc.), the unit cell shown in fig. 14 can obtain electric current, i.e., electric power, flowing from the oxygen electrode 103 to the fuel electrode 101.

There are several types of fuel cells, and depending on the type of electrolyte, there are molten carbonate type, solid polymer type, phosphoric acid type, solid oxide type, and alkaline aqueous solution type. In these fuel cells, the operating temperatures of the molten carbonate type and the solid oxide type are high, and are 600 to 700 ℃ and 800 to 1000 ℃ respectively. Other types of operating temperatures are typically below about 200 ℃.

In the case of a fuel cell having a high operating temperature, the reaction of formula (1) proceeds at the fuel electrode by using energy at the temperature. On the other hand, in the case of a fuel cell having a low operating temperature, how to efficiently cause the above-described reaction in the fuel electrode and the oxygen electrode, in other words, how to increase the reaction rate in each electrode is an important issue. In order to promote the reactions of the formulae (1) and (2), catalysts are used for the fuel electrode 101 and the oxygen electrode 103, and platinum is generally used as the catalyst. Thus, platinum plays an extremely important role for fuel cells operating at low temperatures.

As the catalyst, besides platinum, iridium, palladium, rhodium, ruthenium, an alloy containing at least 2 of these, platinum and an alloy thereof, titanium oxide, and the like can be used. However, as a catalyst for a fuel cell, platinum is used mainly in the actual situation because platinum is most different.

In the case of a fuel cell, a porous carbon electrode is generally used for the fuel electrode 101 and the oxygen electrode 103 in order to allow a fuel fluid or an oxygen fluid to pass therethrough and promote the reaction of the formula (1) or (2) in these electrodes. In the case of a fuel cell operating at a low temperature, catalyst particles such as platinum are supported on the inner surfaces of pores of a porous electrode. As described above, the catalyst, particularly platinum having an excellent action, is an essential material for promoting the reactions of the above formulae (1) and (2).

However, platinum is a noble metal and is extremely expensive, and therefore, it is a factor of increasing the price of the fuel cell. Further, platinum is strongly bonded to CO gas, and CO poisoning occurs due to CO gas in the fuel fluid, CO gas generated by an oxidation reaction in the fuel electrode, and the like. Therefore, platinum has a disadvantage that the function as a catalyst is significantly reduced if CO poisoning occurs.

On the other hand, methanol, hydrogen gas, methane gas, and the like used in fuel cells are generally produced from natural gas hydrocarbons as a raw material, and particularly, hydrogen gas and methane gas contain a small amount of CO gas. In addition, in the case of a fuel cell using methanol, CO is formed in the oxidation process of methanol. CO therebetween is adsorbed on the surface of platinum or the like and is extremely stable. Therefore, when platinum is used as a catalyst and methanol, hydrogen, or the like is used as a fuel, the problem of CO poisoning by platinum cannot be avoided. A catalyst other than platinum may be used, but since it is inferior in catalytic effect to platinum, it has a disadvantage that the reaction rate in the fuel electrode and the oxygen electrode is inferior to platinum.

In a methanol fuel cell, it is considered that CO poisoning of platinum can be suppressed to some extent by adding ruthenium or the like to platinum. The reason for this is considered that ruthenium promotes H₂Oxidation of O to form hydroxide ions, oxidizing CO to CO₂. However, the problem of platinum poisoning cannot be said to have been solved in practice because the catalytic effect of platinum cannot be sufficiently maintained.

Therefore, when platinum is used as a catalyst and methanol or hydrogen is used as a fuel fluid, the problem of CO poisoning by platinum cannot be avoided. On the other hand, catalysts other than platinum are inferior in catalytic effect to platinum. Therefore, the current fuel cell has a disadvantage that the reaction rate between the fuel electrode and the oxygen electrode is slow.

In order to solve the above problem, a fuel cell using no platinum as a catalyst has been proposed (for example, patent document 1). The fuel cell disclosed in patent document 1 includes a fuel electrode, an oxygen electrode, and an electrolyte layer between the fuel electrode and the oxygen electrode, and the fuel electrode is made of a group III-IV compound semiconductor doped with a p-type impurity. In the case of this fuel cell, a reaction is caused in which hydrogen gas is decomposed into hydrogen radicals at the fuel electrode, and the hydrogen radicals are dissociated into hydrogen ions and electrons. Since this reaction proceeds rapidly, it is considered that platinum is not necessary. That is, it is considered that the compound semiconductor doped with the p-type impurity functions as a catalyst for dissociating hydrogen gas into hydrogen ions and electrons.

Further, a fuel cell using a pn junction semiconductor as an electrode has been proposed (for example, patent document 2). The fuel cell disclosed in patent document 2 is a single-cell type in which the entire fuel cell is provided in a mixed gas atmosphere of a fuel gas and an oxygen-containing gas, and is different from a normal double-cell type fuel cell disclosed in patent document 1, for example. The fuel cell disclosed in patent document 2 is composed of a p-type semiconductor layer in which carriers are holes, an n-type semiconductor layer in which carriers are electrons, and a pn mixed layer therebetween, and all layers are porous to the extent that a mixed gas passes through.

In the case of this fuel cell, the mechanism of power generation is considered as follows. Oxygen is adsorbed to the surface of the p-type semiconductor and polarized in the vicinity of a depletion layer (pn junction layer) interposed between the p-type semiconductor and the n-type semiconductor, and hydrogen is adsorbed to the surface of the n-type semiconductor and polarized, whereby positive charges are generated on the surface of the p-type semiconductor and negative charges are generated on the surface of the n-type semiconductor. Adsorbed hydrogen ion (H)⁺) And oxygen ion (O)^2-) React to generate water (H)₂O) is a series of processes, electrons in a valence band in the p-type semiconductor near the depletion layer (pn junction layer) are excited to generate holes in the valence band, and in the generated electron-hole pairs, electrons move to the n-type semiconductor and holes move to the p-type semiconductor side. Based on such a mechanism, it is considered thatCathode) and an n-type semiconductor (anode), and the potential difference can be taken out as electric power.

In the fuel cells using semiconductors disclosed in patent documents 1 and 2, a catalyst is not used. In the fuel electrode and the oxygen electrode, in order to efficiently cause the reaction of the formula (1) or (2), a catalyst is preferably used, and platinum is particularly preferably used. However, as described above, how to promote the reaction between the fuel electrode and the oxygen electrode is a problem, and particularly, when platinum is used as the catalyst, how to prevent CO poisoning of platinum is an important issue. However, no effective measures have been actually taken for improving the reaction rate when a catalyst is used and preventing CO poisoning of platinum, and further improvement of the catalytic activity of platinum is required.

Further, in the conventional methanol fuel cell, there is a big problem called "methanol crossover". The methanol crossover refers to a phenomenon in which methanol supplied to the fuel electrode moves to the oxygen electrode through an intermediate layer such as an electrolyte layer, and reacts at the oxygen electrode to cancel out the power generation effect.

That is, in the conventional fuel cell, methanol crosses from a fuel electrode (anode) to an oxygen electrode (cathode) through an electrolyte, and reacts with oxygen in the oxygen electrode, thereby generating heat without generating electricity. Therefore, a loss of methanol is generated, and the generation voltage of the fuel cell is lowered. For example, it is considered that a voltage drop of 100mV to 140mV occurs at a predetermined current density in the cathode.

Patent documents 3 and 4 describe a method of controlling methanol crossover, and it cannot be said that a sufficient effect is obtained in practice, and the problem of methanol crossover is solved.

Another problem with methanol fuel cells is that activation of the anode is necessary to further increase the potential of the anode as compared to hydrogen fuel cells. As a countermeasure, in order to increase the reaction rate, a large amount of catalyst must be used on the electrode surface. When the amount of the catalyst is large, the cost of the fuel cell increases, and therefore, there arises a problem that the cost must be reduced.

Further, in the existing fuel cell using a solid polymer electrolyte, a catalyst is formed on both sides of the solid electrolyte supported by, for example, carbon powder. In this case, the effect of the catalyst cannot be exhibited efficiently. Further, since the surface area (two-dimensional surface area) is limited, miniaturization in a low-power direct methanol fuel cell is difficult. In order to increase the reaction rate and improve the power generation efficiency, it is necessary to establish an effective method for using the catalyst. As one of the measures, it is required to increase the area of the electrode surface and reduce the amount of catalyst used in the electrode.

Further, development of a small fuel cell for portable terminals such as portable telephones and notebook computers has been desired. In order to meet this demand, it is necessary to miniaturize the electrodes by increasing the reaction rate between the oxygen electrode and the fuel electrode, but in the case of a fuel cell having a low operating temperature, the miniaturization of the fuel cell cannot be achieved without actually solving the above-described problems.

Patent document 1: japanese unexamined patent application publication No. 2004-319250

Patent document 2: japanese laid-open patent publication No. 2004-199877

Patent document 3: U.S. Pat. No. 5,599,638

Patent document 4: specification of U.S. Pat. No. 5,919,583

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made to solve the above problems, and an object of the present invention is to provide a fuel cell, a fuel cell array, a fuel cell module, and a fuel cell system, which can effectively exhibit a catalytic action of a metal-based catalyst or an oxide-based catalyst including platinum, can suppress CO poisoning of platinum, and can be reduced in size and cost.

Means for solving the problems

A fuel cell (1) according to the present invention for solving the above problems is characterized in that: the fuel cell has a pin structure including a fuel electrode made of a p-type semiconductor, an oxygen electrode made of an n-type semiconductor, and an intermediate layer made of an intrinsic semiconductor and present between the fuel electrode and the oxygen electrode, the fuel electrode being porous and permeable to a fuel fluid, a metal catalyst layer is formed on the inner surface of the pores of the porous portion, the oxygen electrode is porous and permeable to oxidizing fluid, a metal catalyst layer is formed on the inner surface of the pores of the porous portion, the intermediate layer is porous and can hold an electrolyte solution, and has a property of allowing hydrogen ions generated in the fuel electrode to pass therethrough and preventing electrons from passing therethrough, the fuel electrode is configured to supply a fuel fluid containing hydrogen to a surface of the fuel electrode and an oxidizing fluid containing oxygen to a surface of the oxygen electrode, and has connection terminals electrically connected to the fuel electrode and the oxygen electrode, respectively.

Further, a fuel cell (2) according to the present invention is characterized in that: the fuel cell has a p-n structure including a fuel electrode made of a p-type semiconductor, an oxygen electrode made of an n-type semiconductor, and an intermediate layer present between the fuel electrode and the oxygen electrode, wherein the fuel electrode is porous and permeable to a fuel fluid, a metal-based catalyst layer is formed on an inner surface of a hole of the porous portion, the oxygen electrode is porous and permeable to an oxidizing fluid, the metal-based catalyst layer is formed on an inner surface of a hole of the porous portion, the intermediate layer is formed on at least one side of the fuel electrode and the oxygen electrode, is porous and can hold an electrolyte solution, and has a property of allowing hydrogen ions generated by the fuel electrode to permeate therethrough without allowing electrons to pass therethrough, and the fuel electrode and the oxygen electrode are joined to each other at a surface on which the intermediate layer is formed so as to supply a fuel fluid containing hydrogen to a surface of the fuel electrode, the fuel electrode is configured to supply an oxidizing fluid containing oxygen to a surface of the oxygen electrode, and has a connection terminal electrically connected to the fuel electrode and the oxygen electrode, respectively.

Further, a fuel cell (3) according to the present invention is characterized in that: has a pn-pn structure comprising: a fuel electrode having a pn junction region in which a fuel fluid supply surface side is formed of a p-type semiconductor layer and another surface is formed of an n-type semiconductor layer, an oxygen electrode having a pn junction region in which an oxidizing fluid supply surface side is formed of an n-type semiconductor layer and another surface is formed of a p-type semiconductor layer, and an electrolyte layer as an intermediate layer between the n-type semiconductor layer of the fuel electrode and the p-type semiconductor layer of the oxygen electrode, wherein the fuel electrode is porous, the p-type semiconductor layer of the fuel electrode is thicker than the n-type semiconductor layer and is permeable to a fuel fluid, a metal-based catalyst layer is formed on an inner surface of a hole of the porous portion, the n-type semiconductor layer is impermeable to a fuel fluid, the oxygen electrode is porous, and the n-type semiconductor layer of the oxygen electrode is thicker than the p-type semiconductor layer and is permeable to an oxidizing fluid, the intermediate layer contains an electrolyte solution and has a property of transmitting hydrogen ions generated by the fuel electrode, is configured to supply a fuel fluid containing hydrogen to the surface of the fuel electrode and an oxidizing fluid containing oxygen to the surface of the oxygen electrode, and has a connection terminal electrically connected to the fuel electrode and the oxygen electrode, respectively.

Further, a fuel cell (4) according to the present invention is characterized in that: in any one of the fuel cell units (1) to (3), at least one of the fuel electrode and the oxygen electrode is light-transmissive.

Further, a fuel cell (5) according to the present invention is characterized in that: in any one of the fuel cell units (1) to (3), the electrolyte in the intermediate layer is irradiated with light.

Further, a fuel cell (6) according to the present invention is characterized in that: in any one of the fuel cell units (1) to (3), a metal-based conductive layer is provided between the catalyst layer and the inner surface of the void in at least one of the fuel electrode and the oxygen electrode.

Further, a fuel cell (7) according to the present invention is characterized in that: in any one of the fuel cell units (1) to (3), the fuel fluid is methanol or hydrogen.

Further, a fuel cell (8) according to the present invention is characterized in that: in the fuel cell (1) or (2), the diameter of the pores of the porous portion having fuel fluid permeability in the fuel electrode and the diameter of the pores of the porous portion having oxidizing fluid permeability in the oxygen electrode are in the order of micrometers, and the diameter of the pores of the porous portion in the intermediate layer is in the order of nanometers.

Further, a fuel cell (9) according to the present invention is characterized in that: in the fuel cell unit cell (3), the diameter of the hole of the p-type semiconductor layer in the fuel electrode and the diameter of the hole of the n-type semiconductor layer in the oxygen electrode are in the order of micrometers, and the diameter of the hole of the n-type semiconductor layer in the fuel electrode and the diameter of the hole of the p-type semiconductor layer in the oxygen electrode are in the order of nanometers.

Further, a fuel cell (10) according to the present invention is characterized in that: in any one of the fuel cell units (1) to (3), the semiconductor material constituting the fuel electrode, the oxygen electrode, and the intermediate layer is any one of silicon, germanium, and an oxide semiconductor including titanium oxide.

Further, a fuel cell (11) according to the present invention is characterized in that: in any one of the fuel cell units (1) to (3), the metal-based catalyst constituting the metal-based catalyst layer is one of platinum, iridium, palladium, rhodium, ruthenium, and an alloy containing at least 2 of these, or titanium oxide.

Further, a fuel cell (12) according to the present invention is characterized in that: in any one of the fuel cell units (1) to (3), the electrolyte solution is acidic.

The fuel cell array (1) according to the present invention is characterized by being configured in such a manner that: a plurality of the fuel cell units of any one of the fuel cell units (1) to (3) are arranged in a planar manner, and are electrically connected in parallel and/or in series, so that electric power generated by the plurality of the fuel cell units is concentrated and output.

The fuel cell array (2) according to the present invention is characterized by being configured in such a manner that: a plurality of the fuel cell units of any one of the fuel cell units (1) to (3) are stacked via the fuel fluid supply means, the oxidizing fluid supply means, and the light introduction means, and are electrically connected in series, and the electric power generated by the plurality of the fuel cell units is added and output.

The fuel cell module according to the present invention is characterized in that: the fuel cell system is provided with the fuel cell array (1), a fuel fluid supply unit, and an oxidizing fluid supply unit, wherein the fuel cell array is arranged between the fuel fluid supply unit and the oxidizing fluid supply unit so that a fluid does not permeate between the fuel fluid supply unit and the oxidizing fluid supply unit, a fuel electrode of the fuel cell array faces the fuel fluid supply unit, an oxygen electrode of the fuel cell array faces the oxidizing fluid supply unit, the fuel fluid supply unit has a fuel introduction unit and a fluid discharge unit, the oxidizing fluid supply unit has an oxidizing fluid introduction unit and a fluid-water discharge unit, and a wall portion of a wall portion surrounding the fuel fluid supply unit and facing the fuel electrode and/or a wall portion of a wall portion surrounding the oxidizing fluid supply unit and facing the oxygen electrode is made of a material that transmits a reactive light, the fuel cell system has an output mechanism for outputting electric power generated and concentrated by the fuel cell array.

The fuel cell system according to the present invention is characterized in that: the fuel cell system is configured such that a plurality of the fuel cell modules are combined into a single unit and connected so as to concentrate the electric power output from the output means of each of the fuel cell modules, and has a fuel cell output unit for outputting the concentrated electric power, and a DC-DC converter electrically connected to the fuel cell output unit.

The term "micron-sized" as used herein means mainly not less than 1 μm and less than 1 mm. The term "nanoscale" mainly means 1nm or more and less than 1 μm. The fuel fluid is a fluid fuel such as methanol or hydrogen, and the oxidizing fluid is a fluid oxidizing substance such as oxygen, air, or a hydrogen peroxide solution.

Effects of the invention

According to the fuel cell units (1) to (12) described above, the fuel cell units basically have a pin or pn junction structure, and the electrolyte solution is located between the p-type semiconductor layer and the n-type semiconductor layer. In these fuel cell units, light is not necessarily irradiated, but when light is irradiated, the catalytic action in the fuel electrode is significantly activated by holes generated by the photoelectric effect, and the catalytic action in the oxygen electrode is significantly activated by electrons generated by the photoelectric effect. In other words, the oxidation reaction rate in the fuel electrode and the reduction reaction rate in the oxygen electrode are significantly increased. This is because oxidation of a fuel fluid such as methanol in the fuel electrode is promoted by a strong oxidation action of holes reaching the fuel electrode, and reduction of an oxidizing fluid in the oxygen electrode is promoted by photoelectrons reaching the oxygen electrode. In addition, the double layer effect (double layer effect) is improved by utilizing the electric field between the electrode and the electrolyte part generated by the photoelectric effect. Therefore, an effect of further promoting the reaction is obtained, and the current density and the energy density of the reaction increase.

In the case of the pin or pn structure, both the electrode and the electrolyte region can be formed on 1 silicon substrate, and therefore a compact, low-cost, high-energy-density fuel cell can be obtained.

Therefore, when the power generation of the fuel cell is constant, the required amount of the catalyst used for the fuel electrode and the oxygen electrode can be reduced, and the electrode, the fuel cell, and the fuel cell can be downsized. In addition, since the catalytic action is activated, a less expensive catalyst can be used. In addition, when the size of the fuel cell unit cell, the amount of the catalyst used, and the like are fixed, the amount of generated electric power per unit cell can be significantly increased.

In particular, when platinum is used as the catalyst, even if a small amount of CO gas is contained in the fuel fluid or CO gas is generated from the fuel fluid, the activity of the reaction in the fuel electrode is high, and therefore, the CO gas is easily oxidized to CO₂. Therefore, even if platinum is used as the catalyst, the problem of CO poisoning by platinum, which is an important problem that is difficult to solve for a general fuel cell, can be solved.

In addition, when a metal-based conductive layer is provided between the inner surface of the hole and the catalyst layer in at least one of the fuel electrode and the oxygen electrode, methanol crossover can be substantially prevented even when methanol is used as the fuel fluid. Therefore, loss of methanol can be prevented, and power generation efficiency can be improved.

Since the fuel cell has the above-described features, the fuel cell according to the present invention can achieve excellent effects of increasing the output, reducing the cost, reducing the size, increasing the life, and the like of the fuel cell by utilizing the features.

Further, according to the fuel cell array (1) or (2), since the cell array is constituted by any one of the fuel cells (1) to (3), it is possible to obtain a fuel cell array having the features of the fuel cells (1) to (3).

Further, according to the fuel cell module, since the fuel cell module is constituted by the fuel cell array (1), it is possible to obtain a fuel cell module having any one of the fuel cells (1) to (3) and the features of the fuel cell array (1).

Further, according to the fuel cell system, since the fuel cell system is formed by the fuel cell module, it is possible to obtain a fuel cell system having the features of any one of the fuel cell units (1) to (3), the fuel cell unit cell array (1), and the fuel cell module. Further, since the fuel cell system includes the DC-DC converter, an output voltage required for the fuel cell system can be easily generated. In particular, since a small fuel cell system is obtained, it is extremely suitable as a power source for portable telephones and personal computers.

Drawings

Fig. 1A is a perspective view schematically showing the basic structure of a fuel cell according to embodiment 1 of the present invention.

FIG. 1B is an enlarged partial cross-sectional view schematically showing a cross-sectional view taken along line IB-IB' shown in FIG. 1A.

Fig. 2A is a perspective view schematically showing the basic structure of a fuel cell according to embodiment 2 of the present invention.

Fig. 2B is a partially enlarged sectional view schematically showing a structure of a cross section taken along line IIB-IIB' shown in fig. 2A.

Fig. 3A is a perspective view schematically showing the basic structure of a fuel cell according to embodiment 3 of the present invention.

Fig. 3B is a partially enlarged cross-sectional view schematically showing a structure of a cross section taken along line IIIB-IIIB' shown in fig. 3A.

Fig. 4A is a schematic plan view showing an example of the distribution and shape of the pores of the fuel electrode.

Fig. 4B is a schematic plan view showing another example of the distribution and shape of the pores of the fuel electrode.

Fig. 5 is a partially enlarged cross-sectional view schematically showing a region composed of micro-scale voids and nano-scale voids.

Fig. 6 is a diagram illustrating a method of forming a porous portion having a predetermined pattern, and is a diagram showing a cross-sectional structure of a substrate in a process of performing pre-etching on the substrate on which the porous portion is formed.

Fig. 7 is a diagram illustrating a method of forming a porous portion having a predetermined pattern, and is a schematic cross-sectional view illustrating a method of further etching a substrate after pre-etching by an anodic etching method.

Fig. 8 is a schematic perspective view showing an example of a supply mechanism for the fuel fluid and the oxidizing fluid.

Fig. 9 is a schematic perspective view showing another example of the supply mechanism of the fuel fluid and the oxidizing fluid.

Fig. 10A is a schematic diagram showing a unit cell array according to the embodiment of the present invention, and is a cross-sectional view showing a unit cell array in which unit cells are connected in parallel.

Fig. 10B is a schematic diagram showing a cell array according to the embodiment of the present invention, and is a cross-sectional view showing a cell array in which cells are connected in series.

Fig. 10C is a schematic diagram showing a cell array according to the embodiment of the present invention, and is a perspective view showing the cell array in which cells are connected in the vertical and horizontal directions.

Fig. 11 is a cross-sectional view schematically showing the structure of a unit cell array according to another embodiment of the present invention.

Fig. 12A is a sectional view schematically showing a fuel cell module according to an embodiment of the invention.

Fig. 12B is a sectional view schematically showing a fuel cell module according to another embodiment of the invention.

Fig. 13 is a block diagram showing the configuration of a fuel cell system according to the embodiment of the present invention.

Fig. 14 is a diagram for explaining the principle of power generation of a fuel cell, and is a schematic diagram showing the basic structure and electrochemical reaction of a unit cell.

Detailed Description

A fuel cell unit cell, a fuel cell unit cell array, a fuel cell module, and a fuel cell system according to embodiments of the present invention will be specifically described below with reference to the accompanying drawings. In the drawings shown below, the same components and positions of actions are denoted by the same reference numerals, and redundant description is omitted.

Fig. 1A is a perspective view schematically showing the basic structure of a fuel cell according to embodiment 1 of the present invention (hereinafter, the fuel cell is simply referred to as a cell). Fig. 1B is a partially enlarged cross-sectional view schematically showing a structure of a cross section taken along line IB-IB' shown in fig. 1A.

Referring to fig. 1A and 1B, the basic configuration and operation principle of the unit cell 1 according to the embodiment will be described below. In the following description, the fuel fluid is methanol, and the oxidizing fluid is oxygen.

The unit cell 1 has a pin type junction structure composed of 3 layers of a p-type semiconductor layer, an n-type semiconductor layer, and an i-type semiconductor layer (intrinsic semiconductor layer) therebetween. The 1 st layer is a fuel electrode 11 constituting an anode and is composed of a p-type semiconductor layer doped with a p-type impurity element such as boron or aluminum. The 2 nd layer is an intermediate layer 12 constituting an electrolytic region and is composed of an intrinsic semiconductor layer not doped with an impurity element (undoped). The 3 rd layer is an oxygen electrode 13 constituting a cathode and is composed of an n-type semiconductor layer doped with an n-type impurity element such as phosphorus or arsenic.

The fuel electrode l1, the intermediate layer 12, and the oxygen electrode 13 are preferably made of porous silicon, for example. In the fuel electrode 11 as a p-type semiconductor layer and the oxygen electrode 13 as an n-type semiconductor layer, as shown in fig. 1B, holes 15a and 15B are formed, and the holes 15a and 15B are separated by walls 16a and 16B, respectively. The fuel electrode 11 and the oxygen electrode 13 are permeable to fuel fluid such as methanol and hydrogen gas, and oxidizing fluid such as oxygen, air, and hydrogen peroxide solution, that is, fuel fluid and oxidizing fluid can enter the pores 15a and 15b of the respective layers. Further, a void 19 is also formed in the intermediate layer.

Here, the diameters of the pores 15a and 15b of the fuel electrode 11 and the oxygen electrode 13 are preferably larger than the diameter of the pores 19 of the intermediate layer 12. For example, the former is in the micron-scale, for example, 20 μm or less, preferably 4 to 8 μm, and the latter is preferably in the nanometer-scale. However, when a gaseous substance such as hydrogen is used as the fuel fluid, the diameters of the pores 15a and 15b of the fuel electrode 11 and the oxygen electrode 13 and the diameter of the pores 19 of the intermediate layer 12 may be substantially equal to each other, and may be on the order of nanometers. In the present specification, the term "diameter" refers to the diameter of the inside of the hole, and for example, when the hole is not circular but is square, it refers to the average diameter of the inside. When voids having different diameters are present, the average diameter of the voids is referred to.

The inner surfaces of the pores 15a and 15b of the fuel electrode 11 and the oxygen electrode 13 are coated with a catalyst such as platinum, ruthenium, or an alloy thereof. Further, it is preferable to have a conductive metal layer such as palladium, nickel, tantalum, niobium, or the like between the inner surface of the holes 15a and 15b and the catalyst layer. The fuel electrode 11 and/or the oxygen electrode 13 are preferably light-transmissive, and are preferably configured such that light reaches the intermediate layer 12 through the fuel electrode 11 and the oxygen electrode 13. When the fuel electrode 11 and the oxygen electrode 13 are not light-transmissive, it is preferable to have a mechanism such as an optical fiber for guiding light into the intermediate layer 12.

Further, the fuel electrode 11 and the oxygen electrode 13 are provided with connection terminals (not shown) corresponding to connection portions with the external circuit 14.

The pores 19 of the intermediate layer 12 are impregnated with an electrolyte solution held therein by a static force generated by capillary action. As the electrolyte solution, sulfuric acid solution (H)₂SO₄) Phosphoric acid solution (H)₃PO₄) And an acidic solution such as trifluoromethanesulfonic acid is suitable. The electrolyte solution does not necessarily have to be an acidic solution, and may be, for example, an alkaline solution or water. This is because hydrogen ions can move from the fuel electrode 11 to the oxygen electrode 13 even if the solution held in the intermediate layer 12 is an alkaline solution or water. Therefore, in this specification, the electrolyte solution also includes an alkaline solution and water.

Examples of the semiconductor material for the fuel electrode 11, the intermediate layer 12, or the oxygen electrode 13 include IV semiconductors such as silicon and germanium including single crystal silicon, polycrystalline silicon, and amorphous silicon, III-IV compound semiconductors such as gallium-arsenic, indium-phosphorus, and aluminum-gallium-arsenic, II-VI compound semiconductors such as cadmium sulfide and copper sulfide, and oxide semiconductors such as titanium oxide, zinc oxide, nickel oxide, tin oxide, iron oxide, cobalt oxide, ferroferric oxide, and copper oxide, and materials that can constitute p-type semiconductors, n-type semiconductors, and intrinsic semiconductors can be used. Of these semiconductor materials, the material used for the fuel electrode 11 and the oxygen electrode 13 is porous and has a property of transmitting a fluid such as a gas or a liquid (fluid permeability).

In addition, a porous material capable of forming an intrinsic semiconductor layer among the above semiconductor materials can be used in the intermediate layer 12. Such as silicon, germanium, etc., which are not doped with impurities. Further, the material used in the intermediate layer 12 has a property of being capable of holding an electrolyte solution or water by capillary force of the pores.

The p-type semiconductor layer of the fuel electrode 11 and the n-type semiconductor layer of the oxygen electrode 13 are thicker than the intermediate layer 12, the former is preferably of micron order, particularly preferably 200 to 500 μm, and the latter is preferably 200 μm or less, particularly preferably 80 μm or less.

As the catalyst used for the catalyst layer covering the inner surfaces of the pores of the fuel electrode 11 and the oxygen electrode 13, noble metals such as iridium, palladium, rhodium, and ruthenium, or alloys containing at least two of them are also suitable in addition to platinum. Further, titanium oxide may be used. Among them, platinum has the most excellent catalytic action. The coating of the metal-based catalyst on the inner walls of the holes of the fuel electrode 11 and the oxygen electrode 13 can be performed by a method such as an atomic layer growth method, a surface organometallic chemical method (surface organometallic chemical method), a plating method, a sputtering method using plasma, or vapor deposition by a CVD method. The atomic layer growth method and the surface organometallic chemical method are particularly suitable for coating of the metal-based catalyst. In the present specification, the catalyst including titanium oxide is referred to as a "metal-based catalyst".

The conductive metal layer can be coated on the inner surfaces of the holes 15a and 15b of the fuel electrode 11 and the oxygen electrode 13 by an atomic layer growth method, an electroplating method, an electrodeposition method, or the like.

Fig. 2A is a perspective view schematically showing the basic structure of a cell according to embodiment 2 of the present invention. Fig. 2B is a partially enlarged sectional view schematically showing a structure of a cross section taken along line IIB-IIB' shown in fig. 2A.

The unit cell 2 shown in fig. 2A and 2B has a pn-junction structure, and is composed of three layers of a p-type semiconductor layer 21, an n-type semiconductor layer 23, and an intermediate layer 22 therebetween. The p-type semiconductor layer as the 1 st layer is a fuel electrode 21 constituting an anode, and is doped with a p-type impurity such as boron or aluminum. Layer 2 is the intermediate layer 22 that constitutes the electrolytic zone. The n-type semiconductor layer as the 3 rd layer is an oxygen electrode 23 constituting a cathode, and is doped with an n-type impurity element such as phosphorus or arsenic.

The intermediate layer 22 is composed of an intermediate layer 22a formed on the 1 surface side of the silicon substrate constituting the fuel electrode 21, and an intermediate layer 22b formed on the 1 surface side of the silicon substrate constituting the oxygen electrode 23. Such an intermediate layer 22 has the advantage of ease of manufacture of the unit cells 2. The intermediate layer 22 may be formed not on both surfaces of the fuel electrode 21 and the oxygen electrode 23, but on only one of them. That is, the intermediate layer 22a and the intermediate layer 22b may be formed. The unit cell 2 is preferably formed by bonding the intermediate layers 22a and 22b to each other.

The fuel electrode 21, the intermediate layer 22 and the oxygen electrode 23 are preferably all composed of porous silicon. In the fuel electrode 21 as a p-type semiconductor layer and the oxygen electrode 23 as an n-type semiconductor layer, as shown in fig. 2B, holes 25a and 25B are formed, and the holes 25a and 25B are separated by walls 26a and 26B, respectively. The fuel electrode 21 and the oxygen electrode 23 are permeable to a fuel fluid such as methanol and an oxidizing fluid such as oxygen, i.e., the fuel fluid and the oxidizing fluid can enter the pores 25a and 25b of the respective layers. Further, the intermediate layer 22 also has a void 29 formed therein.

The diameter of the pores 25a and 25b of the fuel electrode 21 and the oxygen electrode 23 is preferably larger than the diameter of the pores 29 of the intermediate layer 22. For example, the former is preferably in the micron-sized range, for example, 20 μm or less, preferably 4 to 8 μm, and the latter is preferably in the nanometer-sized range. However, when a gaseous substance such as hydrogen is used as the fuel fluid, the diameters of the pores 25a and 25b of the fuel electrode 21 and the oxygen electrode 23 and the diameter of the pores 29 of the intermediate layer 22 may be substantially equal to each other, and may be all on the order of nanometers, for example.

The inner surfaces of the pores 25a and 25b of the fuel electrode 21 and the oxygen electrode 23 are coated with a noble metal such as platinum, iridium, palladium, rhodium, or ruthenium, or an alloy containing at least two of these metals. Further, it is preferable to have a conductive metal layer such as palladium, nickel, tantalum, niobium, or the like between the inner surfaces of the holes 25a and 25b and the catalyst layer.

The pores 29 of the intermediate layer 22 are impregnated with an electrolyte solution, and the electrolyte solution is held in the pores by a static force generated by a capillary. As the electrolyte solution, the same solution as in embodiment 1 can be used.

At least one of the fuel electrode 21 and the oxygen electrode 23 is preferably light-transmissive, and is preferably configured such that light reaches the intermediate layer 22 through the fuel electrode 21 or the oxygen electrode 23. When the fuel electrode 21 and the oxygen electrode 23 are not light-transmissive, it is preferable to have a mechanism such as an optical fiber for guiding light into the intermediate layer 22.

Further, the fuel electrode 21 and the oxygen electrode 23 are provided with connection terminals (not shown) corresponding to the connection portions of the external circuit 14.

Fig. 3A is a perspective view schematically showing the basic structure of a cell according to embodiment 3 of the present invention. Fig. 3B is a partially enlarged cross-sectional view schematically showing a structure of a cross section taken along line IIIB-IIIB' shown in fig. 3A.

The unit cell 3 shown in fig. 3A and 3B is composed of 2 pn-type semiconductor layers having 1 st and 2 nd pn-type junction structures and 3 layers of an intermediate layer therebetween, which are arranged as pn-intermediate layer-pn from the fuel electrode side. The layer 1 is a fuel electrode 31 constituting an anode, and is composed of a p-type semiconductor layer 31a doped with a p-type impurity element such as boron or aluminum, and an n-type semiconductor layer 31b doped with an n-type impurity element such as phosphorus or arsenic. Layer 2 is an intermediate layer 32 that constitutes the electrolyte region. The 3 rd layer is an oxygen electrode 33 constituting a cathode, and is composed of an n-type semiconductor layer 33a doped with an n-type impurity element such as phosphorus or arsenic, and a p-type semiconductor layer 33b doped with a p-type impurity element such as boron or aluminum.

The fuel electrode 31 and the oxygen electrode 33 are preferably made of porous silicon, for example. As shown in fig. 3B, holes 35a and 35B are formed in the fuel electrode 31 and the oxygen electrode 33, which are semiconductor layers of a pn junction structure, and the holes 35a and 35B are partitioned by walls 36a and 36B, respectively. The p-type semiconductor layer 31a of the fuel electrode 31 and the n-type semiconductor layer 33a of the oxygen electrode 33 are permeable to a fuel fluid such as methanol and an oxidizing fluid such as oxygen, respectively, and the fuel fluid and the oxidizing fluid can enter the pores 35a and 35b of the respective layers.

Here, the diameters of the holes 35a and 35b formed in the p-type semiconductor layer 31a of the fuel electrode 31 and the n-type semiconductor layer 33a of the oxygen electrode 33 are preferably larger than the diameters of the holes 39 formed in the n-type semiconductor layer 31b of the fuel electrode 31 and the p-type semiconductor layer 33b of the oxygen electrode 33, the former being preferably on the order of micrometers, for example, 20 μm or less, preferably 4 to 8 μm, and the latter being preferably on the order of nanometers. However, when a gaseous substance such as hydrogen is used as the fuel fluid, the diameters of the holes 35a and 35b formed in the p-type semiconductor layer 31a of the fuel electrode 31 and the n-type semiconductor layer 33a of the oxygen electrode 33 may be substantially equal to the diameters of the holes 39 formed in the n-type semiconductor layer 31b of the fuel electrode 31 and the p-type semiconductor layer 33b of the oxygen electrode 33, and may be all on the order of nanometers, for example.

The thickness of the p-type semiconductor layer 31a of the fuel electrode 31 and the n-type semiconductor layer 33a of the oxygen electrode 33 is preferably larger than the thickness of the n-type semiconductor layer 31b of the fuel electrode 31 and the p-type semiconductor layer 33b of the oxygen electrode 33, the former being preferably on the order of micrometers and particularly preferably 300 to 500 μm, and the latter being preferably 50 μm or less and particularly preferably 10 μm or less.

The inner surfaces of the pores 35a of the p-type semiconductor layer 31a of the fuel electrode 31 and the pores 35b of the n-type semiconductor layer 33a of the oxygen electrode 33 are coated with a catalyst such as a noble metal such as platinum, iridium, palladium, rhodium, or ruthenium, or an alloy containing at least two of these metals. It is preferable to have a conductive metal layer of palladium, nickel, tantalum, niobium, or the like between the inner surfaces of the holes 35a, 35b and the catalyst layer.

The intermediate layer 32 is sealed up and down by sealing plates 34a, 34b, and the space between the fuel electrode 31 and the oxygen electrode 33 is filled with the same electrolyte solution as that used in the embodiments 1 and 2.

At least one of the fuel electrode 31 and the oxygen electrode 33 is preferably light-transmissive, and is preferably configured such that light reaches the intermediate layer 32 through the fuel electrode 31 or the oxygen electrode 33. When the fuel electrode 31 and the oxygen electrode 33 are not light-transmissive, at least one of the sealing plates 34a and 34b is preferably light-transmissive, and is preferably configured such that light reaches the intermediate layer 32 through the sealing plate 34a or 34 b. Further, a mechanism such as an optical fiber for guiding light into the intermediate layer 32 may be provided.

Further, the fuel electrode 31 and the oxygen electrode 33 are provided with connection terminals (not shown) corresponding to the connection portions of the external circuit 14.

Fig. 1B, 2B, and 3B show examples of patterns in which the cross-sectional shapes of the pores of the fuel fluid passing portion of the fuel electrode and the oxidizing fluid passing portion of the oxygen electrode are the same quadrangle and have a regular shape. However, the size and shape of the holes are not necessarily constant, and the holes may be different in size and shape. Further, the depth direction may not be linear but a curved shape. The pattern of the shape, distribution, etc. of the holes when the fuel electrode and the oxygen electrode are viewed on the plane is not limited to a specific pattern.

Fig. 4A and 4B are schematic plan views showing examples of the distribution and shape of the pores of the fuel electrode. Fig. 4A and 4B show an example of the fuel electrode 11 of the unit cell 1 according to embodiment 1. The holes 15a shown in fig. 4A are an example in which holes having a constant planar shape are regularly arranged. The planar shape of the holes 15a is not necessarily constant, and may be formed of holes having different shapes, or may be irregularly distributed. The pores 15a 'of the fuel electrode 11A shown in fig. 4B are in an example of irregular planar shape and are divided by walls 16 a' to be irregularly distributed. As described above, the planar shape of the empty holes 15 a' may be amorphous, and may be irregularly distributed.

The generated current of the unit cells 1 to 3 is mainly determined by the area of the unit cells 1 to 3 and the impurity concentration of the fuel electrode and the oxygen electrode. From the viewpoint of proper performance, commercial scale production, and the like, the size of the unit cells 1 to 3 is preferably 5 to 30mm in length and width, and the thickness is preferably in the order of micrometers to several mm.

In the case of the unit cells 1 to 3 according to embodiments 1 to 3 configured as described above, the reaction between the fuel electrode and the oxygen electrode can be activated, and electric power can be efficiently generated. The reason for this will be mainly described below with respect to the unit cell 1 according to embodiment 1. The unit cells 2 and 3 according to embodiment 2 or 3 are mentioned as necessary.

Methanol and water (H) are supplied as fuel fluid to the surface of the fuel electrode 11, for example₂O), the reaction of the formula (1) shown above occurs, and the dissociation into hydrogen ions (H) occurs⁺) And electron (e)^-) Producing carbon dioxide (CO)₂). Since the intermediate layer 12 is an intrinsic semiconductor layer, electrons cannot move in the intermediate layer 12. In the case of the unit cell 2, a pn junction is present between the fuel electrode 21 and the oxygen electrode 23, and in the case of the unit cell 3Since the pn junction exists in the fuel electrode 31 and the oxygen electrode 33, electrons can be prevented from moving from the fuel electrode to the oxygen electrode by this region. Further, in the case of the unit cell 3, since the intermediate layer 32 is composed of an electrolyte solution, the movement of electrons is prevented in the intermediate layer 32.

On the other hand, hydrogen ions can move to the oxygen electrode 13 through the electrolyte solution held in the pores 19 of the intermediate layer 12 (the pores 29 of the intermediate layer 22 in the case of the cell 2, and the intermediate layer 32 in the case of the cell 3). In the oxygen electrode 13, the electrons moving to the oxygen electrode 13 through the external circuit 14, the hydrogen ions moving through the electrolyte solution in the intermediate layer 12, and the oxygen gas supplied to the surface of the oxygen electrode 13 react with each other in the formula (2) to generate water (H)₂O)。

In the case of the unit cell 1 according to embodiment 1, the activity of the reaction between the fuel electrode 11 and the oxygen electrode 13 is significantly activated by the mechanism described below, and therefore, the above-described series of reaction rates are significantly improved. That is, the unit cell 1 has a pin structure, and the intermediate layer 12 (the intermediate layer 22 in the case of the unit cell 2 and the combination of the pn junction between the fuel electrode 31 and the oxygen electrode 33 and the intermediate layer 32 in the case of the unit cell 3) which is an intrinsic semiconductor layer (i layer) plays an important role which is not possessed by the conventional fuel cell.

In a state of thermal equilibrium, holes move from the fuel electrode 11 of the p-type semiconductor layer to the intermediate layer 12, and electrons move from the oxygen electrode 13 of the n-type semiconductor layer to the intermediate layer 12. Thus, the holes and electrons recombine in the intermediate layer 12 to form a depletion region. As a result, a strong electric field is generated from the oxygen electrode 13 to the fuel electrode 11.

Excited electrons and holes of the above state are generated. In particular, when light reaches the inside of the intermediate layer 12, excited electrons and holes are generated more efficiently because the light is irradiated to the vicinity of a depletion layer existing in the intermediate layer 12. If electrons and holes are generated, they are accelerated by an electric field based on the depletion layer, the electrons move to the oxygen electrode 13 of the n-type semiconductor layer, and the holes move to the fuel electrode 11 of the p-type semiconductor layer. The potential difference between the fuel electrode 11 and the oxygen electrode 13, that is, between the anode and the cathode is balanced with the potential of the intermediate layer 12 by the movement of the electrons and the holes.

In the case of a solar cell having a pin structure, a large number of holes and electrons are generated by high-intensity sunlight, and the holes and electrons move due to the generated potential difference, and therefore, the potential difference is used as a power source. However, in the case of the unit cells 1 to 3 according to embodiments 1 to 3, since a necessary potential difference can be generated with as little current as possible, light is not necessarily necessary, and the intensity of light may be weak even in the case of irradiation with light. The generated potential difference can promote the reaction in each of the fuel electrode 11 and the oxygen electrode 13, and the catalytic effect in each electrode can be significantly improved. In this way, the oxidation reaction in the fuel electrode 11 and the reduction reaction in the oxygen electrode 13 are significantly activated. As a result, the reaction of formula (1) is promoted in the fuel electrode 11, and the reaction of formula (2) is promoted in the oxygen electrode 13.

Therefore, when the power generated by the unit cell 1 is constant, the necessary amount of the catalyst can be reduced, and therefore, the electrode can be made smaller, and the cost reduction and the size reduction of the fuel cell can be achieved. On the other hand, when the size of the fuel cell is fixed, the generated current per unit area can be increased, that is, the power of the fuel cell can be increased.

Further, even if a small amount of CO gas is present in the fuel fluid, the CO gas is easily oxidized to CO because the oxidation activity in the fuel electrode 11 is high₂. Therefore, when platinum is used as the catalyst, the reaction of platinum with CO gas, that is, CO poisoning of platinum is prevented, and the excellent catalytic effect of platinum can be sustained for a long time.

The basic configuration and operation mechanism of the unit cell 1 are described above. In the case of the unit cells 2 and 3, the basic operation mechanism is also substantially the same, and therefore, the description thereof is omitted. In the case of the unit cells 1 and 2 according to embodiments 1 and 2, the electrolyte solution is held in the pores 19 and 29 of the porous intermediate layers 12 and 22 under the condition that the capillary force generated by the capillary phenomenon, that is, the capillary pressure Pc or more expressed by the static law of the following formula (3) is achieved.

Wherein Pc: capillary pressure (unit: N/m)²) And r: radius of the hole (unit: m), δ: surface tension of the electrolyte solution (unit: N/m), θ: wetting Angle (unit:deg.). Therefore, the radius of the pores of the intermediate layer 12 is preferably set according to the surface tension δ of the electrolyte solution held in the pores and the wetting angle θ of the electrolyte solution with respect to the semiconductor material.

As described above, in the unit cells 1 to 3 according to embodiments 1 to 3, when methanol is used as the fuel fluid, it is preferable that the nano-order pores exist between the micro-order pores on the fuel fluid supply surface side of the fuel electrode and the micro-order pores on the oxidizing fluid supply surface side of the oxygen electrode. The micron-sized pores increase the specific surface area of the electrode portion, and have a diameter such that the fuel fluid or the oxidizing fluid can penetrate therein. Further, in the case of embodiments 1 and 2, the nano-scale pores are set to have a function of holding the electrolyte solution and a function of suppressing methanol crossover, and in the case of embodiment 3, they are set to have mainly a function of suppressing methanol crossover. The reason why methanol crossover can be suppressed without impairing the function of the fuel cell is as follows.

Fig. 5 is a partially enlarged cross-sectional view schematically showing a region composed of micro-scale voids and nano-scale voids. Fig. 5 shows an example of the fuel electrode 11 in the unit cell 1 according to embodiment 1.

In the case of the fuel electrode 11 shown in fig. 5, the p-type semiconductor layer of the fuel electrode 11 has voids 15a partitioned by walls 16a, and the conductive metal layer 18 is formed of a metal such as palladium (Pa), nickel (Ni), tantalum (Ta), or niobium (Nb) on the inner surface of the void 15 a. The metal catalyst layer formed on the metal layer is not shown in the figure. The conductive metal layer has an effect of improving the conductivity of the fuel electrode 11 such as silicon and an effect of preventing methanol from penetrating.

The hydrogen ions must move from the fuel electrode 11 to the oxygen electrode 13 (see fig. 1B). In the case of the above metal, hydrogen ions diffuse in the metal layer, and therefore, even if the conductive metal layer 18 is coated on the inner wall surface of the hole 15a, the movement of hydrogen ions is not inhibited. That is, hydrogen ions that have reached the surface of the conductive metal layer 18 are adsorbed on the metal surface, receive electrons from the metal layer, and diffuse in the conductive metal layer 18 as hydrogen atoms. The hydrogen atoms diffuse to reach the other surface of the conductive metal layer 18, i.e., the wall 16a side or the intermediate layer 12. Therefore, electrons are released from the conductive metal layer 18 and become hydrogen ions, which move into the p-type semiconductor layer of the fuel electrode 11 or the intermediate layer 12. Therefore, even if the conductive metal layer 18 is present, the movement of hydrogen ions from the fuel electrode 11 to the oxygen electrode 13 is not inhibited.

On the other hand, methanol cannot pass through the conductive metal layer 18. Therefore, methanol cannot move from the fuel electrode 11 to the oxygen electrode 13, and methanol crossover in the unit cell 1 is almost completely prevented. As shown in fig. 5, the conductive metal is filled in the hole portion of the region a adjacent to the bottom of the hole 15a in the nano-scale hole 19 in the intermediate layer 12, in which the bottom of the hole 15a of the fuel electrode 11 is open. Therefore, methanol crossover can be more effectively prevented.

Preferred methods of manufacturing the unit cells 1 to 3 according to embodiments 1 to 3 are as follows. The porous fuel electrode, oxygen electrode and intermediate layer constituting the main part of the unit cells 1 to 3 are formed by approximately 2 methods. The method 1 is a method of forming a hole having a predetermined shape shown in fig. 4A in a predetermined pattern. The 2 nd method is a method of forming amorphous voids as shown in fig. 4B in a randomly distributed pattern. The latter 2 nd method can be produced by a method such as formation of a plate-like body by a CVD method, chemical etching of sodium fluoride or the like using a plate-like semiconductor material, anodic etching using a Hydrogen Fluoride (HF) solution or the like. However, as a method for forming the porous portion, the following method 1 is suitable.

Fig. 6 and 7 are views for explaining a method of forming a porous portion having a predetermined pattern by the method 1. Fig. 6 is a view showing a cross-sectional structure of a substrate in the process of performing pre-etching on the substrate on which porous portions are formed, and fig. 7 is a schematic cross-sectional view showing a method of further performing etching on the pre-etched substrate by an anodic etching method. In the following, an example in which the substrate is silicon will be described.

In the case of forming porous silicon having patterned pores, first, a silicon substrate 41 of a p-type semiconductor or an n-type semiconductor is formed by a method such as ion implantation. Then, a patterned mask 42 is formed on the 1-surface side of the silicon substrate 41 by photolithography which is generally used in manufacturing of a semiconductor device or the like. Further, with the patterned mask, the silicon substrate 41 is subjected to a pre-patterning by anisotropic etching using a potassium hydroxide (KOH) solution. With this pre-patterning, the concave portion 43 is formed on the silicon substrate 41. Then, the mask 42 is removed.

Next, the pre-patterned portion is further etched by the anodic etching method shown in fig. 7, thereby forming a deep void. In the apparatus shown in fig. 7, an electrolytic solution such as Hydrogen Fluoride (HF) is filled in a container 45, a platinum electrode 46 is immersed therein, and a silicon substrate 41 is attached to an opening of a side wall of the container 45 in a water-tight manner so as to face the platinum electrode 46. Further, the platinum electrode 46 is connected to the negative side of the power source E, and the silicon substrate 41 is connected to the positive side of the power source E. Further, when the silicon substrate 41 is an n-type semiconductor, photochemical HF anodic etching using light is performed, and when the silicon substrate 41 is a p-type semiconductor, HF anodic etching without light irradiation is performed.

The HF anodic etching shown in fig. 7 is used to form, for example, the patterned holes 15a and 15B shown in fig. 1B on the silicon substrate 41. The diameter of the hole depends on the etching conditions such as the resistance of the wafer, the photocurrent, and the concentration of the HF solution, and therefore, the etching conditions are preferably selected according to the target diameter. In addition, the depth of the void depends on the etching time.

After etching to a predetermined depth, for example, in order to form a small-diameter void 19 (for example, on the order of nanometers) in the bottom of the void 15a (for example, having a diameter of the order of micrometers) shown in fig. 1B, the anodic etching may be performed by increasing the current while increasing the concentration of the electrolyte solution (HF).

When the diameters of the pores of the fuel electrode and the oxygen electrode and the diameters of the pores of the intermediate layer are made substantially the same, anodic etching of the oxygen electrode and the intermediate layer may be performed under a constant condition such as the concentration of the electrolyte solution and the current.

The above method is a method of forming pores from one surface of a silicon substrate, but for example, pores having a large diameter of the order of micrometers may be formed from one surface, and pores having a small diameter of the order of nanometers may be formed from the other surface. This method is particularly suitable for forming the pores of the fuel electrode 21 and the oxygen electrode 23 of the unit cell 2 according to embodiment 2 and the pores of the fuel electrode 31 and the oxygen electrode 33 of the unit cell 3 according to embodiment 3.

The silicon substrate is implanted with ions in advance to be an n-type or p-type semiconductor, and is preferably re-doped after etching in order to improve the conductivity of the fuel electrode or the oxygen electrode and control the resistance loss. For example, an oxygen electrode made of an n-type semiconductor is re-doped with phosphorus (P), and a fuel electrode made of a P-type semiconductor is re-doped with boron (B). The doping may be performed by ion implantation, CVD, thermal diffusion, or the like. Although not shown, when phosphorus is doped, for example, phosphoric acid (H) may be used₃PO₄) When the alcohol solution of (A) is introduced into the pores and boron is doped, boric acid (H) can be introduced₃BO₄) The alcohol solution (2) is introduced into the pores, and the pores are heated at 1200 ℃ for about 4 hours, whereby the inner surfaces of the pores can be doped with P or B.

The relationship between the formation of the porous portions of the fuel electrode, the oxygen electrode, and the intermediate layer and the formation of the unit cell is as follows.

In the case of the unit cell 1 according to embodiment 1, the fuel electrode 11, the intermediate layer 12, and the oxygen electrode 13 are separately produced, and the intermediate layer 12 is sandwiched between the fuel electrode 11 and the oxygen electrode 13 as shown in fig. 1A. Further, 1 silicon substrate may be used, and the holes 15a, 15b, and 19 may be formed integrally on the surface on the fuel electrode 11 side, the surface on the oxygen electrode 13 side, and the middle.

In the case of the unit cell 2 according to embodiment 2, the fuel electrode 21 and the oxygen electrode 23 may be separately produced and joined together as shown in fig. 2A. The hole 29 may be formed in either one of the fuel electrode 21 and the oxygen electrode 23. Further, 1 silicon substrate may be used, and the holes 25a and 29 may be formed on the fuel electrode 21 side and the holes 25b and 29 may be formed on the oxygen electrode 23 side, thereby being integrally configured. However, in this case, the void 29 may be formed in either one of the fuel electrode 21 and the oxygen electrode 23.

In the case of the unit cell 3 according to embodiment 3, the fuel electrode 31 and the oxygen electrode 33 may be separately produced, and the unit cell 3 may be assembled by using the sealing plates 34a and 34b so as to form a gap between the fuel electrode 31 and the oxygen electrode 33, as shown in fig. 3A.

The method of retaining the electrolyte solution in the unit cells 1 to 3 manufactured by the above method is as follows. In the case of the unit cells 1 and 2, it is necessary to keep the electrolyte solution in the porous portion of the nanometer order. The electrolyte solution is H₂SO₄、H₃PO₄And trifluoromethanesulfonic acid, the assembled cells 1 and 2 may be immersed in the electrolyte solution in the cell for about 12 hours. As the electrolyte, a solid electrolyte polymer may be used, but in this case, the assembled unit cells 1, 2 may be immersed in a Nafion solution.

Fig. 8 and 9 are oblique schematic views showing examples of the supply mechanism of the fuel fluid and the oxidizing fluid. Fig. 8 and 9 show an example of the unit cell 1.

The fuel fluid supply section 51 and the oxidizing fluid supply section 52 shown in fig. 8 are both of a groove structure, and the groove portions are hermetically sealed or fluid-tightly sealed by plates 53a and 53 b. The grooves can be formed by anisotropic etching on the fuel fluid supply surface side of the fuel electrode 11 and the oxidizing fluid supply surface side of the oxygen electrode 13, for example, by patterning using a photolithography method and a KOH solution.

The fuel fluid supply portion 54 and the oxidizing fluid supply portion 55 shown in fig. 9 are formed of porous bodies, and hold the fuel fluid or the oxidizing fluid in the pores of the porous bodies. When the fuel fluid is hydrogen gas, a hydrogen storage alloy or the like may be used for the fuel fluid supply unit 54.

Fig. 8 and 9 show the case where the fuel fluid supply unit and the oxidizing fluid supply unit have the same structure, but the fuel fluid supply unit may have a groove structure, and the oxidizing fluid supply unit may have a porous body, or vice versa. The fuel fluid supply unit and the oxidizing fluid supply unit are preferably appropriately selected according to the use, function, and the like of the unit cell 1.

Fig. 10A to 10C are views schematically showing a cell array according to the embodiment, fig. 10A is a cross-sectional view showing a cell array 4A in which cells are connected in parallel, fig. 10B is a cross-sectional view showing a cell array 4B in which cells are connected in series, and fig. 10C is a perspective view showing a cell array 4C in which cells are connected in the vertical and horizontal directions. In the following description, the cell arrays 4A to 4C are collectively referred to as a cell array 4. Fig. 10A to 10C show an example in which the unit cell 1 is used.

Fig. 10A is a sectional view showing a unit cell array 4A in which a plurality of unit cells 1 are arranged in a planar manner while being electrically connected in parallel. The larger the area of the unit cell 1, the larger the current. When it is necessary to increase the generated current, it is one method to enlarge the area of the unit cell 1. When it is difficult to enlarge the area of the unit cells 1 from the viewpoint of mechanical strength or the like, it is preferable to connect the unit cells 1 in parallel as shown in fig. 10A. That is, the fuel electrodes 11 and the oxygen electrodes 13 of the respective unit cells 1 can be connected to each other by the external circuits 61 and 62.

Fig. 10B is a sectional view showing a unit cell array 4B in which a plurality of unit cells 1 are arranged in a planar manner while being electrically connected in series. The electromotive force of the unit cell 1 depends on the fuel and oxygen. For example, in the case of a hydrogen fuel cell using hydrogen, the output voltage is desirably about 1.229V. However, the actual output voltage of the hydrogen fuel cell is about 0.6 to 0.85V due to the overpotential irreversibly generated in the electrode. By using the pin or pn semiconductor structure according to this embodiment, the overpotential can be greatly reduced.

When the voltage has to be increased, it is preferable to connect the respective unit cells 1 in series as shown in fig. 10B. That is, the fuel electrode 11 and the oxygen electrode 13 may be connected by the external circuit 63.

Fig. 10C is a perspective view showing a unit cell array 4C in which a plurality of unit cells 1 are arranged in a planar manner and are electrically connected in the vertical and horizontal directions. When it is necessary to increase the voltage and increase the current, it is preferable to arrange the unit cells 1 vertically and horizontally as shown in fig. 10C, for example, to connect the row sides in parallel as shown in fig. 10A and to connect the column sides in series as shown in fig. 10B. When the unit cell 1 having a large area can be used, the unit cell having a large area can be used instead of the unit cells connected in parallel on the row side.

Fig. 11 is a sectional view schematically showing the structure of a unit cell array according to another embodiment. Fig. 11 shows an example in which the unit cell 1 is used. The cell array 5 according to another embodiment is a stacked array in which a plurality of cells 1 are stacked in series. Further, between the respective unit cell arrays 1, as shown in fig. 11, flow field plates 71, 72 and optical fibers 73 are interposed.

The flow field plates 71 and 72 are thin plates and form grooves or narrow tubes (not shown) for flowing a fluid such as a gas therethrough. The flow field plate 71 supplies an oxidizing gas such as air to the oxygen electrode 13, and the flow field plate 72 supplies a fuel fluid such as methanol to the fuel electrode 11, and discharges excess fuel, generated water, and the like. Further, a plurality of optical fibers 73 are inserted between the flow field plates 71 and 72, and light can be guided into the intermediate layer 12 through the surface of the fuel electrode 11 or the surface of the oxygen electrode 13. Further, the optical fiber removes the coating of the portion located between the flow field plates 71 and 72, and allows light to reach the intermediate layer 12.

Further, the fuel electrode 11 and the oxygen electrode 13 are electrically connected between the stacked unit cells 1. When the flow field plates 71, 72 are formed of an electrically conductive material, the electrical connection can be ensured by bringing the flow field plates 71 and 73 into direct contact in the region where the optical fiber 73 is removed. When the flow field plates 71, 73 are formed of a non-conductive material, a conductor is used to electrically connect the fuel electrode 11 and the oxygen electrode 13.

The battery cell array 5 configured as described above can realize a stacked array in which the battery cells 1 are stacked, and the stacked battery cell array 5 can generate a voltage corresponding to the number of stacked battery cells 1.

Fig. 12A is a sectional view schematically showing a fuel cell module according to the embodiment. Fig. 12A shows an example in which the cell array 4A is used. The fuel cell module 6A shown in fig. 12A has a unit cell array 4A, a fuel fluid supply portion 82, and an oxidizing fluid supply portion 83. The fuel fluid supply portion 82 and the oxidizing fluid supply portion 83 are partitioned by the cell array 4A. The partition member 84 shown in fig. 12A is provided as needed.

As will be described later, the cell array 4A is configured to be able to extract a predetermined voltage and current, and the fuel electrode side faces the fuel fluid supply portion 82. Further, the unit cell array 4A is supported between the fuel fluid supply portion 82 and the oxidizing fluid supply portion 83 by the support member 85 so that the fuel fluid and the oxidizing fluid do not permeate through the unit cell array 4A portion.

The fuel fluid is introduced into the fuel fluid supply portion 82 through the fuel fluid introduction port 82a, and the remaining fluid is discharged through the fluid discharge port 82 b. In addition, of the wall portions of the fuel fluid supply portion 82, the wall portion facing the cell array 4A serves as a light transmitting window 82c and is made of a light transmitting material such as glass.

The oxidizing fluid is introduced into the oxidizing fluid supply unit 83 from the oxidizing fluid introduction port 83a, and the remaining oxidizing fluid and water are discharged from the fluid-water discharge port 83 b.

In the fuel cell module 6A configured as described above, a fuel fluid such as methanol is introduced from the fuel fluid inlet 82a of the fuel fluid supply unit 82, an oxidizing gas such as oxygen is introduced from the oxidizing fluid inlet 83a of the oxidizing fluid supply unit 83, and the reaction between the fuel electrode 11 and the oxygen electrode 13 is activated by light irradiated to the intermediate layer 12 of the cell array 4A (see fig. 10A) through the light transmission window 82c, so that the reaction of the above formula (1) actively proceeds in the fuel electrode 11, and the reaction of the above formula (2) actively proceeds in the oxygen electrode 13. As a result, electric power is generated from the cell array 4A, and is extracted as electric power to the outside of the fuel cell module 6A by a current collector (not shown) provided as a current collecting layer in the fuel electrode 11 and the oxygen electrode 13.

Fig. 12B is a sectional view schematically showing a fuel cell module 6B according to another embodiment. The fuel cell module 6B shown in fig. 12B is a fuel cell module particularly suitable as a power source for portable devices, and has a cell array 4A, a fuel fluid supply portion 85, and an oxidizing fluid supply portion 86. The fuel fluid supply portion 85 and the oxidizing fluid supply portion 86 are separated by the cell array 4A. Further, a fluid-permeable partition member 89 shown in fig. 12B is provided as necessary.

In the fuel cell module 6B, the fluid supply source in the fuel fluid supply portion 85 is constituted by the hydrogen absorbing alloy 85a, and as the fuel fluid, for example, hydrogen gas is supplied from the hydrogen absorbing alloy 85a to the unit cell array 4A. The absorption and release of hydrogen in the hydrogen absorbing alloy 85a can be controlled by combining a Peltier element and heating and cooling (see, for example, Japanese patent application laid-open No. 6-265238). The cell array 4A is supported by a flat block-shaped hydrogen absorbing alloy 85a disposed below the cell array 4A in the drawing.

The oxidizing fluid supply part 86 is located above the cell array 4A in the drawing, and supplies, for example, air from the oxidizing fluid inlet 86a to the oxidizing fluid supply part 86, and discharges nitrogen gas, excess oxygen gas, and water or water vapor from the outlet 86 b. In the case of the fuel cell module 6B, the upper wall of the oxidizing fluid supply portion 86, i.e., the wall facing the oxygen electrode side of the cell array 4A, is formed as a light transmission window 86c, and is made of a light transmissive material such as glass, and the oxygen electrode (cathode) of the cell is made light transmissive.

In the fuel cell module 6B configured as described above, when hydrogen gas as a fuel gas is supplied from the hydrogen occluding alloy 85a of the fuel fluid supply portion 85 and, for example, air is introduced from the oxidizing fluid introduction port 86a of the oxidizing fluid supply portion 86, the reaction between the fuel electrode and the oxygen electrode is activated by light irradiated to the intermediate layer of the cell array 4A through the light transmission window 86c, and the reaction of the above formula (1) is actively performed in the fuel electrode and the reaction of the above formula (2) is actively performed in the oxygen electrode. This generates electric power from the cell array 4A, and the electric power is extracted as electric power to the outside of the fuel cell module 6B by current collectors (not shown) provided in the fuel electrode and the oxygen electrode.

Fig. 13 is a block diagram showing the configuration of the fuel cell system 7 according to the embodiment. The fuel cell system 7 is configured by integrally combining a plurality of fuel cell modules 6A (fig. 13 shows an example of the fuel cell module 6A, but may be a fuel cell module 6B), and includes a fuel cell 91 formed by electrically connecting the fuel cell modules 6A, a DC-DC converter 92 electrically connected to the fuel cell 91, a DC-AC converter 93 connected to an output side of the DC-DC converter 92, and an output unit 94. Further, a DC-AC converter 93 is incorporated as necessary, and when AC is not required as a power source, the DC-DC converter 92 is directly connected to the output unit 94.

The fuel cell 91 is composed of a plurality of fuel cell modules 6A, and outputs electric power of a predetermined voltage and current to the DC-DC converter 92.

In the DC-DC converter 92, the electric power transmitted from the fuel cell 91 is boosted to a required voltage in an external load device (not shown). In this case, the current decreases according to the rise in voltage, and therefore it is necessary to set the output of the fuel cell 91, i.e., the configuration of the fuel cell module 6A, so that a desired current can be secured in the external load device.

When the external load equipment needs AC, the power boosted by the DC-DC converter 92 is converted into AC by the DC-AC converter 93, and is output as AC power from the fuel cell system 7 through the output unit 94. As described above, when used as direct current, the DC power is output from the DC-DC converter 92 through the output unit 94 as the output of the fuel cell system 7.

As shown in fig. 11, for example, the output voltage of the unit cells 1 can be increased by stacking the unit cells 1. However, when it is difficult to adopt a structure in which the unit cells 1 are stacked, the output voltage can be easily increased by using the DC-DC converter 92 as in the fuel cell system 7 according to the embodiment.

Claims (16)

1. A fuel cell unit cell having a pin structure including a fuel electrode made of a p-type semiconductor, an oxygen electrode made of an n-type semiconductor, and an intermediate layer made of an intrinsic semiconductor and present between the fuel electrode and the oxygen electrode,

the fuel electrode is porous and permeable to the fuel fluid, a metal catalyst layer is formed on the inner surface of the pores of the porous portion,

the oxygen electrode is porous and permeable to oxidizing fluid, and a metal catalyst layer is formed on the inner surface of the pores of the porous portion,

the intermediate layer is porous and can hold an electrolyte solution, has a property of allowing hydrogen ions generated by the fuel electrode to pass therethrough and preventing electrons from passing therethrough,

a fuel fluid containing hydrogen is supplied to the surface of the fuel electrode, and an oxidizing fluid containing oxygen is supplied to the surface of the oxygen electrode,

having connection terminals electrically connected to the fuel electrode and the oxygen electrode, respectively,

the metal catalyst constituting the metal catalyst layer is one selected from the group consisting of platinum, iridium, palladium, rhodium, ruthenium, and an alloy containing at least 2 of these, or titanium oxide.

2. A fuel cell unit cell having a p-n structure including a fuel electrode made of a p-type semiconductor, an oxygen electrode made of an n-type semiconductor, and an intermediate layer present between the fuel electrode and the oxygen electrode,

the fuel electrode is porous and permeable to the fuel fluid, a metal catalyst layer is formed on the inner surface of the pores of the porous portion,

the oxygen electrode is porous and permeable to oxidizing fluid, and a metal catalyst layer is formed on the inner surface of the pores of the porous portion,

the intermediate layer is formed on at least one side of the fuel electrode and the oxygen electrode, is porous, can hold an electrolyte solution, and has a property of allowing hydrogen ions generated by the fuel electrode to pass therethrough and preventing electrons from passing therethrough,

the fuel electrode and the oxygen electrode are joined at a surface where the intermediate layer is formed,

a fuel fluid containing hydrogen is supplied to the surface of the fuel electrode, and an oxidizing fluid containing oxygen is supplied to the surface of the oxygen electrode,

having connection terminals electrically connected to the fuel electrode and the oxygen electrode, respectively,

the metal catalyst constituting the metal catalyst layer is one selected from the group consisting of platinum, iridium, palladium, rhodium, ruthenium, and an alloy containing at least 2 of these, or titanium oxide.

3. A fuel cell unit cell having a pn-pn structure, the pn-pn structure comprising: a fuel electrode having a pn junction region in which a fuel fluid supply surface side is formed of a p-type semiconductor layer and another surface is formed of an n-type semiconductor layer, an oxygen electrode having a pn junction region in which an oxidizing fluid supply surface side is formed of an n-type semiconductor layer and another surface is formed of a p-type semiconductor layer, and an electrolyte layer as an intermediate layer existing between the n-type semiconductor layer of the fuel electrode and the p-type semiconductor layer of the oxygen electrode,

the fuel electrode is porous, the p-type semiconductor layer in the fuel electrode is thicker than the n-type semiconductor layer and is permeable to a fuel fluid, a metal-based catalyst layer is formed on the inner surface of the pores of the porous portion, the n-type semiconductor layer is impermeable to the fuel fluid,

the oxygen electrode is porous, the n-type semiconductor layer in the oxygen electrode is thicker than the p-type semiconductor layer and is permeable to oxidizing fluid, a metal-based catalyst layer is formed on the inner surface of the pores of the porous portion,

the intermediate layer contains an electrolyte solution having a property of allowing hydrogen ions generated by the fuel electrode to pass therethrough,

a fuel fluid containing hydrogen is supplied to the surface of the fuel electrode, and an oxidizing fluid containing oxygen is supplied to the surface of the oxygen electrode,

having connection terminals electrically connected to the fuel electrode and the oxygen electrode, respectively,

the metal catalyst constituting the metal catalyst layer is one selected from the group consisting of platinum, iridium, palladium, rhodium, ruthenium, and an alloy containing at least 2 of these, or titanium oxide.

4. The fuel cell according to any one of claims 1 to 3, wherein at least one of the fuel electrode and the oxygen electrode is light transmissive.

5. The fuel cell according to any one of claims 1 to 3, wherein the electrolyte of the intermediate layer is irradiated with light.

6. The fuel cell unit cell according to any one of claims 1 to 3, wherein a conductive metal layer is provided between the inner surface of the void of at least one of the fuel electrode and the oxygen electrode and the catalyst layer.

7. The fuel cell unit cell according to any one of claims 1 to 3, wherein the fuel fluid is methanol or hydrogen.

8. The fuel cell unit cell according to claim 1 or 2, wherein the diameters of the pores of the porous portion having fuel fluid permeability in the fuel electrode and the pores of the porous portion having oxidizing fluid permeability in the oxygen electrode are in the micron order, and the diameters of the pores of the porous portion of the intermediate layer are in the nanometer order.

9. The fuel cell unit cell according to claim 3, wherein the diameter of the hole of the p-type semiconductor layer portion in the fuel electrode and the diameter of the hole of the n-type semiconductor layer portion in the oxygen electrode are on the order of micrometers, and the diameter of the hole of the n-type semiconductor layer portion in the fuel electrode and the diameter of the hole of the p-type semiconductor layer portion in the oxygen electrode are on the order of nanometers.

10. The fuel cell unit cell according to any one of claims 1 to 3, wherein a semiconductor material constituting the fuel electrode and the oxygen electrode is silicon, germanium, or an oxide semiconductor.

11. The fuel cell unit cell according to claim 10, the oxide semiconductor being a titanium oxide semiconductor.

12. The fuel cell unit cell according to any one of claims 1 to 3, wherein the electrolyte solution is acidic.

13. A fuel cell unit cell array, characterized in that it is constructed in the following manner: a plurality of the fuel cell units according to any one of claims 1 to 3 are arranged in a planar manner, and are electrically connected in parallel and/or in series, thereby concentrating and outputting the electric power generated by the plurality of the fuel cell units.

14. A fuel cell unit cell array, characterized in that it is constructed in the following manner: a plurality of the fuel cell unit cells according to any one of claims 1 to 3 are stacked via the fuel supply means, the oxidizing fluid supply means, and the light introduction means, and are electrically connected in series to add and output electric power generated by the plurality of the fuel cell unit cells.

15. A fuel cell module comprising the fuel cell unit cell array according to claim 13, a fuel supply portion, and an oxidizing fluid supply portion,

the fuel cell unit cell array is disposed between the fuel supply section and the oxidizing fluid supply section so as not to allow a fluid to pass between the fuel supply section and the oxidizing fluid supply section,

a fuel electrode of the fuel cell array faces the fuel supply portion, an oxygen electrode of the fuel cell array faces the oxidizing fluid supply portion,

the fuel supply portion has a fuel introduction portion and a fluid discharge portion, the oxidizing fluid supply portion has an oxidizing fluid introduction portion and a fluid-water discharge portion,

a wall portion facing the fuel electrode among the wall portions surrounding the fuel supply portion and/or a wall portion facing the oxygen electrode among the wall portions surrounding the oxidizing fluid supply portion is made of a light transmissive material,

there is an output mechanism that outputs the electric power generated and concentrated by the fuel cell unit cell array.

16. A fuel cell system comprising a plurality of the fuel cell modules according to claim 15, wherein the plurality of the fuel cell modules are integrally combined, and are connected so as to concentrate electric power outputted from the output means of each of the fuel cell modules, wherein the fuel cell system comprises a fuel cell output unit for outputting the concentrated electric power, and a DC-DC converter electrically connected to the fuel cell output unit.