JP2012076988A - Ionically conductive thin film material and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ionically conductive thin film material, in particular, a proton-conducting material, having satisfactory ion conductivity in 200-500°C of medium temperature zone, without requiring moistening, and excellent in moldability and long term stability.SOLUTION: This ionically conductive thin film material contains, as its composition, 15-80% of PO, 0-70% of SiO, and 5-35% of RO (total of LiO, NaO, KO, RbO, CsO and AgO), in terms of mol%, and has a thin plate shape, and a thickness thereof is 1-500 μm.

Description

  The present invention relates to an ion conductive thin film material (ion conductor) and a method for producing the same, and more particularly to an ion conductive thin film material having good proton conductivity and a method for producing the same.

  Fuel cells have a high theoretical value for power generation efficiency and can also use waste heat, so they can significantly reduce carbon dioxide and provide sufficient electricity and heat compared to state-of-the-art thermal power generation. Is possible. Further, solid polymer fuel cells represented by perfluoroalkyl sulfonic acid polymers (registered trademark Nafion) and the like have attracted attention as small-scale power generation applications such as home use and in-vehicle use. However, at present, the solid polymer fuel cell has a problem of low power generation efficiency (about 33%) because its operating temperature is as low as around 80 ° C.

  Moreover, although the phosphoric acid fuel cell has been put into practical use, there are problems that the operating temperature is about 200 ° C. and the manufacturing cost is high. Furthermore, since the solid oxide fuel cell has an extremely high operating temperature of about 1000 ° C., there is a problem that inexpensive stainless steel or the like cannot be used as a constituent member of the fuel cell. Under such circumstances, there is a demand for a fuel cell that can operate satisfactorily in the temperature range corresponding to the GAP portion shown in FIG. If the operating temperature of the fuel cell can be increased to about 500 ° C., it is said that overall efficiency exceeding 50% can be achieved.

JP 2002-097272 A

T.A. Norby, Solid State Ionics, 125, 1, 1990 Yoshihiro Abe, NEW GLASS, Vol. 12, no. 3, 1997, p28

  In order to raise the operating temperature to about 500 ° C., it is indispensable to develop an electrolyte exhibiting high proton conductivity or oxygen ion conductivity in the temperature range. However, the actual situation is that no ion-conductive thin film material having practical electric conductivity has been reported yet in an intermediate temperature range of 200 to 500 ° C. (see Non-Patent Document 1).

  Under such circumstances, phosphate glass is currently being studied as a candidate for an ion conductive thin film material that operates in the middle temperature range, particularly a proton conductive thin film material (see Patent Document 1 and Non-Patent Document 2). .

  However, since the phosphate glasses described in Patent Document 1 and Non-Patent Document 2 are produced by a sol-gel method, humidification is necessary at the time of use, heat resistance is low, and moldability (particularly, , The formability into a thin plate shape) and chemical durability also have problems.

  Accordingly, the present invention provides an ion conductive thin film material, particularly a proton conductive thin film material, which has good ion conductivity in the middle temperature range of 200 to 500 ° C. and is excellent in moldability and long-term stability without being humidified. The technical challenge is to create

As a result of diligent research, the present inventors have regulated the contents of P ₂ O ₅ , SiO ₂ , and alkali metal oxide to a predetermined range, and processed them into a thin plate shape (including a film shape). The present inventors have found that the above technical problem can be solved by restricting to a predetermined range, and propose as the present invention. That is, the ion conductive thin film material of the present invention has a composition expressed in mol%, P ₂ O ₅ 15-80%, SiO ₂ 0-70%, R ₂ O (Li ₂ O, Na ₂ O, K ₂ The total amount of O, Rb ₂ O, Cs ₂ O, and Ag ₂ O) is 5 to 35%, has a thin plate shape, and has a thickness of 1 to 500 μm.

Ion conductive thin film material of the present invention, P ₂ O ₅ 15 to 80% of SiO ₂ 0 to 70% containing 5 to 35% of R ₂ O. If it does in this way, even if it does not humidify, while showing favorable ion conductivity in an intermediate temperature range of 200-500 ° C, long-term stability will also improve. In addition, since the meltability is improved in this way, it becomes easy to produce an ion conductive thin film material by a melting method, and as a result, the moldability, homogeneity, and denseness can be improved. In particular, this makes it easy to form a thin glass sheet by the overflow downdraw method, the redraw method, the slot downdraw method, or the like.

  The ion conductive thin film material of the present invention has a thin plate shape and a thickness of 1 to 500 μm. If it does in this way, since a sheet resistance value becomes small in the middle temperature range of 200-500 ° C, in the middle temperature range of 200-500 ° C, ion conductivity becomes high and the performance of an electrochemical device improves. In particular, in this way, when applied to a fuel cell, the resistance of the electrolyte is reduced, so that the resistance loss is reduced, and as a result, the power generation efficiency of the fuel cell is improved. In addition, if it is a thin plate shape, and homogeneity and denseness are favorable, it becomes easy to suppress a crossover in a direct methanol fuel cell.

Secondly, the ion conductive thin film material of the present invention has a composition expressed in mol%, P ₂ O ₅ 15-60%, SiO ₂ 10-60%, R ₂ O (Li ₂ O, Na ₂ O, The total amount of K ₂ O, Rb ₂ O, Cs ₂ O, and Ag ₂ O) is preferably 5 to 35%.

Thirdly, the ion conductive thin film material of the present invention includes at least two kinds of R ₂ O components (Li ₂ O, Na ₂ O, K ₂ O, Rb ₂ O, Cs ₂ O, Ag ₂ O). It is preferable to contain. By doing so, the ion conduction of alkali ions is suppressed by the mixed alkali effect, so that the proportion of proton conduction increases, and as a result, it becomes easy to apply to the electrolyte of the fuel cell. Incidentally, "of R ₂ O component, including at least two kinds," and refers to a state in which 0.1 mol% or more of R ₂ O component is present two or more in the composition.

Fourth, the ion conductive thin film material of the present invention preferably has a molar ratio (Na ₂ O + K ₂ O) / R ₂ O of 0.2 to 1.0. In this way, it becomes easy to improve proton conductivity. “Na ₂ O + K ₂ O” refers to the total amount of Na ₂ O and K ₂ O.

Fifth, the ion conductive thin film material of the present invention preferably has a molar ratio Na ₂ O / R ₂ O of 0.2 to 0.8. In this way, it becomes easy to improve proton conductivity.

Sixth, the ion conductive thin film material of the present invention preferably further contains 0.1 mol% or more of Al ₂ O ₃ as a composition. In this way, since the deliquescence is lowered, long-term stability is easily improved.

Seventh, the ion conductive thin film material of the present invention preferably has an area resistance value (Ω · cm ² ) at 500 ° C. of 30 or less. Here, the “area resistance value at 500 ° C.” can be measured by, for example, an AC impedance method. As a measurement sample, for example, an Ag electrode formed on the surface of a sample (dimension: 1.5 cm × 1 cm, optically polished) with an Ag paste can be used.

  Eighth, the ion conductive thin film material of the present invention is preferably amorphous with a crystallinity of 50% or less. Here, for the “crystallinity”, for example, an X-ray diffractometer (manufactured by Rigaku) is used, and a scattering intensity area and a crystal peak area measured in a diffraction angle 2θ range of 10 to 60 ° are used by a multiple peak separation method. And calculated as the ratio (%) of the crystal peak area to the scattering intensity area.

  Ninth, the ion conductive thin film material of the present invention is preferably used for a fuel cell.

  10thly, the electrochemical device of this invention is characterized by including said ion conductive thin film material.

  Eleventh, the method for producing an ion conductive thin film material according to the present invention is a method for producing the ion conductive thin film material described above, wherein the raw glass is melted and then the obtained molten glass is formed into a thin plate shape. It is characterized by having. In this way, moldability, homogeneity, and denseness can be improved.

  12thly, as for the manufacturing method of the ion conductive thin film material of this invention, it is preferable that the shaping | molding method is any one of the overflow down draw method, the slot down draw method, and the redraw method. These molding methods have the advantage of being easily molded into a thin plate shape.

It is explanatory drawing which shows the relationship between the operating temperature of various fuel cells, and ion conductivity.

  The reason why the composition of the ion conductive thin film material of the present invention is limited as described above will be described below. In the description relating to the composition, “%” indicates mol%.

P ₂ O ₅ is a component that increases ionic conductivity. The content of P ₂ O ₅ is 15 to 80%, preferably 20 to 70%, more preferably 25 to 65%, still more preferably 25 to 60%, particularly preferably 25 to 50%, and most preferably 25 to 45%. %. When the content of P ₂ O ₅ decreases, the ionic conductivity tends to decrease. On the other hand, when the content of P ₂ O ₅ increases, it becomes easy to deliquesce, so that long-term stability tends to decrease.

SiO ₂ is a network former and a component that enhances chemical durability. The content of SiO ₂ is 0 to 70%, preferably 0.1 to 60%, more preferably 1 to 50%, still more preferably 5 to 49%, and particularly preferably 10 to 40%. When the content of SiO ₂ is reduced, the chemical durability tends to be lowered. On the other hand, when the content of SiO ₂ increases, the ionic conductivity tends to decrease, and it tends to devitrify during melting and molding, and the viscosity increases unreasonably, making melting and molding difficult. Furthermore, a temperature range in which the viscosity changes abruptly tends to occur, and the moldability tends to decrease.

R ₂ O is a component that increases the ionic conductivity and is a component that decreases the viscosity and increases the meltability. The content of R ₂ O is 5 to 35%, preferably 8 to 30%, more preferably 10 to 25%. When the content of R ₂ O decreases, the ionic conductivity tends to decrease, and the viscosity increases unreasonably, making melting and molding difficult. On the other hand, when the content of R ₂ O increases, chemical durability tends to decrease. Moreover, it becomes easy to generate | occur | produce the temperature range from which a viscosity changes rapidly, and a moldability will fall easily.

It is preferable that two or more R ₂ O components are contained, particularly three or more. When only one R ₂ O component is used, the mixed alkali effect cannot be enjoyed, so that it is difficult to suppress ionic conduction of alkali ions, and as a result, the rate of proton conduction (proton transport number) tends to decrease.

Li ₂ O is a component that increases the ionic conductivity, and is a component that decreases the viscosity and increases the meltability. The content of Li ₂ O is preferably 0 to 20%, 0 to 15%, particularly preferably 0 to 10%. When the content of Li ₂ O increases, chemical durability tends to decrease.

Na ₂ O is a component that increases the ionic conductivity and is a component that decreases the viscosity and increases the meltability. The content of Na ₂ O is preferably 0 to 25%, 1 to 20%, particularly preferably 3 to 15%. When the content of Na ₂ O increases, chemical durability tends to decrease. When the content of Na ₂ O is reduced, the ionic conductivity is likely to be lowered, and the viscosity is unduly increased to make melting and molding difficult. Furthermore, a temperature range in which the viscosity changes abruptly tends to occur, and the moldability tends to decrease.

K ₂ O is a component that increases the ionic conductivity and is a component that decreases the viscosity and increases the meltability. The content of K ₂ O is preferably 0 to 25%, 1 to 20%, particularly preferably 3 to 15%. When the content of K ₂ O increases, the chemical durability tends to decrease. If the content of K ₂ O decreases, the ionic conductivity tends to decrease, and the viscosity increases unreasonably, making melting and molding difficult. Furthermore, a temperature range in which the viscosity changes abruptly tends to occur, and the moldability tends to decrease.

Ag ₂ O is a component that increases the ionic conductivity and is a component that decreases the viscosity and increases the meltability. The content of Ag ₂ O is preferably 0 to 20%, 0 to 15%, 0 to 10%, particularly not substantially contained, that is, 0.1% or less. When the content of Ag ₂ O is increased, the raw material cost is likely to increase.

The molar ratio (Na ₂ O + K ₂ O) / R ₂ O is preferably 0.2 to 1.0, 0.25 to 1.0, and particularly preferably 0.3 to 1.0. If it does in this way, while it becomes easy to improve proton conductivity, it can enjoy a mixed alkali effect using an inexpensive raw material. “Na ₂ O + K ₂ O” refers to the total amount of Na ₂ O and K ₂ O.

The molar ratio Na ₂ O / R ₂ O is preferably 0.2 to 0.8, 0.25 to 0.7, and particularly preferably 0.3 to 0.65. When the molar ratio Na ₂ O / R ₂ O is out of the above range, it becomes difficult to enjoy the mixed alkali effect, so that it becomes difficult to suppress the ionic conduction of alkali ions, and as a result, the proton conduction ratio is likely to decrease. The molar ratio K ₂ O / R ₂ O is preferably 0.2 to 0.8, 0.25 to 0.7, and particularly preferably 0.3 to 0.65. When the molar ratio K ₂ O / R ₂ O is out of the above range, it is difficult to enjoy the mixed alkali effect, so that it is difficult to suppress ionic conduction of alkali ions, and as a result, the proton conduction ratio is likely to be reduced. The molar ratio Li ₂ O / R ₂ O is preferably 0.8 or less, 0.6 or less, particularly 0.5 or less for the same reason.

Al ₂ O ₃ is a component that suppresses deliquescence and improves long-term stability. The content of Al ₂ O ₃ is preferably 0 to 20%, 0.1 to 16%, 1 to 12%, particularly preferably 2 to 10%. When the content of Al ₂ O ₃ increases, the ionic conductivity tends to decrease, and it tends to devitrify during melting and molding, and the viscosity increases unreasonably, making melting and molding difficult. Furthermore, a temperature range in which the viscosity changes abruptly tends to occur, and the moldability tends to decrease.

In addition to the above components, MgO, CaO, SrO, BaO, ZrO ₂ , TiO ₂ , La ₂ O ₃ , ZnO, Sb ₂ O ₃ are used for the purpose of adjusting viscosity, improving chemical durability, and improving the clarification effect. Fe ₂ O ₃ , SnO ₂ , CeO ₂ , SO ₃ , Cl, As ₂ O ₃ , CuO, Gd ₂ O ₃ , Y ₂ O ₃ , Ta ₂ O ₃ , Nb ₂ O ₅ , Nd ₂ O ₃ , Tb ₂ O ₃ , WO ₃ , V ₂ O ₅ , MoO ₃ , Bi ₂ O ₃ , CoO, Cr ₂ O ₃ , MnO ₂ , NiO, B ₂ O _{3 and the} like can be added. 0 to 5% of each is preferable. However, the content of MgO + CaO + SrO + BaO (the total amount of MgO, CaO, SrO, and BaO) causes a decrease in ionic conductivity. desirable. Also, As ₂ O ₃ , CuO, Gd ₂ O ₃ , Y ₂ O ₃ , Ta ₂ O ₃ , Nb ₂ O ₅ , Nd ₂ O ₃ , Tb ₂ O ₃ , WO ₃ , V ₂ O ₅ , MoO ₃ , The content of Bi ₂ O ₃ , CoO, Cr ₂ O ₃ , MnO ₂ , and NiO causes the raw material cost to rise, so each is preferably 1% or less, and is not substantially contained, that is, 0.1% or less. desirable. B ₂ O ₃ also causes an increase in raw material cost, so 2% or less is preferable, and it is preferable that it is not substantially contained, that is, 0.1% or less.

  In the ion conductive thin film material of the present invention, the thickness is preferably 1 to 500 μm, 2 to 200 μm, 3 to 100 μm, particularly preferably 5 to 50 μm or less. Moreover, when thickness is smaller than 1 micrometer, handling property will fall and the manufacturing efficiency of an electrochemical device will fall. On the other hand, when the thickness is larger than 500 μm, the sheet resistance value increases, the performance of the electrochemical device decreases, and particularly the power generation efficiency of the fuel cell decreases.

In the ion conductive thin film material of the present invention, the area resistance value (Ω · cm ² ) at 500 ° C. is preferably 30 or less, 15 or less, particularly preferably 10 or less. If it does in this way, in the middle temperature range of 200-500 ° C, ion conductivity will become high and the performance of an electrochemical device will improve. In particular, in this way, the resistance of the electrolyte is reduced, so that the resistance loss is reduced, and as a result, the power generation efficiency of the fuel cell is improved.

In the ion conductive thin film material of the present invention, the ion conductivity log ₁₀ σ (S / cm) at 500 ° C. is preferably −5.5 or more, −5.0 or more, particularly preferably −4.8 or more. If it does in this way, it will become suitable as a fuel cell in the 200-500 ° C middle temperature range.

  In the ion conductive thin film material of the present invention, the proton transport number at 500 ° C. is preferably 0.7 or more, 0.8 or more, and particularly preferably 0.9 or more. In this way, since the rate of proton conduction increases, it can be easily applied to a fuel cell.

  The ion conductive thin film material of the present invention is preferably amorphous with a crystallinity of 50% or less. If it does in this way, it will become easy to improve homogeneity and denseness.

  A method for producing the ion conductive thin film material of the present invention will be described. First, raw materials are prepared so as to be in the above composition range. Next, the raw materials prepared in the continuous melting furnace are charged and then melted by heating. Subsequently, the obtained molten glass is supplied to a molding apparatus, formed into a thin plate shape, and then slowly cooled. In this way, an ion conductive thin film material can be produced. In addition, although the ion conductive thin film material of this invention does not completely exclude the aspect produced with a sol-gel method, as mentioned above, such an aspect is disadvantageous from various viewpoints.

  In the method for producing an ion conductive thin film material of the present invention, the melting temperature is preferably 800 ° C. or higher, 1000 ° C. or higher, 1200 ° C. or higher, particularly 1400 ° C. or higher. If it does in this way, it will become easy to shorten melting time, and it will become easy to homogenize ion conductive thin film material.

  By changing the slow cooling rate, it is possible to selectively obtain any of glass that has not undergone phase separation, glass that has undergone phase separation, or crystallized glass in which crystals and glass are mixed. The phase separation and crystallization can also be performed by reheating after slow cooling. In consideration of actual production, glass that is not substantially phase-separated is preferable, and it is preferable not to have a phase separation step by heat treatment.

  As a method for forming the molten glass, a forming method such as a roll-out method, an overflow down-draw method, a slot-down draw method, a float method, or a redraw method can be employed. In particular, the overflow down draw method, the slot down draw method, and the redraw method are preferable because they can be easily formed into a thin plate shape and have excellent surface accuracy.

  Hereinafter, the present invention will be described in detail based on examples. The following examples are merely illustrative. The present invention is not limited to the following examples.

  Tables 1 to 5 show examples (samples Nos. 1 to 34) and comparative examples (samples Nos. 35 to 41) of the present invention.

  Each sample in the table was prepared as follows. First, after preparing the raw materials so as to have the composition in the table, they were put into an alumina crucible and melted at 1400-1600 ° C. for 2 hours. Next, the obtained molten glass was poured out on a carbon plate, formed, and then gradually cooled in an electric furnace maintained at 600 ° C. Subsequently, after processing into a flat plate shape of 1.5 cm × 1 cm × thickness 1.5 mm, the surface of the sample is polished in the order of # 100, # 400, and # 2000 using polishing paper to obtain a measurement sample. It was. The measurement sample was evaluated for ion conductivity, proton transport number, deliquescence, water resistance, vitrification, and moldability. Each sample was confirmed to be amorphous (glass) having a crystallinity of 50% or less by an X-ray diffractometer. A thin plate sample of 500 μm or less was made of molten glass in the same manner as described above using a Pt crucible, molded into a balloon shape using a blower, and then cut into 1.5 cm × 1 cm with a glass cutter to obtain a measurement sample. . The sheet resistance value was measured for this measurement sample. These results are shown in the table.

The ionic conductivity log ₁₀ σ (S / cm) is a value measured by the AC impedance method at each temperature in the table after forming an Ag electrode on the surface of the sample using Ag paste.

  The proton transport number at 500 ° C. was evaluated as follows. First, Pt was sputtered on the surface of the sample to form a Pt electrode. Next, the electromotive force when the hydrogen partial pressure on the other surface was changed after measuring one side of the sample as the reference side and making the atmosphere 1% hydrogen by volume was measured. Subsequently, the proton transport number was calculated from the slope based on the Nernst equation.

  The sample was immersed in pure water, allowed to stand at room temperature for 24 hours, washed and dried, and then the mass change of the sample was measured to obtain an index of deliquescence. In the table, the ratio (%) of the mass decrease with respect to the mass of the sample before immersion is described.

The sample was immersed in pure water in a sealed container, allowed to stand at 60 ° C. for 24 hours, washed and dried, and then the change in mass of the sample was measured to obtain a water resistance index. In the table, the value (mg / cm ² ) obtained by dividing the mass reduction amount with respect to the mass of the sample before immersion by the surface area of the sample is described.

  The molten glass produced in paragraph [0054] was poured out and the presence or absence of vitrification was confirmed. The case where vitrification was confirmed was evaluated as “◯”, and the case where vitrification was not confirmed was evaluated as “x”.

  After the molten glass produced in paragraph [0054] was molded, it was processed into dimensions of 1 cm × 1 cm × 5 mm. Next, this sample was remelted with a burner, and a fiber-like sample was prepared by hand guidance. When producing a fiber-shaped sample, “△△” indicates that very strict temperature control is required, and “△” indicates that strict temperature control is required. Evaluation was made with “◯” indicating that the fiber diameter was uneven, and “◎” indicating that the fiber diameter was uniform without requiring strict temperature control.

The area resistance value (Ω · cm ² ) was obtained by forming an Ag electrode on the surface of the sample using an Ag paste, measuring the resistance value by the AC impedance method at each temperature in the table, and then obtaining the resistance value. It is a value calculated from the resistance value and the area of the electrode. Sample No. The sheet resistance values in 2 to 5 are values estimated from various factors.

  As is apparent from Tables 1 to 5, sample No. 1 to 34 are considered to have a small sheet resistance because the thickness is small. On the other hand, sample No. Since 34-41 is thick, it is thought that sheet resistance is large. Note that there is a correlation between the ionic conductivity and the sheet resistance value, and as the ionic conductivity decreases, the sheet resistance value tends to increase.

  The ion conductive thin film material of the present invention can be applied to an electrochemical device, and is suitable, for example, as an electrolyte for a fuel cell, an electrolyte for a capacitor, a sensing member for a gas sensor, and a humidity detecting member for a humidity control device.

Claims (12)

A composition, in _{mol%, P 2 O 5 15~80%,} SiO 2 0~70%, R 2 O (Li 2 O, Na 2 O, K 2 O, Rb 2 O, Cs 2 O, and Ag _The total amount of ₂ O) An ion conductive thin film material containing 5 to 35%, having a thin plate shape, and a thickness of 1 to 500 μm. A composition, in _{mol%, P 2 O 5 15~60%,} SiO 2 10~60%, R 2 O (Li 2 O, Na 2 O, K 2 O, Rb 2 O, Cs 2 O, and Ag _2. The ion conductive thin film material according to claim 1, comprising 5 to 35%. R ₂ O component _{(Li 2 O, Na 2 O} , K 2 O, Rb 2 O, Cs 2 O, Ag 2 O) of, according to claim 1 or 2, characterized in that it comprises at least two kinds Ion conductive thin film material. 4. The ion conductive thin film material according to claim 1, wherein the molar ratio (Na ₂ O + K ₂ O) / R ₂ O is 0.2 to 1.0. Ion conductive thin film material according to claim 1, the molar ratio Na ₂ O / R ₂ O is characterized in that 0.2 to 0.8. Furthermore, a composition, ion-conducting membrane material according to claim 1, characterized in that it comprises Al ₂ O ₃ 0.1 mol% or more. The ion-conductive thin film material according to claim 1, wherein an area resistance value (Ω · cm ² ) at 500 ° C. is 30 or less.   The ion conductive thin film material according to claim 1, wherein the ion conductive thin film material is amorphous with a crystallinity of 50% or less.   It uses for a fuel cell, The ion conductive thin film material in any one of Claims 1-8 characterized by the above-mentioned.   An electrochemical device comprising the ion conductive thin film material according to claim 1. It is a manufacturing method of the ion conductive thin film material in any one of Claims 1-9,
A method for producing an ion conductive thin film material, comprising: melting a raw material, and then molding the obtained molten glass into a thin plate shape.   The method for producing an ion conductive thin film material according to claim 11, wherein the forming method is any one of an overflow down draw method, a slot down draw method, and a redraw method.