Engineering asymmetric electronic structure of cobalt coordination on CoN3S active sites for high performance oxygen reduction reaction

The efficacy of the oxygen reduction reaction (ORR) in fuel cells can be significantly enhanced by optimizing cobalt-based catalysts, which provide a more stable alternative to iron-based catalysts. However, their performance is often impeded by weak adsorption of oxygen species, leading to a 2e− pathway that negatively affects fuel cell discharge efficiency. Here, we engineered a high-density cobalt active center catalyst, coordinated with nitrogen and sulfur atoms on a porous carbon substrate. Both experimental and theoretical analyses highlighted the role of sulfur atoms as electron donors, disrupting the charge symmetry of the original Co active center and promoting enhanced interaction with Co 3d orbitals. This modification improves the adsorption of oxygen and reaction intermediates during ORR, significantly reducing the production of hydrogen peroxide (H2O2). Remarkably, the optimized catalyst demonstrated superior fuel cell performance, with peak power densities of 1.32 W cm−2 in oxygen and 0.61 W cm−2 in air environments, respectively. A significant decrease in H2O2 by-product accumulation was observed during the reaction process, reducing catalyst and membrane damage and consequently improving fuel cell durability. This study emphasizes the critical role of coordination symmetry in Co/N/C catalysts and proposes an effective strategy to enhance fuel cell performance.