Understanding the Structural Dynamics of Polarons in Transition Metal Oxide Semiconductors by Vibrational Spectroscopy and Charge-Carrier Mobilities
Final Report Abstract
The generation of solar fuels is a crucial area of research, leading to “green hydrogen” or “e-fuels” which can be used to store and transport energy in large quantities. Photocatalytic materials absorb sunlight and directly use the gained energy to catalyze a chemical reaction at the interface. Despite significant research efforts, no photocatalytic material has been found yet which efficiently and economically conducts water splitting or CO2 reduction. Usually transition metal oxides are employed as photocatalysts, a prime example which garnered interest lately is BiVO4 . A particular problem with these oxides is that they feature slow charge transport, inhibiting reaction kinetics. The reason is the formation of polarons in the crystal – the structure displaces in response to the presence of an excess charge causing it to be trapped. The microscopic structure of these polarons is usually determined by electronic structure theory. Remarkably, it was demonstrated that this is in particular difficult for BiVO4 , where the structure of the excess electron hole is ambiguous. More so, it is likely that the polaronic structure can not be determined by theoretical calculations alone. This research aimed to determine the polaron geometry of the excess electron hole through a combined theoretical and experimental approach. We used novel computational tools to calculate temperature-dependent vibrational spectra and charge mobilities for the potential polaron geometries and collaborated with experimentalists for corresponding measurements. Bu comparing experimental and computational data, we aim to definitively characterize the polaron geometry. Importantly, the vibrational spectrum of the polaron geometry is a unique fingerprint and thus provides a direct map between the macroscopic experiment and the microscopic structure, giving the opportunity to “see” the polaron in BiVO4 . Having established the polaron geometry, we aimed at understanding its dynamics in detail, thereby contributing to the problem of too slow charge transport in BiVO4 . Mind that the project is still ongoing and therefore only preliminary data is presented in this report.
Publications
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Revealing the Molecular Origin of Anisotropy around Chloride Ions in Bulk Water. The Journal of Physical Chemistry Letters, 15(11), 3037-3042.
Jindal, Aman; Schienbein, Philipp & Marx, Dominik
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Solvation Properties of Neutral Gold Species in Supercritical Water Studied By THz Spectroscopy. Angewandte Chemie International Edition, 63(28).
Noetzel, Jan; Schienbein, Philipp; Forbert, Harald & Marx, Dominik
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“Molecular dynamics simulation with finite electric fields using Perturbed Neural Network Potentials”.
J. Joll, P. Schienbein, K. M. Rosso & J. Blumberger
