Three Keggin-Type\nPolyoxometalate-Based Tetranuclear\nCu/Ag Nanostructures with Dual Functions of Supercapacitors and Trace\nCr (VI)-Sensitive Detection

Polyoxometalate (POM) nanoclusters are widely used in\nenergy storage\nand sensors due to their excellent redox properties and chemical stabilities.\nThree isomorphic Keggin-type compounds with nanostructures {(Ag<sub>4</sub>L<sub>6</sub>)(SiMo<sub>12</sub>O<sub>40</sub>)} (<b>Ag-SiMo</b>), {(Cu<sub>4</sub>L<sub>6</sub>)(SiMo<sub>12</sub>O<sub>40</sub>)} (<b>Cu-SiMo</b>) and {(Cu<sub>4</sub>L<sub>6</sub>)(GeMo<sub>12</sub>O<sub>40</sub>)} (<b>Cu-GeMo</b>) [L = 4-Oxazol-2-ylmethyl-4H-(1,\n2, 4)triazole]) were successfully synthesized and applied as materials\nfor supercapacitors and electrochemical sensors for Cr (VI) by adjusting\nthe types of metals and POMs. Compared to the parent POMs, <b>Ag-SiMo</b> exhibits higher specific capacitance (502 F g<sup>–1</sup> at a current density of 2 A g<sup>–1</sup>) and better sensitivity\n(54 μA μM<sup>–1</sup>). The findings indicate\nthat incorporating metal–organic components substantially improves\nthe capacitance and sensing capabilities of POMs. This enhancement\nis likely due to several factors: the introduction of extra redox-active\nsites, stabilization of a porous framework, and enhancement of ion\nand electron mobility. This study provides a feasible approach to\nimprove the electrochemical capacitance and sensing performance.