Stability-Enhanced α-Ni(OH)₂Pillared by Metaborate Anions for Pseudocapacitors

α-Ni(OH)2 is an ideal candidate material for a supercapacitor except for its low conductivity and poor stability. In this work, BO2-intercalated α-NixCo(1-x)(OH)2 is synthesized by a hydrothermal method at a low cost. The Co dopant can decrease the charge-transfer resistance and enhance the cyclic stability. The special unsaturated electronic state of BO2- enhances the bonding with metal ions and attracts water molecules. Thus, the BO2- ions support the hydroxide layers as pillars and create efficient paths for proton transportation, optimizing the utilization of α-Ni(OH)2. The three-dimensional (3D) flowerlike morphology supplies an enormous number of active sites, and r-GO is added to improve the conductivity. As a result, the modified α-Ni(OH)2 exhibits the specific capacitance of 2179, 1592, and 1423 F·g-1 at 1, 20, and 40 A·g-1, respectively, showing improved rate performance. Matching with the commercial activated carbon (AC) as an anode, the asymmetric capacitor delivers an energy density of 40.66 W·h·kg-1 when its power density is 187.06 W·kg-1. Meanwhile, it retains 81.5% capacitance of the initial cycle at 5 A·g-1 after 3000 cycles. With conductivity enhanced and structure stabilized, the modified α-Ni(OH)2 confronts broader fields of application.