This review focuses on tungsten oxide (WO₃) and its nanocomposites as photoactive nanomaterials for photoelectrochemical cell (PEC) applications since it possesses exceptional properties such as photostability, high electron mobility (~12 cm² V⁻¹ s⁻¹) and a long hole-diffusion length (~150 nm). Although WO₃ has demonstrated oxygen-evolution capability in PEC, further increase of its PEC efficiency is limited by high recombination rate of photogenerated electron/hole carriers and slow charge transfer at the liquid–solid interface. To further increase the PEC efficiency of the WO₃ photocatalyst, designing WO₃ nanocomposites via surface–interface engineering and doping would be a great strategy to enhance the PEC performance via improving charge separation. This review starts with the basic principle of water-splitting and physical chemistry properties of WO₃, that extends to various strategies to produce binary/ternary nanocomposites for PEC, particulate photocatalysts, Z-schemes and tandem-cell applications. The effect of PEC crystalline structure and nanomorphologies on efficiency are included. For both binary and ternary WO₃ nanocomposite systems, the PEC performance under different conditions—including synthesis approaches, various electrolytes, morphologies and applied bias—are summarized. At the end of the review, a conclusion and outlook section concluded the WO₃ photocatalyst-based system with an overview of WO₃ and their nanocomposites for photocatalytic applications and provided the readers with potential research directions.

Recently, heterostructured photocatalysts have gained significant attention in the field of photocatalysis due to their superior properties compared to single photocatalysts. One of the key advantages of heterostructured photocatalysts is their ability to enhance charge separation and broaden the absorption spectrum, thereby improving photocatalytic efficiency. Zinc oxide is a widely used n-type semiconductor with a proper photoelectrochemical activity. In this study, zinc oxide nanorod arrays were synthesized, and then the surfaces of ZnO nanorods were modified with the p-type semiconductor Co₃O₄ to create a p–n junction heterostructure. A significant increase in the photocurrent for the ZnO/Co₃O₄ composite, of 4.3 times, was found compared to pure ZnO. The dependence of the photocurrent on the morphology of the ZnO/Co₃O₄ composite allows for optimization of the morphology of the ZnO nanorod array to achieve improved photoelectrochemical performance. The results showed that the ZnO/Co₃O₄ heterostructure exhibited a photocurrent density of 3.46 mA/cm², while bare ZnO demonstrated a photocurrent density of 0.8 mA/cm² at 1.23 V. The results of this study provide a better understanding of the mechanism of charge separation and transfer in the heterostructural ZnO/Co₃O₄ photocatalytic system. Furthermore, the results will be useful for the design and optimization of photocatalytic systems for water splitting and other applications.

A simple chemical bath deposition method has been developed to study the formation of nanoplate morphology of tungsten oxide. The obtained materials were characterized by field emission scanning electron microscopy, transmission electron microscopy, x-ray diffractometry, Raman spectroscopy, and UV–vis diffuse reflectance spectroscopy. The photocatalytic activity of the resulting samples was further evaluated by degradation of Rhodamine B under light irradiation. It was found that both synthesis parameters and morphology affected the tungsten oxide photocatalytic activity. Tungsten oxide nanoplates obtained by a simple chemical bath deposition method have demonstrated a higher specific area and higher photocatalytic activity compared to the nanopowders obtained by the hydrothermal method.

In this work, hierarchical WO3 microspheres were synthesized using chemical bath deposition. The morphology of the synthesized sample was studied using scanning electron microscopy (SEM). The hierarchical WO3 microspheres formed from spontaneously self-assembled nanosheets have a high specific surface area. Structural characterizations of sample were performed using X-ray diffraction (XRD) and Raman spectroscopy. Analysis of XRD spectra showed that synthesized particles have a monoclinic modification. The optical properties of the sample were studied using UV-Vis diffuse reflectance absorption spectra. The value of the energy gap calculated from the absorption spectra is 2.2 eV, which indicates high light absorption ability. A photocurrent study was done to investigate the photocatalytic activity. The photoelectrode was prepared using hierarchical WO3 microspheres and polymer deposited on fluorine doped tin oxide (FTO) glass via spin coating technique. A remarkable photocurrent density of 18 A/cm2 at 0.5 V was achieved. The elongated structures improved light absorption ability and photocatalytic activity.