Surface Engineering of Metal Oxide Photoelectrodes for Improved Band Alignment in Solar Water Splitting Cells

Abstract:

Several earth-abundant transition-metal oxides (e.g. Fe₂O₃, CoO, and Cu₂O) possessing suitable band gaps for solar water splitting exist, but energy level alignment is often sub-optimal, i.e. the conduction and valence bands do not straddle the water oxidation and reduction potentials. Here, using a nanocrystalline-TiO₂-based photoelectrochemical cell as a model system, we investigate the effect of tuning the semiconductor energy levels by adding Li⁺ ions to the electrolyte. The effect of LiClO₄ addition on band edges, interfacial recombination resistance, electron diffusion length, and charge-separation efficiency were quantified by impedance spectroscopy and analysis of incident photon-to-current efficiency spectra. We find that the TiO₂ band edges are shifted toward positive potentials by the addition of Li⁺, and that this increases the apparent electron diffusion length without affecting the charge-separation efficiency, most likely due to a change in the driving force for O₂ reduction. These results should prove useful in the modeling and optimization of solar water splitting cells employing metal oxide photoelectrodes.

• Periodical: Materials Science Forum (Volume 879)
• Pages: 832-837
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.879.832
• Online since: November 2016
• Authors: Soong Leong Sim, Ye Ru Liu, Ying Woan Soon, James Robert Jennings*
• Keywords: Lithium-Ion Modification, Photoelectrochemistry, Solar Water Splitting, Surface Engineering, TiO₂

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