DE2263636A1 - FUEL ELEMENT - Google Patents

Description

Our No. 18 364

Es3o Research and Engineering Company
Linden, NJ, V.St.A,

Fuel element

The invention relates to fuel elements for liquid
Fuels that contain aqueous electrolytes and
their anode to accelerate the electrochemical
Oxidation of the fuel contains a precious metal catalyst.

According to the invention it has been found that the electrochemical oxidation of liquid oxidized hydrocarbons burns openly, which are miscible with water, in particular methanol, can be effectively carried out in a fuel element in which an anode, the one
Contains palladium-ruthenium catalyst, and an aqueous electrolyte with a pH of at least about 8 can be used.

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The fuel elements according to the invention contain an anode with a palladium-ruthenium catalyst, a cathode, an aqueous electrolyte having a pH of at least about 8, and a device having the help of which a liquid fuel is fed to the anode. The elements also preferably have one semi-permeable membrane that divides the interior into an anode and a cathode compartment.

The invention is explained in more detail by the drawing.

Fig. 1 is a schematic representation of one according to the invention Elements.

Fig. 2 is a graph showing the Polarization voltage in volts as a function of the current density for palladium-ruthenium electrodes and reference electrodes.

Figure 3 is a graph showing polarization voltage versus current density using a series of palladium-ruthenium electrodes.

According to the present invention, excellent operating characteristics for a fuel cell can thereby be obtained are that in the fuel element an anode which contains a palladium-ruthenium catalyst, and a aqueous alkaline electrolytes with a pH of at least about 8 are used. Fuel elements that make one Containing palladium-ruthenium anode catalysts have low polarization voltages even at high current densities. In contrast, for any given cell voltage (where the actual cell voltage

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the theoretical cell voltage minus the sum of the anode polarization voltage, the cathode polarization voltage and the loss due to the resistance of the electrolyte) is the achievable current densities using of palladium alone or ruthenium alone as the anode catalyst is much lower than the current densities that when using the palladium-ruthenium catalyst used according to the invention can be obtained. The use of an aqueous alkaline electrolyte with a pH of at least about 8 gives significantly lower polarization voltages than when using neutral buffers, for example dipotassium monohydrogen phosphate monopotassium dihydrogen phosphate buffer (pH value = about 7) is the case, and that which occurs when using acidic electrolytes Corrosion problems are avoided.

The inventively used palladium ruthenium catalysts generally have a weight ratio of palladium to ruthenium of from about 95: 5 to about 5: 95 · In other words, the active catalyst metal contains about 5 to about 95 weight -% of palladium and vice versa about. 5 to about 95 wt -.% ruthenium, based on the total weight of palladium and ruthenium. The catalysts preferably have a palladium to ruthenium weight ratio of about 85:15 to about 15:85.

According to a preferred embodiment of the invention Palladium and ruthenium deposited simultaneously on an electrically conductive support. The wearer should have an effective

2 have the same surface area of at least about 5 m per gram. as A porous carbon with a large effective surface is preferred as the carrier material. Various well-known Carbon sorption degrees can be used for this purpose.

3CnB? N / 083Ü

Commercially available preparations of adsorptive carbon often contain materials that adversely affect the performance of the fuel elements. It was found, that improved performance of the fuel element is achieved when the carbon is mixed with a strong mineral acid, such as sulfuric acid, treated and then is washed with water prior to impregnation with the noble metal catalyst. After the acid treatment and washing may optionally include treatment with a strong aqueous base followed by washing done with water to neutralize the acid.

While adsorbent carbon as, carrier material

Adsorptive is preferred, other / materials with large effective surface and high electrical conductivity can be used. Such materials are for example Silicon carbide, tungsten carbide and the like with a correspondingly large effective surface.

The carrier can be mixed with the noble metal catalyst by known methods are impregnated. So the carrier can with aqueous solutions of palladium and ruthenium salts, such as for example palladium chloride and ruthenium chloride, are impregnated. A mixed solvent of water and a water-miscible alcohol, such as isopropyl alcohol, has also proven to be advantageous for the production of ruthenium chloride solutions. The impregnated Support is dried by suitable methods, for example by freeze-drying or heating, and then the palladium and ruthenium salts are reduced to the free metal, hydrogen being a preferred one Is reducing agent. To do this, the dried impregnated carrier can be placed in an oven and hydrogen in Contact with the adsorbent material passed through the furnace

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will. Suitable temperatures for this reduction are from about 25 ° C to about 300 ⁰ C. It can, although other reducing agents such as sodium borohydride may be used, but the use yields of hydrogen surprisingly more effective catalysts than the other when using the reducing agent is the case .

The carrier can be omitted. However, this is generally not a preferred embodiment, since one effective anodes can be obtained using a support with much smaller amounts of noble metal catalyst than without carrier. If the carrier is omitted, palladium-ruthenium mixtures can be used by simultaneous reduction of palladium and ruthenium salts, preferably in one aqueous solution (including aqueous-alcoholic solutions) using a suitable reducing agent, such as hydrogen can be obtained. Raney metal manufacturing processes can be used to advantage will.

The anode also contains an electrically conductive base body, which can be a metal mesh, a plate or the like, a mesh being preferred. Suitable materials for the base body are known in the art; the base body should be conductive and not attacked by the electrolyte. Silver is a preferred base material for the anodes used according to the invention.

The anode can be produced from the impregnated carrier and the base body by known methods. So for example, the connection of the impregnated carrier to the base body by using known binding

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medium, such as polyvinyl chloride, can be achieved. An anode can be obtained by making a paste or a flowable mixture of impregnated carbon, a binder, such as polyvinyl chloride, which can be added in powder form, and a solvent for the binder, such as tetrahydrofuran. The amount of binder is usually relatively small, for example about 10 % or less, based on the weight of the impregnated backing. The liquid or paste is applied to the surface of the mesh and the solvent is evaporated.

If the support is omitted, the palladium-ruthenium catalyst mixture is combined directly with the main body. A finely divided palladium-ruthenium mixture can be produced by making a solution of the mixed salts, for example of palladium chloride and ruthenium chloride, reduced in the absence of an adsorbent material or such a reduction in the presence of silica or another alkali-soluble adsorbent and then the silica with a strong Alkali dissolves. The finely divided palladium obtained in this way

direct;

dium-ruthenium mixture can / with a suitable binder, such as, for example, polyvinyl chloride, can be bound to a conductive base body.

The cathode can have any suitable structure and contain a catalyst which has the electrochemical Reduction of the oxidizing agent accelerated. In the fuel elements according to the invention is used as an oxidizing agent generally either air, oxygenated air, or pure oxygen is used; the preferred one The oxidizing agent is air. The cathode and oxidation

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agents can be made from the known cathodes and oxidizing agents to be selected.

The elements according to the invention also preferably contain a semipermeable membrane between anode and cathode. This membrane divides the interior of the element into an anode and a cathode compartment. Suitable membrane materials are well known in the art.

Is used as the electrolyte in the fuel cells according to the invention an aqueous electrolyte with a pH above about 8 is used. Such electrolytes result in use of the palladium-ruthenium anode catalyst according to the invention higher conductivity with low polarization tensions. The electrolyte can either be an alkaline buffered electrolyte or a strongly basic one Be electrolyte. A preferred electrolyte according to the present invention is a carbonate-bicarbonate buffer; one with regard to each component, 1 molar solution of potassium carbonate and potassium bicarbonate, which is particularly preferred has a pH of about 10.2. Other basic buffers that can be used are, for example the diphosphate-triphosphate buffers, such as dibasic Cesium phosphate and tribasic cesium phosphate with a pH of about 11.7 in a solution with a 1 m concentration of each component. Strongly basic electrolytes, such as potassium hydroxide, can also be used. The electrolytes can be used in any desired concentration. With buffered For electrolytes, it is common to use a solution with a 1 molar concentration of each component, although also other concentrations may be used. A 6 m KOH solution can be used with advantage. Of the

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Carbonate-bicarbonate buffer has the advantage that it repels carbon dioxide is. This means that the carbon dioxide formed by the oxidation of methanol is not in the Electrolyte dissolves. More basic electrolytes, i.e. those with a pH value above about 10.2, dissolve at least part of the carbon dioxide formed by the electrochemical oxidation of the fuel. This carbon dioxide must be removed to keep the fuel element operating. The removal of carbon dioxide is usually effected by removing the electrolyte, the carbon dioxide outside the element and the electrolyte, from which the carbon dioxide has been removed, returns in the circuit. Suitable Methods for removing the carbon dioxide are known and are described, for example, in US Pat. No. 3,511,713.

As indicated earlier, methanol is the preferred fuel for the elements of the present invention. Others with Water-miscible, oxidized hydrocarbons such as ethanol and formaldehyde can also be used will. Methanol is preferred because, as already mentioned, it has a higher energy output per unit volume results.

The fuel elements according to the invention will now be described in more detail with reference to FIG. 1 of the drawing.

In Fig. 1, 10 is a fuel element with a housing 11, an anode 12, a cathode 13, a semi-permeable Membrane 14 between the anode 12 and the cathode 13 and an aqueous electrolyte 15. The membrane 14, which is permeable to ions, divides the interior of the element 10 in an anode compartment 16 and a cathode compartment 17. The

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The element also includes a fuel inlet 18, through which a water-miscible liquid fuel such as methanol is admitted, an inlet 19 for air or another oxidizing agent which is normally gaseous, an oxidation product outlet 20 for carbon dioxide, a gas outlet 21 for unreacted gaseous oxidizing agent and nitrogen as well a drain line 22 for withdrawing an aqueous solution of the electrolyte and fuel. The electrolyte-fuel mixture can be passed into a gas separator 23, in which carbon dioxide is released, and through the gas outlet 24 can be eliminated. The fuel-electrolyte mixture from which the carbon dioxide has been removed is recirculated to fuel inlet 18 through line 25.

The anode 12 contains a palladium-ruthenium catalyst, and can be of any desired physical shape to have; for example, it can be a mesh (as shown) or a plate with which the palladium-ruthenium catalyst, is preferably firmly attached to a porous support such as carbon. The cathode 13 can also be any desired physical Shape, such as that of the network shown. As indicated above, the electrolyte 15 is an aqueous one alkaline electrolyte with a pH of at least about 8.

The fuel element shown in Fig. 1 is used for illustration. Any desired fuel element structure can be used. A preferred structure is one A battery of composite thin bipolar fuel elements such as that disclosed in U.S. Patent No. 3,518,122 will be shown.

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example 1

In this example, a test electrode with a Palladium-ruthenium catalyst and two comparison electrodes, which contained only palladium or only ruthenium as a catalyst, produced and tested. Each electrode included a catalyst made of noble metal or a metal mixture on a carbon support, which is connected with a silver mesh was. For the manufacture of all electrodes, finely divided porous adsorbent carbon was used for Fuel elements used. The two comparison electrodes, the palladium or ruthenium catalysts were labeled A and B, respectively, and the test electrode, the containing a mixture of palladium and ruthenium in a weight ratio of 50:50 was designated F-I. In in each case the total amount of catalyst metal was 4% by weight based on the carbon.

The catalysts for each electrode were prepared by treating the carbon with a solution of Palladium chloride, ruthenium chloride or a mixture of the two salts impregnated and the salt to the corresponding Metal or metal mixture reduced. The catalysts are identified by the same letter as the corresponding one Called electrodes.

The impregnation solution for catalyst A was prepared by dissolving 339 mg palladium chloride, PdCl ₂ (60 wt. 56 or 200 mg Pd) in 2 ml concentrated (36.5 wt. Jt) hydrochloric acid and adding enough deionized water that 5 ml of solution were obtained. The impregnation solution for catalyst B was prepared by adding 521 mg of ruthenium chloride, RuCl, -3H ₃ O (38.6% by weight or 200 mg of Ru) in a mixture of 0.5 ml of deionized water and 4.5 ml of isopropy ! alcohol dissolved. The impregnation

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solution for catalyst P-I was prepared by that 135.6 mg of palladium chloride (90 mg of Pd) were dissolved in concentrated (36.5% by weight) hydrochloric acid and a small amount of water added, 209 mg of ruthenium chloride dissolved in a small amount of water and the two solutions combined to form a To obtain a mixed solution with a volume of 4 ml.

The impregnation solutions for Catalysts A and B were added to separate 5 g portions of carbon, and the impregnation solution for Catalyst PI was added to a 4 g portion of carbon, each added dropwise with stirring into a beaker. The impregnated carbon portions were freeze-dried and placed in a vessel furnace, heated to 200 of ⁰ C and at this temperature for about 3.5 h was maintained., While flows of nitrogen, hydrogen and nitrogen were passed again through the furnace. The reaction with hydrogen converted the palladium chloride and ruthenium chloride to palladium and ruthenium, respectively. This gave the catalysts A, B and PI, which consisted of palladium, ruthenium or a 1: 1 mixture (based on weight) of palladium and ruthenium on carbon.

Three silver nets with a mesh size of 0.420 mm (40 mesh) and dimensions of 3 × 2 cm each were placed on an aluminum foil. Three pastes were prepared by mixing a portion (about 30 mg of carbon and 1.2 mg of catalyst metal) of each of the above supported catalysts in the dry state with 10 % by volume (based on the carbon) of a polyvinyl chloride powder and added a few drops of tetrahydrofuran. Each of the pastes became one of those described above over a 4 cm area

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Crossed out silver nets. By evaporating the tetrahydrofuran, those impregnated with the catalyst were impregnated Portions of carbon bound to the respective grid.

Each of the electrodes prepared as described above was tested in a half-cell, which is a calomel reference electrode and had a direct power supply in the external circuit. It became an aqueous carbonate buffer electrolyte was used, which initially consisted of 1M sodium carbonate and 1M sodium bicarbonate and had a pH of 10.2. The tests were carried out at 75 ° C and various current densities in the range from 0.5 to 20 mA / cm. the Test electrodes were alternately cathodized and anodized, i.e. first used as cathode, then as anode of the test cell, until a constant tension was achieved. This fully activated the catalyst.

The polarization voltages (i.e. the differences between the theoretical and the actually measured voltages at the current densities tested for each electrode are listed in Table I below.

Table I.

Polarization voltages in volts at the specified current densities

Weight _. ,. . . . ., 2 ratio of current density in mA / cm

Electrode Pd: Ru 0.5 _1 _2 _5 10 20

A only Pd 0.39 0.40 0. i * 7 0.53 0.6l B only Ru 0.23 0.25 0.27 0.33 M), 7 P-I 1: 1 0.14 0.17 0.19 0.21 0.27 0, ^ 1

The results of Table I are graphically shown in FIG shown.

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- Vb -

The test electrode P-I was found to give each given current density significantly lower polarization voltages than each of the comparison electrodes A and B. Aus It can be seen from Fig. 2 that a much higher current density can be obtained for any given voltage when the Palladium-ruthenium anode catalyst according to the invention instead an anode catalyst made of palladium or ruthenium alone is used.

Example 2

In this example ten electrodes were used with palladium-ruthenium catalysts different weight ratios of Pd: Ru prepared and tested as described. In each In this case, the electrode contained a mixture of palladium and ruthenium, which was deposited on a porous carbon support which in turn was tied to a silver net.

The carbon used in this example was first impregnated with sulfuric acid and then with potassium hydroxide treated to increase its activity. This treatment was carried out as follows: 20 g servings Carbon (as described in Example 1) were each dispersed in 450 ml of a 30 percent aqueous sulfuric acid, stirred for one hour, filtered through a glass frit, washed with deionized water, filtered again, dispersed in 30 percent aqueous potassium hydroxide for one hour, filtered, washed with deionized water and then with methanol, filtered and dried at 121 ° C.

The carbon thus treated was divided into 5 g portions and impregnated with palladium chloride-ruthenium chloride solutions as described in Example 1. Each impregnation

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solution had a volume of 5 ml. These solutions were prepared by adding the required amounts dissolved the palladium chloride solution of palladium chloride and ruthenium chloride in concentrated hydrochloric acid and water, respectively diluted with water and mixed the two solutions. The impregnated carbon portions were as in Example 1 described heat-treated in a furnace with hydrogen and nitrogen to produce palladium-ruthenium mixtures deposited on carbon to obtain. The amounts used in electrode manufacture are as follows Table II given.

Table II

catalyst
metal, wt .-% Ru Weight ] Metal, mg 85.4 167 Ru (relative to C) 0.67% behaved Salt, PdCl? RuCl _x .3HpO Pd 129.5 150 33 electrode Pd 1% Pd: Ru [mpräKnierunßslösung; 278.3 176.0 133 50 C. 3.33% 1.34% 5: 1 , Wt. , mg; 249.9 259.0 100 67 D. 3% 2% 3: 1 221.6 344.2 53 100 E. 2.67% 2.66% 2: 1 166.6 388.5 50 133 P-2 2% 3% 1: 1 111.6 432.2 33 150 G 1.3 ^% 3.33% 1: 2 83.3 167 HI u.
H-2 1% 1: 3 55.0 JI u.
J-2 0.67% 1: 5

The application of the impregnated carbon to the silver meshes and the testing of the electrodes obtained was carried out carried out according to the procedure of Example 1 with the difference that the test current densities are within a range from 0.5 to 40 mA / cm.

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The polarization voltages for each electrode at the current densities tested are given below in Table HI listed.

Table III

Polarization voltages in volts at the specified current densities

Current density in mA / cm

0.5 1_ 2_ 5_ 10 20 25 40

0.17 0.21 - 0.28 0.37 0.46 0.49 0.62

- 0.27 0.31 0.37 0.47 0.57 0.62 -

0.21 0.23 0.27 0.35 0.44 0.55 0.59 - 0.14 0.17 0.19 0.21 0.27 0.41 -0.19 0.21 0.25 0.29 0.39 0.52 ~
0.12 0.19 0.20 0.23 0.29 0.42 -
0.18 0.20 0.22 0.25 0.32 0.48 -

0.14 0.17 0.18 0.21 0.24 0.33 0.40 -

0.15 0.17 0.18 0.21 0.26 0.37 0.45 -

The results of Table III are graphed in Pig. 3 shown.

electrode Gewients-
relationship
Pd: Ru C. 5: 1 D. 3: 1 E. 2: 1 F-2 1: 1 G 1: 2 HI 1: 3 H-2 1: 3 J-I 1: 5 J-2 1: 5

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Claims (7)

Patent claims: 1. A fuel element containing (a) an anode, one electrically conductive base body and one Contains catalyst consisting of palladium and ruthenium, (b) a cathode, (c) an aqueous electrolyte with a pH of at least about 8 and (c) a feed line for a water-miscible liquid oxidized hydrocarbon fuel to the anode. 2. Fuel element according to claim 1, characterized in that the catalyst is on an electrically conductive carrier is located. 3. Fuel element according to claim 2, characterized in that the carrier consists of carbon. 4. Fuel element according to claim 1, characterized in that that the weight ratio of palladium to ruthenium in the catalyst is in the range of about 95: 5 to about 5:95. 5. Fuel element according to claim 1, characterized in that it is between the anode and the cathode contains a semi-permeable membrane that divides the element into an anode and a cathode compartment. 6. Fuel element according to claim 1, characterized in that the electrolyte consists of an aqueous Alkali metal carbonate bicarbonate buffer. 7. Fuel element according to claim 1, characterized in that the electrolyte consists of an aqueous 309028/0830 i> 263636 Alkali metal hydroxide. For Essο Research and Engineering Company Linden, N.J., V.St.A. (■ (Dr H.J. Wolff) Lawyer 309828/0830 Blank page