Effect of platinum loading on fuel cell cathode performance using hydrocarbonionomers as binders

Abstract

The effect of platinum loading on cathode performance in hydrogen/oxygen fuel cells was investigated using perfluorosulfonic acid (Nafion), sulfonated polyimide (SPI-8) and sulfonated poly(phenylene ether ether ketone) (SPEEK) ionomers as the electrode binder. By lowering the platinum loading, the cathode polarization decreased for MEAs using SPI-8 and SPEEK binders at high humidity (90–100% RH (relative humidity)) due to an improvement of mass transport (oxygen supply and/or water discharge) in the catalyst layer. In contrast, at humidity lower than 80% RH, the effect of platinum loading on the cathode performance differed between these two hydrocarbon (HC) ionomers. When SPI-8 was used as the binder, the cathode polarization increased when lowering the platinum loading due to an increase of activation overpotential. When SPEEK was used as the binder, the effect of platinum loading on the cathode performance was smaller. Such differences can be ascribed to the specific adsorbability of these hydrocarbon binders on the platinum catalyst at low humidity. These results point to crucial factors in achieving higher performance at low platinum loadings and low humidity using HC binders.