Kordesch at Union Carbide

Karl V. Kordesch (Kordesch, 1968) returned to using carbon, but instead of it being the fuel as it was during the early days of direct coal research, it was the electrode material. His interest in using carbon electrodes in alkaline fuel cells originated from his work at the University of Vienna, where he and Marko researched methods of catalyzing carbon with heavy metal oxides for use as oxygen electrodes. They found that the catalyst improved the activity of carbon and also promoted the decomposition of hydrogen peroxide, an intermediate reaction product in alkaline electrolytes, and could therefore produce high current densities in alkaline cells. The trouble with carbon was that its performance was unreliable because of its processing, which produced varying compositions and structures.

Kordesch, in 1955, joined the National Carbon Company (which merged with the Union Carbide Corporation in 1955) and began developing better carbon electrodes for fuel cells, benefiting from the company's technical expertise in carbon production. Four cell configurations were designed — the first two were based on tubular electrodes, and the last two used flat plate electrodes. The first tubular electrode design had hydrogen flowing through one tube and oxygen the other, with KOH electrolyte surrounding both tubes, and with electrical current collected at the ends of the tubes. The second design had one tube inserted into a larger tube to give a concentric cell, and because the outer tube had a larger surface area it was used as the air electrode. This concentric cell had a higher volumetric power density because of its more compact design, and it had a lower resistance polarization because current was collected along the length of the tube rather than at its ends.

In 1960, the tubes were superseded by plate electrodes, 6.35 mm (0.25 in) thick, that were easier to assemble into batteries in terms of current collection and gas manifolds. The final design (in 1963) used a composite electrode, 0.56 mm thick (22 mils), to obtain a "fixed-zone" where the reactions would occur; the porous carbon was the electrochemically active layer and a porous nickel plaque was the mechanical support and an electrical conductor (Kordesch, 1968, p. 401).

The all-carbon electrodes (used in the first three designs) were made from a mixture of base carbon (e.g., lampblack) and a binder (e.g., pitch or sugar), and the mixture was extruded to produce tubes or molded to produce plates. The electrodes were baked to remove the binder, which left a porous material, and then baked again in a CO2 atmosphere for several hours to increase the internal surface area of the carbon. The electrodes were soaked in a solution of metal salts, dried in air, and heated again in a CO2 atmosphere to 700 or 800°C. (For example, a salt made with 1.5 g cobalt nitrate, 3.5 g aluminum nitrate, and 100 ml water would form the spinel, cobalt aluminate, when heated.) The electrodes were wetproofed by being immersed in solutions of waxes or high molecular weight paraffins. To make the planar composite electrodes, the nickel plaque was sprayed with polytetrafluoroethylene (PTFE) to make it waterproof, a mixture of PTFE and inactive carbon powder was sprayed onto the nickel as an intermediate backing layer, and then polyethylene and active carbon were sprayed onto the intermediate backing layer. The three-layer electrode was pressed at 1000 psi between 130 and 140°C.

The performance of the tubular cells reached 0.8 V at 50 mA/cm2. With the planar composite electrode, the cell performance was 0.8 V at 100 mA/cm2 at 65°C and atmospheric pressure, with 9 N KOH electrolyte. When the air pressure was 15 psig, the cell could give 0.8 V at 200 mA/cm2. The electrolyte was circulated through the cell. The Union Carbide alkaline fuel cell stack is shown in Fig. 2.12.

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