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Bismuth vanadate (BiVO 4 ), a material known for its high visible light activity and good stability, is a promising candidate as a photoanode for overall water splitting 1. Its performance is limited by its relatively short charge carrier diffusion length, which has recently been estimated to be ~15 nm 2. For these kinds of photo-absorbers, commercial flat transparent conducting oxide (TCO) substrates are unsuitable since the thickness needed to absorb a sufficient amount of light far exceeds the carrier diffusion length. With this in mind, deposition of very thin semiconductor film onto the internal structure of (micro)porous, conducting substrates can ensure sufficient light absorption 3, whilst ensuring the individual film thickness is uniformly lower than the carrier diffusion length. Nanostructured TCO substrates can be fabricated using a convenient template-free technique called glancing angle deposition (GLAD). The glancing angle deposition method can be used to synthesize different variations of highly oriented submicron-sized pillars, ranging from vertical and tilted columns to zig-zag and helical structures with the help of shadowing effects and substrate rotation 4. The optical and electrical properties of nanostructured TCO’s were found to depend on the type of material and the substrate temperature during deposition. We find that pillars made from tin-doped indium oxide show good conductivity (79 Ohm/sq) and are promising for the fabrication of nanostructured substrates for bismuth vanadate. A recently developed alternative approach is the use of transparent, porous, conducting substrates (TPCS) made from quartz felt, in which the quartz fibers are coated with F-doped SnO 2 5. We found that a BiVO 4 film thickness of 50 nm within these porous substrates is enough to absorb the same amount of light as a compact 400 nm bismuth vanadate film. We will discuss the deposition of BiVO 4 into the TPCS substrates and the photoelectrochemical performance of these porous photoanodes. 1 K. Sivula and R. van de Krol, Nat. Rev. Mater. 1, 15010 ( 2016 ) 2 M. Schleuning, M. Kölbach, F. F. Abdi, K. Schwarzburg, M. Stolterfoht, R. Eichberger, R. van de Krol, D. Friedrich, H. Hempel, PRX Energy 1, 023008 ( 2022 ) 3 U. Björksten, J. Moser and M. Grätzel, Chem. Mater. 6, 858 ( 1994 ) 4 M. M. Hawkeye, M. T. Taschuk and M. J. Brett, “Glancing Angle Deposition of Thin Films”, John Wiley & Sons, Ltd., Chichester, UK ( 2014 ). 5 M. Caretti, E. Mensi, R.-A. Kessler, L. Lazouni, B. Goldman, L. Carbone, S. Nussbaum, R. A. Wells, H. Johnson, E. Rideau, J.-h. Yum, K. Sivula, Adv. Mater. 35, 2208740 ( 2023 )
Jayaraman et al. (Fri,) studied this question.