Achieving highly efficient CO2 to CO electroreduction exceeding 300 mA cm−2 with single-atom nickel electrocatalysts

Abstract

The electrochemical reduction of carbon dioxide (CO₂) to value-added products is a promising approach to reduce excess CO₂ in the atmosphere. However, the selective reduction of CO₂ in aqueous electrolytes has been challenging owing to a competing hydrogen evolution reaction occurring in aqueous electrolytes. In this study, single atom nickel and nitrogen doped three-dimensional porous carbon catalysts are developed for the selective production of carbon monoxide (CO) from CO₂. The catalysts exhibit high CO selectivity with over 99% faradaic efficiency at −0.8 V vs. the reversible hydrogen electrode (RHE), and achieve a high current density of over 50 mA cm⁻² at −1.0 V vs. RHE in a bicarbonate electrolyte. To further improve the CO₂ reduction rate, the accessibility of CO₂ to the catalysts was enhanced by directly supplying gaseous CO₂ to the surface of the catalysts. The catalysts were deposited between a gas diffusion layer and an ion exchange membrane to form a membrane electrode assembly (MEA). Benefiting from the high concentration of CO₂ over the catalyst surfaces and the three-dimensional structure of the catalysts, a high CO production rate exceeding 300 mA cm⁻² with 99% faradaic efficiency can be achieved.