Electrochemical CO₂-to-Formate Conversion Over Positive Charge Depleted Tin Sites

Upgrading CO2 to formate systems is a promising avenue for fuel production, and SnOx is a unique low-cost candidate for this conversion. However, the high oxygen affinity of Sn sites leads to a strong adsorption of O-bound intermediates, resulting in a low efficiency of CO2 reduction. Herein, density functional theory (DFT) calculations confirmed that a H-doping strategy of SnO2 produces partially depleted positive charge Sn sites, weakening the adsorption of HCOO* and boosting the electron transfer kinetics. Experimentally, H-doped commercial SnO2 nanoparticles (H-SnO2) indeed had enhanced intrinsic activity for CO2-to-formate conversion with suppressed hydrogen evolution performance. Remarkably, H-SnO2 achieves over 90.0% formate selectivity within −0.6 to −1.0 V (vs RHE) at the industrial current density of 220 mA cm–2. Electrochemical measurements and in situ Raman spectra analysis together disclosed that H-doping speeds up the kinetic rate for the first electron transfer of CO2 reduction and also promotes formate desorption, resulting in the impressively high current density and selectivity of H-SnO2.