Direct synthesis method of metal oxide and 3D graphene composite by laser irradiation and its applications in flexible micro-supercapacitor

The cutting-edge flexible micro-supercapacitors with high energy density and power density are nowadays engineered to transcend the limits of conventional storage devices. LIG-based interdigitated electrodes (IDEs) are beneficial for high capacitance due to the presence of multiple parallel electrodes in a single plane of polyimide sheet. Most of the research studies were based on the coating of the active materials on the surface of polyimide sheets followed by laser irradiation. Hence transforming to a highly 3D porous graphene based surface decorated with metal nanoparticles. However, too much loading on the surface may cause interconnection between the parallel electrodes which may compromise the device performance for supercapacitors. In this work, metal chlorides such as iron chloride hexahydrate were spread uniformly on the PI surface and then irradiated with laser forming the LIG-Fe (LIG/Fe2O3) based IDE devices. Generally, iron oxide nanoparticles were synthesized from iron chloride hexahydrate by hydrothermal process where very high temperature was achieved inside the autoclave. In our case, this was achieved by laser irradiation paving the way to a robust fabrication process. Now the unburned region between the parallel electrodes contains the soluble counterpart of metal chloride which was removed by a gentle rinse with water, preventing the interconnection between the parallel electrode in LIGFe2O3 based IDE electrodes. The presence of Fe2O3 nanoparticles on the LIG surface was confirmed with FE-SEM images, along with the functional groups by XPS. The standardization was further investigated using cyclic voltammetry, galvanostatic charge-discharge voltammetry, and impedance spectroscopy. It was observed that LIG-Fe has a higher specific capacitance of 16.95 mF/cm2 than LIG of 3.05 mF/cm2 at 0.3 mA/cm2. The specific capacitance of LIG-Fe was further found to be 17.84 mF/cm2 at 5 mV/s and 3.12 mF/cm2 at 100 mV/s. The LIGFe has shown stable performance within a cycle number of 5000 cycles with a retention of 94 % and can be widely used as a micro-supercapacitor energy storage device.