AU601562B2

AU601562B2 - Porous gas electrode

Info

Publication number: AU601562B2
Application number: AU14045/88A
Authority: AU
Inventors: Nikolaj Medic; Jurgen Russow; Rudolf Staab
Original assignee: Hoechst AG
Current assignee: Hoechst AG
Priority date: 1987-04-01
Filing date: 1988-03-31
Publication date: 1990-09-13
Anticipated expiration: 2008-03-31
Also published as: DE3710855A1; EP0285019B1; NO171418B; FI85603C; BR8801512A; FI881499A0; ATE62716T1; ZA882314B; FI881499A; NO881420L; NO881420D0; IN170695B; DE3862416D1; FI85603B; AU1404588A; ES2022502B3; NO171418C; MX174277B; EP0285019A1; JPS63262490A

Abstract

In the electrode, the electrocatalytically active part consists of a nickel wire gauze which is covered at least on one side by a mixture of Raney nickel and polytetrafluoroethylene which is attached to a supporting structure which conducts electric current. The supporting structure consists of a frame (2) and a grid bounded by the latter and consisting of stays (3) or expanded metal (4). <IMAGE>

Description

COMMONWEALTH

6 A QRALI 11 6 2 PATENTS ACT 1952-69 COMPLETE SPECIFICAT!ON

(ORIGINAL)

Form Class Int. Class Application Number: Lodged: ,Complete Specification Lodged: I. Accepted: Published: A--S XL S f Priority: C t Related Art: C" C Name of Applicant: Address Ot Applicant: Actual Inventor: Ar f Address for Service HOECHST AKTIENGESELLSCHAFT 45 Bruningstrasse, D.-6230 Frankfurt/Main Federal Republic of Germany RUDOLF STAAB, JURGEN RUSSOW and NIKOLAJ MEDIC EDWD. WATERS SONS, QUEEN STREET, MELBOURNE, AUSTRALIA, 3000.

Complete Specification for the invention ontitled: POROUS GAS ELECTRODE The following statement is a full description of this i4'vention, including the best method of performing it known to 1.

9 V. a.

t. dA"i HOECHST AKTIENGESELLSCHAFT HOE 87/F 093 D.Ph.HS/AW Description Porous gas electrode The subject of the invention is a porous gas electrode having an electrocatalytically active part comprising a nickel wire gauze which is covered, at least on one side, with a mixture of Raney nickel and polytetrafluoroethylene.

t 2 S. f C The porous gas electrode described in German Offenlegungsschrift 3,342,969 for the generation of hydrogen in an S 10 alkaline medium is remarkable for particularly advantageous properties: it can be produced very inexpensively and has, under the conditions of industrial electrolysis current density: 3 kA/m2; electrolyte concentration: 35% by weight of sodium hydroxide; temperature 85°C a high service life as a cathode which generates hydrogen, i.e. the electrode potential does not vary during a running time of over 3 years within the limits of the measuring accuracy. As a consequence of the special foil-type structure of the electrode, the electrochemical cell system (fueL cell or electrolysis cell) in which said electrode is intended to be used has to be precisely adapted to this special structure in order to be able to operate the electrode in all cases and under optimum conditions. At the present time, however, it is not possible to produce such electrode structures in widths of 1 m and wider, whereas there is no difficulty in producing strips up to approximately 200 mm Swide in any desired length. Since the electrodes are not shape-retaining, it is not sufficient to attach the electrode strips to the frame of the cell because a uniform and optimum distance from the membrane whic defines the electrode space cannot be guaranteed.

In addition, the intrinsic conductivity of said electrodes is so low that, with the required industrial current densities and with the large distance from the current- -4-

I

-2carrying frame, the voltage drop within the electrode from the center to the edge becomes intolerably high. The object of the present invention is to develop for these foil-type electrode strips an electrode construction which makes it possible to use these electrodes as cathodes in membrane cells, such as are usual nowadays in industrial engineering, with clear advantages compared with the cathodes now used.

The object is achieved by a porous gas electrode, wherein St 10 the electrocatalytically active part is mounted on a sup- Sporting framework which conducts electric current. At the same time, the electrocatalytically active part may comr.t prise strips up to 200 mm wide which are connected in an electrically conducting manner to the supporting framework in parallel and at a distance of 5 to 10 mm from each other. The supporting framework may comprise a frame which forms the boundary of a grid. The grid may comprise struts whose distance from each other is at most 200 mm, preferably 100 to 150 mm, or expanded metal, preferably rolled expanded metal, with an open area of at least The advantages of such porous gas electrodes are that the electrocatalytically active parts are located at an optimum .t distance with respect to the membrane and at the same time, S can be connected in an electrically conducting manner to the supporting construction so that no measurable voltage drop occurs within the gas electrode. The porous gas electrode has furthermore the advantage that the free extraction of gas bubbles from the space between membrane and electrode is promoted.

The invention is explained below in greater detail on the basis of drawings and examples depicting only one method of embodiment. In these, Figure 1 shows a detail of a porous gas electrode in which the grid comprise rods; Figure 2 shows a detail of a porous gas electrode in which the grid comprises expanded metal rolled flat; Li 1 'l 1 11 4 -3- Figure 3 shows the voltage as a function of the current density for various widths of the strips.

The electrocatalytically active part, the strips 1 of the porous gas eLectrode, are connected in an electrically conducting manner by welded joints to a supporting framework which conducts electric current. The supporting framework comprises a frame 2 and a grid bounded by the Latter. The grid may comprise rods 3 whose width d may be to 20 mm and which are arranged paraLLeL to each other at a distance c of 50 to 200 mm, preferably 100 to 150 mm.

Alternatively, the grid may comprise rolled expanded metal 4 whose open area should be at Least 60%. The electrocata- Lytically active part is welded to the grid at 5 and to 1 the frame at 6. The distance a between the strips 1 arranged parallel to each other may be 5 to 10 mm, and their width b 10 to 200 mm.

ExampLe Cell voltage and power consumption at constant current density with various strip widths of the electrocataLytically active part were measured in a test cell. The supporting framework comprised a 1.3 mm thick nickel sheet having the dimensions of 560 mm x 210 mm which had a cutout of 500 mm x 78 mm. The strips of the foil-like gas electrode were arranged parallel to the narrow sides of the supporting framework and welded in an electrically conducting manner to its long sides. This gas electrode was arranged as a cathode in a vertically operated membrane m y electrolysis cell so that its long side was vertical and its strips faced the membrane The distance between the strips and the membrane of the type Nafion NX 90902 manufactured by DuPont was 3 mm; the anode was directly in contact with the rear side of the membrane i The cell was operated with 33% sodium hydroxide solution circulated in the cathode space and with saturated, purified sodium chloride solution and with an anolyte concentration of 200 g of NaCl/1 in the drain at 90°C and (4

I

-4with a current density of 3 kA/m 2 referred to the area of 390 cm 2 removed in the nickel sheet. During continuous operation over several days in each case, the foLLowing cell voltages and power consumptions were achieved for the electrodes with strips of various width whose distance from each other was 5 mm in each case: Width of the strips [mm] Cell voltage CV] Power consumption (DC) CkWh/t NaOH] 10 3.24 2.260 25 3.16 2.210 100 3.07 2.140 0 4 ,o o 9e 4 .9 0Q 0 0o oa 0 4 B 9 To determine the characteristic of the three different electrodes, the cell voltage was determined as a function of the current density in the range from 0.5 to 4 kA/m 2 The results are shown graphically in Figure 3 and show that 15 these gas electrodes still operate in the linear region even at 4 kA/m 2 t ii "4I

Claims

1. A porous gas electrode having an electrocatalytically active part comprising a nickel wire gauze which is covered, at least on one side, with a mixture of Raney nickel and polytetrafluoroethylene, wherein the electrocatalytically active part is mounted on a support framework which conducts electric current. A porous gas electrode as claimed in claim 1, wherein the electrocatalytically active part comprises strips which are arranged in parallel and at a distance from each other on the supporting framework.

3. The porous gas electrode as claimed in claim 1, wherein the supporting framework comprises a frame which forms the boundary of a grid.

4. The porous gas electrode as claimed in claim 3, wherein the grid comprises struts arranged in parallel whose distance from each other is at most 200 mm. 4. The porous gas electrode as claimed in claim 4 wherein the distance apart is from 100 to 150 mm.

6. The porous gas electrode as claimed in claim 3, Swherein the grid comprises expanded metal with an open area of at least I :1 1 4 r j i V -6-

7. The porous gas electrode as claimed in claim 2, wherein the strips having a width of up to 200 mm are connected in an electrically conducting manner to the supporting framework at distances of 5 to 10 mm from each other. DATED this 26th day of June, 990. HOECHST AKTIENGESELLSCHAFT o a o 0 0 0~44 a g .0004 00,00 WATERMARK PATENT TRADE MARK ATTORNEYS "THE ATRIUM", 2ND FLOOR, 290 BURWOOD RD HAWTHORN VIC. 3122.

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