Insight into carbon corrosion of different carbon supports for Pt-based electrocatalysts using accelerated stress tests in polymer electrolyte fuel cells

Abstract

Carbon-based catalyst support and Pt catalysts are commonly used in polymer electrolyte fuel cells (PEFCs). During cell start-up and shutdown processes, carbon support oxidation occurs, which leads to losses of electrochemical performance. In this work, carbon corrosion accelerated stress tests (ASTs) were performed and lifetimes of high surface area carbon (HSAC) and graphitized carbon (GrC) supports were investigated. 1000 AST cycles were conducted on Pt/HSAC while 10000 AST cycles were conducted on Pt/GrC due to different carbon corrosion rates, and both Pt/HSAC and Pt/GrC showed rapid decrease of performance at end of life (EOL). Detailed comparisons of electrochemical characterizations were also conducted between Pt/HSAC and Pt/GrC. Electrochemical surface area (ECSA) loss in different levels was found for both Pt/HSAC and Pt/GrC due to Pt loss, Pt detachment and particles coalescence, which also resulted in reduction of SO3− group coverage and more tortuous H+ transportation, leading to decreased catalyst layer ionic conductivity. For Pt/HSAC after 1000 AST cycles, more than 2 times higher ECSA loss but with only 50% greater particle size growth and similar Pt loss strongly suggested that a greater Pt detachment occurred on HSAC support during the AST cycles. Apart from that, it was found that after 1000 AST cycles, graphitized carbon support was much more robust compared to HSAC support, and it showed 2 times less ECSA reduction, 2.5 times less catalyst layer ionic conductivity reduction and 4 times less SO3− group coverage reduction. Double layer capacitances increased for both carbon supports after AST at their EOLs, as more disordered carbon contacts were formed, which created more contacts between solid and ionic materials. This study shows a possibility of Pt/GrC catalysts to meet the Department of Energy (DOE) target of 5000 AST carbon cycles, as the Pt/GrC cell met the target of ≤ 40% ECSA loss of initial area.