Leveraging a 2+2 Electron Pathway to Realize Efficient Oxygen Reduction with Stable Co-Based Cathode Catalysts in PEM Fuel Cells

Nitrogen-coordinated cobalt (Co–Nx) moieties are recognized as active sites for the oxygen reduction reaction (ORR), especially in acidic proton exchange membrane fuel cells (PEMFCs). Herein, we report a high-surface-area cobalt–nitrogen–carbon (Co/N/C) catalyst synthesized via ammonia-assisted pyrolysis of a cobalt-containing polyimide precursor. Transmission electron microscopy confirmed cobalt nanoparticles encapsulated in graphitic carbon shells provided structural stability and enhanced conductivity. X-ray photoelectron spectroscopy (XPS) and NO2– reduction experiments confirmed the formation of Co–Nx sites with an active site density of 0.434 × 1019 sites g–1. Despite a low cobalt loading (1.67 wt %), the catalyst achieved a turnover frequency (TOF) of 0.19 s–1 at 0.8 V (vs RHE), surpassing many high-Co-loading references. Kinetic analysis based on the Nabae model revealed a 2 + 2 electron pathway, wherein H2O2 generated from the initial two-electron reduction is further reduced. When tested in a membrane electrode assembly (MEA), the catalyst exhibited stable fuel cell performance for over 400 h, demonstrating excellent durability and practical viability.