Buffering electrolyte alkalinity for highly selective and energy-efficient transformation of CO2 to CO

Abstract

Electroreduction of CO2 to value-added products is a promising strategy for renewable energy storage using a carbon-neutral cycle. In this work, we report a feasible electrochemical approach to achieving highly efficient CO2-to-CO conversion by buffering electrolyte alkalinity in borate-containing molten salts, where borates acting as a buffer system can regulate the concentration of sequentially released O2− (defined as a base) in the electrolyte, changing the thermodynamic reaction pathway of the CO2 reduction reaction (CO2RR). Taking the CO2RR in LiBO2-containing molten LiCl–Li2CO3 as an example, CO is more preferentially generated in this medium compared with a borate-free electrolyte (where mainly carbon products are produced). The faradaic efficiency for producing CO was over 90% at a current density of 100 mA/cm2, with a very low energy consumption of 1.06 kWh/Nm3-CO at a relatively low temperature (650 °C). This facile and energy-efficient strategy suggests an approach to steering the CO2RR toward desired products with improved energy efficiency.

Keywords

• CO2 reduction
• Molten salt electrolysis
• Borate
• Buffering effect
• CO