Role of doped titanium species in the enhanced photoelectrochemical properties of iron oxide films: Comparison between water oxidation and iodide ion oxidation

• Enhanced efficiency of Ti-doped Fe2O3 photoelectrode for water oxidation
• Comparison between photoelectrochemical water oxidation and iodide oxidation
• The presence of heterogeneity only for the kinetics of water oxidation
• Doped Ti4 + species as photoactive site for four-electron transfer water oxidation
• Accumulation of long-lived photoholes by suppression of surface recombination

The photoelectrochemical properties of titanium-doped iron(III) oxide (α-Fe2O3, hematite) nanoparticulate thin films are investigated using two photoelectrode reactions, the oxidation of water and iodide ions (I−) to elucidate the role of doped Ti4+ species in the enhanced photocurrent. Increase in the calcination temperature of titanium-doped Fe2O3 thin films from 450 °C to 550 °C provides significant enhancement in their efficiency for water oxidation to evolve O2, which is four-electron transfer slow reaction. In contrast, such a calcination effect is not remarkable for oxidation of I− to I3−, which is two-electron transfer fast reaction. The electrochemical impedance spectroscopy (EIS) study indicates that the surface reaction rates feature heterogeneity only for water oxidation. This heterogeneity in EIS responses decreased with increasing calcination temperature. This shows that calcination creates photoactive surface sites with doped Ti4+ species especially for kinetically limited water oxidation. Long-lived photoholes might be effectively captured in the vicinity of these sites to suppress surface recombination and induce multi-electron transfer water oxidation.

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