In-situ growth of Ni(OH)2 nanoplates on highly oxidized graphene for all-solid-state flexible supercapacitors

Pseudocapacitive materials are vitally important to the development of flexible supercapacitors but usually suffer from poor conductivity and stability. In this work, a Ni(OH)2/HGO nanocomposite was fabricated by in-situ growth of Ni(OH)2 nanoplates on highly-oxidized graphene oxide (HGO). A series of characterizations reveal the abundant out-of-plane active sites of HGO enable the uniformly grown Ni(OH)2 nanoplates with smaller crystalline size and stronger anchoring with HGO substrates. Furthermore, benefit from the porous structure and improved conductivity of HGO substrates together with more exposed active sites of Ni(OH)2 nanoplates, the complex Ni(OH)2/HGO electrode exhibits a remarkable specific capacitance of 1430.9F/g at 5 A/g, which is much higher than those of the pure Ni(OH)2 of 329.8F/g and Ni(OH)2 on the untreated GO (Ni(OH)2/GO) of 538.3F/g. Even under an ultrahigh current density of 60 A/g, the specific capacitance of Ni(OH)2/HGO electrodes still reach up to 850F/g, delivering a superior rapid-charging capability. In addition, by using screen-printing techniques, an all-solid-state Ni(OH)2/HGO//activated carbon-based asymmetric flexible supercapacitor is fabricated and displays an excellent areal specific capacitance of 322 mF/cm2, outstanding energy density (0.134 mW h/cm2) and power density (33.6 mW/cm2). Moreover, the capacity of all-solid-state flexible supercapacitors (AFSCs) remains 80 %, even bending to various angles and for 1000 times, showing good flexibility. This work provides inspiration for rational development of Ni(OH)2-based pseudocapacitive materials and high-performance AFSCs for portable and wearable electronics.