Abstract
The present work investigates the role of water on the ion conductivity and oxygen reduction reaction (ORR) performance of metal/water interfaces. Ionomer-free electrodes such as nanostructured thin film (NSTF) electrode have the potential to reduce the loading of platinum (Pt) for polymer electrolyte fuel cells (PEFCs). However, the proton transport mechanism is not well understood. To examine the dependence of ion conductivity and ORR performance on relative humidity (RH), two ionomer/binder-free metal surfaces, Pt and gold (Au), were measured at different RH conditions. The cyclic voltammetry (CV) shows that currents for the double layer, hydrogen and oxide species formation and reduction increase with increased inlet gas RH. This indicates that water films on the Au and Pt black surfaces play an essential role in ion conduction. The increased active area also yields increased ORR current density during fuel cell operation. The results indicate a significant thickness of the ionomer-free cathode is active despite the lack of ionomer.
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