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.

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What faradaic efficiency was measured for O2?

>93% during controlled-potential electrolysis.

What overpotentials are reported for water oxidation?

300 mV at the DPV foot and 440 mV at the CV half-peak.

What does the −0.029 V/pH slope imply?

An unusual 2e−/1H+ redox step in the cycle.

Where is the first oxidation centered?

On the ligand, forming a Cu(II) porphyrin cation radical.

What Cu-based couple appears at 0.06 V?

A diffusion-controlled Cu(II)/Cu(I) couple.

In which buffer was the pH 7 catalytic wave recorded?

0.10 M pH 7.0 phosphate buffer on FTO.

Is the active catalyst molecular or a Cu oxide?

Molecular: oxides would be unstable in acid, yet catalysis persists.

What 2e product forms in acid?

H2O2, with 45% faradaic efficiency.

Can the complex catalyze 2e water oxidation to H2O2?

Yes, in acidic solutions.

What happens after the first 1e oxidation?

The oxidized porphyrin can bind an axial aqua ligand and start water oxidation.

How was H2O2 detected during electrolysis?

By adding sodium iodide after electrolysis below 1.40 V at pH 3.