Boosting the Electrochemical Performance of Graphene-Based On-Chip Micro-Supercapacitors by Regulating the Functional Groups.

The on-chip system-compatible power supply shows a high demand for the rapid development of miniaturization devices, such as wireless sensors, remote detecting devices, etc. Moreover, the ever-increasing trends of multifunctionalities and long-term working conditions of such devices raise a high-performance standard for the power supply. Herein, the high-performance electrochemical energy storage micro-supercapacitors (MSCs) are obtained with a metal current collector-free symmetric graphene-based planar structure, in which the functional group of graphene was regulated extensively via fully compatible microfabrication techniques of blue-violet (BV) laser exposure and air plasma treatment. BV laser exposure enhanced the electrical conductivity by reducing the substantial functional groups. Furthermore, the wettability and active sites are tuned by air plasma treatment, thus creating a slightly functional group onto the graphene surface. The resulting reduced graphene oxide (RGO) shows a very low resistance down to 27.2 Ω sq-1, ensuring its superb electron conductivity for fast electron transfer during the electrochemical reactions. The electrochemical performance measurements reveal an areal capacitance as high as 21.86 mF cm-2, which delivers a power density of 5 mW cm-2 with an energy density of 2.49 μWh cm-2. Moreover, it shows superior long-term stability with 99% retention after 10 000 cycles, which is beyond that of most of the reported graphene-based all-solid-state MSCs.