Tandem effect at snowflake-like cuprous sulphide interfaces for highly selective conversion of carbon dioxide to formate by electrochemical reduction.

Electrochemical carbon dioxide reduction (ECR) is a commercially promising technology to resolve the energy dilemma and accomplish carbon recycling. Herein, a novel electrocatalyst has been investigated to produce formate (HCOOH) highly selectively during ECR by loading SnO@C onto cuprous sulphide (CuS) to form a triplet effect at the interface. Snowflake-like CuS significantly enhances the local concentration of carbon dioxide (CO) and promotes the binding of CO with SnO, and the addition of carbon spheres enhances the electron transport, which is beneficial to the conversion of CO to HCOOH products. The snowflake-like CuS loaded with 1 wt% SnO@C had an HCOOH Faraday Efficiency of 88% at -1.0 V (vs. Reversible Hydrogen Electrode, RHE), and the current density for CO reduction was stabilized at 15.6 mA cm, which was much higher than the HCOOH Faraday efficiency (FE) of 31.0% for pure CuS accompanied by a CO reduction current density of 3.9 mA cm. Combined investigations using in-situ Fourier transform infrared spectroscopy (FT-IR) with in-situ Raman spectra reveal that the active species is Cu. CuS/1%SnO@C can effectively promote the adsorption and activation of carbonate and inhibit the production of CO intermediates. The corresponding density functional theory (DFT) demonstrates that CuS/1%SnO@C can well stabilize the HCOO* intermediate during the ECR process. The interaction between CuS and SnO@C adjusts the surface electronic distribution and accelerates electron transfer, which efficiently improves CO-to-HCOOH conversion. The result obtained from this work provides a simple and efficient electrocatalyst to enhance the HCOOH selectivity of ECR.