Synergistic effect of two complexing agents on the hydrothermal synthesis of self-supported ZnNiCo oxide as electrode material in supercapacitors

Abstract

Choosing and optimizing electrode materials is of paramount importance for preparing a supercapacitor device. The metal oxides and carbon-based materials are known as suitable candidates for this purpose. In this work, zinc-nickel–cobalt oxide (ZNCO) and three-dimensional graphene (3DG) have been applied as positive and negative electrodes, respectively. Both cathode and anode materials were synthesized by a simple one-step hydrothermal method without using a growth substrate. Since time is one of the critical parameters in hydrothermal synthesis method, we prepared ZNCO samples in three different reaction times to optimize this parameter. Synergistic combination of ammonium fluoride and urea as two common complexing reagents on the morphology and electrochemical characteristics of ZNCO was investigated. Moreover, the physicochemical and electrochemical characteristics of ZNCO were compared with those of bimetallic oxides prepared based on Zn, Ni and Co using the same conditions. Results revealed that the trimetallic oxide delivers a higher specific capacity than the bimetallic oxides synthesized in this work. The assembled hybrid supercapacitor by ZNCO-10′//3DG configuration exhibited a wide operating voltage of 1.7 V and the highest areal energy density of 8.52 mWh cm−2 at a maximum power density of 1329.44 mW cm−2. Moreover, it showed excellent cyclic stability and capacity retention of about 119% after 2000 cycles at 25 mA cm−2 current density.