High capacitance for asymmetric supercapacitors based on one-step synthetic nanoflowers/nanocones arrays as cathode and pomelo peel as anode

In this work, NiCoO2 nanoflowers and nanocones are synthesized by one-step hydrothermal method. A layer of NiCoO2 nanoflowers is initially grown on the surface of Ni foam, followed by subsequent growth of NiCoO2 nanocones in order to obtain hierarchical NiCoO2/NiCoO2 nanoflowers/nanocones arrays (NNFC arrays). Various characterization methods are used to ensure the structure, morphology and composition of the materials. The results confirm that the as-prepared sample exhibits high specific surface area and voidage, low electrode internal resistance (0.5Ω), extremely fast diffusion and migration, and high electrochemical performance (1215.2 ​F ​g−1 at 5 ​mA ​cm−2). Furthermore, an all-solid-state supercapacitor (ASC) using NNFC arrays as a cathode, pomelo peel carbon (PPC) as an anode, and polyvinyl alcohol/KOH as separator is assembled. The ASC exhibits excellent specific capacitance (318.7 ​F ​g−1 at 5 ​mA ​cm−2) and large energy density (113.3 ​Wh·kg−1 at 396 ​W ​kg−1). Two ASCs in series can illume a red LED of 1.8 ​V for 30 ​min. The present work provides an effective approach to hydrothermally prepare two different morphologies in one-step, offering a facile and cost-efficient route to design outstanding supercapacitors (SCs).