Surface modification and heterointerface engineering into cobalt-hydroxide nanowires by ion exchange for high-energy asymmetric supercapacitors

The development of novel transition-metal heterostructures with rich redox activities, high capacity values, and stable cycling performance is essential for fabricating high-energy-density supercapacitors. Herein, surface modification and interfacial engineering are applied to cobalt hydroxide nanowires (Co(OH)₂ NWs) through the dual insertion of S²⁻ anions and Ni²⁺ cations using a facile hydrothermal reaction and sulfurization process. The NiS/CoS@Co(OH)₂ hybrid shows high electrochemical performances, achieving an outstanding areal capacity of ∼1.23 mA h cm⁻² at 3 mA cm⁻², and excellent cycling stability. Moreover, an asymmetric supercapacitor (ASC) device is constructed using the NiS/CoS@Co(OH)₂ hybrid as the cathode material and Fe₂O₃@fMWCNTs/NG hybrid as the anode material. The device reaches a high voltage range of 1.6 V, thus generating a high energy density of 83.3 W h kg⁻¹ at 600 W kg⁻¹ power density and a small capacity decay of 8.6% after 10 000 cycles. This study highlights the great potential of transition metal heterojunctions for high-energy supercapacitors.