Facile synthesis of water soluble reduced graphene oxide with a high concentration and its application in printable micro-supercapacitors

Direct printing techniques have generated significant research interest in fabricating flexible and scalable micro-supercapacitors (MSCs). In this study, we report a facile and cost-effective way to synthesize water soluble reduced graphene oxide (WSG) with a high concentration by decoration with aminobenzenesulfonic acid (ABS) and reduction with ascorbic acid. The WSG possesses excellent electrical conductivity (360 S m−1), good water dispersion stability as well as a high zeta potential value (−62 mV at pH 11), and the concentration of the as-prepared WSG could reach 5 mg mL−1, nearly as great as the highest value from previous reports. Then, using this high-concentration WSG dispersion directly as an electrochemically active ink material, micro-supercapacitor electrodes could be facilely fabricated via a direct printing technique on common printing paper, and the all-solid-state flexible MSCs could be further assembled. The results show that these flexible MSCs exhibit high area and volume specific capacitances of 2.67 mF cm−2 and 6.75 F cm−3, maintaining 94.8% of their initial specific capacitance after 5000 cycles at a scan rate of 50 mV s−1. More importantly, the capacitance and potential can be expanded by connecting a WSG-MSC device in parallel and in series, and the assembled devices are further demonstrated to be capable of lighting a liquid crystal display with three WSG-MSCs in series. These findings not only provide a simple way to synthesize WSG with a high concentration, but also facilitate its applications in printable and flexible MSCs with high performance.