Cobalt-Content-Dependent Performance Trade-Off in PtxCo Alloy Catalysts for Fuel Cells

Carbon-supported PtxCo alloy nanoparticles are among the most effective cathode catalysts for proton exchange membrane fuel cells (PEMFCs). However, cobalt leaching from the catalyst into the electrode ionomer negatively impacts cell performance. While this leaching has traditionally been associated with PEMFC operation, recent studies show that it also occurs during electrode fabrication. In this study, we investigated how the cobalt content in PtxCo catalysts influences cobalt leaching during electrode fabrication and its impact on initial cell performance. We identified a cobalt-content-dependent trade-off between performance at low and high current densities, where higher cobalt content enhances low-current density performance but deteriorates high-current density performance. By a comprehensive set of electrochemical and physical characterizations, we showed that increasing cobalt content in PtxCo catalysts with a similar particle size results in higher cobalt leaching during electrode fabrication, which in turn elevates mass transport resistance and thus degrades the high-current-density performance. On the other hand, a higher cobalt content also induces more pronounced compressive strain, which enhances the kinetic performance at low-current density regions.