Construction of Sb-capped Dawson-type POM derivatives for high-performance asymmetric supercapacitors

Modified polyoxometalate (POM) derivatives are promising pseudocapacitive active materials due to their abundant active sites and high redox capacity. Here, we constructed four antimony-capped Dawson-type molybdate clusters with high specific capacitance properties for the first time through the traditional hydro -thermal method, formulated as [Cu(im)2]4{[Cu2(im)2]1/2(im)}[H3/2(Sb1Sb1/3Sb2/3)P2Mo7VMo11VIO62].H2O (1); [Cu (bzim)2][H4Sb1Sb1/2 x 2P2Mo7VMo11VIO62].(bzim)4.2H3O (2); [(bzim)4(NO3)1/2][H5/2Sb2P2Mo3VMo15VIO62].H3O (3); [(bzim)4(bzim)1/3][HSb2P2Mo2VMo16VIO62].H3O (4) (im= imidazole, bzim= benzimidazole). The compounds 1-4 all contain Sb-capped Dawson type {P2Mo18} anions with 3D supramolecular channel structures. Especially, compound 1 expresses a porous 2D metal-organic layer formed by Cu-ims transition metal complexes (TMCs) through the Cu-O interaction, and Sb capped-polyanions are exactly filled in the holes. Importantly, compound 1 exhibits a higher specific capacitance (Cs) value of 1401.75 F g-1 than the other three compounds (1141 F g-1, 1027.3 F g-1, and 978.25 F g-1) at a current density of 1.4 A g-1. In addition, the asymmetric supercapacitor Sb-P2Mo18//AC assembled with compound 1 and active carbon exhibits good cycling stability (89.14 %), and possesses an excellent energy density of 17.78 W h Kg-1, which could be attributed to the high redox capacity and excellent electronic conductivity. The experimental results demonstrate the feasibility of the synthesis strategy and pave the way for exploring novel high-performance polyoxometalate-based pseudocapacitive materials.

Automated summary

Modified polyoxometalate (POM) derivatives with high specific capacitance properties were successfully synthesized through the traditional hydrothermal method. Among them, compound 1 exhibited a higher specific capacitance value compared to the other three compounds, and the assembled asymmetric supercapacitor showed good cycling stability and excellent energy density, indicating the promising potential of these materials for high-performance pseudocapacitive applications.