Tungsten oxide polymorphs and their multifunctional applications

Owing to the natural abundance, easy availability, high stability, non-stoichiometry, and chemical diversity, considerable interest has been devoted to tungsten oxide (WO3-x) nanomaterials, and many advances have been achieved ranging from traditional catalysts and electronics to emerging artificial intelligence. This review focuses on recent progress of WO3-x polymorphs and their multifunctional applications. The structural diversity and crystal phase transitions of WO3-x and recent advances on the general synthesis of various WO3-x nanostructures are first summarized, since the crystal structure and morphology adjustment obviously affect the physiochemical merits of WO3-x materials. Then, their applications and related mechanisms in different fields are demonstrated, such as gas sensing, chromogenic (electro-, photo-, gaso-, and thermochromic), photocatalytic (pollutant degradation and water splitting), and emerging applications (biomedical, antibiotic, and artificial intelligence). With the advances highlighted here and the ongoing research efforts, the continuous breakthrough in functionalized WO3-x nanostructure and their attractive applications is foreseeable in the future.