Three Keggin-Type Polyoxometalate-Based Tetranuclear Cu/Ag Nanostructures with Dual Functions of Supercapacitors and Trace Cr (VI)-Sensitive Detection

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