Electrochemistry
Hard vs soft Ni–Fe catalysts for making hydrogen
Open access · cc by · source: Europe PMC
A matrix of S-bridged Ni–Fe nitrosyl complexes shows how NO ‘softness’ trades catalytic potential against acid strength and TOF in HER.
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Hard vs soft Ni–Fe catalysts for making hydrogen
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Nitrosylated [Ni–Fe]+ and related complex have faradaic efficiencies 68 ± 2% and 58 ± 1%.
The nitrosylated compounds [Ni–Fe] + and were found to have low turnover numbers and faradaic efficiencies, 68 ± 2% and 58 ± 1%, respectively, for H 2 production.
[Ni–Fe′]+ gave a faradaic efficiency of ca. 96%.
In contrast the [Ni–Fe′] + gave a faradeic efficiency of ca. 96%.
Key findings
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.
Methodology
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.
Limitations
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.
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