Cu7S4 nanosheets enriched with Cu-S bond for highly active and selective CO2 electroreduction to formate

Cu has been regarded as the most promising catalyst for electrochemical CO2 reduction reaction (CO2RR), a promising strategy for reducing CO2 emission and converting CO2 to value-added chemicals using renewable electrical energy. Nevertheless, selective formate (HCOO-) production via CO2RR over Cu-based catalysts has been rarely reported because Cu is generally used as the active site for C-C coupling to C2+ products. Herein, we demonstrate that Cu7S4 nanosheets (NSs) can serve as efficient catalysts for CO2RR to HCOO-. Detailed investigations show that, different from CuO that enables the C-C coupling to C2+ products, the Cu-S bond in Cu7S4 NSs favors protonation to produce HCOO-. Impressively, Cu7S4 NSs display a HCOO- faradaic efficiency (FE) of 82.7% with a formation rate of 8.5 mmol h(-1) cm(-2), which has surpassed most reported catalysts for CO2RR to HCOO-. This work provides a highly efficient catalyst for CO2RR to HCOO-, which may promote fundamental research on the catalyst design for CO2RR to target products.