β-Co(OH) 2 Nanosheets: A Superior Pseudocapacitive Electrode for High-Energy Supercapacitors.

In this work, β-Co(OH)2 nanosheets are explored as efficient pseudocapacitive materials for the fabrication of 1.6 V class high-energy supercapacitors in asymmetric fashion. The as-synthesized β-Co(OH)2 nanosheets displayed an excellent electrochemical performance owing to their unique structure, morphology, and reversible reaction kinetics (fast faradic reaction) in both the three-electrode and asymmetric configuration (with activated carbon, AC). For example, in the three-electrode set-up, β-Co(OH)2 exhibits a high specific capacitance of ∼675 F g-1 at a scan rate of 1 mV s-1 . In the asymmetric supercapacitor, the β-Co(OH)2 ∥AC cell delivers a maximum energy density of 37.3 Wh kg-1 at a power density of 800 W kg-1 . Even at harsh conditions (8 kW kg-1 ), an energy density of 15.64 Wh kg-1 is registered for the β-Co(OH)2 ∥AC assembly. Such an impressive performance of β-Co(OH)2 nanosheets in the asymmetric configuration reveals the emergence of pseudocapacitive electrodes towards the fabrication of high-energy electrochemical charge storage systems.