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Copper-based catalysts have shown excellent performance in electrochemical CO 2 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 CO 2 reduction. During the CO 2 reduction process, CuS nanosheets were partially reduced to Cu 0 and reconstructed to a nanowire network. It was found that residual S beneath the Cu 0 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 CO 2 electroreduction, and it is beneficial to understand the mechanism of enhanced selectivity to HCOO − for CuS electrode materials.

This work provides a simple method for the development of a high-activity non-noble metal catalyst for the oxidation of glycerol (GLY) to formate. CuS nanosheet arrays are grown in situ on the brass mesh by low-temperature sulfuration, and then copper nanoparticles are uniformly dotted on CuS nanosheets through disproportionation reaction. As-fabricated Cu-CuS/BM is used for glycerol oxidation reaction (GOR), and the current density can reach 10 mA·cm–2 when the potential is 1.37 V vs RHE. A high selectivity of 86.0% and a Faradaic efficiency of 90.4% for formate production are achieved, and the average selectivity of 20 consecutive cycles of electrolysis is 82.6%, confirming the excellent activity and stability of Cu-CuS/BM. The formation of formate as the main oxidation product that conforms to the primary alcohol oxidation path is proved through high-performance liquid chromatography and in situ Fourier transform infrared spectroscopy. The mechanism of GOR induced by Cu-CuS/BM is proposed through density functional theory calculation and X-ray photoelectron spectroscopy analysis, in which the combination of copper nanoparticles and CuS significantly enhances the adsorption for GLY, and Cu­(II) produced during the GOR facilitates the adsorption for OH– to form Cu­(II)-OHads on the catalyst surface, which is beneficial to the oxidation of absorbed GLY.

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