KR20060120194A - Formic acid fuel cells and catalysts - Google Patents

Abstract

An exemplary fuel cell of the invention includes a formic acid fuel solution in communication with an anode (12, 134), an oxidizer in communication with a cathode (16, 135) electrically linked to the anode, and an anode catalyst that includes Pd. An exemplary formic acid fuel cell membrane electrode assembly (130) includes a proton- conducting membrane (131) having opposing first (132) and second surfaces (133), a cathode catalyst on the second membrane surface, and an anode catalyst including Pd on the first surface.

Description

FORMAT ACID FUEL CELL AND CATALYST

Cross-reference

The present invention discloses US application no. 10 / 407,385, filed April 4, 2003; US Provisional Application No. 60 / 519,095, filed November 12, 2003; US Application No. 10 / 664,772, filed September 17, 2003; And US Application No. 10 / 817,361, filed April 2, 2004, each of which is incorporated herein by reference.

Statement of Government Rights

The present invention is made with government support under the Department of Energy Grant No. DEGF-02-99ER14993 and DARPA Air Force Contract No. F33615-01-C-2172. The government has certain rights in the invention.

The present invention relates generally to formic acid fuel cells, catalysts for formic acid fuel cells, methods for producing formic acid fuel cell catalysts, and formic acid fuel cell membrane electrode assemblies.

A fuel cell is an electrochemical cell in which the free energy change resulting from a fuel oxidation reaction is converted into electrical energy. Applications of fuel cells include battery replacement, minielectronics and microelectronics, automotive engines, power plants and many others. One advantage of fuel cells is that they are actually pollution free.

In hydrogen fuel cells, hydrogen gas is oxidized to form water with the useful electric current generated as a byproduct of the oxidation reaction. The solid polymer membrane electrolyte layer can be used to separate hydrogen fuel from oxygen. The anode and the cathode are aligned on opposite sides of the membrane. Electron flow between the anode and cathode layers of the membrane electrode assembly may be utilized to provide power. However, hydrogen fuel cells are impractical for many applications because of the difficulties associated with storing and handling hydrogen gas.

Organic fuel cells may prove useful as a replacement for hydrogen fuel cells in many applications. In organic fuel cells, organic fuels, such as methanol, are oxidized to carbon dioxide at the anode while air or oxygen is simultaneously reduced to water at the cathode. One advantage over hydrogen fuel cells is that organic / air fuel cells can be operated with liquid organic fuels. This eliminates the problems associated with handling and storing hydrogen gas. Some organic fuel cells require an initial conversion of organic fuel to hydrogen gas by a reformer. Such cells are called "indirect" fuel cells. The need for modifiers increases the size, cost, complexity and start up time of the cell. Another type of organic fuel cell, referred to as a "direct" fuel cell, eliminates these drawbacks by directly oxidizing the organic fuel without conversion to hydrogen gas. Further classification of fuel electricity can distinguish "passive" cells from "active" cells. In active cells, the fuel solution is provided continuously (eg by pumping) for contact with the anode, while in a "passive" cell, a specified amount of fuel solution is provided for the reaction.

Fuel cells, including methanol, formic acid and other organic fuel cells, utilize anode and cathode catalysts to promote efficiency. The catalyst promotes a reduction reaction at the cathode and an oxidation reaction at the anode. Some prior attempts have focused on platinum (Pt) based catalysts, for example two platinum / ruthenium or platinum / palladium anode catalysts. When used in organic fuel cells, known anode catalysts, including Pt-based catalysts, have only low levels of activity compared to those in hydrogen fuel cells. As a result, organic cells tend to require relatively large loading catalysts. This adds significant cost to the fuel cell due to the expensive precious and semi precious metals present in the catalyst.

Exemplary fuel cells of the present invention include an anode catalyst comprising a formic acid fuel solution in communication with the anode, an oxidant in communication with the cathode electrically connected to the anode and Pd. An exemplary formic acid fuel cell membrane electrode assembly includes an anode catalyst comprising a proton conductive membrane having opposing first and second surfaces, a cathode catalyst on the second membrane surface and Pd on the first surface.

Brief description of the drawings

1 is a chart illustrating the catalytic activity of a number of the Pd-M catalysts of the present invention for formic acid reduction, wherein M is Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Au.

2 is Tapel data for an exemplary Pd-V catalyst formulation compared to a commercially available PtRu alloy catalyst for formic acid oxidation.

3 illustrates the chronoamperometric activity of an exemplary Pd-V catalyst for 20 hours of formic acid oxidation.

Figure 4 illustrates the large-time amphoteric activity of Pd-V for methanol oxidation reaction for 20 hours.

5 (a) illustrates the large time amphoteric activity of an exemplary Pd catalyst used in the exemplary formic acid fuel cell of the present invention.

FIG. 5 (b) shows the data of FIG. 5 (a) normalized on the basis of Pd weight per unit.

FIG. 5 (c) shows the data of FIG. 5 (c) normalized to Pd active surface area.

6 illustrates experimental results for exemplary fuel cells and fuel cell catalysts of the present invention.

Figure 7 illustrates the experimental results for the exemplary fuel cell and fuel cell catalyst of the present invention.

8 illustrates experimental results for an exemplary fuel cell and fuel cell catalyst of the present invention.

9 illustrates experimental results for exemplary fuel cells and fuel cell catalysts of the present invention.

10 is a schematic diagram of a first exemplary fuel cell of the present invention.

11 is a schematic diagram of a second exemplary fuel cell of the present invention.

12 is a schematic diagram of a portion of a second exemplary fuel cell of the present invention.

13 is a schematic diagram of a portion of a second exemplary fuel cell of the present invention.

14 is a schematic diagram of an electrical circuit utilizing an exemplary fuel cell of the present invention.

15 is a schematic representation of a portion of a second exemplary fuel cell of the present invention.

Detailed description of the invention

Before describing the exemplary embodiments of the present invention in detail, those skilled in the art will understand that the present invention includes a formic acid fuel cell and a formic acid fuel cell catalyst, and the numerous embodiments of the invention will be understood by reference to the preferred embodiments. Could be. It will further be appreciated that when describing one exemplary embodiment of the present invention, a description of another exemplary embodiment is also made. For example, the description of the catalyst may likewise include the description of the fuel cell when discussing the use of the catalyst in connection with the fuel cell. One aspect of the invention relates to a catalyst for use with a formic acid fuel cell. Exemplary fuel cell catalysts of the present invention include Pd and at least one metal selected from the group of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W or Au. The catalyst of the present invention may be useful as an anode or cathode catalyst [SF1] and may be supported or unsupported. In particular carbon can be used as a support. Exemplary embodiments of the invention include an anode catalyst for a formic acid fuel cell. Pd-based catalysts of the present invention provide a number of advantages and advantages, including the cost, which may be less than three factors less than Pt, and in some conditions, activity levels above the order of magnitude greater than Pt-based catalysts. To illustrate the catalyst of the present invention, a number of exemplary catalysts are prepared and tested.

First group of exemplary catalysts

Ti (Alfa-Aesar 44243), Zr (Alfa-Asa 10594), Hf (Alfa-Asa 10793), V (Alfa-Asa 13783), Nb (Alfa-Asa 10261), Ta (alpha-Asa) 14266), Cr (alpha-assa 4242), Mo (alpha-assa 4141), W (alpha-assa 10416) and Au (alpha-assa 14721) foil samples were washed by sanding with 200 gr sandpaper, followed by Millipore Wash with Millipore water. Each foil is attached to a working electrode in a standard binary electrode electrochemical cell equipped with a platinum counter electrode. Droplets of 0.01 M PdCl ₂ (alpha-assay 11034) are placed between the working electrode and the counter electrode. A potential difference of -450 mV is then applied between the foil electrode and the counter electrode. The potential is maintained until a 0.6 monolayer of Pd is deposited on the metal foil. The dislocation is then removed and the foil is washed in Millipore water.

The foil is then tested in a standard three way electrode electrochemical cell equipped with a platinum counter electrode and a silver / silver chloride reference electrode. The foil adheres to the working electrode in the electrochemical cell without applying a potential. A solution containing 5 M formic acid and 0.1 M sulfuric acid in Millipore water is charged into the cell. Then, a potential of 0.3 V associated with the reversible hydrogen electrode is applied to the cell. 1 shows the current per mg of palladium measured for each catalyst formulation. The current is very high with V providing the highest measurement. Those exhibiting very good performance include Au, Mo, Ti and Mb. The current is also measured as a function of time at 0.3, 0.4, 0.5 and 0.6 V in relation to RHE.

2 shows the current obtained after 2 hours in this experiment. Figure 2 also illustrates the current measured with the Johnson Mathey Hispec 6000 Pt / Ru catalyst of the prior art under the same conditions. 2 shows that the current per mg of noble metal is at least 3 orders of magnitude higher with the Pd / V catalyst of the present invention than with the Pt / Ru catalyst. This is a surprising result suggesting that the practical advantages and advantages are achieved through the catalyst of the present invention. 2 shows the results of a 20 hour test of the Pd / V catalyst of the present invention. It should also be noted that the Pd / V catalyst of the present invention remains very active in the oxidation reaction of formic acid during the 20 hour test. This also shows surprising results.

In addition, the coverage of Pd on V is observed to affect activity. Too high application can be economically disadvantageous due to the relatively high cost of Pd. Too low application can result in undesirable low levels of current density. Although other levels are expected and may be desirable for particular applications, application of about 0.15 to about 0.55 Pd monolayers on V has been found to provide useful levels for current density and current per mg of Pd. In addition, the application of Pd on Zr was observed to affect the activity. Although other levels are anticipated and may be desirable for certain applications, Pd application of about 0.45 to about 1 Pd monolayer on Zr has been found to be useful.

It should be noted that the Pd catalyst can be poisoned over time when used with formic acid fuel cells, resulting in some reduced activity. It is speculated that OH or other poisoning species may bind to the catalytic site and render it unusable for future catalytic activity. It is believed that the addition of metal M, specific examples Au, V and Zr, can prevent or reduce intoxication. In addition, it has been found that the action of poisoning can be reversed significantly, and that poisoning species can be removed through application of high potential. Thus, for example, when operating the formic acid fuel cell of the present invention with a Pd catalyst, it may be useful to apply a high potential intermittently to "clean" the Pd catalyst of the poisoning species.

Exemplary fuel cells of the present invention are connected to a capacitor or other charge storage device so that a sufficient high potential can be applied in some cases to clean the Pd catalyst. Some of the energy generated by the exemplary fuel cell of the present invention can be used to clean a Pd catalyst by charging a capacitor or other storage device over a period of about 30 minutes and then applying a charge, for example, from the capacitor. have.

Second group of exemplary catalysts

To make another group of exemplary catalysts of the present invention, Ti (alpha-assa 44243), Zr (alpha-assasa 10594), Hf (alpha-assasa 10793), V (alpha-assasa 13783), Nb (alpha- Asa 10261), Ta (alpha-assa 14266), Cr (alpha-assa 4242), Mo (alpha-assa 4141), W (alpha-assa 10416) and Au (alpha-assa 14721) foil samples were prepared with 200 gr sandpaper. It is washed by sanding and then by millipore water. Each foil is then placed in 0.01 M PdCl ₂ solution for about 1 minute and then washed with Millipore water. Each foil is then attached to a working electrode in a standard binary electrode electrochemical cell equipped with a platinum counter electrode. A droplet of 0.1 MH ₂ SO ₄ is placed between the working electrode and the counter electrode. A potential difference of -450 mV is then applied for about 30 seconds between the foil electrode and the counter electrode. The dislocation is then removed and the foil is washed with Millipore water. The resulting catalyst of the present invention is the result.

Third Exemplary Catalyst

PdV catalysts are exemplary catalysts of the present invention which are believed to show useful benefits and advantages when used as anode catalysts for formic acid fuel cells. In addition to the process for preparing this catalyst, to further illustrate the exemplary catalyst, the catalyst is synthesized and tested.

First 50 mg of V metal powder (alpha-Asa 12234) are immersed in 1 MH ₂ SO ₄ and then washed in Millipore water. Next, 0.4 mL of 0.01 M PdCl _{2 in} Millipore water is added dropwise to the stirred solution while the powder is vigorously stirred in Millipore water. The active V powder is reacted with Pd ²⁺ ions and the Pd metal precipitates on the V powder surface. Next, 100 mg of Millipore water and a 5 wt% NAFION solution (Solution Technologies) (NAFION was commercially available from tetrafluoroethylene and perfluorovinylether sulfonic acid purchased from DuPont Chemical Co., Delaware, A proprietary catalyst suspension is formulated by sonicating a solution with 18.2 mg with 10 mg of Pd / V for 10 minutes. Then about 40 mg of this catalyst suspension is placed on a graphite rod working electrode (6 mm in diameter) using a micropipette. The electrode is then dried under a heat lamp for 25 minutes to produce a Pd / V catalyst containing about 20 wt% NAFION on the working electrode. The [SF2] working electrode is then placed in a solution of 0.5 M formic acid and 0.1 M sulfuric acid in Millipore water and tested for activity by setting the potential to 0.3 V. The catalyst was found to be very active, having a performance very similar to that of the Pd / V foils discussed above.

Those skilled in the art will appreciate that catalysts of the present invention can be added with promoters such as Au, silver (Ag), selenium (Se), bismuth (Bi), Ru, nickel (Ni), Pt, Mo, W, manganese (Mn) You will understand that you can benefit from it. Other catalysts of the present invention include such promoters.

Fourth group of exemplary catalysts

 Some catalysts have been found to exhibit surprising levels of catalytic activity when used with the formic acid fuel cell of the present invention. For example, supporting a metal catalyst on carbon has been found to significantly increase catalyst activity on a mass basis of metal. For example, it has been found that catalysts containing Pd supported on carbon can realize advantages and advantages over other catalysts, including unsupported Pd. Pd may be in the form of nanoparticles supported on carbon. Another metal comprising at least one of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo or W can be combined with Pd. Pd combined with one or more of Au, V, and Mo and supported on carbon is considered to provide beneficial activity to formic acid fuel cells, and surprising results are further achieved by increasing metal surface area on carbon nanoparticles. In addition to the process for preparing such catalysts, the present invention includes such catalysts. In addition, some methods of synthesizing Pd-based catalysts have been found to produce higher activity catalysts when used with formic acid solution cells than catalysts prepared through other synthesis methods.

To further illustrate additional exemplary catalysts of the present invention and methods for their preparation, the synthesis of three exemplary carbon supported catalysts of the present invention is described. Three exemplary catalysts are 20 wt% Pb catalyst supported on carbon (C), 20 wt% PdAu catalyst supported on carbon, and 40 wt% Pd catalyst supported on carbon. Percentage refers to the weight percent of Pd relative to carbon. For example, the 20 wt% Pd catalyst supported on carbon is 20 wt% Pd and 80 wt% carbon. For the exemplary PdAu catalyst, Pd is provided in a ratio of 50: 1 relative to Au, combined PdAu is 20% by weight in total, and carbon is the remaining weight%.

Different weight ratios of Pd to carbon support will be useful and may be selected based on factors including the fuel solution to be catalyzed and other factors. For the exemplary formic acid fuel cell of the present invention, at least about 5% by weight (eg, 5% Pd, 95% carbon) based on the total weight of the catalyst is considered advantageous. Other weight ratios that are considered useful are at least about 10% Pd based on the total weight of the catalyst and at least about 20% Pd based on the total weight of the catalyst. Increasing weight ratios generally show increased activity, but also increase cost. At some weight ratio points, increased activity is not justified at increased cost. A weight ratio of about 20% is believed to be a useful level of significant catalytic activity while also achieving significant cost savings. Other weight ratios are also contemplated, including up to 5% Pd.

Each exemplary carbon-supported catalyst is prepared by a metal chloride reduction process. First, the carbon (VULCAN XC-72 available from Cabot Corp., Alpharetta, GA) was stirred in 10 M HCl in Millipore water for about 12 hours and then washed with Millipore water until the pH of the wash solution reached 7. Condition by doing. Next, a solution of 8 g / L PdCl ₂ and Millipore water in 5 M HCl is added to the beaker. The amount of solution added depends on the desired weight percent of Pd in the catalyst prepared:

For 20 wt% Pd catalyst on carbon and 20 wt% PdAu catalyst on carbon, add about 5 mL of solution.

For 40 wt% Pd catalyst on carbon, add about 14 mL of solution.

In addition, about 1 mL of a solution of 5 g / L polyvinyl alcohol (PVA) in Millipore water is added to the beaker. Then, 100 mg of conditioned carbon is added with sufficient water to make a total of 1 L. Then 50 mL of freshly prepared 0.05 M NaBH ₄ in Millipore water is added dropwise with vigorous stirring of the solution. Upon completion of this, the pH of the solution is raised to about 11 by addition of 5 M NaOH. The solution is then vigorously stirred for 1 hour, after which the catalyst is allowed to settle for an additional 30 minutes. The carbon supported catalyst is then filtered, washed in millipore water and dried at 80 ° C. for about 8 hours.

In the case of the PdAu catalyst on the exemplary carbon, the HAuCl ₄ solution dissolves a predetermined amount of gold powder (alpha Asa) to give Pd: Au 50: 1 in a minimum amount of aqua regia (3 parts thick HCl to 1 part HN0 ₃ thick). Prepared by providing a final molar ratio and removing HNO ₃ with heating. This is then added to the solution in the same step as the addition of PdCl ₂ which performs the same procedure as above.

Each exemplary catalyst is then tested for activity. The catalyst is tested using the exemplary cell fuel solution of the present invention. All experiments are performed at room temperature in air using conventional three way electrode cells. Electrochemical measurements are performed using Solartron SI 1287 attached to a computer using CorrrWare software. Counter electrode is 25 mm x 50 of 52 mesh platinum treated platinum gauze (woven with 0.1 mm diameter, 99.9%, alpha asa) attached to the platinum wire (0.6 mm in diameter, 12 cm in length, 99.5%, Alpha Asa). Prepared in mm fragments. The reference electrode is Ag / AgCl (BASF, MF-2052) in 3.0 M NaCl. For convenience, the results are recorded against the reversible hydrogen electrode (RHE). Two further exemplary Pd catalysts of the invention are likewise tested, both of which are not supported. One Pd catalyst is high surface area Pd (“Alfa Pd black”) commercially available from Aldrich Chemical Co., and the other is commercially available from Alpha-Asa Chemical. Low surface area Pd (“Alfa Pd black”).

All five catalysts are attached to graphite working electrodes for testing in electrochemical cells. First, 5 mg / mL of a suspension of each catalyst in Millipore water is prepared. Sufficient 5% by weight NAFION solution is then added to produce 20% by weight NAFION in the catalyst layer upon drying. Each catalyst is sonicated for 10 minutes. Next, 50 μL of the suspension is placed on a graphite working electrode using a micropipette and dried under a heat lamp for about 25 minutes. After drying, the electrodes are cooled for about 10 minutes and then washed with Millipore water. All working electrodes are stabilized and no catalyst particles are observed to desorb during the experiment.

Catalyst samples are tested in conventional three-way electrode cells by contacting the working electrode with the interface of a 5 M HCOOH / 0.1 MH ₂ SO ₄ solution contained in the cell. Subsequently, the large-time ammeter method is performed by holding the working electrode at 0.3 V against the reversible hydrogen electrode (RHE) while measuring the current over time. FIG. 5 (a) shows a large time amperometric measurement at 0.3 V versus RHE for each of the five catalysts regardless of the total catalyst weight, whereas FIG. 5 (b) shows activity on a Pd basis per weight. It is shown. By both measurements, low surface area Pb black (Alfa) has the lowest performance and is inactivated after the first two hours. High surface area Aldrich Pd blacks have much better performance and are inactivated much more slowly. FIG. 5 (a) shows that the high surface area Aldrich Pd black exhibits the highest overall activity, with 40 wt% Pd catalyst on carbon followed by 20 wt% PdAu catalyst on carbon, 20 wt% Pd catalyst on carbon and finally low surface area Pd It is shown that the order of black shows the total activity.

However, the result of FIG. 5 (a) does not consider the amount of Pd present in the catalyst. This may be important because it is a major cost factor. Figure 5 (b) records the same data as Figure 5 (a) except that the results are based on Pd content. 5 (b) shows that the inactivation of alpha Pd black is substantially greater than that of other Pd catalysts. The carbon supported catalyst of the present invention initially exhibits a higher current density than Aldrich Pd black. However, Aldrich Pd black deactivates more slowly, thus surpassing the performance of carbon supported catalysts for longer periods of time. The 40 wt% Pd catalyst on carbon has a lower initial current density than the two 20 wt% Pd catalysts and is inactivated more slowly. 5 (a) and 5 (b) show that the addition of small amounts of Au to the carbon supported Pd catalyst enhances the catalyst's performance.

It is believed that similar advantages and advantages will be achieved when one or more metals from the group of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo or W are combined with Pd and supported on carbon. Metal M in combination with Pd can double overall catalyst activity, increase corrosion resistance, reduce toxic effects and have other advantages. In particular, V and Mo are believed to provide advantageous activity levels for formic acid fuel cells when combined with Pd and supported on carbon. Au may be the preferred metal for some applications because of its relatively high corrosion resistance. Catalysts of the present invention include the use of these metals in combination with Pd and supported on carbon as catalysts for formic acid fuel cells. Those skilled in the art will appreciate that exemplary catalysts comprising Pd and any of these metals can be synthesized using methods consistent with the exemplary synthesis of the invention described above with reference to the preparation of exemplary Pd supported on carbon catalysts. I will understand that.

FIG. 5 (c) compares the large time amphoteric activity of the exemplary Pd-based catalyst of the present invention at 0.3 V compared to RHE on a total surface area basis. The carbon supported catalyst has the best initial activity and after 8 hours both the 40 wt% Pd catalyst and the 20 wt% PdAu catalyst on carbon perform the same as Aldrich Pd Black, while the 20 wt% Pd catalyst on carbon is further Inactive. Low surface area alpha Pd blacks have the lowest activity.

In general, exemplary carbon supported catalysts of the present invention perform very well when used with formic acid fuel cells. The performance of these catalysts tends to be lower than the high surface area Aldrich Pd black on the basis of the total catalyst, but when considering the amount of Pd present and comparing the results on a per Pd basis or on an active surface area, the carbon supported catalyst was unsupported It tends to perform equal to or better than black. This is a surprising and advantageous result. The more efficient use of Pd in the carbon supported catalyst of the present invention takes into account that it is possible to significantly reduce the overall Pd loading and thus the overall catalyst cost while maintaining sufficiently high catalytic activity.

It should be noted that some fuel cell arrangements may have practical limits on the total amount of catalyst (eg, Pd and carbon) that can be loaded into the fuel cell membrane. In many cases, this limit is within about 6-8 mg / cm ² of the membrane surface area. This practical limitation has the consequence that in some fuel cell arrangements, the total amount of Pd on the membrane may be significantly less than in the case of unsupported catalysts in some cases. In addition, for fuel cells facing these practical limitations, the improved efficiency of the exemplary catalysts of the present invention may be limited. It should also be noted that for certain amounts of Pd, the catalyst layer will be thicker for the carbon supported catalyst of the present invention than for unsupported Pd. This has the potential to cause some mass transfer problems at high current densities. Despite these potential concerns, the higher activity of the Pd catalyst of the present invention per mass of Pd provides important advantages and advantages, particularly when implemented in formic acid fuel cells.

The 20 wt% PdAu catalyst on carbon has a slightly lower dispersion and active surface area than the 20 wt% Pd catalyst on carbon, but FIG. D1 demonstrates that the PdAu catalyst has higher activity when used with formic acid. This is a surprising result. Although the exact reason is not known, it is believed that this may be related to the ability of Au to promote the electro-oxidation of formic acid in some way. It is believed that such promotion can occur through the electrical modification of the catalyst, the two-body effect or the catalytic activity of gold against poisoning / formic acid.

The fourth group of exemplary catalysts of the invention have a dispersion of less than 5%. As used herein, "dispersion" is to be understood as broadly meaning the number of palladium atoms available for the reaction. For example, a 5% dispersion can mean that only 5% of the catalyst particles are available at the surface and others are not poisoned. It is believed that the improvement of the dispersion will lead to a significant improvement in the performance of the catalyst of the present invention. It is believed that other catalysts of the present invention having a high catalyst dispersion of at least 5% provide higher activity levels than the exemplary catalysts currently discussed. Other catalysts of the present invention may have, for example, but are not limited to, about 10%, about 20% or more, 30% or more, 50% or more or more dispersions.

Dispersions can be improved through, for example, improved nanoparticle manufacturing methods that prevent particle aggregation and / or reduce nanoparticle size. In the synthetic method of the present invention, Pd nanoparticles are prepared by dissolving metal salts in solution and reducing Pd (2+) to Pd metal nanoparticles by adding a reducing agent such as NaBH ₄ . The size of the Pd nanoparticles depends on the strength of the reducing agent, the solvent used, the temperature, the stabilizing polymer used, and the like. Once the nanoparticles are formed, the nanoparticles typically have a surface charge on the particles. Carbon is made so that its surface is acidic. When the pH of the solution changes to basic, the electrostatic attraction between the carbon surface and the Pd nanoparticles causes the Pd to adhere to the carbon. Once the Pd nanoparticles are on the carbon surface, the Pd nanoparticles are retained there.

Thus, two steps occur: 1) formation of nanoparticles and 2) adhesion of the nanoparticles to the carbon surface. In many of the fourth group of exemplary catalysts, the Pd nanoparticles are in the range of 5-10 nm and small portions are present as larger 20-40 nm particles. 20-40 nm particles tend to have lower dispersion. The portion of these larger particles may be relatively small, but the mass ratio becomes considerably larger because the larger particles are much heavier than the smaller particles. Significant improvement of the dispersion can be made by preventing formation even if the number of such larger particles is small. Dispersion increases rapidly as particle size shrinks. In order to realize the increased activity, the other catalysts of the present invention actually all have less than about 10 nm of Pd nanoparticles, and yet another catalyst of the present invention actually has all of the Pd nanoparticles all less than about 5 nm. Exemplary catalysts of the present invention with Pd particle sizes of about 2 nm size result in about 26% dispersion and exemplary catalysts with Pd particles of about 1.2-1.5 nm size are greater than about 50% -60% Achieve dispersion. In addition, smaller particle sizes are believed to improve the binding energy of formic acid and hydrogen to the catalyst.

Exemplary catalysts may also be beneficial through the addition of one or more cocatalysts in small amounts (eg, about 1 weight percent or less) to increase catalytic activity. Exemplary promoters include metals and metal compounds (eg, metal oxides). Cocatalysts can increase catalyst activity in a variety of ways, including electronically modifying the catalyst, removing poisoning from the catalyst surface, blocking side reactions, improving the dispersion of the catalyst, and the like. Examples of suitable promoters are potassium, which improves dispersion, and ceria, which improves dispersion and electronically modifies the catalyst.

Exemplary formic acid fuel cells using a fourth group of exemplary catalysts of the present invention are fabricated to further illustrate some of the advantages and advantages of the present invention. Membrane electrode assemblies ("MEA") with an active cell area of 5 cm ² are fabricated using a direct paint technique to apply a catalyst layer. This technique generally involves painting the catalyst ink on one surface of the film, and then drying to leave the solid catalyst layer. Catalyst inks are prepared by dispersing the catalyst nanoparticles in an appropriate amount of millipore water and 5% recast NAFION® solution (1100 EW, Solution Technology, Inc.). Anode and cathode catalyst inks are painted directly on each side of the NAFION® film.

For an exemplary MEA, the cathode consists of a standard loading of about 8 mg / cm ² unsupported platinum black nanoparticles (27 m ² / g, Johnson Matthey). Other loadings are contemplated, for example in the range of about 2 to about 8 mg / cm ² . A carbon cloth diffusion layer (E-TeK) is placed on top of both the cathode and anode catalyst layers. Both sides of the cathode carbon cloth are coated Teflon (registered product) for water control. Single cell test fixtures consist of a machined graphite flow area with a direct liquid feed and a gold plated plate to avoid corrosion. The anode consists of a carbon supported Pd catalyst or an unsupported Pd catalyst. The anode catalyst loading of the Pd / C catalyst is about 6 mg / cm ² including the mass of the carbon support. The loading of Pd black catalyst is about 2.4 mg / cm ² . For each carbon supported catalyst ink batch, up to 10 mg of catalyst (total weight of carbon and Pd) is produced. Prior to painting the carbon supported catalyst ink on the polymer electrode film, two layers of 5% by weight NAFION solution are painted on top and dried for 1 minute. This NAFION initial layer is believed to be useful for forming a stable carbon supported Pd catalyst layer.

FIG. 6 shows a plot of voltage and current characteristics of an exemplary formic acid fuel cell of the present invention fabricated as such, which is operated using different catalysts of the present invention. All data are calculated at 30 ° C. The current is normalized by the total active surface area. According to FIG. 6, the carbon supported Pd catalyst of the present invention has greater activity per exposed surface area than commercial Pd black catalysts. This is a surprising and beneficial result. PdAu catalysts supported on carbon show the highest activity.

FIG. 7 measures the power density of three exemplary formic acid fuel cells at a constant cell voltage (0.39 V), where different anode catalysts of the present invention are used, respectively. Power data is normalized by total active surface. According to FIG. 7, the carbon supported Pd catalyst has greater activity per exposed surface area than commercial Pd black catalysts. This is a surprising and beneficial result. PdAu catalysts supported on carbon show the highest activity.

8 illustrates the effect of formic acid feed concentration on cell performance by an exemplary fuel cell using different catalysts of the present invention. According to FIG. 8, a formic acid fuel cell using Pd black catalyst at 15 M formic acid provides a power density of about 146 mW / cm ² , which corresponds to a performance reduction of about 42% from its power density at 5 M formic acid. FIG. 8 also shows that formic acid fuel cells with 20 wt% Pd catalyst supported on exemplary carbon catalysts also exhibit performance degradation as the formic acid feed concentration increases from 3 M to 20 M. FIG. However, degradation of Pd catalyst supported on carbon is less severe than that of unsupported Pd black. According to the data of FIG. 8, a formic acid fuel cell with a carbon supported Pd catalyst at 15 M yields a power density of about 107 mW / cm ² , which is only about 23% performance reduction from its power density at 5 M formic acid. Corresponds to This is a surprising and beneficial result.

9 shows a formic acid / air fuel cell polarization plot using 5 M formic acid feed concentration at 30 ° C., further illustrating the performance of the exemplary catalyst and fuel cell of the present invention. Two different anode Pd catalysts are used: 1) 20 wt% Pd catalyst prepared via the synthesis process described above with reference to the fourth group of exemplary catalysts and supported on carbon and 2) commercially available activated 20 wt% alpha-assay Pd catalyst supported on a carbon support. PtBl catalysts are useful for cathodes. The anode and cathode catalyst loadings are about 1.2 mg Pd / cm ² and about 8 mg / cm ^2, respectively. The formic acid flow rate for the anode is about 1 ml / min. Anhydrous air is supplied to the cathode at a flow rate of 390 sccm without back pressure. 9 exemplarily shows that both commercially available catalysts and synthesized catalysts exhibit excellent performance when used with the formic acid fuel cell of the present invention. Surprisingly, even when both catalysts were used with only a dose of about 1.2 mg / cm ^2, the resulting current was consistent with the pre-formed current activity under the same conditions using a much higher loading of about 8 mg / cm ² of unsupported Pd. Generate an active level. This is further evidence that the Pd-based catalyst of the present invention provides significant advantages and advantages when supported on carbon.

While a fourth group of exemplary catalysts of the invention has been illustrated and discussed, it will be appreciated that these are merely exemplary and other catalysts of the invention are contemplated. In addition, although exemplary catalysts of the present invention have been discussed with reference to anode catalysts, these exemplary catalysts may also be used as cathode catalysts.

Exemplary Fuel Cells and MEAs

Another embodiment of the invention relates to a formic acid fuel cell and a membrane electrode assembly ("MEA") comprising the catalyst of the invention. As discussed above, it will be appreciated that such cells and MEAs offer significant advantages and advantages due to the significant performance and low cost of the catalysts of the present invention. Numerous advantages and advantages, including for example, useful levels of electrical energy generation, low crossover and non-toxic and environmentally friendly fuels at temperatures from about ambient to 40 ° C. in relation to formic acid fuel cells over other organic fuel cells. Found out.

First Exemplary Fuel Cell

The schematic diagram of FIG. 10 generally illustrates an exemplary formic acid fuel cell of the present invention with an identification number 10. The fuel cell 10 includes an anode 12, a solid polymer proton conductive electrolyte 14 and a gas diffusion cathode 16. The anode 12 is enclosed in an anode enclosure 18, while the cathode 16 is enclosed in a cathode enclosure 20. The cathode enclosure 20 may be open around so that the cathode 16 is exposed to the atmosphere. When an electrical rod (not shown) is connected between the cathode 12 and the cathode 16 via the electrical connection 22, the electro-oxidation of the organic fuel takes place at the anode 12 and the electro-reduction of the oxidant is carried out at the cathode. Happens at 16.

The occurrence of different reactions at anode 12 and cathode 16 creates a voltage difference between the two electrodes. Electrons generated by electro-oxidation at the anode 12 are conducted through the connection 22 and are finally captured at the cathode 16. Hydrogen ions or protons produced at the anode 12 are transported to the cathode 16 via the membrane electrolyte 14. Therefore, the flow of current is maintained by the flow of ions through the cell and the flow of electrons through the connections 22. This current can actually be used to power an electrical device or to charge a battery, for example.

The anode 12, solid polymer electrolyte 14 and cathode 16 are preferably a single layer or multilayer composite structure, which may be referred to as a membrane electrode assembly (MEA). Preferably, the solid polymer electrolyte 14 is a proton conductive cation exchange membrane containing anionic sulfate, such as perfluorinated sulfonic acid commercially available under the trademark NAFION from DuPont Chemical Co., Delaware. Polymer membrane. NAFION is a polymer of tetrafluoroethylene and perfluorovinylether sulfonic acid. For example, other membrane materials may be used, including membranes of modified perfluorinated sulfonic acid polymers, membranes of polyhydrocarbon sulfonic acid, membranes containing other acidic ligands, and complexes of two or more types of proton exchange membranes.

In some exemplary fuel cells, the formic acid fuel solution may be provided in a removable container 24 that may be attached to the fuel cell 10 by a valve 26 or other mechanism. The container 24 may be, for example, a disposable or remanufactured cartridge. It can cause the flow of fuel solution into the enclosure 18 at an elevated pressure relative to the enclosure 28. The vessel 24 may include, for example, an elastic or other bladder that allows the liquid fuel solution to flow into the enclosure 18. The valve 26 may be closed or open as needed to contact and circulate the anode 12 and the fuel solution. The cartridge arrangement as shown in FIG. 10 is considered to allow the fuel solution to be replaced after the fuel solution is consumed. The fuel solution of the cartridge is initially provided at high concentrations and may gradually be consumed as the chemical reaction occurs across the MEA.

The valve 26 can be adjusted manually or automatically to control the flow of fuel solution, and can also control the rate and energy generation of the chemical reaction. In practice, for example, it may be desirable to isolate the anode 12 from the fuel solution when there is no demand for power generation without using an electrical device. The valve 26 may also be closed to change the container 24 after consumption. Additional valves 26 or similar mechanisms may be provided, for example to seal the vessel 24 and the anode enclosure 18. The process of mixing the water with the concentrated fuel solution takes place in the anode enclosure 18, where there may be a circulation loop in fluid communication with the anode enclosure to provide water for mixing.

Specific exemplary fuel cells are formic acid cells having a solution of at least 10% by weight of formic acid, while others have at least 25% of formic acid. Another may have about 40% to 100% formic acid and about 65% to 100% formic acid. Other formic acid concentrations, including concentrations up to 10%, are contemplated in the practice of the present invention. Fuel solutions having these or other concentrations may be contained in the vessel 24 and flow in contact with the anode 12. The fuel solution concentration at the anode 12 may be different from the concentration in the vessel 24 because it is diluted with, for example, the lower concentration fuel solution present in the anode enclosure 18. In addition, the concentration may change over time as formic acid reacts.

The oxidation reaction occurring at the anode 12 of the formic acid fuel cell takes place as in the following reaction formula.

Scheme 1

_{^{HCOOH - → 2H + + C0 2}} + 2e -

The CO ₂ product flows out of the chamber through a degassing port. The degassing port may be positioned in consideration of size, location and other factors to facilitate the flow passage of gas in the anode enclosure 18 which promotes effective agitation of the fuel solution contained therein. The H ⁺ product of Scheme 1 passes through the polymer electrolyte layer 14 to the cathode 16, and the free electron e ⁻ product flows through the electrical connection 22 to the cathode 16. The reduction reaction at the cathode 16 takes place as in the following scheme.

Scheme 2

_{^{O 2 + 2e - + 2H +}} → 2H 2 0

Oxidizer O ₂ can be obtained from air or other sources.

Pumps or other means may be provided to propel the flow of formic acid fuel solution and the flow of air / O ₂ . Or in the case of a passive organic fuel cell, the anode enclosure can be closed and the gas flow of the anode enclosure can drive the circulation of the formic acid solution.

The H ₂ O product flows out of the cathode enclosure 20 through the removal port 26. In some exemplary fuel cells, the H ₂ O product may be used to adjust the concentration of formic acid fuel solution. For example, a relatively high concentration of formic acid fuel solution may be provided to the vessel 24 and diluted in the anode enclosure with H ₂ O and / or other diluents of the cathode. In addition, additional reservoirs (not shown) connected to the anode enclosure 18 may be provided to contain H ₂ O or other diluents. This may be beneficial in that it provides a very compact and portable container 24 as well as other reasons.

In practical example, the formic acid fuel cell of the present invention has been found to provide a relatively constant and useful level of electrical energy over a relatively wide fuel concentration range. For example, the formic acid fuel cell of the present invention can provide a relatively constant and useful level of electrical energy when operated at formic acid fuel concentrations of about 3 M to about 12 M. Under these circumstances, it may be beneficial to conserve fuel, preserve catalyst, preserve other components from exposure to high concentrations, and operate at low concentrations for other reasons. Thus, the formic acid fuel solution can be provided at a relatively high concentration in the vessel 24 and diluted at the anode. Therefore, the formic acid fuel cell of the present invention may have a slight change in fuel solution concentration over time, and may vary to some extent as it is located within the anode enclosure 18 and / or vessel 24. I can understand.

Each anode 12 and cathode 16 may comprise a catalyst of the present invention that may be supported or unsupported. Exemplary catalysts include those discussed above herein. Pd-based catalysts can be particularly useful when used with the formic acid fuel cell of the present invention for a number of reasons, including cost, low activity energy for formic acid reduction and overall catalytic activity. Pd catalysts are believed to promote a direct reaction pathway that avoids the formation of CO intermediates, as occurs when using some other catalysts.

Pd-based catalysts supported on carbon exhibit particularly surprising levels of activity, as discussed above herein. The carbon supported Pd may be combined with metal M, three examples Au, V and Mo and / or supported on metal M as discussed above herein. The formic acid fuel cell of the present invention using the catalyst of the present invention has been shown to produce relatively high levels of electrical energy while requiring a relatively low catalyst loading. These surprising results offer benefits and advantages, including, but not limited to, cost savings.

When using the preferred MEA, anode 12 and cathode 16 may be comprised of a catalyst layer applied directly to the opposite side of the NAFION membrane. For example, the MEA can be fabricated by painting the anode and cathode catalyst inks directly on the opposite surface of the film 14. In addition, interlayers can also be provided to facilitate conduction, including, for example, Au, C and other meshes or screens. In practice, the anode ink may include any other (s) of the catalyst of the present invention as well as PdAu catalysts unsupported or supported on carbon. When the catalyst ink dries, solid catalyst particles adhere to the membrane 14 to form an anode 12 and a cathode 16. A loading of about 0.05-20 mg / cm ² is considered useful and other useful ranges of 2-8 mg / cm ² and 4-6 mg / cm ² exist. The specific loading may be selected based on the specifically selected catalyst, fuel solution concentration (s), the desired electrical energy output and other factors.

In addition to being supported on fine carbon particles, the catalyst of the invention can be supported on high surface area carbon sheeting in electrical contact with particles of an electrocatalyst. As a specific example, the anode 12 can be formed by mixing a binder such as NAFION with a catalyst of the present invention such as Pd / V and then rolling it over carbon backing paper at an exemplary charge. The backing paper can then be attached to the surface of the NAFION film 14.

Exemplary cathode electrocatalyst alloys and carbon fiber backings may further contain about 10-50% by weight of TEFLON, which provides hydrophobicity to create three phase boundaries and to achieve effective removal of water generated by electro-reduction of oxygen. have. The cathode catalyst backing adheres to the surface of the NAFION electrolyte membrane 14 opposite the anode 12.

It will be appreciated that it may be an advantage and advantage to provide most of the fuel cells 10 of the present invention in parallel or in series.

Second Exemplary Fuel Cell

Referring first to FIG. 11, a single direct liquid feed fuel cell 100 includes an anode current collector 110 and a cathode current collector 120. The anode current collector 110 has an edge 112 that extends substantially perpendicularly from the main planar portion 111 and the anode current collector main planar portion 111 and substantially circumscribes the portion 11. The anode current collector planar portion 111 has an opening 113 to facilitate fluid diffusion through the anode current collector. For example, anode current collector 110 may be formed from gold plated titanium.

The cathode current collector 120 has an edge 122 that extends substantially perpendicularly from the main planar portion 121 and the cathode current collector main planar portion 121 and circumscribes the portion 121. The cathode current collector planar portion 121 has an opening 123 formed therein that facilitates fluid diffusion through the cathode current collector. For example, cathode current collector 120 may be formed from gold plated titanium.

As further shown in FIG. 11, MEA 130 is inserted between anode current collector 110 and cathode current collector 120. MEA 130 includes membrane electrolyte 131 having two opposing major planar surfaces 132, 133. One of the MEA major planar surfaces 132 abuts the anode current collector 110, and the other major planar surface 133 abuts the cathode current collector 120. On the MEA major planar surface 132, a first electrocatalyst layer 134 is disposed. A second electrode layer 135 is disposed on the MEA major planar surface 135. For example, the membrane electrolyte 131 may be formed from a perfluorosulfonic acid membrane such as NAFION.

The anode fluid diffusion layer 140 is inserted between the anode current collector 110 and the MEA 130. The anode fluid dispersion layer 140 includes an electrically conductive material 141. For example, these electrically conductive materials 141 may be stainless steel mesh, gold plated stainless steel mesh, solid gold mesh, gold plated titanium mesh, titanium mesh, niobium mesh, gold plated niobium mesh, platinum plated niobium mesh. Palladium plated niobium mesh, carbon cloth, carbon paper, Teflon coated carbon cloth, Teflon coated carbon paper, gold plated expanded niobium foil, platinum plated niobium foil or palladium plated nidium It can be formed from the foil.

The cathode fluid diffusion layer 150 is inserted between the cathode alternating collector 120 and the MEA 130. The cathode fluid dispersion layer 150 contains an electrically conductive material 151. For example, such electrically conductive material 151 can be stainless steel mesh, gold plated stainless steel mesh, solid gold mesh, gold plated titanium mesh, titanium mesh, niobium mesh, gold plated niobium mesh, platinum plated niobium mesh. Formed from palladium plated niobium mesh, carbon cloth, carbon paper, Teflon coated carbon cloth, Teflon coated carbon paper, gold plated expandable niobium foil, platinum plated niobium foil or palladium plated niobium foil Can be.

The edge of cathode current collector 122 may be press fitting to the edge of anode current collector 112 to form a partial seal. In order to maintain electrical isolation between the anode and the cathode, a layer of electrically insulating material 310 (FIG. 15) needs to be located between the anode current collector and the cathode collector. In the context of the present invention, the term electrically insulating material is to be understood as meaning a material that is a better insulator for electrons than protons. Electrically insulating materials include all classes of typical insulators such as rubber, glass, air and silicon. The electrically insulating material also includes an ion exchange membrane that blocks the flow of electrons while allowing the flow of H ⁺ ions. NAFION is an example of an ion exchange membrane that is an electrically insulating material. The cathode-anode partial seal assists in containing fluid disposed between the anode current collector 110 and the cathode current collector 120. The cathode-anode portion seal may be further strengthened by sealants 312 and 314 (FIG. 15).

In yet another embodiment, the MEA 130 has an edge 136 that circumscribes both sides of the MEA facing the major planar surfaces 132, 133. The cathode current collector edge 122 may press fit with the MEA edge 136 to form a partial seal. The cathode-MEA portion seal may be further reinforced with a sealant 312. The cathode-MEA partial seal assists in containing the fluid disposed between the cathode current collector 120 and the MEA 130. During the press fitting process, the presence of the uncured sealant 312 helps to smooth the MEA edge 136 to prevent tearing.

The MEA edge 136 may further press fit with the anode current collector edge 112 to form a partial seal. The anode-MEA portion seal may be further strengthened by sealant 314. The anode MEA partial seal assists in containing fluid disposed between the anode current collector 110 and the MEA 130. During the press fitting process, the presence of the uncured sealant 314 helps to smooth the MEA edge 136 to prevent tearing.

Referring to FIGS. 13 and 15 in addition to FIG. 11, in a preferred embodiment, the liquid fuel stream 220 passes through the opening 113 in the anode current collector main planar portion 111 and directs towards the anode fluid diffusion layer 140. do. Fluid oxidant 221 passes through opening 123 in cathode current collector main planar portion 121 and is directed towards cathode fluid diffusion layer 150. In an exemplary fuel cell, the liquid fuel stream 220 includes formic acid and the fluid oxidant 221 includes oxygen containing air. Since formic acid exhibits corrosive properties, any sealants 312 and 314 must be adequately resistant to formic acid. One suitable sealant that has not failed the widespread use of formic acid is silicone sealant such as PDMS Silicone Elastomer available from DowCorning®.

12 and 13, the direct feed fuel cell array 200 includes two or more direct liquid feed fuel cells 100 and a frame 210, as described above. For example, the frame 210 may be formed from a rigid electrical insulator, such as a polycarbonate material, Kel-F® or Teflon®.

Frame 210 has two or more edge portions 212, each edge portion 212 containing a channel 214. Each channel 214 may receive an anode current collector edge 112 and a cathode current collector edge 122. In another embodiment, each channel may additionally receive membrane electrolyte edge 136.

Array 200 is configured such that frame 210 and two or more direct liquid feed fuel cells 100 form a partially enclosed volume. Fluid disposed within this volume 240 is partially contained by frame 210 and two or more direct liquid feed fuel cells 100. In one embodiment, one of the fluids disposed within the volume 240 of the array 200 is an organic liquid fuel, such as formic acid. In a further embodiment, the fuel cell array flame channel 214 and the fuel cell assembly edge portion 112, 122, or 136 may be bonded using an adhesive to further contain fluid disposed within the volume of the array 200. Can be combined. As discussed above, in life testing, silicone sealants perform well when used with formic acid. In yet another embodiment, the frame has one or more passages 230 traversing the body of frame 210. Passage 230 allows for convenient fuel supply and venting of the anode oxidation reaction of array 200.

Referring to FIG. 14, an arrangement 200 consisting of two fuel cells 100 is shown in an electrical circuit. The fuel cells 100 are connected in series and the resistive rods 400 are arranged over a series of fuel cells. In such a configuration, electrical power may be generated when current flows through the resistive rod 400. It will be appreciated that many other fuel cells 100 of the present invention may be provided in series or parallel fashion to provide a predetermined level of electrical energy as needed or for other reasons.

Although specific elements, embodiments, and uses of the present invention have been presented and described, those skilled in the art can make modifications without departing from the scope of the present disclosure, particularly in light of the above teachings. It is to be understood that the present invention is not limited thereto.

Claims (34)

An anode (12, 134) and a cathode (16, 135), and an electrolyte (14, 131) interposed between the anode and the cathode; An oxidant in communication with the cathode; Formic acid fuel solution in communication with the anode; And Anode catalyst containing Pd Formic acid fuel cell comprising a. The formic acid fuel cell of claim 1, wherein the anode catalyst further comprises a metal selected from the group of metals Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W and Au. The formic acid fuel cell of claim 1 wherein M is Au. The formic acid fuel cell according to claim 1, wherein M is V. The formic acid fuel cell of claim 1 wherein M is Mo. The formic acid fuel cell in accordance with claim 1, wherein the anode catalyst comprising Pd is supported on carbon. The formic acid fuel cell of claim 6, wherein the Pd comprises nanoparticles supported on carbon. The formic acid fuel cell of claim 7, wherein the Pd nanoparticles are about 10 nm or less. The formic acid fuel cell of claim 7, wherein the Pd nanoparticles are about 5 nm or less. 7. The formic acid fuel cell of claim 6, wherein the anode catalyst is prepared by a metal chloride reduction process. The formic acid fuel cell of claim 6, wherein the Pd comprises at least about 5% by weight of the catalyst based on the total weight of the catalyst. The formic acid fuel cell of claim 6, wherein the Pd comprises at least about 10% by weight of the catalyst based on the total weight of the catalyst. The formic acid fuel cell of claim 6, wherein the Pd comprises at least about 20% by weight of the catalyst based on the total weight of the catalyst. The formic acid fuel cell of claim 6, wherein the anode catalyst has at least about 20% Pd dispersion. The formic acid fuel cell of claim 6, wherein the anode catalyst has at least about 50% Pd dispersion. The formic acid fuel cell of claim 1, wherein the anode catalyst comprises Pd and Au supported on carbon. The formic acid fuel cell of claim 1, wherein the formic acid fuel solution contains at least about 10% by weight of formic acid. The formic acid fuel cell of claim 1, wherein the formic acid fuel solution contains at least about 25% by weight of formic acid. The formic acid fuel cell of claim 1, wherein the formic acid fuel solution contains at least about 40 wt% formic acid. The method of claim 1, further comprising a replaceable cartridge containing the formic acid fuel solution, wherein the cartridge is disposed to be detachably attached to a fuel cell such that the formic acid fuel solution is in communication with the anode. What is formic acid fuel cell. An anode and a cathode, and an electrolyte interposed between the anode and the cathode; An oxidant in communication with the cathode; Formic acid fuel solution having a concentration of at least about 25% formic acid in communication with the anode; And Anode catalyst comprising Pd nanoparticles supported on carbon Formic acid fuel cell comprising a. Proton conductive membranes having opposing first and second surfaces; A cathode catalyst on the second membrane surface; And An anode catalyst comprising Pd on the first surface Formic acid fuel cell membrane electrode assembly comprising a. 23. The formic acid fuel cell membrane electrode assembly of claim 22, wherein the membrane comprises a solid polymer proton exchange membrane. 23. The formic acid fuel cell membrane electrode assembly of claim 22, wherein the membrane comprises a perfluorosulfonic acid ionomer. The formic acid fuel cell membrane electrode assembly of claim 22, wherein the anode catalyst further comprises a metal selected from the group of metals Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, and Au. The formic acid fuel cell membrane electrode assembly of claim 25, wherein the anode catalyst is Au. 23. The formic acid fuel cell membrane electrode assembly of claim 22, wherein the anode catalyst comprising Pd is supported on carbon. The formic acid fuel cell membrane electrode assembly of claim 22, wherein the Pd comprises nanoparticles supported on the carbon. The formic acid fuel cell membrane electrode assembly of claim 28, wherein the Pd nanoparticles are about 10 nm or less. The formic acid fuel cell membrane electrode assembly of claim 22, wherein the Pd comprises at least about 10% by weight of the catalyst based on the total weight of the catalyst. 23. The formic acid fuel cell membrane electrode assembly of claim 22, wherein the anode catalyst comprises Pd and Au supported on carbon. The formic acid fuel cell membrane electrode assembly of claim 22, further comprising at least about 25% by weight of formic acid fuel solution in communication with the anode catalyst layer. 23. The formic acid fuel cell membrane electrode assembly of claim 22, further comprising an electrically conductive material covering the anode catalyst. 34. The formic acid fuel cell membrane electrode assembly of claim 33, wherein the electrically conductive material comprises a metal mesh.

Images