Development of high performance alpha-Co(OH)2/reduced graphene oxide microfilm for flexible in-sandwich and planar micro-supercapacitors

In-sandwich and planar α-Co(OH)2/rGO film-based MSCs were firstly assembled, which show high specific area capacitance and excellent energy density. [Display omitted] Herein, a series of alpha-Co(OH)2/reduced graphene oxide (rGO) microfilms and film-based nanodevices were developed via a new scalable technique. Due to the unique hexagonal nanoplates of ultrathin alpha-Co(OH)2 and the intrinsically conductive nature of rGO sheets, such thin films not only can improve the conductivity of alpha-Co(OH)2 and prevent the re-stacking of alpha-Co(OH)2 and rGO sheets but also short the transport routes of electrons and ions between the electrode and the electrolyte. The optimized alpha-Co(OH)2/rGO flexible electrode presents high specific capacitance (273.86 mF/cm2 at 0.1 mA/cm2), advanced rate capability, and excellent coulombic efficiency. Simultaneously, in-sandwich symmetric and asymmetric supercapacitors assembled with polyvinyl alcohol-KOH gel as the solid-state electrolyte achieved high areal and volumetric specific capacitances. Furthermore, a self-assembled planar alpha-Co(OH)2/rGO micro-supercapacitor (MSC) delivers high specific area capacitance (130F/cm2 at 0.5 mA/cm2) and excellent energy density (20 mWh/cm3@56 mW/cm3), which are superior to most of the recently reported carbon-based and metal hydroxides/oxides/sulfides-based planar MSCs. Also, our planar MSC shows excellent cycling performance, good flexibility, and mechanical stability. This work promotes the syntheses of other two-dimensional metal hydroxides/rGO composite film for high-performance flexible micro-electronics.