Arsenotungstate-Nanostructure-Based Derivatives with One-Dimensional Tunnels for Electrochemical Capacitors and Electrocatalytic Hydrogen Evolution

The assembly of transition metal (TM) complexes/tetranuclear units into arsenotungstate nanostructures generates three polyoxometalate (POM)-based hybrid derivatives, [Co(phen)3]2[AsW12O40]·2H2O (1), (Hbipy)2 [Mn(bipy)3]2[As2W18O62] (2), and (H2bib)5[Co4(H2O)2(AsW9O34)2]·2H2O (3), by a one-step hydrothermal synthesis. Compounds 1–3 are Keggin, Dawson, and a sandwich arsentungstate supramolecular hybrid net with different topology and periodically arranged 1D tunnels, respectively, which exhibit better capacitive performance and electrocatalytic activity due to their structural advantages. In particular, compound 3 shows a higher specific capacitance (Cs), excellent rate capability (Cs of 749.2 F/g at 15 A/g), and capacitance retention rate (95.6% after 5000 cycles), which outdo most pseudocapacitive materials reported so far. In addition, the nickel electrode of 3 has higher catalytic activity for hydrogen evolution reaction (HER). The overpotential is 78 mV, and the Tafel slope is 79.3 mV dec–1 at the current density of 10 mA cm–2 in alkali solution. The i–t curve test at 170 mV for 24 h did not decrease significantly, revealing its good durability. The excellent capacitive and catalytic behaviors of 3 are ascribed to the insertion of tetranuclear cobalt units, a stable sandwich POM skeleton, and the abundant hydrogen bonding, which provide more redox centers and higher ion/electron transfer efficiency.