Micro-Regulate Ionomer Distribution to Increase Pt Utilization for PEMFC

Abstract

In the past decade, numerous Pt-based oxygen reduction reaction catalysts with high specific and mass activities have been developed, promising to reduce the cost of proton exchange membrane fuel cells (PEMFCs). However, the high activities are mostly achieved in rotating disk electrode (RDE) measurement and have rarely been accomplished at the membrane electrode assembly (MEA) level [1].One of the key reasons is the resistance caused by complex mass transport pathways, especially at higher current densities. The size and distribution of the ionomer aggregates in catalyst layers are found to be not uniform and easily affected by the concentration of the ionomer [2]. The proton transport is limited when there is no ionomer on the catalyst surface, while the oxygen transport is hindered when the ionomer film is too thick. Therefore, it is very important to control the ionomer distribution on the surface of catalysts.We designed a research protocol as shown in the figure: mask the Pt surface with carbon monoxide (CO) to change its surface energy and subsequently control the ionomer arrangement in the catalyst layer. The Knudsen diffusion resistance and ionomer diffusion resistance results suggest that the mass transport in the catalyst layer was suppressed by blocking and ionomer lean, indicating micro-construction of the catalyst layer to increase the active Pt area such as the thin and uniform ionomer distribution is an effective solution.