DE1571923A1 - Electrodes for fuel elements and other electrical cells - Google Patents

Description

20 116

American Gyanarata ^ Cpiapany «Wa yne, .New Jers_ey _it- Vo St <, Α _Λ ,

El eic drains for fuel (elements and other electrical cells

The invention relates to an “improved catalyst electrode and to a method for producing such an electrode which is suitable for use in fuel cells with free electrolytes” _o InsTbesondero the invention relates to the production of catalyst electrodes using (a) a liquid-impermeable, but gas-permeable base, which is coated with a layer that contains (b) various inorganic, catalytically active substances and (c) a very "specific type of binders or waterproofing gowns" o The invention particularly relates to the production of shaped -

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th ₉ porous polytetrafluoroethylene © or polytrifluoroethylene electrodes with a coating of either a polyethylene latex emulsion © or a polytetrafluoroethylene emulsion as a binding agent and a water-reducing agent mixed with a catalyst

So far, electrodes have been used in fuel elements » For example, either from platinum black or from a suitable noble metal, made on carbon as a carrier, which are distributed on a metal sheet ", However, such electrodes cannot be used universally » as they fail quickly due to the drowning © of the electrode in the cell matrix · For cells with free Electrolytes, such electrodes have a short lifespan ö To counter the phenomenon of drowning, was suggested binders or water-softening agents, such as ZoBo earth waxes or polytetrafluoroethylene immediately before deforming the platinum resin or dee To add precious metal on carbon as a carrier · Nevertheless, this electrode has not proven to be entirely useful for the Use in cells with free electrolytes highlighted »

The purpose of the invention is therefore to provide an improved slectrode for use in cells bit free electrolyte to create the essentially liquid and raw

BATH ORIGINAL

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casual, but gas-permeable, the invention is also intended to create a highly effective catalyst electrode which can be produced in a simple and economical manner and is operationally reliable ^{from room temperature to a temperature of about 20O 0} _{C o}

The invention provides a method for producing an electrode with good properties, which has increased water impermeability and which can be produced in a simple manner by adding a waterproofing latex and a catalyst metal which, if desired, can be stretched with an electrically conductive filler, are mixed and then this mixture is applied to a base of either hydrophobic, porous poly te met luoräthylen or hydrophobic, porous polytrifluorochloroethylene. The base coated on this catfish is then heated to a sufficiently high level according to the invention and a sufficiently high pressure is applied so that the coating bonds with the base about 10O ⁰ C, preferably at temperature "doors between 125 ° and 200 ⁰ Ce

The electrically conductive filler is, for example graphitic carbon or sootο In addition, can

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on these carbon modifications, if desired, catalytically active substances can be deposited · Usually from about 0 to 80 $> and preferably from about 55 $ to 75 $> conductive fillers, based on the weight of the solid electrode odor, can be used »

As mentioned above, it is necessary to first get a water repellent Composition mixed with the mentioned catalytically active metal and the electrically conductive

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gen filler composition to use »This combination reduces the possibility of drowning during the operation of the cell »If not a water repellent · composition is added, the usability of the electrode is noticeably reduced after a relatively short time » Examples of water repellent compositions which may be used here are either polyethylene latex or Polytetrafluoroethylene latex emulsions »In general can be from about 1 wt .-% to about 40 wt .-% detergent Material, based on the weight of the whole Electrode solids, su the conductive filler material, are added before the catalyst is deposited or is mixed in »

The catalyst, which is from .1 wt .- ^ to 98 wt .- ^, based on the weight of the electrode solids,

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usually consists of metal »such as ζ · Bo platinum _f palladium, ruthenium, silver» nickel or a mixture of these metals ο The metal can be deposited on the carbon, which has previously been made waterproof; by reducing the metal, which is in the form of an acid or a salt, for example by sodium borohydride reduction of chloroplatinic acid and platinum , colloidal silicon dioxide or aluminum oxide from 1 » to 40 #, based on the total weight of the electrode solids, can be added.

In general, for example, either the polyethylene or the polytetrafluoroethylene emulsion through Dispersing discrete particles formed from polyethylene or polytetrafluoroethylene in distilled water that either a niohtionisoht · or anion extinguished Emulsifiers such as ethoxylated ootylphenol, ethoxylated fonylphenol or an alkali metal Contains alkylaryleulfonic acid. Advantageous trweiee know any available in the Bendel, niohtionisoh · «or anionic emulsifiers of the defined class Ver

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applied to stabilize the dispersion. The amount of emulsified parts is usually from 40 to 60 #, based on the ßesamtraulelon · The resulting mixture is mixed duroh and duroh · The mixture is then evenly over a porous · polytetrafluoroethylene or a porous polytrifluoronlorethylene film or sheet of usually 1.587 mm (V'6 inch) or 0.793 mm (1/32 inch) thickness or less, and distributed duroh Queteohen dried · Significant water Engtn be removed and then, under heat and shaped Druok A temperature of about 10O ⁰ C to about 120 ⁰ C and ' a pressure of about 7 kg / cm (100 pel) is sufficient to divide the electrode according to this invention

The electrode thus formed is then washed with either aqueous hemic acids or bases the soluble additives eu remove aliphatic alcohols, like 2οB. Ethyl alcohol or isopropanol or equivalents of these alcohols, can be used to prevent occlusion Emulsifier or a. to remove lubricants used for molding, which are normally dl · catalytic ^ Would impair the effect of the manufactured electrode

The overall operability of the novel electrode depends on the arrangement of the electrode in a fuel cell with free electrolytes from · The catalytically effective

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The surface must face the electrolyte and the surface formed by the base must face the incoming gas. Air introduced. On the other hand, Wasβereteff or Kohlenwasserstoffgae _f bB as propane, Torbanden. The total reaction can be expressed as follows ι

At the anode

O ₅ H ₈ + 6 H ₂ 0 >> 3 CK) ₂ + 20 H ⁺ 2 Oe

At the cathode

5 O ₂ + 2Oe + 10 H ₂ 0> 20 OH "

Torteilhafterweiee, the element usually from 25 bie 100 ⁰ O operated wordene If higher feaperaturen be desired, over a wide temperature range waeeerdiehtsiaohende polytetrafluoroethylene Yerbindungen rerwendett these temperatures are used · In this case, know temperatures up to 200 ⁰ zn O endure ·

The invention is illustrated by way of example using the drawing explained in more detail

In Figure 1, a sueasmengesotste electrode 1 is shown, which has a hydrophobic, porous, gas-permeable polytetrafluoroethylene or Polytrifluorohloräthylen-Unterlage 2, one of the catalytic converters connected to the terminal 3 and which has an average pore size of 2 to 25 microns.

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BATH ORIGINAL

Figure 2 shows a cell 4 with free electrolyte, the one chamber 5, in which the electrolyte is located, which is introduced through an opening Sa » the electrode 6, which is shown in Figure 1, and its catalytically active surface 7 facing the electrolyte is, and the gas-permeable polytetrafluoroethylene or polytrifluorochloroethylene pad is located Surface θ delimits the chamber 9, which contains a fuel or an oxidizing agent in the end plate 10. The electrode 6 contains current collectors or leads 11 and 12 »which are catalytically active in the shaped Layer 7 are embedded. Inert seals such as made of polytrifluorochloroethylene or silicone rubber, 1? and H hold the electrode 6 and faceplate 10 in place so that the outflow of liquid electrolyte from the chamber 5 is prevented, openings 15 and 16 are provided to the gas chamber 9 eugänglioh au Make and discharge lines 17 and 18 are arranged to remove excess gas. The fuel element Bit screwing 19 and nuts 20, as shown, are kept busaramen

The invention is further illustrated by means of the examples All parts are given in parts by weight, unless otherwise stated

0 0 9 8 3 U / U 2 4 bad

BtjjtPltl 1

A mixture of 0.89 parts of platinum black powder, 0.2 parts of colloidal Silioiundloxyd and 0.22 parts by volume of polytetrafluoroethylene Rauleion (60 ^ solids) is mixed with 3.8 parts of water and poured on a 7 τ 14 on croBe A 1.587 mm (1/16 inch) thick, porous polytetrafluoroethylene layer is applied with an average pore size of 9 / x . The soil is dried under nitrogen for 15 minutes and small amounts of water are then added to coat the layer and allow the soil to spread enable, so that the cracks are btdeokt in the catalyst layer "Finally, the Elektrodensohieht is with the very easily vapor-deposited surface between the Polytetrafluoräthylenfiln 0.0508 mm (2 nils) and plates for 10 minutes at 100 ⁰ C and a pressure of 7 kg / cm ( 100 pei) pressed ₀ The Sohioht is immersed for 20 minutes in Triohloräthylen, rinsed with ethyl alcohol, washed with deionized water and then again for 1 hour at room temperature Only immersed in 23% aqueous potassium hydroxide solution in order to dissolve the colloidal silicon dioxide, after which the old aqueous sulfuric acid is removed from the still old distilled water. Two discs with a diameter of 34 * 929 (1-3 / 8 inches) each are cut out of this electrode layer. A disc with a diameter of 26.515 mm (1-1 / 8 lach) au »« inta

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Piatineiob having a clearance of 0.55 mm Ifaaohenweite {A3 mesh) is then embedded in each side of the catalyst Elektrodensohelbe described above at a temperature LAT 80hen 9O ⁰ C and 100 ⁰ O and a pressure of 7 kg / cm (100 pal).

The electrodes are then exposed in a cell Electrolyte tested similar to that shown in Figure 2. The electrolyte block is 3.175 am (1/8 inch) thick. BIe Spaces between the polytrifluorochloroethylene side panels and the electrodes are bits of open polypropylene tape tandem holders filled in · The electrolyte bloom is filled with 2N perchloric acid and the cell is owned a resistance of 0.13 0ha at room temperature »

The cell gives a terminal voltage of I ₁ 03 ToIt currentless or unloaded), if it is operated with hydrogen and oxygen · The electrolyte is removed from the cell and 4c perchloric acid is used instead. The cell then has an internal resistance of 0.09 ohms at room temperature and an effective electrode area of 5 or ² . Until the cell is operational are tabulated below.

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Tabel

Current density Bejfcriebespannunjg in 4n HClO ₄ (mA / om *) in 2n HClO ₄ 0.87 20th 0.89 0.77 100 0.79 0.70 200 0.72 0.61 400 0.63 0.56 500 0.58 0.56 735 0.58 0.47 793 0.45 Beieuiele2-10

Sine amount of catalytically active powder as shown in table II is listed below, is associated with an equivalent end en. Amount of Folytetrafluoräthylendispereion and distilled water mixed to make a slurry form * This elongation is applied with a squeegee on a Foil either made of porous polytetrafluoroethylene or Polychlorotrifluoroethylene nit an average Pore diameter of around 9 microns, o excess Water is removed under a stream of nitrogen. The catalyst solution is not completely dried. so that enough water remains in it to prevent the surface from tearing and to prevent the smooth surface Support dispersion of the Ketalysato mixture You coated, porous layer is then sandwiched between a Polytetrafluoroethylene Filia (0.0508mm - 0.002 inch thick)

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inserted and pressed between plates for 10 minutes at 100 to 110 ⁰ C and 10 _r 5 kg / cm ² (150 pol). Compartment cooling under pressure to about 30 ⁰ C, the Sohicht is removed from the press and τοη the layer during The polytetrafluoroethylene film surrounding the Pres-Bene is loosened.An electrode is then cut out of the layer from materials, such as ZoBo platinum gauze with a mesh size of 0.35 mm (45 mesh) or another suitable, fine-meshed wire screen is inserted into the catalytic surface of the electrode embedded under pressure and serves as a current collector. This surface faces the electrolyte in the assembled cell, as can be seen from FIG

The electrode as well as the cell's own adhesion are in Table II summarized below.

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electrolyte - 13 -
Table II 1571923 at
game 2n HOlO. Electrode
composition Volt clamps
tension without
Belaetun * 2 Piatinao black (9 mg / cm) 1.04

2n HC10

1n HClO 2n

1.03

tracted) 10% Teflon bandage on a 1.587 mm (1/16 inoh) thick 'porous Teflon layer

Platinum black (9 mg / om) $ 13 Teflon binder on a 1.587 mn (1/16 inch) strong porous Teflonsobioht

Platinum black (9 mg / om) 2OjS silicon dioxide (extracted) 10 lb teflon binder on a 0.793 mm (1/32 inohm) thick porous Polytrifluorohloräthylenensohloht

Platinsohwar "(9 Hf / oa) 157 'Silioiumdioxyd (not extracted) \ 15J * Polytetrafluoräthylenblndemlttel on a 7793 ram (1/32 inch) strong, porous Polytrlfluorohloräthylenenschioht with an average pore diameter of 3 Ji

2n H010 _A same as example 5, de- 1.02

* but with colloidal silicon dioxide, which is extracted with alkali

2n HOlO ₄ board ohwar e (6 mg / om) 1.03

* 27 # silicon dioxide (extracted), 10 ° C Teflon binder on a 1.587 mm (1/16 inohm) thick porous Tefloneohloht

0.98

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Table II (continued) Bel Electrode Volt Inhibitor

match electrolyte composition apnnmmg _t without

8 1n HBF ₁ platine ohwarζ (9 ag / cra) 1 _t O5 * 20 £ silicon dioxide (extracted), 10 * Teflon binder on a 1.587 (1/16 inoh) thick porous Teflon layer

Ethylene Waeseretoff- containing free electrolyte

Fuel cell

9 2n HClO _A platinum black (9 ng / cm) 0.49

* Λ% Teflon binder on a 1.587 mm (1/16 inch) thick porous Teflon resin

10 2n HClO. Board black (9 ag / om) 0.5

* 21 ^ silica (extracted) 10 ?? teflon binder on a 1.587 wm (1/16 inch) thick porous teflon sheet

Teflon let polytetrafluoroethylene Example 11

The procedure of Example 9 is repeated, old the Exception that 3 pieces of oil fiber filter material in The shape of crosses can be cut out into the electrolyte chamber be introduced, in * u ensure that the collector screens do not touch each other. The electrolyte compartment is filled with 6N sulfuric acid and the compound Cell has an internal resistance of 0.11 Ohm «

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The terminal voltage without load is 1.06 volts, operated on the basis of hydrogen-oxygen

The overall characteristics of the cell are as follows Table III

Current density tension (mA / om ² ) 20th 0.865 100 0.77 200 0.70 400 0.56 500 0.49 733 0.17 Example 12

An electrode layer is formed by evenly distributing a mixture of 0.86 parts of platinum black, 19 parts of silicon dioxide, 1.9 parts by volume of a polyethylene latex containing 10 pounds of solids and 1.2 parts by volume of water on a 98 ca piece of porous polytetrafluoroethylene · The sol is cleaned and extracted with alkali to remove the silicon dioxide. Platinstroakollektcren are then pressed into the electrode from the layer hei 100 to 11O ⁰ O and a pressure of 7 kg / ca (100 psi) for 10 minutes · An electrode from the layer is then with Eusammen

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an electrode, which is manufactured according to example 9, tested »The following results are found · The electrolyte let 2n perchloric acid, the strength dee Blektrolytbloekee is 3 »175 mn (1 / Θ inch) and the Row resistance 0.13

Table IV

Current density Lead electrode potential Example 13 (mA / em ^z ) fVolt) 20th 0.92 100 0.82 200 0.74 400 0.60 762 0.32

A mixture of 1.130 parts of platinum black, 0.17 parts of aluminum oxide, 0.33 parts by volume of polytetrefluoroethylene emulsion and 1.2 parts of water is applied to a piece of porous polytetrefluoroethylene with a surface area of 109 on ² treated and then placed in 6N H9SO4 for 3 hours in order to remove most of the aluminum oxide. Finally the layer is accustomed with water

A platinum gauge is embedded in an electrode with a diameter of 34.925 ram (1-3 / ⁶ inch) from this layer and the layer is coated with an electrolyte.

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block of 3 »175 ππ (1/8 inch) thick against a standard electrode, The electrolyte tested as described in Example 9 in a hydrogen-oxygen cell is 2n perchloric acid ο The line resistance is 0.15 Ohm »The results are listed below«

Table V Current density cell voltage

(mA / om ² ) Electrode potential without load 1.087 V.

20 0.89

100 0.74

200 0.62

400 0.29

Example 14

An electrode ^ ohient is made by 1.17 parts one chemically deposited on graphite in a ratio of 1: 1 Platinum, 3 parts of water and 0.22 part by volume

ο a polytetrafluoroethylene emulsion to a 98 era large Surface of a porous polytetrafluoroethylene soMcht applied become »The castle is made with organic solvents and water treated to remove the impurities, such as SSoBo organic lubricants and emulsifiers, from it to be removed c An electrode is cut out of this schioht and along with a 3.175 mm (1/8 inch) thick cell with a free electrolyte made up of 2n perchloric acid, examined The cell possesses

BATH ORIGINAL

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an internal resistance of 0.16 ohnio hit hydrogen ~ Oxygen operation and a counter electrode! which is prepared according to Example 9, are those in the following Table VI tabulated results obtained

Table VJE Current density cell voltage

(mA / cm ^z ) Potential in the unloaded state (current Q) - 1.06 volts

20 0.89

100 0.78

200 0.68

400 0.49

Example 15

An anode is made by placing a mixture of 0.98 parts Platinechwarζ, 0.28 parts colloidal Sllloiumdioxyd, 0.16 parts by volume of a polytetrafluoroethylene suspension and 3.5 parts of distilled water on a 7 ζ 7 cm area of a 1.587 mm (1/16 inoh) is applied strong porous Polyt6trafluoräthylensoniont ο the applied Misohung is in an oven for 4 minutes at 110 ^c 0 · in the dried thick Katalysatoreohioht fled cracks form * a few tropics (4) water is added to moisten the mixture The giants are smoothed with a stainless steel scraper. The rubbery mixture is then dried in air until the crack is just beginning to form

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begins · You will then be placed under an electrode pad 0.05 mm (2 mil) thick polytetrafluoroethylene release film arranged and gleiohnäßlg with a plastic Spaohtel distributed. 3 layers of blotting paper are applied to the bare side of the porous Teflon carrier and the protected layer is then covered with panels

A 2

a face at 1100 and 14 kg / cm (200 pel) pressed during heating is opened the press several sharks and discharged the Waooerdämpfe "Finally, when no water vapor more eum fore comes, the layer is 10 minutes at 100 to 110 ⁰ C and 14 kg / cm ² (200 pel) pressed o The layer is then cooled to room temperature and removed from the press. The layer is then treated with a base and organic solvents in order to remove the emulsifier and the colloidal silicon oxide. A 34.925 mm (1-3 / 8 inch) disk is cut from the sheet and a 28.575 mm (1-1 / 8 inch) current collector with a 0.35 mm (45 mesh) mesh is embedded in the electrode surface.

The cathode is manufactured according to Example 1. The electrodes are used in the form of a block that enables that 5 cm of the electrode surface exudes the electrolyte The polytrifluoroethylene electrolyte block is 6.35 mm (1/4 inch) thick and machined in such a way that a tube

with a 6.35 am (1/4 inch) outer diameter β iah τοη Diea extending above and below the block makes ββ possible to use the block with a source of 85% phosphoric acid connect below »17 electrolyte can, if desired, to be changed

The two electrodes are measured in a fuel element with the following results «

Internal resistance at 15O ⁰ O iat 0.29 Ohra. The Hullatroma voltage (voltage without load) is 0.97 ToIt, if aie is eaten with hydrogen-oxygen operation and 135 to 154 ⁰ C, the following results are determined!

Table YII

Current density ι Cell voltage (volts) (mA / cm ² ) 0.6 0.94 6.0 0.91 60.0 0.75 118 0.63 150 0.39 238 0.33 284 0.20 jeiiDiel 16

The construction of the cell according to Example 15 is exactly repeated, with the exception that propane and ala fuel

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Oxygen can be used as an oxidizing ^{agent at 15O 0} C ο

The following results are achieved:

Table VIII

tension without load 0.91 volts Current density Cell voltage (mA / onr) (Volt) 0.6 0.78 1.9 0.72 4.0 0.67 12.3 0.57 19.2 0.53 26.8 0.48 63.2 0.35 91.2 0.27 135 0.16

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Claims (1)

Claims ο Electrode for fuel elements with free electrolyte, characterized by the following combinations
(A) a hydrophobic pad made of polytetrafluoroethylene or polytrifluorochloxethylene and - (b) a composition which is molded onto this base and which 1o) an electrically conductive filler in an amount between 0 and 80 pounds,
2o) a catalyst in an amount of clay about 1 to 98 # and 3.) a water-repellent composition in an amount τοη 1 to 40 $> , where the percentages are based on the weight of the solid electrode height. 2ο electrode according to claim 1, because it is known that the low-carbon filler is a graphitic carbon is. 3 · Electrode according to claim 1, characterized by that the catalyst Platin Isto ta 4ο electrode naoh Anepruoh 1, daduroh marked that The water-repellent composition in polyethylene dispersion is· 8AD 0RK3INAI 009834/1424 ^NAL 5- electrode naoh claim 1, characterized »that the water-repellent composition is a polytetrafluoroethylene dispersion 6β fuel element with an electrode according to one of claims 1 to 5, characterized by a "chamber" around to take up the electrolyte on two opposite sides of an electrode naoh one of the Claims 1 to 5 is limited, the catalytic The surface of these electrodes faces the electrolyte in the chamber and the free surfaces of the hydrophobic, porous base facing a room «which contains both the oxidizing agent and the fuel, wherein a conductor is embedded in the conductive substrate, separated by inlet openings, including the oxidizing one To introduce gas and the hydrogen, and through outlet pipes to remove the excess of the supplied oasis deduct 7β fuel cell according to claim 6, characterized by that the fuel is hydrogen θ «fuel cell according to Claim 6, characterized by that the fuel gas is propane 9ο fuel cell according to claim 6, characterized by that the oxidizing agent is oxygen " BADORiGiNAL 009834 / U24 1O ₀ fuel cell according to claim 6, characterized in that the oxidizing agent is air " 009834 / U2 * _BAD