Redox‐Additive‐Enhanced High Capacitance Supercapacitors Based on Co2P2O7 Nanosheets. Issue 12 (18th April 2017) - Khan, Ziyauddin
Abstract : Cobalt pyrophosphate (Co2 P2 O7 ) has emerged as an attractive material due to its high specific energy and redox behavior of cobalt, however, problems associated with its poor specific capacitance and cyclic stability have prevented its realization. Here, the authors circumvent these problems by hydrothermally synthesizing layered Co2 P2 O7 nanosheets (lateral size ≈300 nm with average thickness ≈15 nm) and demonstrate significant improvements in the specific capacitance of Co2 P2 O7 nanosheets by the addition of a redox additive (K3 Fe(CN)6 ) into KOH aqueous electrolyte. Without the additive, Co2 P2 O7 nanosheets show specific capacitance of 286 F g −1 at 1 A g −1 current density. However, by introducing 0.1m redox additive to the electrolyte the specific capacitance of Co2 P2 O7 nanosheets increased more than twofolds (580 F g −1 at 1 A g −1 current density), which is due to the improvement of redox reactions at the electrode/electrolyte interface and the enhanced ionic conductivity of electrolyte. Furthermore, with the redox additive, Co2 P2 O7 nanosheets show an excellent cyclic stability (96% retention of its initial capacitance) and coulombic efficiency (99% retention) up to 5000 cycles at high current density 10 A g −1 . Abstract : Cobalt pyrophosphate nanosheets, synthesized by a facile hydrothermal method, are studied for supercapacitor application in aqueous electrolyte. The electrochemical performance of nanosheets is enhanced more than twice using low amount of redox additive. With redox additive, prepared nanosheets display 580 F g −1 at 1 A g −1 current density in 0.68 V potential window with exceptional cyclic stability up to 5000 cycles.