Ligand engineering regulates the electronic structure of Ni-N-C sites to promote electrocatalytic acetylene semi-hydrogenation

Compared with traditional thermal catalytic hydrogenation technology, electrocatalytic acetylene semi-hydrogenation (EASH) is a green and environmentally friendly method. EASH utilizes renewable electricity under normal temperature and pressure conditions, and uses water as a hydrogen source to electrocatalytically semi-hydrogenate acetylene to ethylene. Ni-based single-atom catalysts (SACs) have shown good application prospects in EASH, but there is still much room for optimization. The axial coordination regulation of the active center is a potential means to improve its activity. In this work, the activity and selectivity of NiN₄ SACs with 14 axial ligands (X) for EASH were systematically studied via density functional theory (DFT). First, the binding energy and ab initio molecular dynamics simulation results show that all the NiN₄-X can exist stably. Second, the Gibbs free energy diagram shows that the activation and adsorption of C₂H₂ is the rate-determining step of the reaction. The introduction of the –ONO ligand enhances the activation and adsorption of C₂H₂ by NiN₄, which is beneficial to the occurrence of EASH and inhibits the side reactions of hydrogen evolution. The two parameters ${\Delta G}_{\ast CHCH}$ and ${\Delta G}_{\ast {\mathrm{CH}}_{2}C{H}_3}$ can be used as characteristic descriptors to predict the activity and selectivity of EASH. Finally, the catalytic activity mechanism was explained from the perspective of electrons and orbitals, and it was found that the $d_{z^2}$ orbital played a leading role in the axial ligand regulation of C₂H₂ catalytic activity. This work provides a new method for the development of efficient EASH catalysts.