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Anisotropic Electron Transport Limits Performance of Bi2WO6 Photoanodes
journal contribution
posted on 2020-08-20, 18:08 authored by Benjamin Moss, Haonan Le, Sacha Corby, Kazuki Morita, Shababa Selim, Carlos Sotelo-Vazquez, Yunuo Chen, Alexander Borthwick, Anna Wilson, Chris Blackman, James R. Durrant, Aron Walsh, Andreas KafizasBi2WO6 is one of the simplest members of
the versatile Aurivillius oxide family of materials. As an intriguing
model system for Aurivillius oxides, BiVO4 exhibits low
water oxidation onset potentials (∼0.5–0.6 VRHE) for driven solar water oxidation. Despite this, Bi2WO6 also produces low photocurrents in comparison
to other metal oxides. Due to a lack of in situ studies, the reasons
for such poor performance are not understood. In this study, Bi2WO6 photoanodes are synthesized by aerosol-assisted
chemical vapor deposition. The charge carrier dynamics of Bi2WO6 are studied in situ under water oxidation conditions,
and the rate of both bulk recombination and water oxidation is found
to be comparable to other metal oxide photoanodes. However, the rate
of electron extraction is at least 10 times slower than the slowest
kinetics previously reported in an oxide photoanode. First-principles
analysis indicates that the slow electron extraction kinetics are
linked to a strong anisotropy in the conduction band. Preferred or
epitaxial growth along the conductive axes is a strategy to overcome
slow electron transport and low photocurrent densities in layered
materials such as Bi2WO6.