Polyoxometalate-enabled photoreduction of graphene oxide to bioinspired nacre-like composite films for supercapacitor electrodes

A bioinspired nacre-like composite film was successfully fabricated by a polyoxometalate of H3PW12O40 (HPW) assisted reduction of graphene oxide to graphene under an ultraviolet irradiation at room temperature. It was found that nanosized HPW clusters were uniformly attached onto the graphene surface and hence sandwiched between graphene sheets within the composite film. The self-supported composite film electrode shows high specific capacitance of 337.5 F/g at a scan rate of 5 mV/s and 156.9 F/g at a current density of 0.5 A/g, respectively. The specific capacitance remains 98.5% after running 1000 cyclic voltammetry loops at 100 mV/s and retains 98.3% after 1000 galvanostatic charge-discharge cycles at 5 A/g, respectively. Furthermore, the retention of initial specific capacitance was calculated to be 86.4% with increasing the scan rate from 5 to 100 mV/s and up to 94% with increasing the current density to 10 A/g from 0.5 A/g, showing high rate capability. Such free-standing composite film electrodes exhibit excellent electrochemical performance due to the unique nacre-like layered architecture and synergistic effects between electric double-layer graphene and pseudo-capacitive HPW clusters.