Computational Study of Electrochemical CO2 Reduction on 2D Graphitic Carbon Nitride Supported Single-Atom (Al and P) Catalysts (SACs).

To mitigate the adverse effects of CO₂ emissions, CO₂ electroreduction to small organic products is a preferable solution and potential catalysts include the single-atom catalyst (SAC) which comprises individual atoms dispersed on 2D materials. Here, we used aluminum and phosphorus as the active sites for CO₂ electroreductions by embedding them on the 2D graphitic carbon nitride (g-C₃N₄) nano-surface. The resulting M-C₃N₄ (M=Al and P) SACs were computationally studied for the CO₂ electroreduction using density functional theory (DFT) and ab-initio molecular dynamics (AIMD) simulations. Computations showed that CO₂ can be adsorbed to the active sites in forms of a frustrated Lewis pair (Al/N or P/N) or single atom Al or P. The adsorbed CO₂ can be converted to various intermediates by gaining proton and electron (H⁺+e^-) pairs, a process simulated as electroreduction. While both SACs prefer to produce HCOOH with low potential determining steps (PDSs) and small overpotential values of 0.25 V and 0.08 V for Al-C₃N₄ and P-C₃N₄ respectively, to produce CH₄, P-C₃N₄ exhibits a lower potential barrier of 0.9 eV than Al-C₃N₄ (1.07~1.17 eV).