How Nitrogen-Doped Graphene Quantum Dots Catalyze Electroreduction of CO₂ to Hydrocarbons and Oxygenates

Abstract

Recently, metal-free nitrogen-doped graphene quantum dots (NGQDs) have been experimentally demonstrated to electrochemically convert CO 2 into high-order hydrocarbons and oxygenates, after more than 30 years since the identification of copper as an active metal catalyst for such conversions. However, the physicochemical principle of such catalytic activity for NGQDs has remained unclear. Here, by performing first-principles simulations, we have systematically investigated the underlying mechanisms governing the whole process. The introduction of N atoms into edges of graphene quantum dots enhances their bonding with *COOH, effectively promoting the reduction of CO 2 to CO. By including the influences of water, we reveal that the selective production of CH 4 over CH 3 OH is attributed to a much lower kinetic barrier for the conversion of adsorbed *CH 2 OH to *CH 2 via water molecule mediated proton shuttling. Further, adsorbed *CH 2 provides active sites for the coupling with CO to generate C 2 products, including both C 2 H 4 and C 2 H 5 OH. These results offer theoretical insights into the reduction pathways of CO 2 on NGQDs, which may facilitate the design of metal-free carbon-based catalysts for efficient CO 2 reduction.