Pyrazine reservoirs that lower cobalt HER overpotential
Moving a redox-active pyrazine on a cobalt polypyridine ligand cuts hydrogen-evolution overpotential by about 200 mV versus pyridine analogues in water.
Source
Bioinspired design of redox-active ligands for multielectron catalysis: effects of positioning pyrazine reservoirs on cobalt for electro- and photocatalytic generation of hydrogen from water
Study at a glance
- Design
- Other — Cobalt PY4/PY3PZ complexes for aqueous electrocatalytic and photoredox H2 evolution with DFT
- N
- Molecular catalysis study — no sample N
- Population
- Cobalt redox-active ligand complexes in aqueous catalytic assays
- Outcome
- Overpotential and H2 evolution as a function of pendant pyrazine redox reservoirs
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Inspect source passages
Pyrazine reservoirs that lower cobalt HER overpotential
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
Pyrazine gas-phase EA is ca. 0.6 eV more positive than pyridine.
Because the gas phase electron affinity of pyrazine is ca. 0.6 eV more positive than pyridine, , it can be reduced at modest potentials and could serve as a redox-active component to facilitate the two-electron reduction of protons to hydrogen.
A ca. 200 mV improvement in overpotential versus pyridine analogs is reported.
Catalyst isomers display markedly different reactivities depending on the relative position of the non-innocent pyrazine moiety, with a ca. 200 mV improvement in overpotential compared to pyridine analogs that lack pendant redox reservoirs.
What they did
Authors synthesized cobalt complexes of PY4/PY3PZ ligands, compared Zn(II) redox-inactive analogues, measured aqueous electrocatalysis and photoredox H2 at pH 7 with GC, and used DFT to parse metal- vs ligand-centered redox.
What they found
Pyrazine’s gas-phase EA is ~0.6 eV more positive than pyridine. Isomer position of the non-innocent pyrazine changes reactivity, with ~200 mV better overpotential than pyridine ligands lacking pendant redox reservoirs. Zn controls help separate ligand vs metal redox.
The limits
What it doesn't show
Device-level solar-to-hydrogen efficiency and long-term seawater durability beyond the reported buffered/seawater context of prior related catalysts are not the focus of this ligand-position study.
Key terms
- Redox-active ligand
- A ligand (here pyrazine) that stores electrons to enable multielectron catalysis at milder potential.
- Overpotential
- Extra driving force beyond thermodynamics needed to evolve H2 at a useful rate.
- Pyrazine vs pyridine
- Isostructural N-heterocycles; pyrazine is easier to reduce (~0.6 eV).
- Zn(II) control
- Redox-inert analogue that reveals ligand-centered electrochemistry.
- Pendant redox reservoir
- A ligand site that accumulates reducing equivalents near the metal.
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Quiz yourself
Overpotential improvement vs pyridine analogues:
Common questions
How large is the overpotential gain?
About 200 mV vs pyridine analogues.
Does pyrazine position matter?
Yes: isomers differ markedly.
Why Zn complexes?
To disentangle metal- vs ligand-centered redox.
Medium?
Water at neutral pH, including photocatalytic H2.
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