Hard vs soft Ni–Fe catalysts for making hydrogen
A matrix of S-bridged Ni–Fe nitrosyl complexes shows how NO ‘softness’ trades catalytic potential against acid strength and TOF in HER.
Source
A matrix of heterobimetallic complexes for interrogation of hydrogen evolution reaction electrocatalysts
What they did
Authors prepared NiN2S2·Fe(NO)n bimetallics, solved oxidized/reduced crystal structures, measured CVs and bulk electrolysis with GC headspace H2, and computed protonation/hydride paths.
What they found
All cores are butterfly M(μ-SR)2Fe. Nitrosylated [Ni–Fe]+ and a related complex give faradaic efficiencies of 68±2% and 58±1% (vs ~96% for [Ni–Fe′]+). TOF from CV is 39.7 s−1 vs 26.7 s−1. Soft NO-rich acceptors catalyze at milder potential but need stronger acid and give lower TOF. Computations split heterolytic H−/H+ coupling vs reductive elimination.
The limits
What it doesn't show
These are moderately efficient molecular HER catalysts in organic acid/electrolyte, not device-level water electrolyzers; Tafel behavior in aqueous pH 7 is not established.
Key terms
- Hydrogen evolution reaction (HER)
- Electrocatalytic 2H+ + 2e− → H2.
- Metallodithiolate ligand
- MN2S2 unit that binds a second metal through bridging thiolates.
- Non-innocent NO
- Nitrosyl that stores electrons and shifts redox potential of Fe(NO)2 units.
- Faradaic efficiency
- Fraction of passed charge that produces H2.
- Hemi-labile thiolate
- A bridging S that can open a site for proton or hydride binding.
Flashcards
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Quiz yourself
Shared structural motif of the matrix:
Common questions
What core geometry is conserved?
Butterfly M(μ-SR)2Fe.
What does adding NO ligands buy you?
Milder catalytic potential at the cost of stronger acid and lower TOF.
Which complex is ~96% faradaic?
[Ni–Fe′]+.
Two computed H2-release modes?
Heterolytic hydride–proton coupling vs reductive elimination from two hydrides.
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