Photochromic materials have been extensively studied because they are quite attractive and promising for many applications. Tungsten oxide (WO₃), a typical photochromic material, has attracted considerable attention. So far, many advances have been achieved in different subfields of WO₃ photochromism, mainly focused on the enhancement of WO₃ photochromic properties, which depends not only on the chemical features but also on the microstructures, interface and hybrid components. This review aims to summarize recent progress in different advanced strategies to improve WO₃ photochromic properties, such as a fast photoresponse (within 1 min), strong and stable photochromism, visible-light coloration and reversible photochromism. However, it is still challenging to achieve these properties for large-scale commercial applications. In addition, many previous studies have been limited to lab research purposes, although some photochromic WO₃-based devices have been fabricated. To address the above-mentioned issues clearly, this review will provide a discussion of the following aspects. First, the fundamental photochromism of WO₃ is described. Secondly, various advances towards improving its photochromic properties will be summarized. Thirdly, the optical applications of WO₃-based photochromic materials will be reviewed and discussed. And finally, a perspective on the development trends in WO₃-based photochromic materials and devices is proposed.

This study demonstrates the tailorable self-weaving of bimetallic nickel–cobalt (Ni–Co) hydrogen phosphate nanotubes into one-dimensional (1D) microspindles or two-dimensional (2D) sheet-like structures by utilizing monodispersed Ni–Co glycerate spheres as sacrificial templates. The conversion process is achieved through a two-step solvothermal method in the presence of phosphoric acid (H₃PO₄) as a phosphorus source and promoter of the self-weaving process. The formation of such nanotube-assembled architectures is promoted by the “peeling-self-weaving” mechanism, in which the bimetallic Ni–Co hydrogen phosphate nanotubes initially grow on the surface of the Ni–Co glycerate spheres due to the reactions between Ni and Co metals bonded to the glycerate anions with hydrogen phosphate anions present in the solution. This is followed by the peeling of the overgrown nanotubes from the etched glycerate spheres and their self-weaving into 1D or 2D architectures depending on the Ni/Co molar ratio. The electrocatalytic test results reveal the superior activity of the Ni-rich Ni–Co hydrogen phosphate electrode for oxygen evolution reaction (OER) compared to its Co-rich and equimolar counterparts, leading to smaller overpotential of 320 mV and lower Tafel slope of 84 mV dec⁻¹. Post-OER analysis of this sample reveals that the high OER activity is derived from the formation of active Ni–Co oxyhydroxide phase on its surface.

Layered double hydroxides (LDHs) containing first‐row transition metals such as Fe, Co, and Ni have attracted significant interest for electrocatalysis owing to their abundance and excellent performance for the oxygen evolution reaction (OER) in alkaline media. Herein, the assembly of holey iron‐doped nickel‐cobalt layered double hydroxide (NiCo‐LDH) nanosheets (‘holey nanosheets’) is demonstrated by employing uniform Ni–Co glycerate spheres as self‐templates. Iron doping was found to increase the rate of hydrolysis of Ni–Co glycerate spheres and induce the formation of a holey interconnected sheet‐like structure with small pores (1–10 nm) and a high specific surface area (279 m² g⁻¹). The optimum Fe‐doped NiCo‐LDH OER catalyst showed a low overpotential of 285 mV at a current density of 10 mA cm⁻² and a low Tafel slope of 62 mV dec⁻¹. The enhanced OER activity was attributed to (i) the high specific surface area of the holey nanosheets, which increases the number of active sites, and (ii) the improved kinetics and enhanced ion transport arising from the iron doping and synergistic effects.

This review summarizes the recent progress of WO_3−x for switchable smart devices, focusing on the synthesis, film fabrication, and strategies to improve EC properties, followed by challenges and future development in multifunctional devices.