Etching and isolation technique for synthesis of CNTs-encapsulated NiSe2/CoSe2 for supercapacitor applications

The microstructure of carbon nanotubes (CNTs) plays a pivotal role in determining their performance as electrode materials. Herein, CNTs encapsulating NiSe 2 /CoSe 2 nanoparticles (CNT@NiCo-Se) are derived from Ni-Co Prussian blue analogue (Ni-Co PBA), and the CNTs possess smaller diameter and larger interlayer spacing due to the “etching and isolation technique” that is adopted to prevent the accumulation of Ni/Co in Ni-Co PBA during the calcination process. CNT@NiCo-Se exhibits a specific capacity  of 105.1 mAh g −1 at a current density of 1 A g −1 , which is 375 % higher than that obtained without isolation strategy, which resulted in the microstructure advantages of smaller diameter and larger interlayer spacing. The actual reason is that smaller diameter and larger interlayer spacing correspond to higher charge transfer density and increased the –OH binding energy (OHBE) according to density functional theory (DFT) calculation results. In addition, the assembled asymmetric supercapacitor (ASC) device exhibits a high energy density of 46.3 Wh kg −1 at 801 W kg −1 and a high power density of 8000 W kg −1 at an energy density of 12.0 Wh kg −1 , and the initial specific capacitance of 80.4 % can be maintained after 10,000 cycles at 10 A g −1 . More importantly, this work provides a novel strategy for microstructure adjustment of CNTs in the field of energy storage and conversion.