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

Two-dimensional (2D) titanium carbide (Ti₃C₂T_x), 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.