ES2372755B1 - POLYMER FUEL CELL. - Google Patents

Abstract

Polymeric fuel cell. # The present invention relates to a polymeric fuel cell manufactured with the SU-8 photoresin, all components of the fuel cell, current collectors and MEA, are manufactured based on this same material. In addition, the present invention also relates to its method of obtaining and the uses of said fuel cell.

Description

Polymeric fuel cell.

The present invention refers to a polymeric fuel cell manufactured with the SU-8 photoresin, all the components of the fuel cell, current collectors and MEA, are manufactured based on this same material. Furthermore, the present invention also refers to its method of obtaining and the uses of said fuel cell.

Prior art

The demand for miniaturized energy sources has increased rapidly in recent years due to the spread of portable electronic equipment. Numerous different strategies have been developed to address this need using micromachining technologies. In this regard, fuel micropiles have acquired great interest as portable energy sources due to their high efficiency and theoretical energy density. Fuel cells ensure a more durable and more reliable portable power supply than conventional batteries, since their energy is stored as fuel, rather than being part of the energy source (A. Kundu et al. Journal of Power Sources , 170 (1) (2007) 67-78 and in SK Kamarudin et al. Journal of Power Sources, 163 (2) (2007) 743-754). The miniaturization of these power generating devices promises greater efficiency and performance, but complete system integration remains a key challenge. In most of the cases described, the architectures of the fuel micropiles require complex and bulky wrappings to hold the components together. However, innovative designs of fuel micropiles have been devised as alternatives to achieve highly compact systems (N. Kuriyama et al. Sensors and Actuators A: Physical, 145-146 (2008) 354362).

In the search for a fully integrated and low-cost device, polymeric materials have recently been proposed for the production of the components of the fuel micropiles. Because their microfabrication procedures are fast and versatile, polymers have already proven to be suitable for a number of functions and applications in chips (G. S. Fiorini, D. T. Chiu, BioTechniques, 38 (3) (2005) 18). In recent years, interesting strategies have been described in relation to developments of fuel micropiles, for example, Shah et al. in Sensors and Actuators B: Chemical, 97 (2-3) (2004) 157-167, they used different microfabrication techniques to develop a micropile of fuel with polydimethylsiloxane (PDMS) as support and battery housing and Chan et al, in Journal of Micromechanics and Microengineering, 15 (1) (2005) 231-236, applied micromachining techniques to produce Gaussian bell-shaped microchannels in methyl polymethacrylate (PMMA) by means of a CO2 laser, obtaining a micropile of high power fuel powered by hydrogen. In addition, UV-sensitive resins such as SU-8 have proven to be excellent candidates for obtaining small-sized polymeric components and high-precision microstructure (A. d. Campo, C. Greiner, Journal of Micromechanics and Microengineering, 17 (6) ( 2007) R81), for example, Hsieh et al. (in Microsystem Technologies, 10 (2) (2004) 121-126) described the use of metallized UV sensitive resins as flow field plates and Cha et al. (in Electrochimica Acta, 50 (2-3) (2004) 795-799) used the same material to make current collectors in one of the first described attempts to obtain a fully polymeric microDMFC. Recently, Weinmueller et al. (in Journal of Power Sources, 195 (12) (2010) 3849-3857) described a micropile of methanol direct conversion fuel based on the microstructuring of a thin film of metallized photosensitive polymer, in which the flexible abilities of SU-8 resin.

Description of the invention

The present invention provides a polymeric fuel cell comprising an electrodomembrane assembly (MEA) sandwiched between two current collectors.

A first aspect of the present invention relates to a polymeric fuel cell, which comprises:

to.

a sandwich membrane between two current collectors, and

b.

two electrodes that are each attached to both sides of the membrane or in each of the current collectors,

characterized in that the membrane comprises a microporous SU-8 polymer, a proton exchange polymer and where the current collectors comprise the partially metallized microporous SU-8 polymer.

It is partially metallized, since as shown in Figure 1, the metallic zone of the collector is the one that overlaps with the corresponding active zone of the membrane, the active zone (also called the junction) of the membrane being the microporous zone filled with proton exchange polymer.

In the present invention, "SU-8" is understood as an epoxy based polymeric photoresin, in particular it refers to a glycidyl ether derived from Bisphenol-A novolac.

In a preferred embodiment the electrode comprises at least one catalyst that is selected from platinum, ruthenium, osmium, tin, cobalt, palladium or any combination thereof.

In another preferred embodiment the electrode is carbon based when deposited on the membrane, in this case forming an electrode-membrane assembly (MEA).

In a preferred embodiment, the proton exchange polymer is solidified in the micropores of the SU-8 polymer.

Preferably the proton exchange polymer is Nafin.

In a preferred embodiment the microporous SU-8 polymer has a pore size between 50 and 500 µm.

Preferably the distance between the micropores of the SU-8 is between 10 and 500 μm.

In another preferred embodiment the thickness of the membrane is less than 200 μm.

Preferably the SU-8 current collector is partially metallized with a layer of metals on the face that is in contact with the membrane.

In a preferred embodiment the metal layer is selected from titanium, nickel, gold, chromium or any combination thereof.

In another preferred embodiment the thickness of the metal layer is between 5 and 5000 nm.

In a second aspect, the present invention relates to a method of obtaining the fuel cell of the invention comprising the steps:

to.

Filling the microporous structure of the SU-8 polymer with the proton exchange polymer,

b.

protection of the microporous structure junction zones obtained in (a),

C.

deposition of the electrode on both sides of the product obtained in (b),

d.

protection of the SU-8 polymer junction zone from current collectors,

and.

partial metallization of the current collectors obtained in (d), and

F.

assembly of the product obtained in (c) with the product obtained in (e).

A third aspect of the present invention refers to the method of obtaining the fuel cell of the invention, which comprises the steps:

to.

Filling the microporous structure of the SU-8 polymer with the proton exchange polymer,

b.

protection of the bonding zone of the SU-8 polymer from the current collectors.

C.

partial metallization of the current collectors obtained in (b),

d.

deposition of the electrode on the metallic face of the product obtained in (c), and

and.

assembly of the product obtained in (a) with the product obtained in (d).

In a preferred embodiment the process of the present invention further comprises a stage prior to step (a) of UV lithography of the surface of the SU-8 polymer, to form the microperforations or micropores.

Preferably the filling of step (a) is carried out with a solution comprising the ion exchange polymer and a subsequent evaporation of the solvent. This filling is done in order to provide the ionic conductivity required to the SU-8 membranes.

In a preferred embodiment the protection of the junction zone is carried out by deposition of polydimethylsiloxane (PDMS) or a polyacetate, which acts as a shadow on the current collector to prevent metal deposition on the central active area, and on the membrane to prevent the deposition of the electrode on the central active area.

Preferably the deposition of the electrode is performed by spraying or electrodeposition, and more preferably the deposit has a metal charge between 0.1 to 4 mg / cm². The deposition can be done with a mixture of PtRu / C for the anodic zone and Pt / C for the cathodic zone.

To provide electrical conductivity to the current collectors, in a preferred embodiment the partial metallization of the collectors is carried out by means of cathodic metal spraying. In a more preferred embodiment the metals are selected from titanium, nickel, chromium or any combination thereof. And in another more preferred embodiment the metal layer obtained by spraying has a thickness between 20 and 60 nm.

In another preferred embodiment, the process of the invention further comprises an electrodeposition of metals on the metallized surface previously obtained by spraying. In a more preferred embodiment the metals are selected from among nickel, gold, chromium or any combination thereof. And in another more preferred embodiment the thickness of the metal layer obtained by electrodeposition is between 1 and 5 μm.

Once the fuel cell components are obtained separately, the collectors can be placed by alienation on both sides of the membrane, forming a sandwich.

Preferably, the fuel cell assembly is carried out by hot pressing between two current collectors obtained in (d) at a temperature between 80 and 200 ° C and at a pressure between 1 and 20 atm. After assembly it can be cooled by natural convention.

Preferably the fuel cell assembly is made with a material that is selected from methacrylate, polyketone, polycarbonate or an acrylic derivative. Encapsulating the components between two pieces of said materials, being able to be tightened by screws.

In a preferred embodiment the process of the present invention further comprises milling the assembled product, to allow access of the reactants, which can be any fuel with air.

By "milling" in the present invention is meant the cutting of a machined material, made with a rotary tool of several rows.

The views of the fuel cell assembly are shown in Figure 2.

A third aspect of the present invention refers to the use of the fuel cell described above, for obtaining energy where the fuel is selected from alcohol, hydrogen, formic acid or glucose. In a preferred embodiment the alcohol fuel is selected from between methanol or ethanol. And in a more preferred embodiment the fuel is methanol.

Since the dimensions of the fuel cell can be of the order of micrometers, one possibility of the present invention is to obtain a compact microDMFC (direct conversion methanol fuel micropile) in which all components are made of the resin SU-8. In addition, the present development not only takes advantage of the mechanical and structuring properties mentioned for this resin, but also exploits the ability of SU-8 components to join together by a hot pressing process to obtain a micropile of direct conversion fuel for compact methanol. Additionally, issues such as reducing the complexity of the device have determined its design, designed to operate under passive operation conditions (diffusion transport of fuel) with a minimum amount of Pt catalyst. As will be shown below, in First, all the components of the fuel cell are independently characterized and validated. The assembly is then carried out in order to evaluate the performance of the fuel cell for methanol concentrations and different temperatures.

Throughout the description and the claims the word "comprises" and its variants are not intended to exclude other technical characteristics, additives, components or steps. For those skilled in the art, other objects, advantages and characteristics of the invention will be derived partly from the description and partly from the practice of the invention. The following examples and drawings are provided by way of illustration, and are not intended to be limiting of the present invention.

Description of the fi gures

Figure 1. Exploded view of the SU-8 components of the fuel cell in which the main parts are identified.

Figure 2. Shows the views of the fuel cell, a) Shows the exploded view of the components of the SU-8 of the fuel cell without the proton exchange polymer, b) Shows the cross section of the mounted fuel cell, c ) Shows the exploded view of the SU-8 components of the fuel cell with the proton exchange polymer and the partial metallization of the manifolds, and d) shows the diagram of the assembled fuel cell.

Figure 3. Illustrations and cross-sectional views of the different manufacturing stages of the electrode-membrane assembly: a) porous SU-8 membrane released from the substrate, b) micropore filling with Nafin® and c) deposition of the base electrodes carbon The extensions show a circular area of 5 mm in diameter.

Figure 4. Nyquist graph of the EIS measurements for different SU-8 membranes filled with Nafon® at room temperature in air. The insert shows a detail of the high frequency values of the impedance.

Figure 5. Polarization curves of the SU-8 fuel micropile pressed by an outer casing operating with methanol concentrations of 2M and 4Mode temperatures.

Figure 6. a) Illustration of the two assemblies of the fuel micropile during characterization. b) Side view of the SU-8 fuel micropile (the scale bar in the box corresponds to 200 μm).

Figure 7. Polarization curves of the compact SU-8 fuel micropile operating with methanol concentrations of 2M and 4Moint temperatures.

Examples

The invention will now be illustrated by tests carried out by the inventors, which demonstrates the specificity and effectiveness of the polymer fuel cell or cell, its method of obtaining and its use with an alcoholic fuel.

The objective of the present example was to obtain a simple and compact design of a fuel micropile. For this reason, the system is based on a feed of methanol and diffusion air, which reduces complexity and allows discarding any auxiliary device. The fuel micropile consists of a three-component assembly made of the SU-8 photoresist: an electrode-membrane (MEA) assembly sandwiched between two current collectors. Figure 1 represents an exploded view of the proposed fuel micropile showing the structure of the MEA and the current collectors.

The MEA consists of a membrane of a size of 10 x 10 mm with a central area of 5 x 5 mm, provided with an orderly arrangement of micropores in a grid. These micropores are filled with a proton exchange polymer and are responsible for the proton conductivity of the SU-8 membrane. In this configuration, the SU-8 structure acts as a mechanical support for the proton conductive polymer and, at the same time, offers the possibility of directly joining the other SU-8 components of the fuel cell.

A total thickness of the SU-8 membrane of 170 μm was established, since this is the nominal thickness of a film of Nafon® 117, the polymer electrolytic membrane that is typically used in direct conversion methanol fuel cells. Membranes were manufactured with three different layout designs; the micropore side length was set at 250 μm and increasing membrane opening ratios were defined by establishing separations between the pores of 250 μm, 100 μm and 50 μm, in order to maximize the area of proton conductivity without compromising the mechanical stability of The structure of SU-8. After that, the active area was coated with a thin layer of carbon-based electrodes. The SU-8 frame around the active area was left uncovered for subsequent connection with the current collectors.

The SU-8 current collectors have a size of 10 x 14 mm and a thickness of 250 μm. The structures are also provided with a grid of passage holes over an area of 5 x 5 mm, coinciding with the active area of the MEA. In this way, the SU-8 structures act as current collectors and, at the same time, supply the reactants on both sides of the MEA by diffusion. In this case, two different current collector designs were manufactured for the anode and cathode sides; both designs are provided with holes of passage in grid of 100 μm of side, but the separations between the holes are established as 50 μm in the anode and 100 μm in the cathode. It has been shown that in a passive microDMFC, the imbalance between the reasons for opening the cathode and the anode prevents the cathode flooding and minimizes the transfer of methanol. A frame around the hole grid was left uncovered to allow attachment to the MEA, as indicated in Figure 1.

Manufacture and characterization of the SU-8 components of the fuel cell

The photolithography procedure was optimized to obtain suitable SU-8 released structures, capable of joining each other by a subsequent hot pressing procedure. Some lithography parameters, such as heating times and exposure dose, must be adjusted to find a compromise between a total exposure and a level of polymerization of the photoresist suitable for thermal bonding.

The lithography of the SU-8 components was performed on Si wafers of 100 mm and 500 μm thick, polished on one side only. The first stage consisted of the deposition of a sacrificial layer that must be removed at the end of the procedure to release the SU-8 structures. For this, a layer of OmnicoatTM (Microchem Corp., MA, USA) is applied on the substrate by centrifugation (speed: 2,000 rpm, time: 35 s), followed by a heating stage at 200 ° C for 1 min to evaporate the solvent From this point on, different procedures were used for the manufacture of current collectors and electrode-membrane assemblies. The current collectors were manufactured using a single layer of SU-8 100, while the membranes required a multilayer SU-8 50 procedure (both from Microchem Corp., MA, USA).

Electrode-membrane assembly manufacturing

The manufacture of the SU-8 electrode-membrane assembly consists of a series of steps that can be grouped into three main stages: 1) obtaining the photoresist structures by a UV lithography procedure; 2) functionalization of the membranes by filling the cavities in said membranes with a proton exchange polymer and 3) deposition of the carbon-based electrode by spraying with compressed air. Each of these stages is described in detail in the following sections and can be followed in Figure 3.

Porous structure of SU-8

The SU-8 membrane is composed of two layers of SU-8. The first layer defines an orderly arrangement of grid micropores over a 5x5 mm area centered on the membrane. The second layer defines a 2.5 mm wide frame around the micropore arrangement. For its manufacture, the first SU-8 50 layer was applied by centrifugation at 2,000 rpm for 35 s to obtain a thickness of 50 μm. The light heating of this layer consisted of 60 min at 25 ° C, 6 min at 65 ° C, 30 min at 95 ° C and 10 hours of cooling to 25 ° C on a hot plate, with linear increases between temperatures. The UV exposure was performed with an MA6 / BA6 mask aligner (Karl Süss MicroTec GmbH, Germany) at a dose of 190 mJ cm − 2, using a transparent sheet printed as a mask to define the membrane with the micropore arrangement. Heating after exposure consisted of 1 min at 65 ° C on a hot plate followed by 5 min at 95 ° C in a convection oven. The second SU-8 50 layer was then applied by centrifugation at 1,000 rpm for 35 s to obtain a thickness of 120 μm. The light heating of this second layer consisted of 60 min at 25 ° C, 6 min at 65 ° C, 60 min at 75 ° C and 10 hours of cooling to 25 ° C on a hot plate. The exposure of this layer was done with a dose of 270 mJ cm − 2, using a mask to define the frame around the micropore arrangement in the membrane. Heating after exposure consisted of 1 min at 65 ° C on a hot plate followed by 12 min at 95 ° C in a convection oven. Finally, the two layers were developed simultaneously for 30 min with stirring in the developer mr-600 Dev (Micro Resist Technologies GmbH, Germany) and then washed in 2-propanol and deionized water. To release the revealed SU-8 structures from the substrate, the OmnicoatTM layer was removed by soaking the wafers with stirring in the developer ma-D 332 / S (Micro Resist Technologies GmbH, Germany). The duration of this stage varied from a few minutes to several hours, depending on the geometric design of the SU-8 structure. Figure 3a shows an illustration and a cross-sectional view of the manufactured SU-8 porous membrane.

SU-8 membranes filled with Nafon®

In order to provide the SU-8 membranes with the required proton conductivity, their microperforations were filled with a liquid solution of a proton-exchange polymer (in this case, a perforated solution of the 20% Nafon® resin by weight in lower aliphatic alcohols and Sigma-Aldrich water) which solidified after evaporation of the solvent. The empty cavities of both SU-8 layers (the 50 μm thick grid and the 120 μm thick frame) were filled with 20-25 μl volumes of the solution, depending on the membrane design, by means of a micropipette The grid frame defined by the second level of lithography served as a Nafon® solution reservoir during refilling and subsequent evaporation of the solvent. In this way, Nafon® could be limited to the desired area, avoiding any dripping or spillage, and the content in each membrane was precisely controlled. Figure 3b shows an illustration and a cross-sectional view of the porous SU-8 membrane filled with Nafon®.

The aptitudes of the Na-on®-filled SU-8 membranes with respect to proton conductivity were evaluated by electrochemical impedance spectroscopy (EIS). Since the solution of the Nafon® resin used to fill the membranes was supplied in protonated form (H +), it was not necessary to activate the membranes before measurement. Therefore, the membranes were only hydrated by soaking them in deionized water at 80 ° C during the interior of a custom made support in order to avoid deformation of the SU-8 structure by temperature. The assembly used to obtain the measurements consisted of a symmetric electrochemical cell in which the membranes were placed between two thin Pt plates. The EIS measurements were performed using an impedance / gain-phase analyzer (SI 1260, Solartron Analytical) in the frequency range of 0.1 Hz to 1 MHz and a small AC amplitude in the range between 25 and 100 mV at room temperature in ambient air saturated with water (ambient humidity = 100%). The impedance spectra were acquired and analyzed with the ZPIot and ZView software. Before measuring the conductivity of the membrane the electrodes of the battery were short-circuited to determine the contact resistance. This series resistance was considered as compensation for the battery measurements. Figure 4 shows the Nyquist graph of the EIS measurements obtained from the different types of membrane. The insert shows a detail of the high frequency range of the impedance. The values of the proton conductivity of the membranes were calculated according to an analysis procedure described in the publication of P. Esquivel et al. Journal of Micromechanics and Microengineering, 19 (6) (2009) 065006. Table 1 shows a summary of the main characteristics of the measured membranes and the calculated values for proton conductivity.

It can be seen that the protonic conductivity obtained for the hybrid membranes (σ total) was 10 ± 1, 23 ± 1 and 28 ± 1mScm − 1 for the membranes A, B and C, respectively. These values were obtained considering an effective membrane area of 5 x 5 mm (Atotal), that is, including the contribution of the non-active part of the membrane SU8. Taking into account only the area filled with the Nafon® polymer, the conductivity values associated with the electrolyte (σactive) turned out to be very similar between all membranes, with values of approximately 43 ± 2mScm − 1. These results confirm the correct functionality of the proton conductive polymer once incorporated into the porous matrix of SU-8. The variability found in the conductivity value for the different support matrices could be attributed to slight discrepancies in the actual thickness of the membrane with respect to the value of 170 μm used for the calculations.

After measurements, all manufactured membranes showed good mechanical stability. No fracture or significant combustion was observed, which proves that the SU-8 matrix was able to contain the volumetric expansion of hydrated Naphon® without its structure being affected. For this reason, the SU-8 membranes were used with the highest opening ratio to manufacture the MEAs for the fuel micropile.

TABLE 1

Summary of membrane parameters and measured proton conductivities

Carbon based electrode layers

The deposition of the catalyst was performed by spraying a catalytic ink on the selected membranes. In order to define the active area to deposit the catalyst, the membranes were placed between plastic sheets from which squares of 5x5mm were cut. Thus, the sheets acted as a template during catalyst pulverization. The catalyst suspension was prepared by mixing the catalyst (PtRu / C 30% by weight, atomic ratio Pt: Ru 1: 1, for the anode and Pt / C 40% by weight for the cathode, Johnson Matthey ), with a 5% solution of the Nafin® (Aldrich) ionomer, isopropanol (Merck) and Milli-Q water. The content of Na fi on® in the ink was 55% by weight. The amount of Nafon® in the ink has been optimized to prevent flooding of the electrodes or decrease the performance of the individual battery. The suspension was dispersed in an ultrasonic bath for 45 minutes. Then, the ink was sprayed on one side of the membrane and the general process was repeated to deposit the catalyst on the other side of the membrane. In each case, the metal load was 1.0 mg cm − 2. Figure 3c shows an illustration and a cross-sectional view of the SU-8 MEA obtained.

Manufacture of fuel cell current collectors

For the manufacture of the SU-8 current collectors, a layer of SU-8 100 was applied on the wafer by centrifugation at 1,000 rpm for 35 s to obtain a 250 μm thick layer. The light heating consisted of a series of thermal steps performed on a hot plate, beginning with a rest period of 60 min at 25 ° C, followed by 6 min at 65 ° C, 90 min at 95 ° C and 10 hours of cooling to 25 ° C. UV exposure was performed with a dose of 400 mJ cm − 2. Heating after exposure consisted of 1 min at 65 ° C on a hot plate followed by 20 min at 95 ° C in a convection oven. Finally, the layer was developed in mr-600Dev with stirring for 1 hour and then washed in 2-propanol and deionized water. The revealed SU-8 collectors were released from the substrate by removing the OmnicoatTM layer in the ma-D 332 / S developer with stirring.

In order to provide the current collectors with electrical conductivity, a bilayer of 50 nm of Ti and 50 nm of Ni was deposited by sputtering (MRC-903, MRC Systems) on one of its sides. A custom piece of polydimethylsiloxane (PDMS) was placed as a shadow mask over the current collector to prevent metal deposition on the central active area of 5 x 5 mm. Thus, the surface around the active area keeps the SU-8 exposed and available to join directly to the SU-8 MEA by hot pressing. After this, the PDMS mask took off from the SU-8 structure, leaving the metal layer at the desired points. The cathodic spray applied layer was then used as the mother layer for the electrodeposition of a 1.5 μm thick Nide layer and a thin Au layer to prevent oxidation.

The electrical resistivity of the SU-8 current collectors was characterized by measurements of four probes, performed in a test sample with the same metallization but of the appropriate dimensions. The sheet metal strength resulted in a value of 46.6 mΩ per square, which was in accordance with the nominal strength of the materials for the deposited thickness.

Results and Discussion

Assembly and characterization of the fuel micropile

Once all components were obtained separately, the fuel micropile was mounted by aligning two current collectors on both sides of the MEA. Before proceeding with the thermal bonding of all these SU-8 components, a preliminary test of the SU-8 fuel cell was carried out, using the same outer shell developed for an analogous strategy for a silicon fuel micropile [J. P. Esquivel et al. Journal of Power Sources, 194 (1) (2009) 391-396]. The components were encapsulated by placing them between two machined pieces of methacrylate that were tightened by four screws. A 5.2 x 5.2 mm square window was milled through the acrylic pieces to allow reactants (diluted methanol and air) access to the active areas through the current collectors. On one of the edges of the two pieces a rounded groove was defined to fit the electrical connectors to the current collectors. The galvanic static polarization curve of the fuel micropile was obtained with a multimeter with integrated source, Keithley 2400 SourceMeter, using the own LabVIEW software. The characterization was carried out with methanol concentrations of 2 M and 4 M - since these values are generally within the range of concentrations that produce optimum yields of the fuel cell in passive devices - and at temperatures of 22 ° C (room temperature ) and 40 ° C. Figure 5 shows the polarization curves obtained with this assembly.

It can be seen that at room temperature (22 ° C) the fuel micropile reaches a maximum power density of 2.20 mW cm-2, regardless of the methanol concentration. There are no significant differences in open circuit voltage (OCV) due to methanol transfer and the V-curves are controlled primarily by ohmic losses. When the battery temperature increases to 40 ° C, the maximum power densities rise to 3.75 mW cm − 2 and 4.15 mW cm − 2 for fuel concentrations of 2 M and 4 M, respectively. This is mainly due to the improvement in the performance of the fuel micropile in the ohmic region due to the increase in the proton conductivity of Nafon® at increasing temperatures. This time, a visible improvement can be observed in the region limited by the transport of the l-V curve as the methanol concentration of 2Ma4M increases.

After this test, the SU-8 structures were joined together by a hot pressing procedure to obtain the compact device. A suitable support was made to align and press the current collectors and the MEA together. The alignment was done by inserting four needles through the small circular holes located in the corners of the SU-8 components. The assembly was then placed in a commercial hot press (P / O / Weber, Germany) and heated at 85 ° C for 10 min and at 120 ° C with a force of 2 kN for 20 min. Then, the assembly was cooled by natural convection and the attached SU8 fuel micropile was released for testing. With this assembly, the total volume of the device is reduced more than 50 times (0.12 cm3 compared to 6.75 cm3). Figures 6a and 6b show photographs of the two assemblies tested and a side view of the compact device, in which the significant reduction in size between the two strategies is clearly observed.

The characterization was carried out under the same conditions as for the previous assembly. Figure 7 shows the polarization curves obtained. After the union of the components, all curves have higher voltage values in open circuit conditions (500-580 mV) and then a sudden voltage drop, due to activation losses. After that, the curves are mainly controlled by ohmic losses, without showing limitations in the mass transport region. In this case, the fuel micropile produced a very similar maximum power density with the two methanol concentrations and working temperatures tested. With a concentration of 2 M, the temperature increase from 22ºC to 40ºC increased the power density from 0.35 to 0.55 mW cm − 2, while with 4 M, the power increased from 0.40 to 0.65 mW cm − 2.

Discussion

The results show a clear difference in the power supplied by the SU-8 fuel micropile depending on the assembly. When tightened with an external acrylic housing, the maximum power density of 4.15 mW cm − 2, obtained at 40 ° C and with a methanol concentration of 4 M, is comparable to the results described in the literature for other manufactured microDMFCs partly with components of SU-8 [H. -Y. Cha et al.

Electrochimica Acta, 50 (2-3) (2004) 795-799. And in C. Weinmueller et al. Journal of Power Sources, 195 (12) (2010) 3849-3857], It is important to keep in mind that, unlike previous work, this strategy reduces both the complexity of the device and its cost, thanks to the use of a power supply of methanol and air by diffusion and the minimization of the amount of Pt catalyst at 1 mg cm -2. In addition, the Nafon® continuous film, typically used in other strategies, has been replaced in this case by a porous SU-8 membrane filled with Naphon®. The use of the membrane clearly increases the level of integration of the final device, although it reduces the area of available proton conductivity by 36%.

When the components join together forming a compact device, the maximum power density produced by the SU-8 fuel micropile decreases to 0.65 mW cm − 2. This is due to an increase in voltage losses in the ohmic region of polarization curves. It can be seen that the curves in Figure 7 have the same slope, regardless of the temperature and the concentration of methanol, which indicates the existence of a significant contact resistance between the membrane and the current collectors. That is, although the SU-8 components are satisfactorily connected and no fuel leakage is observed, the pressure applied between them is lower than the pressure exerted by the external housing. However, despite the decrease in its performance, the drastic reduction in the dimensions of the device achieved with this strategy results in a substantial increase in the volumetric power density of 0.15 mW cm − 3 when using the external housing at 1.35 mW cm − 3 in the strategy of the compact device.

Conclusions

In the example of the present invention a strategy is presented for obtaining a fully polymeric fuel micropile, based on the SU-8 photoresist. All the components of the fuel cell (current collectors and MEA) are made of the same material, whose connection capabilities are exploited to obtain a highly compact device. Integration is achieved in two stages; Firstly, by incorporating a polymer electrolyte into a porous SU-8 membrane and, secondly, by joining all SU-8 components together.

The fuel micropile was first characterized using an outer shell to validate the functionality of its components. Despite the simplicity associated with the passive fuel supply and the low catalyst content, the performance of the present fuel micropile is comparable to that of the few polymeric devices described so far. After validation, the components were joined together by hot pressing, in order to obtain the compact device. The characterization of the assembly showed a decrease in power density due to an increase in contact resistance. However, the drastic reduction in the dimensions of the device by dispensing with the external housing resulted in a higher volumetric power density.

However, the results presented demonstrate the potential of this strategy to obtain fully polymeric energy sources and benefit from the advantages associated with SU-8 resin technology (for example, high chemical and mechanical stability of the structures, high resolution of patterns, low cost). In addition, the use of this technology offers additional opportunities for the integration of a fuel micropile into a variety of polymeric devices, such as the chip laboratory (lab-on-chip) and other micro-fluidic platforms.

Claims (31)

1. Polymeric fuel cell comprising:

to.

a sandwich membrane between two current collectors, and

b.

two electrodes that are each attached to both sides of the membrane or in each of the current collectors,

characterized in that the membrane comprises a microporous SU-8 polymer, a proton exchange polymer and where the current collectors comprise the partially metallized microporous SU-8 polymer.

2.

Fuel cell according to claim 1, wherein the electrode comprises at least one catalyst that is selected from platinum, ruthenium, osmium, tin, palladium, cobalt or any combination thereof.

3.

Fuel cell according to any of claims 1 or 2, wherein the electrode is carbon based when deposited on the membrane.

Four.

Fuel cell according to any one of claims 1 to 3, wherein the proton exchange polymer is solidified in the micropores of the SU-8 polymer.

5.

Fuel cell according to any of claims 1-4, wherein the proton exchange polymer is Nafin.

6.

Fuel cell according to any one of claims 1 to 5, wherein the microporous SU-8 polymer has a pore size between 50 and 500 µm.

7.

Fuel cell according to any one of claims 1 to 6, wherein the distance between the pores of the SU8 is between 10 and 500 µm.

8.

Fuel cell according to any one of claims 1 to 7, wherein the thickness of the membrane is less than 200 μm.

9.

Fuel cell according to any of claims 1-8, wherein the SU-8 current collector is partially metallized with a layer of metals on the face that is in contact with the membrane.

10.

Fuel cell according to claim 9, wherein the metal layer is selected from titanium, nickel, gold, chromium or any combination thereof.

eleven.

Fuel cell according to any of the 9 or 10, where the thickness of the metal layer is between 5 and 5000 nm.

12.

Method of obtaining the fuel cell according to any of claims 1 to 11, comprising the steps:

to.

Filling the microporous structure of the SU-8 polymer with the proton exchange polymer,

b.

protection of the microporous structure junction zones obtained in (a),

C.

deposition of the electrode on both sides of the product obtained in (b),

d.

protection of the SU-8 polymer junction zone from current collectors,

and.

partial metallization of the current collectors obtained in (d), and

F.

assembly of the product obtained in (c) with the product obtained in (e).

13.

Method of obtaining the fuel cell according to any of claims 1 to 11, comprising the steps:

to.

Filling the microporous structure of the SU-8 polymer with the proton exchange polymer,

b.

protection of the bonding zone of the SU-8 polymer from the current collectors.

C.

partial metallization of the current collectors obtained in (b),

d.

deposition of the electrode on the metallic face of the product obtained in (c), and

and.

assembly of the product obtained in (a) with the product obtained in (d).

14.

Method according to claim 12 or 13, further comprising a stage prior to step (a) of UV lithography of the SU-8 polymer.

fifteen.

Process according to any of claims 12 to 14, wherein the filling of the microporous structure is carried out with a solution comprising the ion exchange polymer and a subsequent evaporation of the solvent.

16.

Method according to any of claims 12 to 15, wherein the protection of the junction zones is carried out by deposition of polydimethylsiloxane or a polyacetate.

17.

Method according to any of claims 14 or 15, wherein the deposition of the electrode is performed by spraying or electrodeposition.

18. The method according to claim 17, wherein the tank load is between 0.1 to 4 mg / cm².

19.

Process according to any of claims 12 to 18, wherein the partial metallization is carried out by means of cathodic metal spraying.

twenty.

Process according to claim 19, wherein the powdered metals are selected from titanium, nickel, chromium or any combination thereof.

twenty-one.

Process according to any of claims 19 or 20, wherein the metal layer obtained by spraying has a thickness between 20 and 60 nm.

22

Method according to any of claims 19 to 21, further comprising an electrodeposition of metals on the metallized surface.

2. 3.

Process according to claim 22, wherein the electrodeposited metals are selected from nickel, gold or any combination thereof.

24.

Method according to any of claims 22 or 23, wherein the thickness of the metal layer obtained by electrodeposition is between 1 and 5 μm.

25.

Method according to any of claims 12 to 24, wherein the assembly is carried out by hot pressing, at a temperature between 80 and 200 ° C and at a pressure between 1 and 20 atm.

26.

Process according to any of claims 12 to 25, wherein the assembly is carried out with a material selected from methacrylate, polyketone, polycarbonate or acrylic derivative.

27.

Method according to any of claims 12 to 26, which further comprises milling the assembled product.

28.

Use of the polymeric fuel cell according to any one of claims 1 to 11, as the fuel cell of a fuel selected from alcohol, hydrogen, formic acid or glucose.

29.

Use according to claim 28, wherein the alcohol fuel is selected from methanol or ethanol.

30

Use according to claim 29, wherein the fuel is methanol.

SPANISH OFFICE OF THE PATENTS AND BRAND Application no .: 201031024 SPAIN Date of submission of the application: 02.07.2010 Priority Date: REPORT ON THE STATE OF THE TECHNIQUE 51 Int. Cl.: See Additional Sheet RELEVANT DOCUMENTS

Category

Documents cited Claims Affected

TO

CHA, H-Y. et al. Fabrication of all-polymer micro-DMFCs using UV-sensitive photoresist. Electrochimica Acta 2004, Vol. 50, pages 795-799. See Summary, Introduction and Experimental. 1-30

 TO

HSIEH, S-S. et al. SU-8 flow field plates for a micro PEMFC. Journal of Solid State Electrochemistry 2005, Vol. 9, pages 121-123. See page 122. 1-30

TO

US 2004053100 A1 (STANLEY K. G et al.) 18.03.2004, paragraph [0037]. 1-30

TO

CHA, S.W. et al. Electrochemical impedance investigation of flooding in micro-flow channels for proton exchange membrane fuel cells. Journal of Power Sources 2006, Vol. 161, pages 138-142. See Experimental. 1-30

Category of the documents cited X: of particular relevance Y: of particular relevance combined with other / s of the same category A: reflects the state of the art O: refers to unwritten disclosure P: published between the priority date and the date of priority submission of the application E: previous document, but published after the date of submission of the application

This report has been prepared • for all claims • for claims no:

Date of realization of the report 03.11.2011

Examiner M. C. Bautista Sanz Page 1/4

REPORT OF THE STATE OF THE TECHNIQUE Application number: 201031024 CLASSIFICATION OBJECT OF THE APPLICATION H01M8 / 10 (2006.01) H01M8 / 02 (2006.01) H01M2 / 16 (2006.01) Minimum documentation sought (classification system followed by classification symbols) H01M, Y02E Electronic databases consulted during the search (name of the database and, if possible, terms of search used) INVENES, EPODOC, WPI, NPL, XPESP, HCAPLUS State of the Art Report Page 2/4  WRITTEN OPINION Application number: 201031024 Date of Written Opinion: 03.11.2011

Statement

Novelty (Art. 6.1 LP 11/1986)

Claims Claims 1-30 IF NOT

Inventive activity (Art. 8.1 LP11 / 1986)

Claims Claims 1-30 IF NOT

The application is considered to comply with the industrial application requirement. This requirement was evaluated during the formal and technical examination phase of the application (Article 31.2 Law 11/1986).  Opinion Base.- This opinion has been made on the basis of the patent application as published. State of the Art Report Page 3/4  WRITTEN OPINION Application number: 201031024 1. Documents considered.- The documents belonging to the state of the art taken into consideration for the realization of this opinion are listed below.

Document

Publication or Identification Number publication date

D01

CHA, H-Y. et al. Electrochimica Acta, Vol. 50, pp. 795-799. 2004

D02

HSIEH, S-S. et al. Journal of Solid State Electrochemistry, Vol. 9, pp. 121-123. 2005

D03

US 2004053100 A1 (STANLEY K. G et al.) 03/18/2004

D04

CHA, S.W. et al. Journal of Power Sources 2006, Vol. 161, pp. 138-142. 2006

2. Statement motivated according to articles 29.6 and 29.7 of the Regulations for the execution of Law 11/1986, of March 20, on Patents on novelty and inventive activity; quotes and explanations in support of this statement The object of the invention is a polymeric fuel cell in which the membrane and the current collectors are made with the SU-8 epoxy photoresin as well as obtaining the battery and its use to obtain energy from different fuels. Document D01 discloses a completely polymeric micro-DMFC fuel cell in which the ion exchange membrane is sandwiched between two sheets of polymers with anode and cathode channels and two layers of photosensitive polymers thus acting as current collectors, fuel diffusion layer and catalyst supports. The formation of channels is carried out by ultraviolet photolithography with the SU-8 epoxy resin and the final assembly of the assembly is done by hot pressing (See summary; Introduction and Experimental). Documents D02 to D04 disclose polymeric fuel cells in which the SU-8 epoxy resin is used for flow field plates made by photolithography and Nafion as an ion exchange membrane (See D02: page 122; D03: paragraph [0037] ; D04: Experimental). None of the cited documents, nor any relevant combination thereof, discloses a polymer fuel cell in which the membrane is formed by a proton exchange polymer solidified in the micropores of the SU-8 polymer and in which the current collectors are made with the same microporous SU-8 epoxy polymer. Therefore, the invention defined in claims 1 to 30 meets the requirements of novelty and inventive activity according to articles 6.1. and 8.1. of patent law 11/1986. State of the Art Report Page 4/4