Nano-sheet-like KNiPO4 as a positive electrode material for aqueous hybrid supercapacitors

Abstract

A facile sol-gel thermolysis route was adopted to synthesize KNiPO4 nano-sheets for the design of hybrid supercapacitors. The phase purity, homogeneity, and functional groups present in the synthesized KNiPO4 were characterized through X-ray diffraction and FTIR measurements. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images showed that the nano-sheet-like particles were loosely stacked. The electrochemical properties of the KNiPO4 electrode were studied in various aqueous-based electrolytes such as 1M LiOH, 1M NaOH, and 1M KOH to explore their superior performances. Among these electrolytes, the KNiPO4 electrode provided a maximum specific capacity of 278 Cg−1 in 1M KOH at 5mVs−1. A hybrid supercapacitor was fabricated using the synthesized KNiPO4 as the positive electrode and activated carbon as the negative electrode in a 1M KOH aqueous electrolyte. The supercapacitor exhibited a specific capacitance of 48Fg−1 in 1M KOH at 0.6mAcm−2 and energy density of 13Whkg−1 at a power density of 59Wkg−1. In addition, the hybrid system retained 93% of its initial specific capacitance even after 2000 cycles. A KNiPO4-based hybrid system thus exhibits superior characteristics and hence is a promising candidate for high-performance electrochemical energy storage devices.