Trace Sn modified Zn catalysts for efficient CO2 electroreduction to HCOOH†

Metallic Zn-based electrocatalysts mainly trigger the CO reaction pathway in the electrochemical CO₂ reduction reaction. In contrast, Sn-based electrocatalysts exhibit decent activity toward CO₂ reduction to HCOOH. However, Sn is more expensive than Zn. Herein, a trace Sn doped Zn electrocatalyst with a leaf-like structure (ZnSn), synthesized by co-electrodeposition, exhibits significantly enhanced HCOOH selectivity over a wide potential window with concomitant H₂ suppression. The optimized catalyst with a low Sn content of 0.27 wt% shows a high HCOOH mass activity of 111.11 mA mg_Sn⁻¹ and a C₁ faradaic efficiency of 90% at −0.98 V vs. RHE. Dual active sites favor the tandem reaction with CO₂ first strongly adsorbing on Zn sites and further transferring to Sn sites. Density functional theory (DFT) and in situ Raman spectroscopy confirm that the synergistic effect between Zn and Sn leads to the O-bonding mode of CO₂ adsorption, modifying the chemical environment and electronic structure and thus strengthening the adsorption of the *OOCH intermediate. The enhanced HCOOH efficiency on Sn-modified Zn sites indicates the possibility of metal–metal interactions to control selectivity and improve electrocatalytic activity.