Attenuating metal-substrate conjugation in atomically dispersed nickel catalysts for electroreduction of CO₂ to CO

Atomically dispersed transition metals on carbon-based aromatic substrates are an emerging class of electrocatalysts for the electroreduction of CO₂. However, electron delocalization of the metal site with the carbon support via d-π conjugation strongly hinders CO₂ activation at the active metal centers. Herein, we introduce a strategy to attenuate the d-π conjugation at single Ni atomic sites by functionalizing the support with cyano moieties. In situ attenuated total reflection infrared spectroscopy and theoretical calculations demonstrate that this strategy increases the electron density around the metal centers and facilitates CO₂ activation. As a result, for the electroreduction of CO₂ to CO in aqueous KHCO₃ electrolyte, the cyano-modified catalyst exhibits a turnover frequency of ~22,000 per hour at -1.178 V versus the reversible hydrogen electrode (RHE) and maintains a Faradaic efficiency (FE) above 90% even with a CO₂ concentration of only 30% in an H-type cell. In a flow cell under pure CO₂ at -0.93 V versus RHE the cyano-modified catalyst enables a current density of -300 mA/cm² with a FE above 90%.