Boosting the High Working Voltage of an Aqueous Symmetric Supercapacitor by a Phosphotungstic Acid-Based Coordination Polymer Coating with Polypyrrole

The low working voltage limits the energy density and feasibility of practical applications of aqueous supercapacitors (SCs) to some extent. Herein, new CuPW12@PPy (n, n = 1, 2, 3) nanocomposites were designed and fabricated by involving the hydrothermal synthesis of crystalline H4[Cu2(bix)4][PW12O40]2·8H2O (CuPW12) and subsequently pyrrole in situ oxidation polymerization on the CuPW12 surface. These were then used as electrode materials to widen the working voltage of SC. As expected, CuPW12@PPy (n, n = 1, 2, 3) can operate stably within −0.6 to 1.0 V while inhibiting the hydrogen evolution reaction, which exhibits higher specific capacitance in 2 M H3PO4. Specifically, CuPW12@PPy (2) shows a 711.2 F g–1 specific capacitance at 1.5 A g–1, attributed to the high ion/electron transportation and their synergy from the conductive PPy covering the CuPW12 surfaces. Finally, the assembled symmetric SC cell can operate at 1.6 V and deliver a 43.67 Wh kg–1 energy density and 1280 W kg–1 power density at 1.0 A g–1 and a 91.3% capacitance retention at 5 A g–1 after 10,000 cycles.