LaTiO₂N particle-based photoelectrodes are interesting for water-splitting applications as they exhibit high performance¹ and show good fabrication reproducibility by simple dipping procedures². Such photoelectrodes can potentially overcome the efficiency-cost trade-off of solar hydrogen³. The impact of morphology and material combinations on multi-physical phenomena must be understood to provide design guidelines for these photoelectrodes. Numerical modeling can identify the main material challenges that cannot be capture by experimental measurements but requires to know the material properties of LaTiO₂N. These properties are very sparse in the literature and therefore it is challenging to obtain them. We used a combined experimental-numerical approach to extract optical and electronic material properties of LaTiO₂N, not available in the literature, and to provide design guidelines for high-preforming particle-based photoelectrodes. 

Experimental techniques (UV-Vis spectrophotometry and electrochemical impedance spectroscopy) were used to determine complex refractive index and flatband potential of LaTiO₂N. These experiments were combined with density functional theory calculation to determine density of states of conduction and valence bands, permittivity and mobilities. A 2D numerical model was developed, incorporating an electromagnetic wave propagation model, charge transport and conservation in the semiconducting particles, and semiconductor-electrolyte charge transfer⁴. This model was compared to the experimentally measured current-voltage behavior, and used to determine effective lifetimes and water oxidation reaction kinetic by fitting. Two types of electrodes were studied: bare LaTiO₂N-particle photoelectrodes with TiO₂ inter-particle necking, and modified electrodes with additionally NiO_x/CoO_x/Co(OH)₂ catalysts and Ta₂O₅ passivation layer³.

A hole mobility of bulk LaTiO₂N of 46cm²V^-1s^-1 was calculated, and compared well to nitride semiconductors such as GaN⁴. Experimental results showed higher photocurrent under back illumination compared to front illumination. The numerical model confirmed this behavior. The model was then used to explore the impact of co-catalyst deposition on the performance of LaTiO₂N photoelectrode.

The combined multi-scale experimental-numerical approach allowed for the determination of LaTiO₂N bulk material properties, identification of material challenges, and shows to be a useful design tool for particle-based photoelectrodes.

References

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Y. K. Gaudy and S. Haussener, J. Mater. Chem. A, 2016, , 3100–3114.