Sulfur-Tuned Main-Group Sb-N-C Catalysts for Selective 2-Electron and 4-Electron Oxygen Reduction.

Abstract

The selective oxygen reduction reaction (ORR) is important for various energy conversion processes such as the fuel cells and metal-air batteries for the 4e^- pathway and hydrogen peroxide (H₂O₂) electrosynthesis for the 2e^- pathway. However, it remains a challenge to tune the ORR selectivity of a catalyst in a controllable manner. Herein, an efficient strategy for introducing sulfur dopants to regulate the ORR selectivity of main-group Sb-N-C single-atom catalysts  is reported. Significantly, Sb-N-C with the highest sulfur content follows a 2e^- pathway with high H₂O₂ selectivity (96.8%) and remarkable mass activity (96.1 A g^-1 at 0.65 V), while the sister catalyst with the lowest sulfur content directs a 4e^- pathway with a half-wave potential (E_1/2 = 0.89 V) that is more positive than commercial Pt/C. In addition, practical applications for these two 2e^-/4e^- ORR catalysts are demonstrated by bulk H₂O₂ electrosynthesis for the degradation of organic pollutants and a high-power zinc-air battery, respectively. Combined experimental and theoretical studies reveal that the excellent selectivity for the sulfurized Sb-N-Cs is attributed to the optimal adsorption-desorption of the ORR intermediates realized through the electronic structure modulation by the sulfur dopants.