Dinitrosyl iron complexes: From molecular electrocatalysts to electrodeposited‐film electrodes for hydrogen evolution reaction

Abstract

AbstractClean and large‐scale production of hydrogen via water splitting triggered by active, robust, and low‐cost electrocatalysts is a promising and sustainable strategy for energy conversion and storage. In this study, a series of four‐coordinated chelating amine‐bound {Fe(NO)2}10 dinitrosyl iron complexes (DNICs) [(L)Fe(NO)2] were synthesized to investigate how the electronic structure of [Fe(NO)2] unit of DNICs was tailored to promote the electrocatalytic hydrogen evolution reaction (HER) triggered by the homogeneous DNICs' molecular catalysts and the heterogeneous DNIC‐derived electrodeposited‐film electrodes. The electrochemical studies demonstrate that HER onset potentials of those DNICs in neutral sodium sulfate aqueous solution are dependent on their IR ν(NO) stretching frequencies, indicating that the electron‐rich [Fe(NO)2] core modulated by the synergistic cooperation of the electron‐donating ability and steric effect of methyl‐/hydrogen‐substituted diamine‐coordinated ligands, presumably, benefits the formation of metal‐hydride intermediate to reduce the required onset potential. In contrast with homogeneous catalyst retaining its molecular integrity during the catalytic HER process, it is noticed that DNICs [(L)Fe(NO)2] act as the precursor of the active heterogeneous HER catalyst during the electrocatalytic HER process. It is presumed that the intermolecular hydrogen‐bonding interactions among DNICs [(L)Fe(NO)2] may control the particle sizes of DNIC‐derived electrodeposited film to modulate HER efficiency.