DE102013112288A1 - Ruthenium/palladium/carbon catalyst useful for electro-oxidation of the formic acid in formic acid fuel cells comprises palladium and ruthenium deposited on a carbon support - Google Patents

Abstract

Ruthenium/palladium/carbon catalyst comprises palladium and ruthenium deposited on a carbon support. The nominal atomic ratio of ruthenium to palladium in the catalyst is 0.2-1.5. Independent claims are also included for: (1) producing ruthenium/palladium/carbon catalyst comprising (a) providing palladium/carbon catalyst with a palladium crystallite size of less than 5 nm, and (b) subsequently depositing ruthenium on the produced palladium/carbon catalyst; and (2) a formic acid fuel cell comprising a cathode, preferably palladium/carbon catalyst, an ion-conducting membrane, and an anode, preferably palladium catalyst refined with ruthenium, where the palladium catalyst refined with ruthenium is ruthenium/palladium/carbon catalyst.

Description

The invention relates to a Ru / Pd / C catalyst, a method for producing the Ru / Pd / C catalyst, its use in a formic acid fuel cell and such a fuel cell.

The fuel cells are electrochemical cells, in which the free enthalpy of the fuel oxidation is converted into electrical energy high performance.

In a formic acid fuel cell, hereinafter referred to as DFAFC (Direct Formic Acid Fuel Cell), the formic acid is electro-oxidized to carbon dioxide and water ( 1 ). Low-temperature formic acid fuel cells are used as a power source for portable devices such as mobile phones or laptops, which is an alternative to batteries.

The most widely studied fuel cells are hydrogen and methanol fuel cells. These fuel cells have a number of disadvantages that limit their commercialization. A major problem with the hydrogen fuel cell is the storage of hydrogen and high cost of platinum - the main catalyst, as well as a low mass fraction of platinum in the earth's crust. The basic problems with the methanol fuel cell are: slow kinetics of the anode reaction; high rate of penetration of the fuel through the ion-conducting membrane separating the anode from the cathode; necessary supply of water which is one of the reagents of the anode reaction; Dehydration of the ion-conducting membrane by methanol; necessary use of expensive platinum.

The formic acid fuel cell offers numerous advantages, including high power density and high electromotive force (in comparison with the methanol fuel cell). Formic acid is a liquid that is easy to dispose of and store, is relatively safe - in low concentrations it is used as a food preservative. In addition, the formic acid fuel cells offer the possibility of using palladium as a catalyst for the electro-oxidation of formic acid [ Yimin Zhu, Zakia Khan, RI Masel, The Behavior of Palladium Catalysts in Direct Formic Acid Fuel Cells, Journal of Power Sources 139 (2005) 15-20 ; S. Ha, Z. Dunbar, RI Masel, Characterization of a High Performance Passive Formative Acid Fuel Cell, Journal of Power Sources 158 (2006) 129-136 ; Robert Larsen, Su Ha, Joseph Zakzeski, Richard I. Masel, Unusually active palladium-based catalysts for the electrooxidation of formic acid, Journal of Power Sources 157 (2006) 78-84 ; S. Ha, R. Larsen, RI Masel, Performance characterization of Pd / C nanocatalyst for direct formic acid fuel cells, Journal of Power Sources 144 (2005) 28-34 ; such as Xingwen Yu, Peter G. Pickup, Mechanistic study on the deactivation of carbon supported Pd during formic acid oxidation, Electrochemistry Communications 11 (2009) 2012-2014 ]. Palladium is 2.5 times cheaper than platinum, and the mass fraction of palladium in the earth's crust is higher.

In a number of the patent publications [ WO 03/088402 A1 ; US 7,132,188 ; US 2007/0099064 ; WO 2005/081706 A2 ; US 2005/0136309 ; US 7,7490,974 ; such as US 2,007,154,743 ] reserved the use of palladium nanoparticles deposited on carbon supports or remaining in the form of palladium black as catalysts for the electro-oxidation of formic acid in fuel cells.

However, a palladium catalyst is stable at the DFAFC anode only when using a very expensive high purity formic acid [ Xingwen Yu, Peter G. Pickup, Mechanistic study on the deactivation of carbon supported Pd during formic acid oxidation, Electrochemistry Communications 11 (2009) 2012-2014 ; Wai Lung Law, Alison M. Platt, Priyantha DC Wimalaratne and Sharon L. Blair, Effect of Organic Impurities on the Performance of Direct Formic Acid Fuel Cells; Journal of The Electrochemical Society, 156 (5) B553-B557 (2009) ; A. Mikołajczuk, A. Borodzinski, P. Kedzierzawski, L. Stobinski, B. Mierzwa, R. Dziura, Deactivation of carbon supported palladium catalyst in direct formic acid fuel cells, Applied Surface Science 257 (2011) 8211-8214 ; Mingjun Ren, Yongyin Kang, Wei He, Zhiqing Zou, Xinzhong Xue, Daniel L. Akinsc, Hui Yang, Songlin Feng, Origin of Performance Degradation of Palladium-based Direct Formic Acid Fuel Cells, Applied Catalysis B: Environmental 104 (2011) 49 -53 ; such as Won Suk Jung, Jonghee Han, Sung Pil Yoon, Suk Woo Nam, Tae-Hoon Lim, Seong-Ahn Hong, Performance degradation of Pd anode catalyst, Journal of Power Sources 196 (2011) 4573-4578 ]. In analytically pure formic acid containing trace amounts of impurities with the -CH ₃ group, such as acetic acid, methyl formate or methanol, the palladium catalyst is deactivated within a few hours ( 2 ). The main cause of deactivation is the oxidation of these impurities with the formation of carbon oxide, which strongly adsorbs to the palladium surface, thereby reducing its active surface accessible to formic acid. The rate of deactivation increases with the increasing content of the formic acid impurities, the concentration of the acid to be used and the current density [ Wai Lung Law, Alison M. Platt, Priyantha DC Wimalaratne and Sharon L. Blair, Effect of Organic Impurities on the Performance of Direct Formic Acid Fuel Cells, Journal of the Electrochemical Society, 156 (5) B553-B557 (2009) , such as A. Mikołajczuk, A. Borodzinski, P. Kedzierzawski, L. Stobinski, B. Mierzwa, R. Dziura, Deactivation of carbon supported palladium catalyst in direct formic acid fuel cells, Applied Surface Science 257 (2011) 8211-8214 ].

Another solution to the problem of deactivating the palladium catalysts in a fuel cell supplied with the formic acid of limited purity is a periodic activation of the fuel cell with the anode pulses. Yimin Zhu, Zakia Khan, RI Masel, The Behavior of Palladium Catalysts in Direct Formic Acid Fuel Cells, Journal of Power Sources 139 (2005) 15-20 ; Robert Larsen, Su Ha, Joseph Zakzeski, Richard I. Masel, Unusually active palladium-based catalysts for the electrooxidation of formic acid, Journal of Power Sources 157 (2006) 78-84 ; S. Ha, R. Larsen, Y. Zhu, RI Masel, Direct Formic Acid Fuel Cells at 600 A / cm 2 at 0.4 V and 22 ° C, Fuel Cells 4 (4) (2004) 337-343 ; US 7,7490,974 B2 ; such as US 2007154743 ]. During such pulses, the anode potential is so high that CO adsorbed on Pd is oxidized to CO ₂ . Such activation, however, requires that the anode be brought to high potentials, which means that it is necessary to reverse the polarization of the fuel cell, thus providing the fuel cell with the energy from the outside. This leads to a reduction in the energy yield of a fuel cell and may also cause the dissolution of the palladium catalyst. For periodic activation, an electronic circuit is necessary, which allows an accumulation of electric charge, whereby the structure of the fuel cell is complicated and the cost of their production grow.

Another method of producing a stable fuel cell supplied with formic acid of limited purity is to use a PtRu alloy as an anode catalyst. The disadvantage of such a catalyst is the use of expensive platinum [ S. Ha, R. Larsen, Y. Zhu, RI Masel, Direct Formic Acid Fuel Cells at 600 A / cm 2 at 0.4 V and 22 ° C, Fuel Cells 4 (4) (2004) 337-343 , such as Craig M. Miesse, Won Suk Jung, Kyoung-Jin Jeong, Jae Kwang Lee, Jaeyoung Lee, Jonghee Han, Sung Pil Yoon, Suk Woo Nam, Tae-Hoon Lim, and Seong-Ahn Hong, Direct Formic Acid Fuel Cell Portable Power System for the operation of a laptop computer, Journal of Power Sources 162, (1), 2006, 532-540 ].

The authors of the present patent application have made attempts to refine the palladium catalysts deposited on the carbon support Vulcan XC-72 with ruthenium by reducing the ruthenium ions with various reducing agents. The prepared Ru / Pd / C catalysts were analyzed at the anode of a reagent-grade formic acid fuel cell.

Unexpectedly, when operating the fuel cell at a given current value, the voltage of the fuel cell began to oscillate. As the starting material for the preparation of the catalysts described herein, a 20 weight percent palladium catalyst was used on a carbon support. The ruthenium was deposited by the reduction of formic acid, sodium borohydride (NaBH ₄ ) or hydrazine. The nominal atomic ratio of ruthenium to palladium in the catalysts was in the range of 0.05 to 1.5. It was found that when using the catalysts at the fuel cell anode where the ratio was higher than 0.2, the firing cell voltage oscillated spontaneously. The mean value of the fuel cell voltage was approximately constant during the measurement. On the other hand, with a Ru: Pd atomic ratio less than or equal to 0.2, the fuel cell voltage did not oscillate and stabilized at a lower level than the catalysts in which the fuel cell voltage spontaneously oscillated.

US Patent Application No. US 20080241642 comprises catalysts for the oxidation of formic acid containing a noble metal (Pd, Pt, Au, Rh, Ir and Os) with the addition of other metals (Sn, Ru, Mo, Re, V, Bi, Pb, Au and Sb). The patent application reserves, inter alia, a Pd-Ru system, but the inventors give neither application examples, nor examples of the preparation of ruthenium-refined palladium catalysts, nor do they show that such catalysts remain stable in the operation of a fuel cell, as well in that for some of these catalysts the fuel cell voltage spontaneously oscillates.

The publication US 2010/0086831 A1 In contrast, the catalysts comprise the single-phase PdRu alloys with the optional addition of a third metal in an amount of up to 10%, which can be used at the anode of the fuel cell, including the hydrogen fuel cell and the methanol fuel cell. The inventors of this invention give no example of the use of such catalysts in a formic acid fuel cell, as well as show that such catalysts are stable in operation of the fuel cell, as well as that for some of these catalysts the fuel cell voltage spontaneously oscillates. This solution also differs fundamentally from the solution proposed by the inventors of the present application in which Pd and Ru are present as separate metals without forming an alloy.

It is therefore the object of the present invention to provide a new and better Ru / Pd / C catalyst. More particularly, the invention relates to the use of this novel catalyst in a formic acid fuel cell wherein the formic acid includes organic contaminants and the catalyst is capable of self-regeneration during operation of the fuel cell.

According to the invention, a Ru / Pd / C catalyst, in particular for the electro-oxidation of formic acid, comprising palladium and ruthenium deposited on a carbon support, is characterized in that the nominal atomic ratio of ruthenium to palladium in this Ru / Pd / C catalyst in the range of 0.2 to 1.5.

Preferably, ruthenium is in metallic form without forming an alloy with palladium.

An inventive Ru / Pd / C catalyst used in a formic acid fuel cell activates itself by spontaneous oscillations of the fuel cell voltage, which do not require external power supply.

• a) ein Pd/C-Katalysator, vorzugsweise mit einer Pd-Kristalliten-Größe unter 5 nm, bereitgestellt, und anschließend
• b) auf dem hergestellten Pd/C-Katalysator Ruthenium (Ru) mit der Bildung eines Ru/Pd/C-Katalysators abgeschieden wird.

Moreover, the present invention comprises a process for producing the Ru / Pd / C catalyst, characterized in that it comprises the following steps, in which:

• a) provided a Pd / C catalyst, preferably with a Pd crystallite size below 5 nm, and then
• b) depositing on the prepared Pd / C catalyst ruthenium (Ru) with the formation of a Ru / Pd / C catalyst.

Preferably, in step a), the palladium deposited on a carbon support is used as the Pd / C catalyst, wherein the carbon support is selected from the group comprising Vulcan XC-72, Carbo Medicinalis Ligni, carbon nanotubes, carbon nanofibers, and graphene.

Preferably, in step b), ruthenium is formed either by the reduction of ruthenium salts in aqueous solution using a reducing agent or by impregnation (coating) of the Pd / C catalyst with ruthenium hydroxide, followed by reduction of this ruthenium hydroxide using a reducing agent on the Pd / C catalyst deposited.

Preferably, in step b) ruthenium chloride (RuCl ₃ ) is used as the ruthenium salt.

Preferably, in step b) sodium borohydride (NaBH ₄ ), formic acid (HCOOH) or hydrazine (N ₂ H ₄ ) is used as a reducing agent reducing ruthenium ions.

Preferably, the nominal atomic ratio of ruthenium to palladium in the prepared Ru / Pd / C catalyst is in the range of 0.2 to 1.5.

The present invention also encompasses the use of the Ru / Pd / C catalyst prepared by the process as defined above for the electro-oxidation of formic acid in the formic acid fuel cells.

The present invention also includes a formic acid fuel cell consisting of a cathode, which is preferably a Pt / C catalyst, an ion-conducting membrane, and an anode, which is a ruthenium-refined palladium catalyst, characterized in that the ruthenium refined palladium catalyst is the above-described Ru / Pd / C catalyst.

According to the present invention, the ruthenium promoted palladium catalyst (Ru / Pd / C) in which the molar ratio of ruthenium to palladium is 0.2 to 1.5 is intended for the anode of a formic acid fuel cell wherein the formic acid contains organic impurities such as methanol, methyl formate, acetic acid, formaldehyde, and these are in the range of 45 ppm to 600 ppm, preferably corresponding to at least 45 ppm, 190 ppm, 600 ppm or 600 ppm.

By generating spontaneous oscillations of the fuel cell voltage, the Ru / Pd / C catalyst is capable of self-regeneration, thereby purifying the palladium surface from the products of the electrochemilization of these formic acid contaminants.

During operation of the formic acid fuel cell, the Ru / Pd / C catalyst is stable and at the anode of this fuel cell, the formic acid is spontaneously activated by the periodic change of the anode potential. The fuel cell voltage spontaneously oscillates at an atomic ratio of ruthenium to palladium greater than 0.2, preferably from 0.2 to 1.5.

The invention will now be explained in more detail with reference to a preferred embodiment with reference to the accompanying drawings. Show it:

1 the low-temperature formic acid fuel cells according to the prior art,

2 the fuel cell voltage as a function of the operating time of a Prior art formic acid fuel cell, anode: 20% Pd / Vulcan (Premetek), 0.5 mg _Pd cm ^-2 ; Flow rate of reagent grade 3M HCOOH 1 ml min ^-1 ; Cathode: 60% Pt / Vulcan (Premetek), 4 mg _Pt cm ^-2 , air flow 400 ml min ^-1 ; 30 ° C, 10 mA cm ^-2;

3 the dependence of the power density of a fuel cell on its service life, wherein

3a this dependence for the period of 30-60 min, for the catalyst shows 0.25 RuPd (NaBH ₄ );

3b this dependence for the period of 130-160 min, for the catalyst shows 0.25 RuPd (NaBH ₄ );

3c this dependence for the period of 230-260 min, for the catalyst shows 0.25 RuPd (NaBH ₄ );

3d this dependence for a period of 330-360 minutes for the catalyst 00:25 RuPd (NaBH ₄₎ shows;

4 the dependence of the power density of a fuel cell on its service life, wherein

4a this dependence for the period of 30-60 min, for the catalyst 0.5 RuPd (NaBH ₄ ) shows;

4b this dependence for the period of 130-160 min, for the catalyst 0.5 RuPd (NaBH ₄ ) shows;

4c this dependence for the period of 230-260 min, for the catalyst 0.5 RuPd (NaBH ₄ ) shows;

4d this dependence for the period of 330-360 min, for the catalyst 0.5 RuPd (NaBH ₄ ) shows;

5 the dependence of the power density of a fuel cell on its service life, wherein

5a this dependence for the period of 30-60 min, for the catalyst shows 0.25 RuPd (HCOOH);

5b this dependence for the period of 130-160 min, for the catalyst shows 0.25 RuPd (HCOOH);

5c this dependence for the period of 230-260 min, for the catalyst shows 0.25 RuPd (HCOOH);

5d this dependence for the period of 330-360 min, for the catalyst shows 0.25 RuPd (HCOOH);

6 the dependence of the power density of a fuel cell on its service life, wherein

6a this dependence for the period of 30-60 min, for the catalyst shows 0.15 RuPd (HCOOH);

6b this dependence for the period 130-160 min, for the catalyst shows 0.15 RuPd (HCOOH);

6c this dependence for the period of 230-260 min, for the catalyst shows 0.15 RuPd (HCOOH);

6d this dependence for the period of 230-260 min, for the catalyst shows 0.15 RuPd (HCOOH);

7 the dependence of the power density of a fuel cell on its service life for a commercially available 20% Pd / Vulcan catalyst from Premetek and

8th , the comparison of the power density of a formic acid fuel cell, after 6 hours of operation, with the application of various anode catalysts at a constant current density of 10 mA / cm ² ; the green color indicates the Ru / Pd / C catalysts described in Examples 1-3 of the present patent application (voltage oscillation generating), the blue color marks the Ru / Pd / C catalyst described in Comparative Example 1 (no fuel cell voltage oscillations), and the pink color marks the commercially available Pd / C catalyst described in Comparative Example 2 (no oscillations of the fuel cell voltage).

Preferred embodiments

example 1

On a magnetic stirrer was a beaker with 1 g of commercially available 20% Pd / Vulcan catalyst (BASF Fuel Cells) having a Pd-crystallite size of about 3 nm, 0.114 g RuCl ₃ · 2H ₂ O (ABCR Co.), and 200 ml of water. After mixing for 30 minutes the mixture was gradually added at ₄ Solution 22 ± 1 ° C with a by dissolving 0.064 g of NaBH ₄ in 50 ml of deionized water (Millipore ^®) prepared NaBH. After mixing for 2 hours, the catalyst (Millipore ^®) was washed five times with deionized water, and then dried under reduced pressure for 12 hours at 80 ° C. After the preparation shown that was Atomic ratio of ruthenium to palladium in this catalyst at 0.25. The prepared catalyst was characterized by the symbol 0.25 RuPd (NaBH ₄ ).

The stability measurements of prepared catalysts were carried out on a self-made formic acid fuel cell.

The ion-conducting membrane used was Nafion 115 from DuPont. On the cathode, the 60% Pt / Vulcan catalyst from Premetek was used. For the preparation of the anodes, the investigated, with ruthenium-refined palladium catalysts were used. Carbon fabrics were used as diffusion layers: at the cathode, a fabric with Teflon addition (Carbon Cloth Designation B 30% Wet Proofing B1B30WP from BASF Fuel Cell), and at the anode a fabric without Teflon additive (Carbon Cloth Designation B-1, Designation B, from Clean Fuel Cell Energy). The catalysts were applied to the carbon cloths in amounts: 4 mg Pt x cm ^-2 at the cathode and 2.5 mg catalyst x cm ^-2 at the anode. The measurements of the deactivation rate of the catalysts were carried out at 30 ° C. The fuel used was relatively inexpensive analytically pure formic acid from Chempur. This acid contained impurities responsible for the deactivation of the palladium catalyst not containing ruthenium as a promoter [ Wai Lung Law, Alison M. Platt, Priyantha DC Wimalaratne and Sharon L. Blair, Effect of Organic Impurities on the Performance of Direct Formic Acid Fuel Cells, Journal of the Electrochemical Society, 156 (5) B553-B557 (2009) , such as A. Mikołajczuk, A. Borodzinski, P. Kedzierzawski, L. Stobinski, B. Mierzwa, R. Dziura, Deactivation of carbon supported palladium catalyst in direct formic acid fuel cells, Applied Surface Science 257 (2011) 8211-8214 ]: Methanol 50 (ppm), acetic acid 200 (ppm), formaldehyde 600 (ppm) and methyl formate 600 (ppm). After dilution with deionized water (Millipore ^®), except for the concentration of 3 M, with a fuel cell of this acid was supplied with flow rate of 0.5 or 0.7 ml min ^-1. As the oxidizer on the cathode side, pure oxygen flowing at a flow rate of 1000 ml min ^{-1 was} used. The stability tests of catalysts were carried out with a DC method at current 10 mA cm ^-2 .

In this case, the standard catalyst stability test described above was conducted at the anode of a formic acid fuel cell at 30 ° C at a flow rate of 3 M HCOOH of 0.5 ml min ^-1 . The test was conducted by a DC method at a current of 10 mA cm ^-2 . The exam results are in 3a - 3d represented where the spontaneous oscillations of the fuel cell voltage can be seen. The average power of the fuel cell, which was determined for the 30-minute periods shown in these diagrams, was also plotted on these diagrams. The average power of the fuel cell decreased only insignificantly within 6 hours of measurement and aspired asymptotically to the value of 4.2 mW / cm ² , indicating that the catalyst regenerated spontaneously.

Example 2

To a magnetic stirrer was added a beaker containing 1 g of commercially available 20% Pd / Vulcan catalyst (BASF Fuel Cells) having a Pd crystallite size of about 3 nm, 0.229 g RuCl ₃ .2H ₂ O (ABCR Co.), and 200 ml of water. After mixing for 30 minutes the mixture was gradually added at ₄ Solution 22 ± 1 ° C with a by dissolving 0.064 g of NaBH ₄ in 50 ml of deionized water (Millipore ^®) prepared NaBH. After mixing for 2 hours, the catalyst (Millipore ^®) was washed five times with deionized water. The prepared catalyst was dried at 80 ° C under reduced pressure for 12 hours. After the preparation shown, the atomic ratio of ruthenium to palladium in this catalyst was 0.5. The prepared catalyst was identified by the symbol 0.5 RuPd (NaBH ₄ ).

In this case, the standard catalyst stability test described above was conducted at the anode of a formic acid fuel cell at 30 ° C at a flow rate of 3 M HCOOH of 0.5 ml min ^-1 . The stability test of the catalyst was carried out by a DC method at a current of 10 mA cm ^-2 . The exam results are in 4a - 4d represented where the spontaneous oscillations of the fuel cell voltage can be seen. The average power of the fuel cell, which was determined for the 30-minute periods shown in these diagrams, is also plotted on these diagrams. The mean power of the fuel cell decreased only insignificantly within 6 hours of measurement and aspired asymptotically to the value of 4.1 mW / cm ² , indicating that the catalyst regenerated spontaneously.

Example 3

To a magnetic stirrer was added a beaker containing 1 g of commercially available 20% Pd / Vulcan catalyst (Premetek) with a Pd crystallite size of about 3 nm, 0.114 g RuCl ₃ .2H ₂ O (ABCR Co.), and 200 ml Water provided. After 30 minutes of mixing, the mixture was warmed to 60 ± 1 ° C and then gradually added with 5.64 ml of a 0.5 M HCOOH solution. After mixing for 2 hours, the catalyst (Millipore ^®) was washed five times with deionized water, and then 12 Hours dried at 80 ° C under reduced pressure. After the preparation shown, the atomic ratio of ruthenium to palladium in this catalyst was 0.25. The prepared catalyst was characterized by the symbol 0.25 RuPd (HCOOH).

In this case, the standard catalyst stability test shown above was conducted at the anode of a formic acid fuel cell at 30 ° C at a flow rate of 3 M HCOOH of 0.7 ml min ^-1 . The stability test of the catalyst was carried out by a DC method at a current of 10 mA cm ^-2 . The exam results are in 5a - 5d represented where the spontaneous oscillations of the fuel cell voltage can be seen. The average power of the fuel cell, which was determined for the 30-minute periods shown in these diagrams, is also plotted on these diagrams. The mean power of the fuel cell decreased insignificantly within 6 hours of measurement and was asymptotically approaching 4.3 mW / cm ² , indicating that the catalyst regenerated spontaneously.

Example 4

A 20% Pd / Vulcan catalyst from Premetek (1 g) was mixed with water (100 ml) and maintained on a magnetic stirrer for 30 minutes at a speed of 400 revolutions / minute. The prepared mixture was then gradually added with a solution of 0.114 g RuCl ₃ × 2H ₂ O in 100 ml of water and kept on the magnetic stirrer for a further 30 minutes at a speed of 400 revolutions / minute. The mixture was gradually added with 0.1 M NaOH in small portions until the pH of the mixture reached 8. The mixture was heated to 50 ° C and held on the magnetic stirrer for 60 minutes at a speed of 400 revolutions / minute. The produced precipitate was filtered off and washed several times with deionized water. After drying at 80 ° C for 2 hours under reduced pressure, the catalyst was reduced with 5% H ₂ in N ₂ at 200 ° C for 30 minutes. The Ru: Pd ratio in the prepared catalyst was 0.25.

Comparative Example 1

On a magnetic stirrer was a beaker with 1 g of commercially available catalyst 20% Pd / Vulcan (BASF Fuel Cells) having a Pd-crystallite size of about 3 nm, 0.091 g RuCl ₃ · 2H ₂ O (ABCR Co.), and 200 ml of water. After mixing for 30 minutes, the mixture was heated to 60 ± 1 ° C, followed by gradual addition of 4.51 ml of a 0.5 M HCOOH solution. After mixing for 2 hours, the catalyst (Millipore ^®) was washed five times with deionized water. The prepared catalyst was dried at 80 ° C under reduced pressure for 12 hours. After the preparation shown, the atomic ratio of ruthenium to palladium in this catalyst was 0.2. The prepared catalyst was identified by the symbol 0.2 RuPd (HCOOH).

The standard stability test of the catalyst at the anode of a formic acid fuel cell was carried out at 30 ° C at a flow rate of 3 M HCOOH of 0.7 ml min ^-1 . The stability test of the catalyst was carried out by a DC method at a current of 10 mA cm ^-2 . The exam results are in 6a - 6d shown. The average power of the fuel cell, which was determined for the 30-minute periods shown in these diagrams, is also plotted on these diagrams. There are no spontaneous oscillations of the fuel cell voltage and the power density of the fuel cell decreases insignificantly. After 6 hours of measurement, the power density reached 3.33 mW / cm ² , significantly less than the power density of the fuel cells produced using catalysts with a higher Ru: Pd ratio at the anode (as described in Examples 1) -3).

Comparative Example 2

The standard stability test of a commercially available 20% Pd / Vulcan catalyst from Premetek having a Pd crystallite size of about 3 nm at the anode of a self-made formic acid fuel cell (as described above) was performed under the following conditions: flow rate of 3 M formic acid 0.7 ml min ^-1 and oxygen flow rate 1000 ml / min. The exam results are in 7 shown. No spontaneous oscillations of the fuel cell voltage were observed and the catalyst was significantly de-activated after 6 hours of operation.

The results achieved on the anode catalysts of the formic acid fuel cells and disclosed in the present patent application are in 8th summarized. It can be seen that the catalysts described in Examples 1-3, in which the fuel cell voltage showed oscillations, showed a higher power density (4.2 ± 0.1 mW cm ^-2 ) after 6 hours of operation than the catalysts in Comparative Examples 1 and 2, in which the fuel cell voltage showed no oscillations (corresponding to 3.3 ± 0.1 and 1.8 ± 0.1 mW cm ^-2 ).

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 03/088402 A1 [0006]
• US 7132188 [0006]
• US 2007/0099064 [0006]
• WO 2005/081706 A2 [0006]
• US 2005/0136309 [0006]
• US 77490974 [0006]
• US 2007154743 [0006, 0008]
• US 77490974 B2 [0008]
• US 2010/0086831 A1 [0013]

Cited non-patent literature

• Yimin Zhu, Zakia Khan, RI Masel, The Behavior of Palladium Catalysts in Direct Formic Acid Fuel Cells, Journal of Power Sources 139 (2005) 15-20 [0005]
• S. Ha, Z. Dunbar, RI Masel, Characterization of a High Performance Passive Direct Formic Acid Fuel Cell, Journal of Power Sources 158 (2006) 129-136 [0005]
• Robert Larsen, Su Ha, Joseph Zakzeski, Richard I. Masel, Unusually active palladium-based catalysts for the electrooxidation of formic acid, Journal of Power Sources 157 (2006) 78-84 [0005]
• S. Ha, R. Larsen, RI Masel, Performance Characterization of Pd / C Nanocatalyst for Direct Formic Acid Fuel Cells, Journal of Power Sources 144 (2005) 28-34 [0005]
• Xingwen Yu, Peter G. Pickup, Mechanistic Study of the Deactivation of Carbon Supported Pd during Formic Acid Oxidation, Electrochemistry Communications 11 (2009) 2012-2014 [0005]
• Xingwen Yu, Peter G. Pickup, Mechanistic Study of the Deactivation of Carbon Supported Pd during Formic Acid Oxidation, Electrochemistry Communications 11 (2009) 2012-2014 [0007]
• Wai Lung Law, Alison M. Platt, Priyantha DC Wimalaratne and Sharon L. Blair, Effect of Organic Impurities on the Performance of Direct Formic Acid Fuel Cells; Journal of The Electrochemical Society, 156 (5) B553-B557 (2009) [0007]
• A. Mikołajczuk, A. Borodzinski, P. Kedzierzawski, L. Stobinski, B. Mierzwa, R. Dziura, Deactivation of Carbon Supported Palladium Catalyst in Direct Formic Acid Fuel Cells, Applied Surface Science 257 (2011) 8211-8214 [0007]
• Mingjun Ren, Yongyin Kang, Wei He, Zhiqing Zou, Xinzhong Xue, Daniel L. Akinsc, Hui Yang, Songlin Feng, Origin of Performance Degradation of Palladium-based Direct Formic Acid Fuel Cells, Applied Catalysis B: Environmental 104 (2011) 49 -53 [0007]
• Won Suk Jung, Jonghee Han, Sung Pil Yoon, Suk Woo Nam, Tae-Hoon Lim, Seong-Ahn Hong, Performance degradation of Pd anode catalyst, Journal of Power Sources 196 (2011) 4573-4578 [0007]
• Wai Lung Law, Alison M. Platt, Priyantha DC Wimalaratne and Sharon L. Blair, Effect of Organic Impurities on the Performance of Direct Formic Acid Fuel Cells, Journal of the Electrochemical Society, 156 (5) B553-B557 (2009) [0007 ]
• A. Mikołajczuk, A. Borodzinski, P. Kedzierzawski, L. Stobinski, B. Mierzwa, R. Dziura, Deactivation of Carbon Supported Palladium Catalyst in Direct Formic Acid Fuel Cells, Applied Surface Science 257 (2011) 8211-8214 [0007]
• Yimin Zhu, Zakia Khan, RI Masel, The Behavior of Palladium Catalysts in Direct Formic Acid Fuel Cells, Journal of Power Sources 139 (2005) 15-20 [0008]
• Robert Larsen, Su Ha, Joseph Zakzeski, Richard I. Masel, Unusually active palladium-based catalysts for the electrooxidation of formic acid, Journal of Power Sources 157 (2006) 78-84 [0008]
• S. Ha, R. Larsen, Y. Zhu, RI Masel, Direct Formic Acid Fuel Cells at 600 A / cm 2 at 0.4 V and 22 ° C, Fuel Cells 4 (4) (2004) 337-343 [0008]
• S. Ha, R. Larsen, Y. Zhu, RI Masel, Direct Formic Acid Fuel Cells at 600 A / cm 2 at 0.4 V and 22 ° C, Fuel Cells 4 (4) (2004) 337-343 [0009]
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Claims (11)

A Ru / Pd / C catalyst, in particular for the electro-oxidation of formic acid, comprising carbon-supported palladium and ruthenium, characterized in that the nominal atomic ratio of ruthenium to palladium in this Ru / Pd / C catalyst is in the range of 0.2 to 1.5 is included. A catalyst according to claim 1, characterized in that ruthenium is in metallic form without forming an alloy with palladium. Catalyst according to claim 1 or 2, characterized in that it activates itself when used in a formic acid fuel cell, by spontaneous oscillations of the fuel cell voltage, which do not require external energy supply. Process for producing the Ru / Pd / C catalyst, characterized in that it comprises the following steps: a) a Pd / C catalyst, preferably having a Pd crystallite size below 5 nm, is provided, and subsequently b) Ruthenium (Ru) is deposited on the produced Pd / C catalyst with the formation of a Ru / Pd / C catalyst. Process according to claim 4, characterized in that in step a) the palladium deposited on a carbon support is used as Pd / C catalyst, the carbon support being selected from the group comprising Vulcan XC-72, Carbo Medicinalis Ligni, carbon nanotubes, carbon nanofibers and graphene, is selected. A method according to claim 4 or 5, characterized in that in step b) ruthenium either by the reduction of ruthenium salts in aqueous solution using a reducing agent or by the impregnation (coating) of the Pd / C catalyst with ruthenium hydroxide, and then the reduction of this Rutheniumhydroxids using a reducing agent, is deposited on the Pd / C catalyst. A method according to claim 6, characterized in that in step b) ruthenium chloride (RuCl ₃ ) is used as the ruthenium salt. Process according to any one of the preceding claims from 4 to 7, characterized in that in step b) sodium borohydride (NaBH ₄ ), formic acid (HCOOH) or hydrazine (N ₂ H ₄ ) is used as a reducing agent reducing the ruthenium ions. A process according to any of the preceding claims from 4 to 8, characterized in that the nominal atomic ratio of ruthenium to palladium in the prepared Ru / Pd / C catalyst is in the range of 0.2 to 1.5. Application of the Ru / Pd / C catalyst prepared by the process defined above in claims 4 to 9 for the electro-oxidation of formic acid in the formic acid fuel cells. Formic acid fuel cell, consisting essentially of a cathode, which is preferably a Pt / C catalyst, an ion-conducting membrane, and an anode, which is a ruthenium-refined palladium catalyst, characterized in that the ruthenium-refined palladium catalyst A Ru / Pd / C catalyst according to claims 1 to 3.

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