Ag/Cu-phen Complex-Assembled Keggin Polyoxotungstate Nanoclusters for Electrochemical Capacitors and Bi-function Biosensor Performance

Two Cu/Ag-phen complex-modified hybrid supermolecule frameworks, [Ag(phen)₂]₃[Ag(phen)₃][AsW^VW^VI₁₁O₄₀]·2H₂O (AWA) and [Cu^I(phen)₂]₄[Cu^I₅(phen)₄Cl₄][AsW^V₂W^VI₁₀O₄₀]·4H₂O (AWC) (phen = 1,10-phenanthroline), were obtained via hydrothermal synthesis. AWA exhibits a unique 3D open network structure in which the metal–organic layer {[Ag(phen)₂]₃}_n alternates with the inorganic nanocluster hybrid layer. In AWC, the five-nuclear complex {Cu₅(phen)₄Cl₄} and the dinuclear complex {Cu₂(phen)₄} act as bridging units, extending the Keggin cluster into a 3D complex network with orderly tunnels. AWC can also be viewed as a 4, 4, 6-linked net with the topology {4³²;6³⁰;8⁴}{4⁴;6²}{4⁶}₂. Due to the introduction of Cu/Ag-phen complexes, compounds AWA and AWC exhibit excellent capacitance performance. The charge storage mechanisms of the two compounds include diffusion-controlled battery behavior and capacitance-controlled pseudocapacitance behavior, and the contribution rate of pseudocapacitance increases with the increase of scan rate and gradually dominates. The specific capacitance, conductivity, and cycle stability of AWC are better than those of AWA due to the introduction of polynuclear complexes and the structural characteristics of ordered pores. The asymmetric supercapacitor (AC–CPE//AWC–CPE), composed of AWC and AC as the anode and cathode, respectively, has an energy density of 58.4 Wh kg^–1 at a power density of 801.2 W kg^–1. After 10 000 cycles, the capacitance retention rate is 92.9%, and the Coulombic efficiency is as high as 99.2%. In addition, AWC-GCE showed high catalytic activity and good sensing performance for H₂O₂ and AA.