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[Display omitted] • Hierarchical 1D/2D Ni(OH) 2 /PCC is fabricated via a facile hydrothermal route as the positive electrode. • The porous corn stigma-derived carbon with the 3D open framework is preparated as the negative electrode. • Explore the excellent electrochemical performance of 1D/2D Ni(OH) 2 /PCC by DFT. • The hybrid supercapacitor displays supeiror energy and power density. Enhancing the energy density of supercapacitors is of great scientific and technological importance, producing a larger energy density than traditional symmetrical carbon supercapacitors. Herein, a hybrid supercapacitor based on an activated corn stigma-derived carbon (PCC) electrode combined with a large-capacity faradic 1D nanofiber/2D nanosheet Ni(OH) 2 electrode is designed to fulfill this goal. Benefiting from the highly conductive, porous construction, and 3D open framework of PCC electrode couple with unique hierarchical 1D nanofiber/2D nanosheet Ni(OH) 2 , such 1D/2D Ni(OH) 2 /PCC electrode is capable of increasing accessible active sites, shortening ion-diffusion path, and accelerating mass transfer. More importantly, DFT calculations unveil that 1D/2D Ni(OH) 2 /PCC composites own high electrical conductivity and OH– adsorption energy. Therefore, the specific capacity of the 1D/2D Ni(OH) 2 /PCC composite electrode reaches 655.9C g−1 at the current density of 1 A/g. Moreover, such hybrid 1D/2D Ni(OH) 2 /PCC||PCC supercapacitor show an outstanding energy density and power density of 38.6 Wh kg−1, and 1.03 kW kg−1, respectively. This work provides the possibility of fabricating hierarchical hydroxide/bio-carbon as a better electrode for high-energy–density electrochemical supercapacitors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hierarchical NiC 2 O 4 /Ni(OH) 2 nanospheres are synthesized via a simple two-step hydrothermal method as the positive electrode. • The porous biomass-derived carbon with the honeycomb structure is obtained from pine petals as the negative electrode. • Hierarchical NiC 2 O 4 /Ni(OH) 2 nanospheres and the porous biomass-derived carbon possess a high specific capacity. • The hybrid supercapacitor exhibits excellent energy and power density. 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 NiC 2 O 4 /Ni(OH) 2 nanospheres, consisting of subunits of NiC 2 O 4 nanorods and Ni(OH) 2 nanospheres, are synthesized via a two-step hydrothermal method. The hierarchical NiC 2 O 4 /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 NiC 2 O 4 /Ni(OH) 2 ||PBC based on hierarchical NiC 2 O 4 /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. [ABSTRACT FROM AUTHOR]