Substituent effects in carbon-nanotube-supported diiron monophosphine complexes for hydrogen evolution reaction

In order to explore substituent effects of PR3-phosphine ligands of diiron dithiolato complexes on the catalytic performances of [FeFe]-hydrogenase mimics for hydrogen evolution reaction (HER) in an aqueous medium, three new diiron monophosphine complexes [{(mu-SCH2)2N(C6H4CH2CH2OH)}Fe2(CO)5{P(C6H4R-4)3}] (labeled as FePR; R = F, H, and Me) were prepared and can be further linked covalently into carbon nanotube (CNT) to construct the target CNT-supported hybrids denoting as CNT-f-FePR. The molecular structures of diiron com-plexes FePR are well characterized through element analysis, fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR) and X-ray crystallography, whereas the formations of target hybrids CNT-f- FePR have been confirmed by using X-ray photoelectron spectroscopy (XPS), Raman and FT-IR. Notably, the electrochemical HER performances of target hybrids CNT-f-FePR (R = F, H, and Me) are studied and compared in 0.1 M H2SO4 aqueous solution by means of linear sweep voltammetry (LSV), cyclic voltammetry (CV), elec-trochemical impedance spectroscopy (EIS), and density functional theory (DFT) calculation. Among these hy-brids, the CNT-f-FePF hybrid exhibits a more efficient HER activity in an aqueous media based on their electrochemical observations that the CNT-f-FePF hybrid with F-substituted phosphine has lower applied overpotential, smaller Tafel slope, larger electrochemical active surface area, smaller charge transfer resistance, and lower hydrogen chemisorption free energy relative to its analogues CNT-f-FePH and CNT-f-FePMe with H-or Me-substituted phosphines.

Automated summary

In this study, three new diiron monophosphine complexes were synthesized and covalently linked to carbon nanotubes to investigate their catalytic performances for the hydrogen evolution reaction in an aqueous medium. The CNT-f-FePF hybrid with a F-substituted phosphine showed higher activity for hydrogen evolution in water.