Facile construction of nickel cobalt boride and layered Ti-MXene heterostructure as high-energy-density electroactive materials of supercapacitors

Abstract

Transition metal boride (TMB) is considered as a promising battery-type material of supercapacitors (SCs), owing to abundant electrochemically active sites, strong electrical conductivity, high chemical and thermal stability, and high theoretical capacity. However, serious aggregations of TMB substantially reduces structural stability and electrochemical performance. A conductive support is required to improve TMB dispersion and promote energy storage ability. In this study, a basic wet chemical reduction method is utilized to synthesize cobalt boride (CoB), nickel boride (NiB), and nickel cobalt boride (NiCoB) as battery-type materials of SCs. The NiCoB presents superior electrochemical results due to the highest theoretical capacity and abundant redox states of Ni and Co. Two-dimensional titanium carbide (MXene) is further incorporated in NiCoB (NiCoB/MXene), which demonstrates a significant specific capacity of 1240 C g⁻¹ at 1 A g⁻¹ and an outstanding rate capability of 73.9% (916 C g⁻¹ at 40 A g⁻¹), attributing to higher conductivity, enhanced dispersion of NiCoB on MXene, and synergistic effects from capacitive MXene and redox active NiCoB. A hybrid SC assembled by NiCoB/MXene and activated carbon electrodes delivers a maximum energy density of 80.5 W h kg⁻¹ at 850 W kg⁻¹, and maintains a high capacitance retention of 83.4% over 20,000 cycles.