A copper porphyrin oxidizes water at low overpotential
A molecular Cu(II) porphyrin evolves O2 at 300–440 mV overpotential in neutral phosphate buffer with >93% faradaic efficiency.
Source
Low overpotential water oxidation at neutral pH catalyzed by a copper(ii) porphyrin
Inspect source passages
A copper porphyrin oxidizes water at low 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.
Faradaic efficiency for O2 evolution is >93%.
The evolved O 2 during CPE was then determined, revealing a faradaic efficiency of >93% for O 2 evolution (Fig.
Overpotentials are 300 mV (DPV foot) and 440 mV (CV half-peak).
These give η = 300 mV (at the initial foot of DPV) and 440 mV (at the half-peak position of the CV wave) for catalytic water oxidation, respectively.
What they did
Authors ran CV, DPV, and controlled-potential electrolysis of a copper(II) porphyrin in phosphate buffers, quantified O2 and H2O2, and used spectroscopy to assign a ligand-centered cation radical as the first oxidation.
What they found
At pH 7 the catalyst shows a strong water-oxidation wave with η = 300 mV (DPV foot) and 440 mV (CV half-peak) and >93% FE for O2. Pourbaix slope −0.029 V/pH implies a 2e−/1H+ step. In acid it also makes H2O2 (45% FE). The first oxidation is the porphyrin radical, not Cu(III).
The limits
What it doesn't show
A device-level solar-to-fuel efficiency and long-term PEM electrolyzer durability are not reported; H2O2 selectivity in acid is only 45%.
Key terms
- Overpotential (η)
- Extra voltage beyond the thermodynamic water-oxidation potential needed to drive O2 evolution.
- Faradaic efficiency
- Fraction of charge that produces the intended product (here O2 or H2O2).
- Porphyrin cation radical
- Ligand-centered 1e oxidation of the Cu(II) porphyrin that starts catalysis.
- 2e−/1H+ step
- Unusual Pourbaix slope near −29 mV/pH indicating two electrons per proton.
- Molecular WOC
- A discrete molecular water-oxidation catalyst, here remaining intact versus Cu oxides.
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O2 faradaic efficiency is:
Common questions
What overpotentials are quoted?
300 mV at the DPV foot and 440 mV at the CV half-peak.
How efficient is O2 production?
>93% faradaic efficiency during CPE.
Is the first oxidation on copper?
No—it is a Cu(II) porphyrin cation radical.
What happens in acid?
2e oxidation to H2O2 with 45% FE.
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