In Situ Formed “Sn1–XInX@In1–YSnYOZ” Core@Shell Nanoparticles as Electrocatalysts for CO2 Reduction to Formate

Abstract Electrochemical reduction of CO 2 (CO 2 RR) 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 CO 2 RR with high selectivity toward formate formation. In this work, the CO 2 RR 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 CO 2 RR the amorphous SnInOx pre‐catalyst thin films are reduced in situ into Sn 1– X In X @In 1– Y Sn Y O 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 CO 2 RR 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 KHCO 3 ). While extensive structural investigation during CO 2 RR 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.