Abstract
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%.