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

Abstract

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.

Keywords: Electrochemical; Electron transport; Formate; Snowflake; Tandem effect.