Two-Dimensional Carbon Nitride as a Support of Single Metal Atom for Carbon Dioxide Reduction Reaction

Abstract

Electrochemical conversion of CO2 into added-value chemicals is an important approach to recycle CO2. Heterogeneous catalysis is widely used in industrial applications because of the possibility of facile separation, which reduces the operating costs, although heterogeneous catalysts often have limited selectivity. In contrast, homogeneous catalysts are very selective although they have limited industrial applications due to their cost, the use of precious metals, and the difficulty in separating and recovering the catalysts. Currently, the research community is trying to combine the properties of homogeneous and heterogeneous catalysts. From the heterogeneous catalyst perspective, research has been focused on creating smaller and dispersed catalyst particles. Single-atom catalysts (SACs), which comprise atoms of metal species dispersed on a solid support, are expected to bridge the homogeneous and heterogeneous catalyst properties.The work described herein explores, by means of density functional simulations, the electrocatalytic CO2 reduction reaction (CO2RR) using several single transition metal atoms anchored in 2D graphitic carbon nitride (g-C3N4),1 focusing on the group XI transition metals since they include Cu, the only transition metal capable of reducing CO2 to hydrocarbons and alcohols with acceptable faradaic efficiencies. Moreover, the Cu1/g-C3N4 system has been experimentally evaluated as CO2RR electrocatalysts. 2D g-C3N4 has been demonstrated to be a competitive candidate for electrocatalytic CO2 reduction since it can act as an active support for single metal-atom catalysts, mainly Cu, Pd, and Pt, and the deposition of Au single atom was experimentally characterized.The computational hydrogen electrode model has been used to explore the suitability of several transition metals atoms anchored to C3N4, showing that single atoms enhance the catalytic activity of the system as the first proton–electron transfer is thermodynamically favored in comparison to bare carbon nitride support. Our theoretical interpretations are consistent with the experimental results using Cu1/g-C3N4,2 revealing that the competitive H2 generation is favored due to the strong CO binding energies. This fact reinforced the capability of our computational models to predict the behavior of several single metal atom electrocatalysts to reduce CO2, for instance, predicting that Au can promote the methane formation after eight electron-proton transfer processes. Our computational study paves the road to finding suitable metals that catalyze the first proton–electron transfer in the carbon dioxide reduction reaction. Posada-Pérez, A. Vidal-López, M. Solà, and A. Poater, 2023, Phys. Chem. Chem. Phys, 25, 8574.Cometto, A. Ugolotti, E. Grazietti, A. Moretto, G. Bottaro, L. Armelao, C. Di Valentin, L. Calvillo and G. A. Granozzi, npj 2D Mater. Appl., 2021, 5, 63. Figure 1