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

The importance of tin oxide (SnOx) 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 SnOx layer exhibited potential-dependent CO2 reduction activity consistent with previously reported activity. In contrast, an electrode etched to expose fresh Sn-0 surface exhibited higher overall current densities but almost exclusive H-2 evolution over the entire 0.5 V range of potentials examined. Subsequently, a thin-film catalyst was prepared by simultaneous electrodeposition of Sn-0 and SnOx 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 SnOx layer. Our results implicate the participation of SnOx in the CO2 reduction pathway on Sn electrodes and suggest that metal/metal oxide composite materials are promising catalysts for sustainable fuel synthesis.