Unraveling Meso-Substituent Steric Effects on the Mechanism of Hydrogen Evolution Reaction in Ni Porphyrin Hydrides Using DFT Method.

Substituents at the site of metalloporphyrins profoundly influence the hydrogen evolution reaction (HER) mechanism. This study employs density functional theory (DFT) to computationally analyze Ni-porphyrin and its hydrides derived from tetrakis(pentafluorophenyl)porphyrin molecules, presenting stereoisomers in or -positions. The results reveal that the spatial resistance effect of -substituted groups at the and positions induces significant changes in Ni-N bond lengths, angles, and reaction dynamics. For position substituents forming complex , a favorable 88.88 ų spherical space was created, facilitating proton coordination and the formation of H molecules; conversely, position substituents forming complex impeded H formation until bimolecular complexes arose. Molecular dynamics (MD) analysis and comparison were conducted on the intermediation products of and , focusing on the configuration and energy changes. In the products, H molecules underwent separation after 150 fs and overcame the 2.2 eV energy barrier. Subsequently, significant alterations in the spatial structure were observed as complex deformed. In the case of , it was influenced by the distinctive "sandwich" configuration; the spatial structure necessitated overcoming a 6.7 eV energy barrier for H detachment and a process observed after 2400 fs.