An aqueous high-performance hybrid supercapacitor with MXene and polyoxometalates electrodes

Two-dimensional (2D) titanium carbide (Ti3C2Tx), MXene, is an attractive pseudocapacitive electrode material that exhibits its highest capacitance at a negative potential in an aqueous protic (H2SO4) electrolyte. Developing hybrid supercapacitors (HSCs) using diverse cathode materials is the best way to identify a material with high energy density in aqueous electrolytes. However, it is difficult to find redox-active positive cathode materials that are suitable for use with MXene in an H2SO4 electrolyte. Here, 2D nanocomposite of reduced graphene oxide (rGO) decorated with phosphomolybdic acid (PMo12) polyoxometalates (POMs) are reported as promising cathode materials suitable for use against an MXene anode. The complementary potential window of MXene and rGO-POMs along with the redox activity and 2D nanostructured features of these materials can significantly enhance the electrochemical properties of HSC cell. An all-redox active HSC cell with rGO-POM cathode and MXene anode can deliver a maximum specific energy and power of 50.46 Wh/kg and 7000 W/kg, respectively, with capacitance retention of 87.12 % over 10,000 cycles and superb energy and coulombic efficiency over all applied current densities. These results suggest that the rGO-POMs cathode can be potentially coupled with an MXene anode in a protic electrolyte to enhance the electrochemical parameters of the HSC cells.