Nickel molybdate nanorods supported on three-dimensional, porous nickel film coated on copper wire as an advanced binder-free electrode for flexible wire-type asymmetric micro-supercapacitors with enhanced electrochemical performances

Abstract

Wire-shaped micro-supercapacitors attracted extensive attentions in next-generation portable and wearable electronics, due to advantages of miniature size, lightweight and flexibility. Herein, NiMoO4 nanorods supported on Ni film coated Cu wire are successfully fabricated thorough direct deposition of Ni film onto Cu wire as the conductive substrate, followed by growth of the NiMoO4 nanorods on Ni film coated Cu wire substrate by means a hydrothermal annealing process. The prepared 3D, porous electrode demonstrates extremely high areal specific capacitance of 12.03F cm−2 at the current density of 4 mA cm−2 and retained capacitance of 8.23 F cm−2 at a much higher current density of 80 mAcm−2. The electrode, also, shows an excellent cycling stability with capacitance retention of 99.3% after 3000 cycles. The superior electrochemical performance can be attributed to the high area surface, low contact resistance between NiMoO4 nanorods and Cu wire current collector and presence of a 3D and porous structure provides many electroactive sites and sufficient open space for easy diffusion of the electrolyte ions during redox reactions. Benefiting from their structural features, a fiber shaped asymmetric micro-supercapacitor based on NiMoO4/Ni film/Cu wire as the positive electrode and carbon fiber coated with reduced graphene oxide as the negative electrode is assembled. The fabricated fiber device presents a wide potential window between 0 and 1.7 V and exhibits high specific capacitance of 0.504F cm−2 (38.8F cm−3) at a current density of 4.8 mA cm−2 with a high energy density of 202 µWh cm−2 (15.6 mWh cm−3) at a power density of 4050 µW cm−2 (313 mWh cm−3). The energy density retains 124 µWh cm−2 (9.54 mWh cm−3) when the power density is increased to 13530 µW cm−2 (1040.73 mWh cm−3). In addition, the asymmetric device exhibits an outstanding cycling stability (98.5% capacitance retention after 1000 consecutive cycles) and good mechanical stability. Therefore, this work suggested the promising potential of NiMoO4 nanorods supported on Ni film coated Cu wire as an advanced electrode material for construction of flexible and portable next-generation energy storage micro-devices with superior electrochemical performances.