Synergistic marriage of CO2 reduction and sulfide oxidation towards a sustainable co-electrolysis process

Current CO2 electrolyzers suffer from low economic feasibility due to the huge energy demand of water oxidation and the recovery of low-value oxygen. Herein, an energy-efficient co-valorization electrolysis is reported by coupling CO2 reduction with sulfide oxidation, utilizing a dual doped cobalt hydroxide anode and an electrochemical-reduced Bi cathode in a flow-cell electrolyzer. Benefiting from the accelerated reaction kinetics, the assembled electrolyzer saves 40% of the energy request to drive the CO2RR-SOR electrolysis as compared to the CO2RR-OER counterpart at 100 mA/cm2. The CO2 gas and S2- pollutant are recycled to value-added formate and sulfur solid with Faraday efficiencies higher than 90%, doubling the net revenue of CO2 electrolysis. Furthermore, a solar-driven CO2RR-SOR system using a commercial Si cell was constructed to yield a current density of more than 100 mA/cm2 during 6 h operation with a solar-conversion efficiency of 5.8 ± 0.4%, demonstrating a sustainable co-electrolysis system. [Display omitted] •Dual doped cobalt hydroxides were developed to catalyze the SOR with a low overpotential.•A hybrid electrolyzer of CO2RR-SOR was constructed for a sustainable co-valorization process.•Up to 40% of the energy request was saved using the CO2RR-SOR electrolyzer as compared to the CO2RR-OER counterpart.•A solar-conversion efficiency of 5.8 ± 0.4% at an industrial-relevant current density was achieved.