Monolayer Nickel Cobalt Hydroxyl Carbonate for High Performance All-Solid-State Asymmetric Supercapacitors.

The emergence of atomically thick nanolayer materials, which feature a short ion diffusion channel and provide more exposed atoms in the electrochemical reactions, offers a promising occasion to optimize the performance of supercapacitors on the atomic level. In this work, a novel monolayer Ni-Co hydroxyl carbonate with an average thickness of 1.07 nm is synthesized via an ordinary one-pot hydrothermal route for the first time. This unique monolayer structure can efficiently rise up the exposed electroactive sites and facilitate the surface dependent electrochemical reaction processes, and thus results in outstanding specific capacitance of 2266 F g(-1). Based on this material, an all-solid-state asymmetric supercapacitor is developed adopting alkaline PVA (poly(vinyl alcohol)) gel (PVA/KOH) as electrolyte, which performs remarkable cycling stability (no capacitance fade after 19 000 cycles) together with promising energy density of 50 Wh kg(-1) (202 µWh cm(-2)) and high power density of 8.69 kW kg(-1) (35.1 mW cm(-2)). This as-assembled all-solid-state asymmetric supercapacitor (AASC) holds great potential in the field of portable energy storage devices.

Nickel Cobalt Hydroxide @Reduced Graphene Oxide Hybrid Nanolayers for High Performance Asymmetric Supercapacitors with Remarkable Cycling Stability.

Nanolayered structures present significantly enhanced electrochemical performance by facilitating the surface-dependent electrochemical reaction processes for supercapacitors, which, however, causes capacitance fade upon cycling due to their poor chemical stability. In this work, we report a simple and effective approach to develop a stable, high performance electrode material by integrating 2D transition metal hydroxide and reduced graphene oxide sheets at nanometer scale. Specifically, a hybrid nanolayer of Ni-Co hydroxide @reduced graphene oxide (Ni,Co-OH/rGO) with an average thickness of 1.37 nm is synthesized through an easy one-pot hydrothermal method. Benefiting from the face to face contact model between Ni-Co hydroxide and rGO sheets, such unique structure presents superior specific capacitance and cycling performance as compared to the pure Ni-Co hydroxide nanolayers. An asymmetric supercapacitor based on Ni,Co-OH/rGO and three-dimensional (3D) hierarchical porous carbon is developed, exhibiting a high energy density of 56.1 Wh kg(-1) along with remarkable cycling stability (80% retention after 17 000 cycles), which holds great promise for practical applications in energy storage devices.