Synergistic N-heterocyclic carbene and C2N integration for efficient and selective metal-free photocatalytic CO reduction to C2H5OH

Abstract

In the pursuit of sustainable and highly efficient catalysts for the reduction of CO to valuable multi-carbon fuels, this study presents a novel metal-free catalyst, C/C2N, created by integrating N-heterocyclic carbene (NHC) into a C2N monolayer. Utilizing density functional theory, we demonstrate that this integration effectively addresses the individual limitations of C2N and NHC, neither of which can stably adsorb CO molecules on their own. The synergistic effect of C2N and NHC facilitates distinct CO adsorption energies on the C2N surface (−0.08 eV) and at the NHC site (−0.83 eV), leading to an exceptionally low C–C coupling energy barrier of 0.41 eV, surpassing traditional metal-based catalysts. Computational results reveal that C/C2N exhibits outstanding activity and selectivity in reducing CO to C2H5OH, with a remarkably low free energy barrier of only 0.34 eV, further reducible to 0.20 eV under alkaline conditions. Furthermore, the integration of NHC into the C2N monolayer markedly narrows its band gap, enhancing visible light absorption and optimizing band edge positions, suggesting its potential for visible-light-driven reactions. Our findings establish C/C2N as an effective and selective metal-free photocatalyst with a notably low C–C coupling energy barrier, offering a novel avenue for CO conversion to multi-carbon fuels.