3D Nanostructured WO₃ Photoanode for Water Splitting

Photoelectrochemical (PEC) water splitting has been studied extensively as an environmentally friendly technology for hydrogen production using solar energy. After the PEC water splitting using TiO₂[1] was proven, various studies have been conducted using semiconductor metal oxides such as ZnO [2], Fe₂O₃[3], WO₃ [4], and BiVO₄ [5], as they are earth-abundant and considered best candidates for photoelectrodes. Among them, WO₃ is considered a promising material for photoanodes which has advantages of high electron mobility, good hole diffusion length, and chemical stability for water splitting. Various nanostructures of WO₃ such as hydrothermal growth [6], E-beam evaporation [7], sputtering [8], and electrodeposition [9] have been investigated for enhancing the PEC performance. In this study, facile fabrication of 2D nanostructures of WO₃ was achieved by reverse nanoimprint lithography, and the 3D nanostructures of WO₃ film was also confirmed. For the comparison of the photoanodes having 3D nanostructured WO₃ film with the planar thin WO₃ film, we investigated light absorbance by UV-vis absorbance, photocurrent densities by LSV (Linear Sweep Voltammetry), and impedances by EIS (Electrochemical Impedance Spectroscopy) of each photoanodes. The 3D nanostructured WO₃ photoanodes has smaller contact resistance and higher light absorbance properties, thus achieved 2 times higher photocurrent density in 3D structured photoanodes than that of planar thin film.<br/>References<br/>1. Finegold, L. & Cude, J. L. Biological sciences: One and two-dimensional structure of alpha-helix and beta-sheet forms of poly(L-Alanine) shown by specific heat measurements at low temperatures (1.5-20 K). <i>Nature</i> <b>238</b>, 38–40 (1972).<br/>2. Hu, Y. <i>et al.</i> Large-scale patterned ZnO nanorod arrays for efficient photoelectrochemical water splitting. <i>Appl. Surf. Sci.</i> <b>339</b>, 122–127 (2015).<br/>3. Commandeur, D., McGuckin, J. & Chen, Q. Hematite coated, conductive y doped ZnO nanorods for high efficiency solar water splitting. <i>Nanotechnology</i> <b>31</b>, (2020).<br/>4. Soltani, T., Tayyebi, A. & Lee, B. K. Sonochemical-driven ultrafast facile synthesis of WO3 nanoplates with controllable morphology and oxygen vacancies for efficient photoelectrochemical water splitting. <i>Ultrason. Sonochem.</i> <b>50</b>, 230–238 (2019).<br/>5. Chen, B. <i>et al.</i> An antenna/spacer/reflector based Au/BiVO4/WO3/Au nanopatterned photoanode for plasmon-enhanced photoelectrochemical water splitting. <i>Appl. Catal. B Environ.</i> <b>237</b>, 763–771 (2018).<br/>6. Fan, X. <i>et al.</i> Layered double hydroxide modified WO3 nanorod arrays for enhanced photoelectrochemical water splitting. <i>Appl. Catal. A Gen.</i> <b>528</b>, 52–58 (2016).<br/>7. Kim, J. H., Kim, D. H., Yoon, J. W., Dai, Z. & Lee, J. H. Rational Design of Branched WO3 Nanorods Decorated with BiVO4 Nanoparticles by All-Solution Processing for Efficient Photoelectrochemical Water Splitting. <i>ACS Appl. Energy Mater.</i> <b>2</b>, 4535–4543 (2019).<br/>8. Su, J., Guo, L., Bao, N. & Grimes, C. A. Nanostructured WO3/BiVO4 heterojunction films for efficient photoelectrochemical water splitting. <i>Nano Lett.</i> <b>11</b>, 1928–1933 (2011).<br/>9. Yun, G., Balamurugan, M., Kim, H. S., Ahn, K. S. & Kang, S. H. Role of WO3 Layers Electrodeposited on SnO2 Inverse Opal Skeletons in Photoelectrochemical Water Splitting. <i>J. Phys. Chem. C</i> <b>120</b>, 5906–5915 (2016).