Supramolecular Host-Guest Assembly Based on Phosphotungstate Nanostructures for Pseudocapacitive and Electrochemical Sensing Applications

Flexible ligands and multinuclear complexes were as-sembled into nanoscale {P2W18O62} polyoxometalates (POMs) to generate two phosphotungstate hybrid derivatives, (H(2)bip)(2){H2P2 W18O62}center dot 2H(2)O (1) and (bipy)(0.5){Ag(bipy)(2)}{Ag-4(bipy)(7)}-{NaP2W18O62}center dot H2O (2) (bip = 1,5-bis(imidazole-1-yl)pentane; bipy = 2,2 ' -bipy), via a precursor hydrothermal method. Compound 1 is a bip ligand modified 4,8-connected supramolecular net with {4(15);6(12);8}{4(5);6}(2) topology. In compound 2, the monocore complexes {Ag(bipy)(2)} and tetranuclear complexes {Ag4(bipy)(7)} self-associate to generate two supramolecular chains A and B, respectively, which are further alternately joined together to form a unique metal-organic framework with irregular cavities via weak actions and pi- pi stacking. The Na-linked {P2W18O62} dipolymers as guest units were embedded into the holes, leading to a 3D supramolecular host-guest assemblies. The capacitive performance test reveals that 2-GCE/-CPE presents improved specific capacitance (802.4 and 752.1 F/g at 3 A/g), cycle efficiency (93.6 and 94.8% after the 5000th cycle), and electrical conductivity compared to the precursor and bip ligand modified compound 1. The electrocatalytic comparative data shows that 2-GCE has enhanced electrochemical redox capacity compared to the precursor and compound 1. Further sensing tests display that 2-GCE shows strong electrochemical responses to H2O2/AA at voltages of -0.41/ 0.36 V with a lower detection line of 0.33/0.05 mu M, a wider linear range of 1.0 mu M to 3.18 mM/0.15 mu M to 2.33 mM, merit selectivity, and reproducibility. The excellent capacitive and sensing performances are related to increased redox centers, improved ion/electron conversion efficiency, and host-guest structural stability resulting from the introduction of multinuclear complexes, irregular holes, and abundant pi-pi stacking. This study not only enriches the variety of Dawson-type POMs but also provides a feasible idea for enhancing their electrochemical capacitance and sensing performance.