Nanoscale Degradation Study of a Commercial Pt–Co/C Fuel-Cell Electrocatalyst at Elevated Temperature Utilizing Identical-Location Scanning Transmission Electron Microscopy

Understanding the degradation mechanisms of Pt-based alloy electrocatalysts under realistic operating conditions, such as elevated temperature, is essential for improving the durability of proton exchange membrane fuel cells (PEMFCs). This study investigates the degradation behavior of a commercial PEMFC Pt-Co/C electrocatalyst on the individual nanoparticle scale, employing identical location scanning transmission electron microscopy (IL-STEM), in combination with electrochemical methods. The catalyst was subjected to the modified US Department of Energy protocol at an elevated temperature (fast potential cycling between 0.6 and 0.95 V_RHE with a 3 s hold at each potential limit for 10,000 cycles in 0.1 M HClO₄ at 60 °C) in order to partially simulate real-world operating conditions. To evaluate the specific role of temperature in the degradation process, additional experiments were carried out at room temperature. The primary aim was to elucidate temperature-dependent nanostructural changes and correlate them with electrochemical characterization. Results reveal distinct alterations in Pt-Co alloy nanoparticles' morphology, such as necking and increased circularity. These are driven by surface energy minimization via coalescence, dissolution, and redeposition mechanisms. By correlating nanoscale observations with changes in the intrinsic electrochemical properties, our study provides crucial insights into the degradation pathways at elevated temperatures, informing the design of more durable catalyst formulations for future fuel cell devices.