Platinum with Graphene Nanopocket Catalysts for Improved Phosphoric Acid Tolerance for High-Temperature Ion-Pair Polymer-Based Fuel Cells

High-temperature polymer electrolyte membrane fuel cells (HT-PEMFC) are increasingly considered for heavy-duty vehicle (HDV) and aircraft applications; however, the use of phosphoric acid for proton conductivity reduces catalyst activity. The development of a durable catalyst that is able to withstand phosphoric acid poisoning is paramount to the advancement of HT-PEMFC for heavy-duty applications. In this study, stability tests and catalyst accelerated stress tests (ASTs) were conducted at 160 °C under high humidity to probe the durability of a graphene nanopocket-protected platinum supported on high-surface-area Ketjenblack carbon (Pt@Gnp/KB) compared to commercial platinum on Ketjenblack carbon (Pt/KB) in phosphoric acid-rich environments. The progression of Pt degradation was evaluated by quantifying relative changes in electrochemical surface area (ECSA) via CO displacement and stripping. The Pt@Gnp/KB catalyst is found to be highly stable at low cell voltages and water-rich environments by reducing phosphoric acid species coverage compared to Pt/KB. After 150 h of catalyst AST, Pt@Gnp/KB retained over 50% of initial ECSA, which is superior to that of Pt/KB, which retained only 20% ECSA. This work illustrates a potential pathway for catalyst development for ion-pair HT-PEMFC operating at elevated temperatures. In addition, this work confirms challenges previously observed and further elucidates mechanisms and procedures associated with the use of CO stripping for estimating ECSA at 160 °C.