Alkalinity Promoting Formate Production from CO2 over a Wide Electrochemical Potential Window on a Sns Catalyst

Abstract

Tin-based nanomaterials are attractive low cost electrocatalysts which offers prospect of large-scale CO2 reduction, particularly for selective formate production. However, drawbacks such as large overpotential, low current density and narrow electrochemical potential window render the applicability of this catalyst. Herein, we report the dramatic influence of electrolyte alkalinity in widening potential window for CO2 electroreduction in a flow-cell system based on SnS nanosheets. The optimized SnS catalyst operated in 1 M KOH enables the achievement of a maximum formate conversion Faradaic efficiency of 88 ± 2 % at -1.3 V vs. RHE with the current density of ~ 120 mA cm-2. Alkaline electrolyte was found suppressing the hydrogen evolution across all potentials which is particularly dominant at the less negative potentials, as well as CO evolution at more negative potentials which in turn widens the potential window for formate conversion (>70% at the potential range of -0.5 to -1.5 V vs. RHE). Comparison to SnOx counterpart indicates sulphur acts to suppress hydrogen evolution, although electrolyte alkalinity also plays a role in hydrogen supression. A long term current and formate conversion stability of over 30h at -1.5V vs. RHE was obtained by reducing accumulation of carbonate or bicarbonate and buffered the pH in the KOH catholyte. This study offers new insights into strategy in boosting electrochemical potential window on Sn-based catalyst operable at a wide potential window, and the integration of desirable features of a high current density and long term stable system as demonstrated in this electrocatalytic system offers promise for implementation of large-scale formate production from CO2.