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
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.
Flashcards
Research intelligence for this paper
See its role on concept claims, tensions it is part of, placement history, and related discoveries.
Quiz yourself
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.
More on Electrochemistry