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

Abstract

Cyclic voltammograms for titanium-doped a-Fe20, 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 Vfb. 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 2RTIF negative of Vfb, >2RT/F for Vrb < V < 0.3 V and < 2RTIF 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 + H 2 0 + e--+ H02(ad) -k OHbeing rate-determining with titanium donors mediating change transfer.

Conductive-Matrix-Mediated Alkaline Fe(III/VI) Charge Transfer: Three-Electron Storage, Reversible Super-Iron Thin Film Cathodes

“…Therefore, it is unlikely that reduction peaks I and III arise from the oxygen produced at higher potentials. In alternate alkaline systems consisting of passive iron electrodes containing Fe(II) sites, Fe(II) are the active sites for oxygen reduction, which commences at approximately −0.20 V vs Ag/AgCl. − Nicol et al observed that alkalinity increase resulted in the strong inhibition of oxygen reduction in the presence of Fe(VI) . When the scan was reversed just after the second reduction wave (peak II), the broad oxidation wave peak IV, centered at ∼0.35 V, was visible and remained evident upon repeated cycling and corresponds to the broad oxidation wave centered at 0.02 V. Cyclic voltammetry was also studied in the anodic direction, followed by a reverse sweep starting at various potentials.…”

Tailoring (Bio)chemical Activity of Semiconducting Nanoparticles: Critical Role of Deposition and Aggregation

“…The situation is essentially different in the presence of dissolved O 2 (Figure 7b). Oxygen will preferably be adsorbed on the most negatively charged facets or surface sites of the hematite layer and can further be reduced 52 because the necessary conditions for this reaction are satisfied. In fact, the potential of half-reaction (C) is below E F , while the electron level distribution of dissolved O 2 in the solution overlaps with the conduction band of hematite.…”

The Effect of Doping with Ti(IV) and Sn(IV) on Oxygen Reduction at Hematite Electrodes

“…[5][6][7][8][9][10] The rate of oxygen reduction on hematite doped with Ti͑IV͒ has been shown to increase with dopant concentration. 11 There are two hypotheses on how the M͑IV͒ ions increase the number of Fe͑II͒ sites. In the first, the M͑IV͒ ion is believed to substitute for Fe͑III͒ in the hematite lattice.…”

“…22,23 Second, the reduction of oxygen takes place in a voltage range where deep donor levels, which appear to be associated with dopants, are filled with electrons and may mediate charge transfer. 11,25,26 Finally, the reduction of oxygen is an important reaction in natural systems and is the most important cathodic reaction in the corrosion of iron. 3,4,22,24 In the experiments described here, we examined hematite doped with Sn͑IV͒ and Ti͑IV͒ at two different doping levels.…”