Sulfur-doped cobalt–nitrogen–carbon materials for efficient oxygen electrocatalysis

Abstract

The oxygen reduction reaction (ORR) is central to clean energy technologies such as metal–air batteries, but its sluggish kinetics typically rely on precious metal catalysts. Herein, a sulfur-functionalized cobalt–nitrogen–carbon catalyst (S@Co–N–C) was successfully synthesized via a thiourea-assisted pyrolysis strategy using a two-dimensional (2D) zeolitic imidazolate framework (ZIF) as the precursor. Experimental characterization revealed that S-doping effectively modulated electronic structures of Co–N₄ sites, significantly enhancing the intrinsic ORR activity of the Co–N–C material. In 0.1 M KOH, S@Co–N–C exhibited a half-wave potential (E_1/2) of 0.895 V (vs. RHE), surpassing that of commercial Pt/C (20 wt%; 0.870 V vs. RHE). Density functional theory (DFT) calculations confirmed that the introduction of S atoms optimized the d-band center of Co sites and reduced the *OH desorption energy barrier, thereby accelerating ORR kinetics. Furthermore, a Zn–air battery assembled with S@Co–N–C delivered a peak power density of 210 mW cm⁻², outperforming the Pt/C + RuO₂ benchmark (140 mW cm⁻²). S@Co–N–C also demonstrated superior stability for both the ORR and Zn–air battery compared to the control sample Co–N–C and commercial benchmark. This study provides new insights into the design of non-precious metal ORR catalysts with high stability and elucidates the critical role of S-doping in M–N–C materials.