In Situ Formed “Sn_1–XIn_X@In_1–YSn_YO_Z” Core@Shell Nanoparticles as Electrocatalysts for CO₂ Reduction to Formate

Abstract Electrochemical reduction of CO₂ (CO₂RR) driven by renewable energy has gained increasing attention for sustainable production of chemicals and fuels. Catalyst design to overcome large overpotentials and poor product selectivity remains however challenging. Sn/SnOx and In/InOx composites have been reported active for CO₂RR with high selectivity toward formate formation. In this work, the CO₂RR activity and selectivity of metal/metal oxide composite nanoparticles formed by in situ reduction of bimetallic amorphous SnInOx thin films are investigated. It is shown that during CO₂RR the amorphous SnInOx pre‐catalyst thin films are reduced in situ into Sn_1–XIn_X@In_1–YSn_YO_z core@shell nanoparticles composed of Sn‐rich SnIn alloy nanocores (with x < 0.2) surrounded by InOx‐rich bimetallic InSnOx shells (with 0.3 < y < 0.4 and z ≈ 1). The in situ formed particles catalyze the CO₂RR to formate with high faradaic efficiency (80%) and outstanding formate mass activity (437 A g_In+Sn⁻¹ @ −1.0 V vs RHE in 0.1 m KHCO₃). While extensive structural investigation during CO₂RR reveals pronounced dynamics in terms of particle size, the core@shell structure is observed for the different electrolysis conditions essayed, with high surface oxide contents favoring formate over hydrogen selectivity.