A Supercapacitor with High Specific Volumetric Capacitance Produced by 12-Phosphomolybdate Anchored on Graphene Balls

Rational design and exploitation of graphene-based supercapacitors with high specific volumetric capacitance are highly desired, yet very challenging. Herein, a series of CGB/PMo12 (n) hybrids (n = 1, 2, 3, 4), namely, Keggin-type 12-phosphomolybdate (PMo12) anchored on highly crumpled 3D graphene balls (CGB), were successfully synthesized through a water-in-oil emulsion method. As expected, the CGB/PMo12 (n) as electrode materials for supercapacitors exhibit higher specific volumetric capacitance in 1 M H2SO4 media. Specifically, CGB/PMo12 (3) show a specific capacitance of 632 F cm–3 (340 F g–1) at 1 A g–1. This is mainly attributed to more electrochemically active sites of PMo12 and the conductive substrate of CGB, high packing density (1.86 g cm–3), and their synergy. Furthermore, the assembled symmetric supercapacitor cell delivers a maximum energy and power density of 18.6 Wh kg–1 (34.6 Wh L–1) and 597 W kg–1 (1110 W L–1) at 1 A g–1, respectively, and 89.6% capacitance retention after 20000 cycles.