Dry Preparation of PTFE-Bonded Gas Diffusion Electrodes

The anodes consist mainly of a mixture of the Raney nickel catalyst, copper powder, and PTFE powder on a copper grid as described by Riihling [50]. The Raney nickel catalyst is composed of highly porous metal particles and is formed from an aluminum-nickel alloy by dissolving the aluminum. The advantages of using the Raney material are described above. 

After reactive mixing of the different materials for the electrodes, the PTFE powder, the copper powder, and the oxidized nickel catalyst in a knife mill, the powder is rolled into a self-carrying strip using a calender. This self-carrying strip is then rolled on to a metal grid to form the electrode. The rolled electrode has a thickness of 100-350 am. 

The PTFE is smeared during this process and forms ultrathin PTFE fibers and a PTEE film that cover the oxidized catalyst (Eigure 4.4). 

Because of the PTEE film, only a low porosity can be measured at the surface of the rolled electrode, and the active surface is therefore too small for acceptable performance. The pore system and the specific surface area of the AFC anodes 

2 Concepts of Alkaline Fuel-Cell Design Concepts 109 

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