Here we demonstrate a simple strategy for the large-scale synthesis of void-induced and graphene-wrapped nickel oxide (VGWN) hybrids using domestic microwave irradiation. When a homogeneously mixed aqueous suspension of partially microwave exfoliated graphene oxide (MEGO) sheets and nickel nitrate nanoparticles is irradiates with a microwave, the in situ formation of voids with wrapping of NiO nanoparticles with graphene sheets is easily realized. The novel VGWN hybrid materials were used for investigation of electrochemical capacitive behaviours. Remarkably, such hybrid structure provides the right combination of electrode properties for high-performance supercapacitors and cyclic stability. The wrapping of graphene sheets on the NiO nanoparticles can offer highly conductive pathways by bridging individual NiO nanoparticles together, thus facilitating the charge/discharge rate and cycling performance of supercapacitors. The hybrid materials displayed enhanced capacitive performance (549 F g⁻¹ at 10 mV s⁻¹). Additionally, over 88% of the initial capacitance was retained after repeating the cyclic voltammetry test for 2500 cycles. The enhanced electrochemical performance can be ascribed to the synergic effects of the two components' voids and wrapping, suggesting VGWN hybrids as novel electrode materials promising potential applications as high-performance energy storage devices.

In this work we present graphene-based in-plane flexible interdigitated micro-supercapacitor devices fabricated through direct laser writing onto ultra-thin graphite oxide (GO) films. The fabrication route is simple, fast, additive-free, mask-free and cost effective. This involves direct micro-writing of reduced graphene oxide (rGO) by a pulsed UV laser on a very small area (1.14 cm²). The fabricated micro-supercapacitor contains nineteen pairs of rGO electrodes separated by the unreduced portion of the GO film. The single laser patterned rGO electrode presents low resistivity, while the unpatterned portion is non-conducting. Under the optimized laser parameters the 2.2 μm ultra-thin GO films were completely and uniformly reduced. The electrochemical measurements showed that the micro-supercapacitor, packed in a glass cavity, and in the presence of a liquid electrolyte have a capacitance nearly 288% higher (288.7 mF cm⁻³) compared to the as-fabricated device (0.36 mF cm⁻³). The as-fabricated micro-supercapacitor without electrolyte also shows some capacitance due to the presence of free ions in the unreduced portion of GO which plays a crucial role. Furthermore, the cycling stability of the as-fabricated micro-supercapacitor is robust, with not much performance degradation for more that 5000 cycles.