High-performance hybrid supercapacitors based on hierarchical NiC2O4/Ni(OH)2 nanospheres and biomass-derived carbon

The high-performance hybrid supercapacitor (HSC) with high power capability and stable cyclability is intensively pursued as a next-generation energy storage device. Here, a kind of hierarchical NiC2O4/Ni(OH)2 nanospheres, consisting of subunits of NiC2O4 nanorods and Ni(OH)2 nanospheres, are synthesized via a two-step hydrothermal method. The hierarchical NiC2O4/Ni(OH)2 nanosphere positive electrode, benefiting from the synergistic effect of unique hierarchical structure and built-in electric fields, significantly boosting electron transmission capability and accelerating the ion/electron transfer rate, delivers an excellent specific capacity of 668 C g−1 at 1 A g−1. In addition, the porous biomass-derived carbon (PBC) with the honeycomb structure from pine petals as the negative electrode shows a remarkable electrochemical performance, exhibiting a specific capacitance of 249.7 F g−1 at 1 A g−1. As such, an assembled HSC of NiC2O4/Ni(OH)2||PBC based on hierarchical NiC2O4/Ni(OH)2 nanospheres positive electrode and PBC negative electrode display a conspicuous energy density of 31.07 Wh kg−1, and a power density of 833.47 W kg−1 at a maximum potential window of 1.7 V. This innovative hierarchical engineering of double nickel-based composites with bio-carbon provides an advanced enlightenment for high-performance HSCs.