Electrochemical reduction of ammonia-captured CO2 to CO over a nickel single-atom catalyst

Abstract

Carbon reactive capture and conversion offers a sustainable route to valuable chemicals and fuels while aiding Green House Gas (GHG) reduction. Direct electrochemical conversion of capture solutions like bicarbonate avoids the energy demands of conventional CO₂ regeneration. Ammonium bicarbonate (NH₄HCO₃) is particularly attractive due to its low decomposition temperature and ability to supply in situ CO₂ from dilute sources without requiring purified CO₂. Meanwhile, single-atom catalysts (SACs) with nitrogen-coordinated metal sites further enhance CO₂ reduction efficiency using Earth-abundant materials. In this study, we demonstrate a nickel single-atom catalyst (Ni-SAC)-based electrolyzer that utilizes NH₄HCO₃ as the CO₂ source, achieving significantly improved CO production performance compared to the conventional silver cathodes used in the CO₂ reduction reaction (CO₂RR) to produce CO. The Ni-SAC cathode exhibited a Faradaic efficiency of 60.1% for CO production at −200 mA cm⁻², while the silver cathode achieved a Faradaic efficiency of only 2%, likely due to ammonium-induced poisoning. Furthermore, the integration of a customized microporous layer onto the electrode significantly increased the Faradaic efficiency from 64% to 83% at −100 mA cm⁻², emphasizing the crucial role of electrode structure optimization in enhancing CO selectivity. These findings demonstrate a sustainable and economically viable strategy for green CO production directly from CO₂ capture solutions.