Confined PMo₆W₆ for energy storage

Mixed-addenda polyoxometalate (e.g., PMo_xW_12-x) by “orbital engineering” allows the functionalization of the single-addenda cluster surface, which offers new electronic properties. However, the well-known agglomeration phenomenon greatly limits the full understanding of its unique redox properties. It makes sense to fully stimulate the intrinsic multi-electron activity of mixed-addenda polyoxometalate by confining engineering to apply in energy technology. With the verification of potential candidate PMo₆W₆ possessing remarkable stability with fully exposed activity sites in a confined state by theoretical analysis, we achieve the precise confinement of the single PMo₆W₆ molecule in porous carbon (PC) with a matched pore aperture (PMo₆W₆@PC). As a result, PMo₆W₆@PC-based supercapacitor shows high energy densities of 0.308 mWh cm⁻² at power densities of 43.2 mW cm⁻², outperforming most polyoxometalate-based supercapacitors. Moreover, the device exhibits a capacity retention of over 80.4 % at 8 mA cm⁻² after 8000 cycles. This improved electrochemical redox activity may be ascribed to the strong orbital electronic coupling between W and Mo atoms of PMo₆W₆ by confinement engineering. This work proves that the confined PMo₆W₆ can maximize the advantages of PMo₁₂O₄₀ and PW₁₂O₄₀, which provides a theoretical basis for other mixed-addenda polyoxometalate species.