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 H-4[Cu-2(bix)(4)][PW12O40] (2)center dot 8H(2)O (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.