Ultrafast microwave synthesized Ni2Co-S 2D sheet architectures battery-type electrodes for structure-tunable superior hybrid supercapacitor

Abstract

NiCo-S has been regarded as a promising battery-type electrode for efficient supercapacitors owing to its hybrid orbitals, abundant reserve and multiple valence states. The tailored morphology and crystalline structure of NiCo-S can be achieved by using microwave methods profiting from the uniform heat distribution. Herein, a facile, “atmosphere-free” and highly-efficient microwave-assisted method was used to fabricate Ni2Co-S 2D sheet materials with hierarchical porosity and excellent electrochemical behaviours as battery-type electrodes for hybrid supercapacitor. Considerable metal ratio regulation endowed Ni2Co-S specific structure of 2D sheets with metal-nanoparticles and abundant active sites with variable valence state. Based on the simulation results, the low OH bond energy for Ni2Co-S promoted the deprotonative reaction in the electrochemical charge/discharge process, and the synergistic interaction of Ni and Co at the surface contributed to more free electrons, more active sites for the redox reaction and superior OH− adsorption ability. Ni2Co-S exhibited excellent capacity of 1440 F g−1 at 1 A g−1 and rate retention of 74.3 % 1 to 20 A g−1. In addition, the hybrid supercapacitor assembled by Ni2Co-S delivered a superior energy density of 65.2 Wh kg−1 at 400 W kg−1, along with a stable cycling lifespan with 82 % of capacity retention and 100 % of Coulombic efficiency after 30,000 cycles. The present strategy can modulate NiCo-S phase and structure via ultrafast microwave synthesis, which provides a novel insight for development of high-performance supercapacitors.