Hierarchical cocoon-like Co9S8-N@NC for ambient reduction of sulphur dioxide to sulphur via proton-coupled electron transfer

Abstract

Electrochemical SO2 reduction reaction (SO2RR) is an attractive approach for recycling sulphur resources at room temperature, but this is difficult to achieve in solution owing to the interference of complex oxysulphur anions caused by SO2 conversion. Herein, a silkworm cocoon-like Co9S8-N@NC heterostructure (denoted as CoDC-pn) was constructed for SO2RR in protonic acid. This unique heterostructure induces the electron-deficient Co sites on CoDC-pn that promote SO2 activation and retard hydrogen evolution side-reaction. CoDC-pn delivers a S8 yield rate of 113.1 μmol h−1 mgcat−1 and faradaic efficiency of 70.0 % at –0.1 V. In-situ characterizations and mechanistic investigations confirm that SO2RR is a proton-coupled electron transfer process, in which protons can effectively inhibit the adverse conversion of SO2 to other oxysulphur species and attend the successive hydrodeoxygenation of *SO2 to *S followed by parallel atomic S polymerization for S8 formation. These findings provide a creative route and insight for exploring highly selective SO2-to-S8 conversion at ambient conditions.