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

Abstract

Clean 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.

The Biologically Relevant Coordination Chemistry of Iron and Nitric Oxide: Electronic Structure and Reactivity

“…Complexes 99 , 142 and 153 were incorporated into heterogeneous electrodes to constitute remarkable HER catalysts, capable of reducing protons from water. Liaw and coworkers used the {Fe­(NO) 2 } 9 /{Fe­(NO) 2 } 10 redox couple in DNICs to design complexes for a solid-state hydrogen evolution cathode. ,, The low-cost PMDTA-bound DNIC 142 , deposited on an electrode, exhibits a low onset potential of -717 mV versus SHE in a neutral 1.0M KCl solution to generate H 2(g) from water . The catalytic activity of DNICs can be further tuned by ligand design.…”

“…Additional wound healing effects were seen by Yuan, Lu, Liaw and Wang using a mercaptoethanol-bound DNIC to promote angiogenesis and wound healing in diabetic mice by a sustained release of NO, activating the NO-sGC-cGMP pathway (see Section ). This same complex was also used to regulate the IIS, AMPK and mitochondrial signaling pathways in C. elegans by O 2 -triggered release of NO • to extend the lifespan of this organism …”

Dinitrosyl iron complexes (DNICs) acting as catalyst for photocatalytic hydrogen evolution reaction (HER)

“…The elemental composition and chemical state of the active particles were further characterized by X-ray photoelectron spectra (XPS) (Figure S11). [51][52][53] The Fe 2P spectrum shows two intense peaks (2P 1/2 and 2P 3/2 ) and two broad peaks (shark satellite signal). Fe 2P 3/2 appears binding energy at 710.0 and 711.8 eV attribute to Fe 2+ and Fe 3+ , respectively.…”

“…Aiming at the implementation of {Fe(NO) 2 } 10 -reduced DNICs [Et 4 N][( Me DDB)Fe(NO) 2 ] and [(PMDTA)Fe (NO) 2 ] À as molecular electrocatalysts for HER in aqueous solution, however, cyclic voltammogram displaying the crossing character demonstrated that the in situ generated electrodeposited-film electrode is the dominant HER catalyst in aqueous condition. [47,[51][52][53] In this report, {Fe(NO) 2 } 10 DNIC [(2-AMP)Fe(NO) 2 ] (2-AMP = 2aminomethylpyridine) (1) was synthesized to serve as photocatalyst and precursor of active Fe 3 O 4 particles (major) working in concert with Fl (Fluorescein) and Et 3 N to build up the multi-component photocatalytic hydrogen evolution system in MeOH-H 2 O solution for light-driven hydrogen generation.…”

“…[ 47,48 ] Also, a recent study demonstrates that the influence of backbone length and bite angle of chelating thiolate‐bound DNICs on the redox and chemical properties of [Fe(NO) 2 ] core may initiate the rational design of DNICs as a molecular catalyst for water splitting. [ 49–51 ] It is known that the homogeneous catalysts for electrocatalytic H 2 ‐generation from water require aqueous compatibility, reversible redox process, low‐valence metal cores, and capability for providing exchangeable coordination sites to accommodate water/hydride/dihydrogen. DNIC [( Me DDB)Fe(NO) 2 ] with the incorporation of the redox‐active non‐innocent ligand Me DDB ( N,N′ ‐bis‐[2,6‐diisopropylphenyl]‐1,4‐diaza‐2,3‐dimethyl‐1,3‐butadiene) acting as a molecular electrocatalyst reveals that the reversible {( Me DDB)Fe(NO) 2 } 9 {( Me DDB)Fe(NO) 2 } 10 {( Me DDB)Fe(NO) 2 } 11 interconversion may trigger the electrocatalytic H 2 generation in THF solution containing 50 mM H 2 O.…”