Dynamic Hydrogen Bubbling Templated AgSn@ SnO_x Electrocatalyst for Selective Electrochemical CO₂ Reduction—Adjusting the Binding Energy of the HCOO* Intermediate

A facile electrochemical synthesis of 3D hierarchical porous AgSn@SnO_x core–shell catalysts has been demonstrated as efficient candidates for CO₂ reduction to formate. The AgSn@SnO_x (30 s) catalyst showed excellent selectivity towards formate (FE_HCOOH = 96% ± 4.90; j_HCOOH = −10.5 mA cm⁻² at −0.9 vs. RHE) with negligible HER activity. Tafel analysis and adsorption affinity studies suggest that AgSn@SnO_x (30 s) has faster reaction kinetics and the lowest adsorption energy, implying the formation of oxygen vacancies under cathodic conditions, which stabilize *CO₂^.− radicals and achieve lower binding energy. DFT calculations showed that the AgSn@SnO_x core–shell structure accelerates the formation of formic acid by modifying the binding energy of the HCOO*intermediate. Additionally, this structure improved the faradaic efficiency of C₁ production by suppressing the competitive hydrogen evolution reaction (HER), which is considered the main side reaction in the CO₂RR. The AgSn@SnO_x catalyst stands out as one of the most efficient electrocatalysts for CO₂ reduction to formate, when compared to other formate-selective electrocatalysts. It demonstrated superior performance in terms of formate partial current density and formate faradaic efficiency. All in all, AgSn@SnO_x core–shell catalysts showed great potential for efficient CO₂ reduction to formate, which could have significant implications for sustainable energy production.