Transition metal oxide@hydroxide assemblies as electrode materials for asymmetric hybrid capacitors with excellent cycling stabilities.

In this work, three-dimensional cactus-like Co 3 O 4 @Ni(OH) 2 electrode materials are grown directly on Ni foam via a two-step hydrothermal method. The as-prepared products possess a specific capacitance of 464.5 C g -1 at 0.5 A g -1 and 91.67% capacitance retention after 20 000 cycles. The as-assembled device using the as-synthesized samples as positive electrodes delivers an energy density of 112.5 W h kg -1 at a power density of 1350 W h kg -1 . The superior electrochemical performance of the electrode materials can be attributed to their unique structure, the synergistic effect between Co 3 O 4 and Ni(OH) 2 materials and reversible reaction kinetics. It suggests that the products are potential alternatives in future energy storage devices.