Organoselenium Ligand Enabled Selective Electron Tuning for Switchable Hydrogen Evolution Reaction.

Abstract

Unraveling the electronic structure of metal complexes can bring various catalytic possibilities for hydrogen evolution reaction (HER). However, the electronic effect of metal and ligands modulating and switching the reaction center for HER has yet to be comprehensively analyzed. Herein, we report nickel selenoether electrocatalysts which show tunable reaction centers (nickel or ligand) for HER using mild weak acetic acid in less deprotonating DMF solvent. Synthesized nickel selenoether electrocatalysts which follow a ligand-centered pathway demonstrated remarkably high turnover frequency (kobs) upto 14000 s-1 with 93% Faradaic Efficiency (F.E.). Whereas Ni-electrocatalyst having N-donor and selenoether ligands follow a metal-centered HER and show kobs value of 2110 s-1 with F.E. of 98%. A kinetic isotopic effect (KIE) study using CD3CO2D provides kH/kD = 0.49 and 13.01 values for two types of catalysts suggestive of metal-centered and ligand-centered catalytic behavior, respectively. Also, EPR studies revealed nickel-centered and ligand-centered radicals in two types of Ni-electrocatalysts. Mechanistically, the EPR, CV, and DFT computation studies suggest that the electron density of the selenoether ligand plays a crucial role by acting as an electron reservoir in deciding the reaction pathways, whether hydride formation occurs at metal-centered leading to Ni-H intermediate or ligand-centered pathways for HER.