Synchronous Defect and Interface Engineering of NiMoO₄ Nanowire Arrays for High-Performance Supercapacitors

Developing high-performance electrode materials is in high demand for the development of supercapacitors. Herein, defect and interface engineering has been simultaneously realized in NiMoO₄ nanowire arrays (NWAs) using a simple sucrose coating followed by an annealing process. The resultant hierarchical oxygen-deficient NiMoO₄@C NWAs (denoted as "NiMoO_4-@C") are grown directly on conductive ferronickel foam substrates. This composite affords direct electrical contact with the substrates and directional electron transport, as well as short ionic diffusion pathways. Furthermore, the coating of the amorphous carbon shell and the introduction of oxygen vacancies effectively enhance the electrical conductivity of NiMoO₄. In addition, the coated carbon layer improves the structural stability of the NiMoO₄ in the whole charging and discharging process, significantly enhancing the cycling stability of the electrode. Consequently, the NiMoO_4-@C electrode delivers a high areal capacitance of 2.24 F cm^-2 (1720 F g^-1) at a current density of 1 mA cm^-2 and superior cycling stability of 84.5% retention after 6000 cycles at 20 mA cm^-2. Furthermore, an asymmetric super-capacitor device (ASC) has been constructed with NiMoO_4-@C as the positive electrode and activated carbon (AC) as the negative electrode. The as-assembled ASC device shows excellent electrochemical performance with a high energy density of 51.6 W h kg^-1 at a power density of 203.95 W kg^-1. Moreover, the NiMoO₄//AC ASC device manifests remarkable cyclability with 84.5% of capacitance retention over 6000 cycles. The results demonstrate that the NiMoO_4-@C composite is a promising material for electrochemical energy storage. This work can give new insights on the design and development of novel functional electrode materials via defect and interface engineering through simple yet effective chemical routes.