Tin Oxide Dependence of the CO2 Reduction Efficiency on Tin Electrodes and Enhanced Activity for Tin/Tin Oxide Thin-Film Catalysts

Abstract

The importance of tin oxide (SnO_x) to the efficiency of CO₂ reduction on Sn was evaluated by comparing the activity of Sn electrodes that had been subjected to different pre-electrolysis treatments. In aqueous NaHCO₃ solution saturated with CO₂, a Sn electrode with a native SnO_x layer exhibited potential-dependent CO₂ reduction activity consistent with previously reported activity. In contrast, an electrode etched to expose fresh Sn⁰ surface exhibited higher overall current densities but almost exclusive H₂ evolution over the entire 0.5 V range of potentials examined. Subsequently, a thin-film catalyst was prepared by simultaneous electrodeposition of Sn⁰ and SnO_x on a Ti electrode. This catalyst exhibited up to 8-fold higher partial current density and 4-fold higher faradaic efficiency for CO₂ reduction than a Sn electrode with a native SnO_x layer. Our results implicate the participation of SnO_x in the CO₂ reduction pathway on Sn electrodes and suggest that metal/metal oxide composite materials are promising catalysts for sustainable fuel synthesis.