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.