Abstract
An account is given of the development of electrocatalysts for the phosphoric acid (phosphoric acid) fuel cell starting from unsupported platinum black and ending with carbon‐supported platinum alloys. The incentive for this work was the need to reduce the cost of the phosphoric acid fuel cell by reducing the amount of platinum it contained while simultaneously raising its performance. Equally important was the concurrent effort aimed at optimizing the structure of the polytetrafluoroethylene (PTFE)‐bonded, gas‐diffusion electrodes so that the noble metal catalysts were used as effectively as possible. Methods to control the structure of the catalyst layer were devised based on studies of the way in which aqueous dispersions of the supported catalyst and PTFE interact. Procedures used to prepare electrodes in the laboratory were modified and scaled up for production purposes. A novel process for depositing catalyst layers on electrode substrates was developed and several different coating technologies were evaluated for applying PTFE‐bonded, silicon carbide, electrolyte‐retaining matrices to the electrodes. Some operating conditions that can have an adverse affect on the life of the electrodes are considered. Most of the work described here originated in the laboratories and workshops of International Fuel Cells — a unit of United Technologies Corporation — and culminated in the PC25 phosphoric acid fuel cell power plant.