Development of a Dinitrosyl Iron Complex Molecular Catalyst into a Hydrogen Evolution Cathode

Abstract

Despite extensive efforts, the electrocatalytic reduction of water using homogeneous/heterogeneous Fe, Co, Ni, Cu, W, and Mo complexes remains challenging because of issues involving the development of efficient, recyclable, stable, and aqueous-compatible catalysts. In this study, evolution of the de novo designed dinitrosyl iron complex DNIC-PMDTA from a molecular catalyst into a solid-state hydrogen evolution cathode, considering all the parameters to fulfill the electronic and structural requirements of each step of the catalytic cycle, is demonstrated. DNIC-PMDTA reveals electrocatalytic reduction of water at neutral and basic media, whereas its deposit on electrode preserves exceptional longevity, 139 h. This discovery will initiate a systematic study on the assembly of [Fe(NO)2] motif into current collector for mass production of H2, whereas the efficiency remains tailored by its molecular precursor [(L)Fe(NO)2].

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

“…As expected from synergistic cooperation of the electron‐donating ability and steric effect of chelating amine‐coordinated ligands, the redox potential of the reversible {Fe(NO) 2 } 9 /{Fe(NO) 2 } 10 redox couple of {Fe(NO) 2 } 10 DNIC 6 ( E 1/2 = −0.34 V [CH 3 CN]) displays less negative value than those ( E 1/2 = −0.44, −0.41, −0.41, and −0.41 V [CH 3 CN]) of {Fe(NO) 2 } 10 DNICs 1 and 3 – 5 . The feasibility of {Fe(NO) 2 } 10 DNICs 1 and 3 – 6 as homogeneous molecular electrocatalysts active for two‐electron water reduction, in line with the reported [(PMDTA)Fe(NO) 2 ] triggering electrocatalytic HER via the reversible redox shuttling {Fe(NO) 2 } 9 ↔{Fe(NO) 2 } 10 ↔reduced‐state[{Fe(NO) 2 } 10 ] redox states, is then explored. Sodium sulfate (Na 2 SO 4 ) was chosen as an electrolyte for the electrocatalytic study, and the saturated calomel electrode (SCE) was used as the reference.…”

“…As reported in the previous study on the implementation of DNICs as homogeneous HER electrocatalysts in aqueous solution, the subsequent deposition of the amount of iron (oxy)hydroxide on graphite electrode during the electrocatalytic HER process demonstrated that DNICs act as a precursor of the heterogeneous HER catalyst . After the extended electrolysis of 1.0 M Na 2 SO 4 aqueous solution with DNICs 1 / 3 – 6 (1 mM) at an applied potential of −1.20 V (vs. SHE) for 1 hr, DNICs 1 / 3 – 6 were reduced to generate catalytically active film on the glassy carbon electrodes that act as the heterogeneous electrodeposited‐film electrodes for HER.…”

“…XPS spectra show that the Fe 2p major peaks at 711.0, 711.5, 711.3, 711.6, and 711.4 eV for 1‐C , 3‐C , 4‐C , 5‐C , and 6‐C , respectively, were assigned to iron(III) oxides, presumably resulting from the degradation of DNICs (Figure S4). In addition, the O 1s peaks within the range of 530.9–530.1 eV may suggest the presence of iron oxides (Figure S5). In contrast to the very weak signals of N 1s spectra of 1‐C , 3‐C , 4‐C , and 5‐C , a significant signal (400.0 eV) found in 6‐C was assigned to the residual TMEDA ligand (Figure S6).…”

“…In the previous investigation, the cyclic voltammetric studies of DNICs reveal two reversible one‐electron redox states associated with {Fe(NO) 2 } 9 ↔{Fe(NO) 2 } 10 ↔[{Fe(NO) 2 } 10 ‐L • ] − redox states, implicating the possibilities of DNICs to promote versatile chemical reactions associated with two‐electron HER process . Recently, we demonstrated that the {Fe(NO) 2 } 10 dinitrosyl iron complex (DNIC) [(PMDTA)Fe(NO) 2 ] (PMDTA = pentamethyldiethylene triamine) plays a significant role in triggering electrocatalytic HER in neutral 1.0 M KCl aqueous solution, through the reversible redox shuttling among {Fe(NO) 2 } 9 , {Fe(NO) 2 } 10 , and reduced‐state [{Fe(NO) 2 } 10 ] electronic states . Alternatively, {Fe(NO) 2 } 10 DNIC [(PMDTA)Fe(NO) 2 ] was employed as a precursor to derive the electrodeposited solid‐state HER catalysts .…”

“…Recently, we demonstrated that the {Fe(NO) 2 } 10 dinitrosyl iron complex (DNIC) [(PMDTA)Fe(NO) 2 ] (PMDTA = pentamethyldiethylene triamine) plays a significant role in triggering electrocatalytic HER in neutral 1.0 M KCl aqueous solution, through the reversible redox shuttling among {Fe(NO) 2 } 9 , {Fe(NO) 2 } 10 , and reduced‐state [{Fe(NO) 2 } 10 ] electronic states . Alternatively, {Fe(NO) 2 } 10 DNIC [(PMDTA)Fe(NO) 2 ] was employed as a precursor to derive the electrodeposited solid‐state HER catalysts . It is demonstrated that the components of the electrodeposited catalyst are the mixture of the metallic iron and iron oxides .…”