A study of oxygen reduction on carbon-supported platinum fuel cell electrocatalysts in polybenzimidazole/phosphoric acid

An investigation of the oxygen reduction reaction (ORR) on carbon-supported Pt catalysts used as fuel cell electrodes in phosphoric acid-imbibed polybenzimidazole (PBI) is reported. Electrodes of different thickness were investigated by employing catalysts with different loadings of Pt on carbon and different amounts of PBI. The electrochemical surface areas (ESAs) of the catalyst were measured using cyclic voltammetry. ESAs decreased with an increase in Pt loading on the catalyst but were not significantly affected by changes in acid content in the catalyst electrodes. The influence of phosphoric acid and temperature on ORR was determined using linear sweep voltammetry. High levels of phosphoric acid (16 per repeat polymer unit (PRU)) in the cathode catalyst layer were detrimental to ORR performance. Good oxygen reduction performance was obtained with a 40 per cent Pt/C catalyst incorporating phosphoric acid at a level of 3 PRU. Kinetic parameters (transfer coefficient, exchange current density, and oxygen reaction order) were determined.