Cu/Ag Complex Modified Keggin-Type Coordination Polymers for Improved Electrochemical Capacitance, Dual-Function Electrocatalysis, and Sensing Performance

Different metal–organic units were introduced into the {PMo12} polyoxometalate (POM) system to yield three porous coordination polymers with distinct characteristics, {Cu(pra)2}[{Cu(pra)2}3{PMo11VIMoVO40}] (1), [{Ag5(pz)6(H2O)0.5Cl}{PMo11VIMoVO40}] (2), and [{Cu3(bpz)5(H2O)}{PMo12O40}] (3) (pra = pyrazole; pz = pyrazine; bpz = benzopyrazine), via an in situ hydrothermal method. In comparison with the maternal Keggin cluster and most reported POM electrode materials, compounds 1–3 exhibit larger specific capacitances (672.2, 782.1, and 765.2 F g–1 at a current density of 2.4 A g–1, respectively), superior cyclic stability (91.5%, 89.3%, and 87.8% of cycle efficiency after 5000 cycles, respectively), and boosted conductivity, which may be attributed to the introduction of metal–organic units. The result indicates that metal–organic units can effectively enhance the capacitance performance of POMs. This may be due to the fact that they provide additional redox centers, induce the formation of stable porous structures, and improve ion/electron transfer efficiency. Compounds 1–3 present excellent electrocatalytic activity in reducing peroxide (H2O2) and oxidizing ascorbic acid (AA). In addition, compound 2 shows an outstanding sensing performance detection of AA and H2O2.