Improving the capacitive performance of phosphomolybdic acid using methylene blue or natural red for solid-state suprcapacitors

Abstract

The main way to improve the specific energy of a supercapacitor is to implement rational design and engineering of electrode materials. In this work, methylene blue (MB, C16H19N3SCl) and neutral red (NR, C15H18N4Cl) have been chosen as cation to react with H3PMo12 to form organic–inorganic hybrid materials of (C16H18N3S)3PMo12O40 and (C15H17N4)3PMo12O40 (abbreviated as MB3PMo12 and NR3PMo12). [PMo12O40]3− and organic cation are connected by electrostatic interaction and hydrogen bond. When applied as electrode materials, MB3PMo12/NR3PMo12 electrode shows a high specific capacitance (354/241 F g−1) in 0.5 M H2SO4. The MB3PMo12 electrode, moreover, supply an amazing specific capacitance of 583 F g−1 when NH4VO3 is used as a redox additive for 0.5 M H2SO4. The solid-state supercapacitor of MB3PMo12//MB3PMo12 can operate at a voltage of 1.0 and provide a moderate specific energy. We believe that this work provides inspiration for the design and preparation of excellent supercapacitors electrodes based on polyoxometalates.