Recent advances in {P 4Mo 6}-based polyoxometalates

The reduced phosphomolybdate {P₄Mo₆X₃₁}^n- (X = O or OH) ({P₄Mo₆}) is an important member of polyoxometalates (POMs) with fully reduced Mo atoms, multiple oxygen coordinate sites, excellent optical response and electrochemical properties which have attracted the extensive interests of researchers. In the past few decades, the development of {P₄Mo₆}-based POMs has been relatively slow compared with the classical polyoxometalates and most studies mainly focus on the synthesis of novel structures, and some property studies in fluorescent properties, photocatalytic degradation of organic dye and electrocatalytic reduction of hydrogen peroxide. Recently, {P₄Mo₆}-based POMs have received increasing interest due to their unique structure advantages and potential applications in photocatalysis, electrocatalysis, electrochemical sensors, and proton conduction. This review summarizes the development process of {P₄Mo₆}-based POMs in nearly ten years, mainly involving the structures, synthesis, and applications in diverse fields as well as nanocomposites with {P₄Mo₆}-based POMs as precursors and their applications. However, there are still some challenges such as improving the scalability of {P₄Mo₆}-based POMs and intensively studying the relationship between structures and performances. Future research will explore more potential applications in energy storage and conversion such as hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and battery materials. This review will be helpful for researchers to gain a rapid understanding of this area and value for the future development of {P₄Mo₆}-based POMs.