Oxygen reduction on titanium-doped α-Fe₂O₃ electrodes in aqueous alkali

Abstract

Cyclic voltammograms for titanium-doped α-Fe₂O₃ electrodes in 0.1 M NaOH exhibited small reduction and re-oxidation peaks negative of -0.4 V (s.h.e.) and for electrodes initially held negative of this potential, the onset of the photocurrent occurred at potentials well positive of V_fb. These results are interpreted as due to the penetration of hydrogen into the lattice. The activity for oxygen reduction increased with dopant concentration and plots of steady-state log i against V exhibited slopes of absolute value approximately 2RT/F negative of V_fb, >2RT/F for V_fb < V < 0.3 V and < 2RT/F at more positive than 0.3 V. No oxygen reduction current was observed for oxygen partial pressures less than c. 0.45 atm. This effect was independent of electrode potential, dopant concentration and almost independent of pH. The results are interpreted in terms of the step

O₂ + H₂0 + e- → HO₂(ad)+ OH^- being rate-determining with titanium donors mediating change transfer.