Composites made of lotus-seedpod-derived carbon and nickel hydroxide sulfate nanofibers: Advanced materials for supercapacitor electrodes

Abstract

Nickel hydroxide sulfate (NSOH) is a promising electrode material for supercapacitors (SCs) for its high redox activity, good cycling stability and low self-discharge rate. However, agglomeration of the nanocrystalline NSOH during charge-discharge cycles reduces the charge transfer rate in the electrodes and through the electrode/electrolyte interfaces and thus degrades capacity and durability. This work reports a strategy to avoid this drawback by embedding NSOH nanofibers (NFs) within activated lotus-seedpod-derived carbon (ALSC) to stimulate synergistic effect between the NSOH and the carbon skeleton toward high-performance electrodes for SCs. The created ALSC@NSOH electrode achieves a desirable specific capacity of 414.9 mAh g⁻¹ (2,987.6 F g⁻¹), which is 2.1 times that of the carbon-free NSOH electrode, and preserves 87.6 % of the initial capacity after 10,000 galvanostatic charge-discharge (GCD) cycles. Encouragingly, the hybrid supercapacitor (HSC) configurated with ALSC@NSOH//ALSC obtains a high energy density of 129.33 Wh kg⁻¹ at 817.39 W kg⁻¹ and an impressive durability of 86.7 % capacity retention for up to 5,000 GCD cycles. This work develops a methodology for transforming waste into energy storage materials, which is beneficial for waste disposal and fossil fuel emissions alleviation and is significant to the environment and circular economy.