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 SnO2@C onto cuprous sulphide (Cu2S) to form a triplet effect at the interface. Snowflake-like Cu2S significantly enhances the local concentration of carbon dioxide (CO2) and promotes the binding of CO2 with SnO2, and the addition of carbon spheres enhances the electron transport, which is beneficial to the conversion of CO2 to HCOOH products. The snowflake-like Cu2S loaded with 1 wt% SnO2@C had an HCOOH Faraday Efficiency of 88% at -1.0 V (vs. Reversible Hydrogen Electrode, RHE), and the current density for CO2 reduction was stabilized at 15.6 mA cm-2, which was much higher than the HCOOH Faraday efficiency (FE) of 31.0% for pure Cu2S accompanied by a CO2 reduction current density of 3.9 mA cm-2. Combined investigations using in-situ Fourier transform infrared spectroscopy (FT-IR) with in-situ Raman spectra reveal that the active species is Cu+. Cu2S/1%SnO2@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 Cu2S/1%SnO2@C can well stabilize the HCOO* intermediate during the ECR process. The interaction between Cu2S and SnO2@C adjusts the surface electronic distribution and accelerates electron transfer, which efficiently improves CO2-to-HCOOH conversion. The result obtained from this work provides a simple and efficient electrocatalyst to enhance the HCOOH selectivity of ECR.