doi.org/10.1002/asia.70317 Review www.chemasianj.org Tungsten Oxide-Based Thin Films Prepared by Physical Vapor Deposition Techniques for Photoelectrochemical Water Splitting: A Review Muhammed L. Fatty, [a] Budur A. Almabadi, [a] Abuzar Khan, [b] Badriah Sultan, [c] and Qasem A. Drmosh* [a, b] The global energy demand has raised concerns about environ- mental sustainability and economic stability. This has led to sig- nificant efforts to identify renewable and green energy sources. Hydrogen production through the water splitting reaction offers a promising pathway, since it yields hydrogen and oxygen as by- products. The photoelectrochemical technique has emerged as one of the effective methods for water splitting, offering vast potential for hydrogen production on a large scale. Among the various semiconductor photoelectrodes, tungsten oxide (WO 3 ) has attracted considerable attention due to its suitable band gap, good chemical stability, and strong absorption in the visible region. This review addresses the fabrication of WO 3 -based thin films prepared using physical vapor deposition (PVD) techniques, including thermal evaporation, sputtering, pulsed laser depo- sition (PLD), and electron-beam evaporation. Reported studies highlight that sputtered WO 3 films often achieve high pho- tocurrent densities and improved crystallinity, while PLD enables precise control over stoichiometry and nanostructure. Neverthe- less, key challenges persist, such as controlling stoichiometry and phase stability, charge-carrier recombination, limited light absorption due to the wide band gap, low conductivity, and structural defects. The review concludes strategies to overcome these limitations, such as conducting thermal and electron- beam evaporation, combining CVD and PVD techniques, and optimizing sputtering conditions. 1. Introduction The rapid population growth has led to a significant increase in energy demand. By mid-century, the global population is expected to reach nine billion, which may account for more than double the energy demand. [ 1 ] This growing demand highlights the urgent need to explore sustainable and long-term energy solutions. The energy consumed to support human activities such as transportation, industrial processes, information technol- ogy, and agricultural practices comes from various sources, with fossil fuels like coal, oil, and natural gas providing around 81% of the total demand. As future energy needs are projected, a key question emerges on how long the rising demand can be sustainably met. Fossil fuels have environmental consequences such as the release of greenhouse gases into the atmosphere, resulting in climate change. Furthermore, mining and drilling activities can disrupt and harm local ecosystems. These draw- [a] M. L. Fatty, B. A. Almabadi, Q. A. Drmosh Department of Materials Science and Engineering, King Fahd University of Petroleum and Minerals (KFUPM), Dhahran 31261, Saudi Arabia E-mail: drmosh@kfupm.edu.sa [b] A. Khan, Q. A. Drmosh Interdisciplinary Research Center for Hydrogen Technologies and Carbon Management, King Fahd University of Petroleum and Minerals (KFUPM), Dhahran 31261, Saudi Arabia [c] B. Sultan Department of Physics, College of Science, King Khalid University, P.O. Box 9004, Abha 61413, Saudi Arabia backs emphasize the necessity of shifting towards cleaner and more reliable alternatives. Advancements in technology and the adoption of renewables have not only led to declining costs but have also contributed to reductions in greenhouse gas emissions, although with varying progress across different regions of the world. [ 2 ] In this context, renewable energy sources have emerged as promising candidates to address both environmental and energy security concerns. Despite significant progress, substantial chal- lenges remain in developing energy technologies that are not only sustainable and eco-friendly but also affordable and widely accessible. Solar, wind, geothermal, hydro, marine energy, and H 2 technology sources hold great potential for building sustainable energy infrastructures. Among these alternatives, H 2 stands out due to its versatility and potential to complement intermittent renewable sources. Unlike solar and wind, H 2 can be efficiently stored and transported. However, the predominant method for H 2 production is steam methane reforming, which relies on fossil fuels and generates substantial carbon emissions, limiting its environmental benefits. A transition to green H 2 production is imperative to harness the full potential of H 2 as a clean energy source. Water electrolysis is one of the promising approaches in achieving this transition, which is a method that eliminates direct carbon emissions and enhances the sustainability of H 2 as a vital element in the global energy transition. [ 3 ] and uses an electric current to split water into its constituent H 2 and O 2 molecules, [ 1,3–7 ] Importantly, electrolysis itself produces no emissions or byproducts other than H 2 and O 2 , underscoring its Chem Asian J. 2025, 0, e70317 (1 of 17) © 2025 Wiley-VCH GmbH