Porphyrin-like Fe-N₄ sites with sulfur adjustment on hierarchical porous carbon for different rate-determining steps in oxygen reduction reaction

We developed a strategy based on coordination polymer to synthesize singleatom site Fe/N and S-codoped hierarchical porous carbon (Fe₁/N, S-PC). The as-obtained Fe₁/N, S-PC exhibited superior oxygen reduction reaction (ORR) performance with a half-wave potential (E_1/2, 0.904 V vs. RHE) that was better than that of commercial Pt/C (E_1/2, 0.86 V vs. RHE), single-atom site Fe/N-doped hierarchical porous carbon (Fe₁/N-PC) without S-doped (E_1/2, 0.85 V vs. RHE), and many other nonprecious metal catalysts in alkaline medium. Moreover, the Fe₁/N, S-PC revealed high methanol tolerance and firm stability. The excellent electrocatalytic activity of Fe₁/N, S-PC is attributed to the synergistic effects from the atomically dispersed porphyrin-like Fe-N₄ active sites, the heteroatom codoping (N and S), and the hierarchical porous structure in the carbon materials. The calculation based on density functional theory further indicates that the catalytic performance of Fe₁/N, S-PC is better than that of Fe₁/N-PC owing to the sulfur doping that yielded different rate-determining steps.