Exploring the Multifarious Role of the Ligand in Electrocatalytic Hydrogen Evolution Reaction Pathways

In recent years, researchers have shifted their focus towards investigating the redox properties of ancillary ligand backbones for small-molecule activation. Several metal complexes have been reported for the electrocatalytic H2 evolution reaction (HER), providing valuable mechanistic insights. This process involves efficient coupling of electrons and protons. Redox-active ligands stipulate internal electron transfer and promote effective orbital overlap between metal and ligand, thereby, enabling efficient proton-coupled electron transfer reactions. Understanding such catalytic mechanisms requires thorough spectroscopic and computational analyses. Herein, we summarize recent examples of molecular electrocatalysts based on 3d transition metals that have significantly influenced mechanistic pathways, thus, emphasizing the multifaceted role of metal-ligand cooperativity. Recent years have seen an emerging interest in the scientific world to exploring the multifaceted properties of redox-active ligands towards the design and synthesis of robust and efficient molecular electrocatalysts exhibiting HER. This Review highlights the role of metal-ligand cooperativity on mechanistic pathways utilizing 3d transition metal-based complexes.+image

Automated summary

In recent years, researchers have focused on investigating the redox properties of ancillary ligand backbones for small-molecule activation. Metal complexes have been used for the electrocatalytic H2 evolution reaction (HER), providing insights into the coupling of electrons and protons. Redox-active ligands facilitate electron transfer and promote effective orbital overlap, enabling efficient proton-coupled electron transfer reactions. Thorough spectroscopic and computational analyses are necessary for understanding catalytic mechanisms. This review summarizes recent examples of molecular electrocatalysts based on 3d transition metals and highlights the role of metal-ligand cooperativity in mechanistic pathways.