Heterogeneous N-heterocyclic carbenes: Efficient and selective metal-free electrocatalysts for CO reduction to multi-carbon products

Electrochemical reduction of CO2 to valuable multi-carbon products is an important potential solution to environmental and energy crises caused by fossil fuel burning. As an effective way to address the drawbacks of direct CO2 reduction, the reduction of CO to multi-carbon products remains a challenge, specially lacking high-efficient, selective and low-cost metal-free catalysts. N-heterocyclic carbenes (NHCs) have been shown to be effective metal-free catalysts for converting CO2 to CO or C1-products, but the facile release of CO limits the further reduction to valuable multi-carbon fuels. In this study, using density functional theory calculations, we developed heterogeneous NHCs by incorporating NHCs into the graphene lattice and found that these NHCs could stably adsorb and effectively activate CO molecules, enabling the efficient conversion of CO into CH3OH, C2H4 and C2H5OH with low limiting potentials, i.e., –0.70, –0.45 and –0.36 V, respectively. These limiting potentials for C2-products are lower than those of most known metal-based or metal-free electrocatalysts. Moreover, competitive hydrogen evolution reaction can be effectively inhibited. The excellent catalytic performance is attributed to the charge transfer between NHCs and CO as well as the strong hybridization of C-2p orbitals of carbene carbon atoms in NHCs and carbon atoms in CO molecule. Our findings suggest that these heterogeneous NHCs exhibit high catalytic activity and selectivity for the conversion of CO to valuable C2-products. This study is the first report of NHC-based metal-free electrocatalysts for the conversion of CO to multi-carbon products, which will offer cost-effective opportunities for CO2 reduction.