CuS Nanosheet Arrays for Electrochemical CO₂ Reduction with Surface Reconstruction and the Effect on Selective Formation of Formate

Copper-based catalysts have shown excellent performance in electrochemical CO2 reduction, but there has not been much study on copper sulfides. In our work, a simple and low-temperature chemical bath deposition method was used to fabricate CuS nanosheet arrays on brass, on which a Faradaic efficiency over 70% and a production rate over 50 mA·cm–2 for formate were obtained at a low potential of −0.7 V vs RHE when used as a catalytic electrode for CO2 reduction. During the CO2 reduction process, CuS nanosheets were partially reduced to Cu0 and reconstructed to a nanowire network. It was found that residual S beneath the Cu0 layer lowered the binding energies of intermediates HCOO* and *COOH, promoting their desorption and the successive formation of HCOOH or HCOO–, thus regulating the high selectivity of the product. This work provides a convenient and economical method for developing a highly active electrocatalyst for producing HCOOH in CO2 electroreduction, and it is beneficial to understand the mechanism of enhanced selectivity to HCOO– for CuS electrode materials.