Water Oxidation and Oxygen Monitoring by Cobalt-Modified Fluorine-Doped Tin Oxide Electrodes

Electrocatalytic water oxidation occurs at fluoride-doped tin oxide (FTO) electrodes that have been surface-modified by addition of Co(II). On the basis of X-ray photoelectron spectroscopy and transmission electron microscopy measurements, the active surface site appears to be a single site or small-molecule assembly bound as Co(II), with no evidence for cobalt oxide film or cluster formation. On the basis of cyclic voltammetry measurements, surface-bound Co(II) undergoes a pH-dependent 1e–/1H+ oxidation to Co(III), which is followed by pH-dependent catalytic water oxidation. O2 reduction at FTO occurs at −0.33 V vs NHE, allowing for in situ detection of oxygen as it is formed by water oxidation on the surface. Controlled-potential electrolysis at 1.61 V vs NHE at pH 7.2 resulted in sustained water oxidation catalysis at a current density of 0.16 mA/cm2 with 29 000 turnovers per site over an electrolysis period of 2 h. The turnover frequency for oxygen production per Co site was 4 s–1 at an overpotential ...