Reaching the Fundamental Limitation in CO2 Reduction to CO with Single Atom Catalysts

Abstract

The electrochemical CO2 reduction reaction (CO2RR) to value-added chemicals with renewable electricity is a promising method to decarbonise parts of the chemical industry. Recently, single metal atoms in nitrogen-doped carbon (MNC) have emerged as potential electrocatalysts for CO2RR to CO with high activity and faradaic efficiency, although the reaction limitation for CO2RR to CO is unclear. To understand the comparison of intrinsic activity of different MNCs, we synthesized two catalysts through a decoupled two-step synthesis approach of high temperature pyrolysis and low temperature metalation (Fe or Ni). The highly meso-porous structure resulted in the highest reported electrochemical active site utilisation based on in situ nitrite stripping; up to 59±6% for NiNC. Ex-situ X-ray absorption spectroscopy confirmed the penta-coordinated nature of the active sites. The catalysts are amongst the most active in the literature for CO2 reduction to CO. Our density functional theory calculations (DFT) show that their binding to the reaction intermediates approximates to that of Au surfaces. However, we find that the TOFs of the most active catalysts for CO evolution converge, suggesting a fundamental ceiling to the catalytic rates.