Recent progress in ligand-centered homogeneous electrocatalysts for hydrogen evolution reaction
Electrocatalytic hydrogen evolution reaction (HER) is a critical process in a sustainable energy conversion system. Many metal complexes as small-molecule catalysts for electrochemical H2 evolution have been reported over recent decades, which have made a great contribution to a detailed understanding of their catalytic mechanisms. In most reported mechanistic pathways, metal hydride species are always considered as key intermediates during H2 formation, with the metal centre at the active site docking both electrons and protons. These metal-centred HER routes need to employ metal ions with open coordination sites, which can accommodate multiple redox states to involve two-electron hydride transfer for H2 production. By comparison, an alternative approach, specifically focusing on redox-active ligand-centred electrocatalytic HER, has garnered increasing attention over the last six years. This review highlights recent progress in metal and metal-free ligand-centred homogeneous electrocatalytic HER since 2012 and discusses it according to two categories: organic ligand-centred and inorganic ligand-centred HER. In addition, some existing issues and suggestions for future directions in this catalytic area have been provided.
- This article is part of the themed collection: 2019 Inorganic Chemistry Frontiers Review-type Articles