Unleashing asymmetric polyoxometalate redox activators on 2D interfaces for high-performance hybrid energy storage

Abstract

Polyoxometalates (POMs) are an intriguing class of compounds with remarkable redox capabilities, making them prime candidates for energy storage applications. However, the challenge lies in their heightened solubility, which limits their direct use as electrode materials. The successful confinement of POMs into suitable templates becomes pivotal in creating supercapacitors with elevated energy and power densities. Our study showcases the successful integration of asymmetric POMs (Mo and W) onto two-dimensional (2D) templates, specifically graphene oxide and MXene. The synergy could benefit from the inherent charge storage capabilities of the high surface area 2D substrates that could provide a template for uniform dispersion of POMs enabling additional faradaic capacitances at electrode/electrolyte interface. A hybrid supercapacitor (HSC) fabricated effectively utilizes these faradaic capacitances across an extended potential window of 1.2 V in a 2 M H2SO4 solution, yielding impressive capacitance values of 110.4 F/g at a current density of 1 A/g. Furthermore, our synthesis strategy could effectively anchor POMs resulting in a high capacitive retention of 92.4% at high scan rates of 50 mV/s after 5000 cycles. Our approach can be effective in designing POM based pseudo capacitive electrodes with excellent structural stability and surface properties that can be relevant to many electronic and energy applications.