DE1904610A1 - Electrode for fuel cells - Google Patents

Description

PATENT LAWYERS

DIPL.-ING. GÜNTHER KOCH DR. TINO HAIBACH

Jan. 30, 1969

8 MUNICH 2,

OUR MARK: 11 813

MATSUSHITAELECTRIG INDUSTRIAL CO., LTD., Osaka, Japan

Electrode for fuel cells

The invention relates to an electrode for Batteries that contain a catalyst in the form of a mixture Includes nickel and copper, and particularly relates to an electrode for fuel cells used as fuel Hydrazine, sodium borohydride or formalin is used «

With the so-called fuel cells, where a fuel is oxidized in an electrochemical way to generate electrical energy, the use of compounds turns out to be such as hydrazine and sodium borohydride as fuel in so far as advantageous as it is possible to adjust the polarization of the fuel electrode in the cell to which the fuel is supplied will be minimized even if the cell is discharged at a high current density because the ~ compounds called have a high activity · Therefore has the use of such compounds as fuel for high voltage fuel cells of small dimensions already received special attention. Namely, it is possible to use a fuel cell of the type in which a oxidizing electrode, which is treated with a suitable oxidizing agent, e.g. Iiuft, cooperates, and one with the Fuel cooperating fuel electrode each other are arranged opposite, with the Eanm between the electrical

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which is filled with an electrolyte, so 'to form that the cell can be discharged at a high current density by placing the electrodes with an appropriately chosen way Catalyst provides «To the ones with the fuel electrode The catalysts used include those belonging to the platinum group, including platinum and to the catalysts used in conjunction with the oxidizing electrode include silver, metal oxides, and active carbon, - It should be noted that these catalysts are compared are cheap to those of the platinum group.

As already mentioned, platinum, palladium and alloys of platinum with other metals are primarily used as catalysts for the fuel electrode because they are very active Choice of the amounts of catalyst to be used has been proposed. Further, since the aforesaid metals are very expensive, studies have been carried out with the aim of reducing the amount of the catalyst used in an electrode by promoting the activity of the catalyst, and in this respect quite satisfactory results have been obtained. It is found that the use of an amount of catalyst of 1 milligram / or less per square centimeter of electrode area is sufficient. However, in a large-sized battery comprising a plurality of cell units juxtaposed to enable high performance, a large amount of the catalyst is required as a whole, and the cost of the catalyst is a fairly large proportion of the cost of the entire cell now is further to be noted that the cost of the catalyst, which represent a considerable part of the total cost of a fuel cell, which represent the major factor of such fuel cells is determined by the practical utility, because if one judges the cost of a fuel Selle _s comparing these costs with the Costs of other Stromer-sseugungsvorrichtungen and energy sources, Z ₀ B ₀ those of

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Solar cells, air-metal batteries, ordinary primary and secondary elements, as well as motors,

Referred to from & ene (reasons would be the use of base metals as catalysts highly desirable and it has been attempted to use nickel black (nickel black) NickeIbοrid, iron, and mixtures of these substances to which additives as _s Electrochemical catalysts for hydrazine, sodium borohydride and hydrogen be attached.

On the other hand, the price of a fuel cell is of course in relationship to Sntladungsdauer and the life of such a ZeIIe ₀ It is highly desirable that a fuel cell can be achieved a long service life and discharged at a large current density ,, Pur-the means electrochemical catalyst so that the catalyst must maintain its activity for a very long period of time.

The above-mentioned nickel black and the nickel boride are very cheap compared to platinum, so that their price does not in any way prevent their use, but these substances have the disadvantage that they do not maintain their activity for a very long period of time Used as a catalyst for the fuel electrode of a fuel cell that is operated e.g. with hydrazine as fuel, the catalyst remains active during the initial stage of the discharge and the voltage is kept constant with a minimal polarization of the electrode. Up to now, a voltage drop at the fuel electrode has not been given great importance, since the oxidizing electrode _t z «B _0, an air diffusion electrode, which works with it, only has a short service life, which therefore also determines the service life of the fuel cell. Since the investigations carried out in the meantime on oxidizing electrodes were successful and it is now possible to extend the service life of an oxidizing electrode, the service life of a fuel cell is now determined by the voltage drop on the fuel electrode

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a period of several hundred hours "upon discharge no significant voltage drop, but the voltage goes at the fuel electrode compared to its value "during the The initial stage of the discharge to a noticeable extent; back if the duration of the discharge is several thousand hours, and therefore there is a significant voltage drop Investigations into the cause of this voltage drop have shown that the voltage drop is primarily due to the Oxidation of the surface of the catalyst metal is due, however, that also parts of the catalyst from the electrode removed, which also causes a voltage drop caused. During the discharge process, these catalyst metals are in the presence of a reducing substance such as Hydrazine polarized anodically, and this is probably the reason that. The catalysts during a long Period of time exposed to general oxidation «This Oxidation is further promoted when other disorders occur.

■ demands, for example, when the electrolyte contains too little fuel, or if the cell is taken out, a current that is larger than the normal discharge current _β If the 'voltage in the former case has dropped so far once that the fuel electrode generates oxygen, can the original voltage cannot be restored even if a copious amount of fuel is supplied to the electrode. Admittedly arise at. Mckelschwarz the disadvantages mentioned, but there are

• Notable advantages of this material in that it enables high performance initially and that it is resistant to alkaline substances ₀ ■ ",

The object of the invention is now that initial performance of such a nickel catalyst as a result to improve ^ that the properties of the material are improved in order to avoid the very slow oxidation of the To suppress the catalyst and thereby the catalytic © To maintain the activity of the catalyst at a high level even for a long period of time. According to the invention it has been shown that the stated object could be achieved by adding copper to the Bickel black Bis

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now the "use of a Mckel ^ copper catalyst." studied to promote chemical reactions, but never attempted a Mickel copper catalyst as an electrochemical catalyst for a long period of time, particularly as a catalyst for the fuel electrode to use a fuel cell, since copper is alkaline Substances is not stable. When using a nickel-copper catalyst as a catalyst, for chemical reactions, the activity of the catalyst has only been shown in Relationship to the d-band from the point of view of the alloy explains, and so far it has never been reported that the use of copper enables oxidation von Ifiekel to suppress that in an Itzkali electrolyte takes place despite the presence of a reducing compound such as hydrazine in the electrolyte, and therefore that it does It is possible to use copper to maintain the catalytic activity of nickel, i.e. to prevent the oxidation of To prevent nickel in a caustic potash electrolyte »

It has been shown that copper to a large extent for the formation of Uickelschwarz from an ITickelsalz under the Exposure to hydrazine or the like contributes. If you just react a Hickelsalz with hydrazine in caustic potash lets Fickelschwarz even then not be in one form sufficient extent if you use the substances during a can react with each other for a very long time. If, however, there is only a small amount of copper salt in the crucible salt, is first made from the copper salt by the action of copper Hydrazine is released, and the copper thus made available acts as a factor preventing the formation of nickel black from the Uickelsalz made possible within a very short period of time. One can take this fact as indirect evidence that the oxidation of the nickel black by the contained therein Copper is suppressed ",

If, as already mentioned, you use "ugly blackness" as a catalyst used, one can see the potential of the fuel electrode even then do not increase back to the original value,

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if you add a large amount of fuel again, after the potential once due to a lack of fuel has dropped so far that oxygen is produced; if that Nickel black, however, contains copper, the electrode can reach its original potential again, with only one small amount of copper ions is formed in the electrolyte. This phenomenon can also be taken as evidence that the copper suppresses the oxidation of the nickel; however, in practice there is no fuel shortage in a fuel cell, since it is usually necessary for a sufficient fuel supply is taken care of.

The catalyst mixture of nickel black and copper can in principle be produced by reducing a mixed aqueous solution which contains a nickel salt and a copper salt. This reduction can be effected by heating the mixed solution in a reducing atmosphere, for example in hydrogen, or by precipitating the catalyst in the aqueous solution by electrolytic means, or by combining the catalyst with hydrazine or the like in one treated with alkaline material ", the last of these processes is to be regarded as the most expedient", because the two first-named processes prove to be inexpedient due to the activity of the resulting catalyst _9, the solid bond between the catalyst and the electrode and the complexity of their implementation. "

The knowledge of making an electrode containing the catalyst can be broadly divided into three different methods; In the first method, the catalyst is brought into the form of an electrode using only pressure and a binder. In the second method, the catalyst is added to a powder which serves as a carrier and this is mixed using a binder % formed by printing an electrode serving as a carrier compound or mass is experienced in the third ^ 'formed into a Elelctrodenunterlage, and then the catalyst is on

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the surface of the pad applied in the first process a powdery catalyst is e.g. Polystyrene solution or a powdery fluorine-containing resin mixed, and this mixture becomes so with the application of pressure shaped so that a metal screen serving as reinforcement is embedded in the material. In the second method, the Catalyst e.g. "mixed with powdered carbon, and thereafter, the electrode is manufactured in the same manner as in the first method. The third method is e.g. Ulckelpowder sintered on the surface of a metal sieve, and then the catalyst is applied to the sintered nickel body »

The invention thus provides one that can be manufactured at low cost Electrode before reducing the catalytic Activity that occurs when Bxckel is the only catalyst is used, is reduced to a minimum, at which the effectiveness of the catalyst during a very long time Can be sustained, and which makes it possible to improve the performance of a cell using the electrode of the present invention.

The invention and advantageous details of the invention are in the following on the basis of sefeematic drawings explained in more detail using exemplary embodiments

Fig «. 1 is a vertical section through one according to the invention Air hydrazine fuel cell,

FIG. 2 shows in a graphic representation the current-voltage characteristic of the hydrazine electrode _{or the like used in the fuel cell according to FIG}

3 shows the time-voltage characteristic curve in a graphic representation the hydrazine electrode of the fuel cell according to Fig. 1.

Fig. 4 is a vertical partial section through, © ine others Embodiment of a Saiierstoff-hydrazine fuel -

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cell according to the invention.

Fig. 5 shows schematically a device for measuring the discharge characteristics of the fuel cell ο

The invention is described below with reference to embodiments in which with the help of the mentioned Electrodes produced by the second and third methods are used as hydrazine electrodes of a hydrazine fuel cell be o

example 1

Nickel nitrate (M (KO ₅ ) .6H ₂ O) and copper nitrate (Cu (UTO ^) ₂ · 3Η ₂ 0) were mixed in such a proportion that there would be a ratio of 2s1 between the nickel ions and the copper ions. One part by weight of this mixture was dissolved in 2 parts by weight of water to prepare an aqueous solution of the nitrates, an excess amount of a 15 percent aqueous solution of sodium carbonate was added to the aqueous solution of the nitrates while it was kept at a temperature of 40 ° C, and the mixture was sufficiently stirred, - ^ as precipitated material was deposited, and to this material was gradually added a mixed solution consisting of one mole of caustic potash and one mole of hydrazine hydrate (100 percent solution of UpH ^ .H ₂ O). Did the reduction happen quickly _? and a black metal powder was produced. "- After thoroughly washing with water, the metal powder was dried at normal temperature under a reduced pressure. Then, 2 parts by weight of carbon powder and 0.7 part by weight of an ethylene tetrafluoride-propylene hexafluoride copolymer were added to one part by weight of the black metal mixture and these substances were mixed thoroughly in a mixer. The powdery mixture was molded into a mold so as to enclose a metal sieve placed in the center of the mold, and then a pressure of 350 kg / cm was applied to the material to produce a to produce © electrode eiaer thickness of "1.1 mm * The metal screen .wurds k at a vorbestimm · · U = σ α" 3/1 ö © J.

th point exposed by removing the electrode material, and a. connecting piece made of a thin nickel sheet was connected to the metal screen by spot welding. This electrode according to the invention, which is produced quietly in FIG. 1, is referred to as electrode A in the following. Yergleichszweeken to an electrode having Hickelsehwarz as a catalyst was also prepared iri the manner described, but only _t Uickelnitrat was -Uses; this electrode is referred to as electrode B in the following.

Air-hydrazine fuel cells of the type shown in FIG. 1 were produced, an electrode A or an electrode B being used as the hydrazine electrode, and the discharge characteristics of the two cells were compared with one another. The ^ eIIe according to Mg ₀ 1 comprises a hydrazine electrode 1, a supply line 1 ', a thin air electrode 2, which is produced under pressure as a molded body from a mixture of active carbon, silver and a water-repellent material, a line 2 connected to the air electrode. and a fuel 3 »which consists of an aqueous solution of caustic potash with a specific gravity of 1.35 and contains 2 $> hydrazine hydrate. The fuel is supplied to the hydrazine electrode 1 ″ via an inlet opening 3 ′ and discharged from the cell via an outlet opening 3 ″. Furthermore, the cell comprises a separator 4 made of asbestos and a container 5 made of polyvinyl chloride. Fog * 2 illustrates the relationship between the current intensity and the voltage of rows A and B in the event that the cells are discharged at different values of the current service. The measurements were carried out at a temperature of 30 ° C. * Fig. 2 does not reveal in that the electrode a to the electrode B, is particularly superior "from Fig. 3, however, where the results of a continuous discharge of the electrodes are shown at a current density of 55 mk / om, it is seen that is substantially the voltage drop of the electrode a, low than that of the electrode B, and that of the electrode a in their discharge during a very long% & t% a ataMle Spanntxng refer Isasm "Dia temperature -άββ Blelrfcrolyten feetrug _&&! di®sem case

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32 "to" 38 ° C, however, it should be noted that there is the same tendency of the course of the characteristics even with higher or lower Temperatures of the electrolyte gives »An examination of the influence of a difference in current density at this temperature also showed that the difference between the values of the voltage drop for both electrodes was greater becomes p when the current density is higher than 55 mA / cm than when the current density was below this value

Example 2

Mekelnitrat and copper nitrate were mixed in such a proportion ₉ that a ratio of 3s1 between the JTickelionen and copper ions resulted in _P and this mixture was achieved in that wurdef annexed ₉ 8 part by weight of water to 1 part by weight of the mixture it east obtained in this / manner an aqueous solution of the ETitrate _e A sintered Mckel plate of known type with a porosity of and a thickness of 0.3 m was in the aqueous solution

the litrate immersed for 5 min at 35 ° 0 _? in order to saturate the pores of the sintered plate, whereupon the plate was dried for 2 hours at 95 ° G. Mol-an. -Aqueous solution of caustic potash "at Baiimtampersirar .5 ißin.-long. - and then also at room temperature in 5 mol of an aqueous solution of caustic potash containing 3 percent hydrazine hydrate, each of which the plate was immersed for 2 to 3 hours in this solution left "worr - 'was the ₈ wu de ^ the solution auf-- 45 ° O warmed> and the plate remained for a further Stunöe in the solution. Under these conditions give the hit rate sufficient amounts of nickel and copper from _e Thereafter, the plate was washed with water, Baneeii was very feiein © on d © r Otearflache the sintered plate existing · long üqb catalyst ent · = removed, and the plate wmrä © fe @ i terafegesetstöa Druok ge ~. "dries® this plate tmri © la ä © ^ w © lter ©" b @ a bssohriebenen-way to manufacture © iaer !! © kti'odfi-irtrwtaä.eto Eweclaiäßig ein® Al & schlußleittassg sna Bsta®M © a. © ines Strode -ass- einai?

Spot welding attached "before the catalyst to the plate is applied o

Pigβ 4 shows in a partial section an oxygen-hydrazine fuel cell _p constructed from layers in which electrodes of the type described above are used as hydrazine electrodes. In Pig «. 4 the different cell units are labeled 01, C2 etc. Each cell unit comprises two hydrazine electrodes 11, a line 11 leading to the hydrazine electrodes, two oxygen electrodes "12s · Ah-. Terminal lines 12 * for the oxygen electrodes, and an electrolyte 13 containing the fuel, which is a 30 percent aqueous solution of caustic potash is, the 1 _f 8fo hydrazine hydrate contains "the electrolyte is the cell units respectively 'supplied via an outlet opening 13' via an inlet opening 13 discharged further comprises each cell unit two separators 14 and a container 15" Ten of the according to Pig. 4 cells constructed units were connected to each other, and the discharge characteristics of this layer-built cell was examined with the aid of the device shown in Pig. 5 According to Pig. 5, the fuel cell 22 in a container 2T arranged _s and a fuel-containing electrolyte 23 is the cell via a pump P supplied “The nitrogen released during the reaction gas is released into the atmosphere through an outlet 24. An 80-prosentige aqueous solution 25 of hydrazine hydrate is automatically supplied to the container 21 via a flow regulator 26. Furthermore, oxygen is supplied from a pressure container to the container 21 via a pipe 27, and a very small amount of unused oxygen and a small amount of nitrogen gas ₉ which escape from the electrolyte after these gases have flowed around the oxygen electrodes, are discharged via a line 28

A cell with the electrode according to the invention, which is in hereinafter referred to as cell C, and eiae Tergleichszelltj, in which the electrodes only contain nickel black as a catalyst, and which is hereinafter referred to as cell D,

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were repeatedly discharged at intervals of 10 hours for 100 hours at a current density of 70 mA / cm. Although it was found that after a discharge time of 10 hours there was no significant difference between the terminal voltages of cells C and D, that is, the terminal voltage of the Cell C was 7 * 7 V and that of cell D was 7.5 T, but it was found that this difference increased progressively in the further course of the discharge, and that cell C was superior to cell D; in other words, the - terminal voltage of the Z _e ll.e C was 7.8 15 while the terminal voltage of the cell D to a total discharge time of 350 hours was 7.6 T; After a total discharge time of 500 hours, cell G had a terminal voltage of 7.5 V and cell D one of 7? 2 Yj after a total of

P th discharge time of 800 hours, the terminal voltage of cell C was 7.3 V and that of Z ₆ He D 6.8 Vj after a total discharge time of 1200 hours, the terminal voltage of cell 0 7 * 1 V and that of cell B 6 .4 Vf after a total discharge time of 1,800 hours, cell C had a terminal voltage of 6.9 V and cell D a terminal voltage of 6.0 V; Finally, after a total discharge time of 2500 hours, the terminal voltage was 0 6.7 V and that of the cell was 5 ₃ 7 V. During the discharge, the potential of the oxygen electrodes remains essentially unchanged, and the greater part of the voltage drop is produced by changing the potential of the hydrazine electrodes -

. suppliedο '

From the above examples 1 and 2 it can be clearly seen that the catalyst consisting of nickel and copper maintains its activity for a much longer period than the catalyst consisting solely of nickel. An addition of copper to the winding proves to be effective, regardless of how small the amount of copper added, because the effect of the copper is that it suppressed the oxidation of the nickel attached in a ratio of 1: 2 or 1: 3, but noted ■ $

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that even the addition of a very small amount of copper z, _o * B in the ratio of 1:10 to a noticeable "effect brought The preferred range within which the nickel copper is attached, is between 0.05 and 0.5 copper ions per nickel ion .

Because the effect of copper as described above consists in the suppression of the oxidation of the nickel, it should be noted that the Fickel has been the same up to now common substances, e.g. Iron, silver, cobalt and tungsten, can add, and that also a catalyst that contains these additives in addition to the addition of copper, in the area the invention falls «,

Patent claims s

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Claims (3)

PA ¹ S E Έ T CLAIMS 1 _e electrode for batteries ,, gek en η ζ e'i ch η et through, a pad that carries a catalyst composed of nickel and copper _{or similar} 2. An electrode according to claim 1, characterized geke η η i ze et η _t that the catalyst is prepared by the reduction of a lischlösung a nickel salt and a copper salt with caustic alkali and a reducing agent, " 3. Electrode according to claim 1, characterized in that g e k en η - ζ e 1 c h η e t j that the electrode by way of forming a Catalyst and a binder is produced by applying pressure, and that the catalyst by the Reduction of a mixed solution of a Uiekelsalζes and a Copper salses made with Xtzkali and a reducing agent isβ 4 · Electrode according to claim 1 _S characterized g'e characteristic. I show η e. t _f that the electrode is formed untei 'application of pressure of a mixture, containing a catalyst, to alkaline substances resistant, electrically conductive powder and a binder _g and the catalyst by reduction of a mixed solution of a. "Nickel salt and a copper salt is made with caustic potash and a reducing agent, 5e electrode according to claim 1, characterized η geke η - characterized in that the electrode is "prepared by the implementation of elaboration Tasch rides that serve ^ a to alkaline substances resistant ₉ electroconductive powder with a Misöhlösung a lickelsalzes and impregnate a copper salt gu, the powder with the help of © 009834/1803 --g - -... ■ "■■■" ■■ ·. ■ to reduce caustic potash and a reducing agent and then to bring the powder together with a binding agent into the shape of an electrode using pressure, 60 electrode according to claim 1, characterized in that g e k e η η, that the electrode is made by carrying out operations that serve to produce a To generate electrode pad, on this pad a mixed solution of a Hickelsalt and a copper salt apply and then the solution on the surface of the pad to reduce with the help of caustic potash and a reducing agent, 7 o Electrode according to claim 1, characterized in that the catalyst has a third substance, e.g. Iron, silver, cobalt or tungsten is attached «, 00 98-34 / 160 Lee on the back