Understanding the Unique Selectivity of Cobalt Phthalocyanine in Multielectron Reduction of Carbon Dioxide

Abstract

Metal–nitrogen–carbon (M–N–C) single-atom catalysts (SACs) have emerged as promising heterogeneous electrocatalysts for the CO₂ reduction reaction (CO₂RR). However, the predominant production of CO over multielectron products remains a challenge for most M–N–C SACs, with the exception of cobalt phthalocyanine (CoPc). In this study, the comparison of CoPc and a series of analogous M–N–C SACs was systematically investigated using density functional theory calculations to unravel the factors contributing to the selectivity of CoPc in catalyzing multielectron CO₂RR. The relationship between the selectivity and the electronic configuration of M–N–C SACs was revealed. The half-filled d_z² orbital of the cobalt ion lead to moderate chemisorption of *CO on CoPc, enabling the subsequent protonation of *CO. In addition, we identified a unique type of hydrogen bond in which the C atom of *CO acts as the proton acceptor (C···H–O hydrogen bond), which significantly promotes the proton transfer to *CO and selectivity for multielectron products. Only the *CO on CoPc was observed to form the C···H–O hydrogen bond, elucidating the unique multielectron CO₂RR performance of CoPc. In addition, we further elucidated the formation mechanism of the C···H–O hydrogen bond, which provides an alternative strategy to accelerate proton transfer in electrochemical reactions by utilizing this unconventional hydrogen bond.