Jump to main content
Jump to site search

Issue 48, 2017
Previous Article Next Article

Reaction mechanism of hydrogen evolution catalysed by Co and Fe complexes containing a tetra-dentate phosphine ligand – a DFT study

Author affiliations

Abstract

The reaction mechanism of the electro-catalytic proton reduction in neutral phosphate buffer enabled by mononuclear cobalt and iron complexes containing a tetra-dentate phosphine ligand (MP4N2, M = Fe, Co) has been elucidated by density functional calculations. The phosphate from the buffer was found to play a crucial role by coordinating to the metal and delivering a proton to the metal hydride in the H–H bond formation. For the more efficient cobalt catalyst, the starting species is a CoII complex with a hydrogen phosphate and a water molecule ligated at the two vacant coordination sites. Two sequential proton-coupled electron transfer reductions lead to the formation of a CoII–H intermediate with a dihydrogen phosphate ligand, and the reduction potentials for these two steps were calculated to be −0.58 V and −0.72 V, respectively. Subsequently, the H–H bond formation takes place via coupling of the CoII–H and the proton from the dihydrogen phosphate ligand. The total barrier was calculated to be 18.2 kcal mol−1 with an applied potential of −0.5 V, which can further decrease to only 11.2 kcal mol−1 with an applied potential of −0.8 V. When the phosphate is displaced by a water molecule, the total barrier for the dihydrogen formation increases by 7.3 kcal mol−1. For the iron catalyst, the overall mechanism is essentially the same; however, the first reduction (FeII/FeI, potential of −1.13 V) is likely the rate-limiting step. The calculated results are in good agreement with the experimental data, which showed an onset potential of −0.50 V for the cobalt complex and −1.03 V for the iron complex.

Graphical abstract: Reaction mechanism of hydrogen evolution catalysed by Co and Fe complexes containing a tetra-dentate phosphine ligand – a DFT study

Back to tab navigation

Supplementary files

Publication details

The article was received on 12 Sep 2017, accepted on 20 Nov 2017 and first published on 21 Nov 2017


Article type: Paper
DOI: 10.1039/C7CP06222B
Citation: Phys. Chem. Chem. Phys., 2017,19, 32589-32596
  •   Request permissions

    Reaction mechanism of hydrogen evolution catalysed by Co and Fe complexes containing a tetra-dentate phosphine ligand – a DFT study

    Y. Zhang and R. Liao, Phys. Chem. Chem. Phys., 2017, 19, 32589
    DOI: 10.1039/C7CP06222B

Search articles by author

Spotlight

Advertisements