Biomass activated carbon supported Keggin-type polyoxometalate as an electrode material for high-performance acidic aqueous supercapacitors

Abstract

Activated carbon (SSAC-OP) with micropore and mesopore was prepared by using soybean straw as a carbon source. Redox-active H3PMo12O40 (PMo12) was introduced into SSAC-OP by solution impregnation to obtain composite PMo12/SSAC-OP. The effect of loading amount of PMo12 on the supercapacitive performance of the composite was investigated. BET and EDS results confirmed that PMo12 is adsorbed in the micropores of 1–2 nm and mesopores of SSAC-OP, as well as on the carbon wall of SSAC-OP. Meanwhile, SSAC-OP with positive charge is more firmly connected with PMo12 anions via the effect of electrostatic attraction. CV and GCD test results proved that the composite materials have both electric double layer capacitance and pseudocapacitance characteristics. The CV curve of 10-PMo12/SSAC-OP obtained from SSAC-OP impregnating the initial concentration of PMo12 solution of 10 mM shows four pairs of obvious reversible redox peaks, which indicates that the protonation of PMo12 anion in the reduction process is sufficient. The composite 10-PMo12/SSAC-OP has a specific capacitance as high as 397.02F g−1 at scan rate of 5 mV s−1. The assembled symmetric supercapacitor delivers an energy density of 23.90 Wh kg−1 under the power density of 1016.05 W kg−1, with 97.96 % capacitance retention after 10,000 cycles at 3 A g−1.