One-step mild synthesis of Mn-based spinel MnIICrIII2O4/MnIIMnIII2O4/C and Co-based spinel CoCr2O4/C nanoparticles as battery-type electrodes for high-performance supercapacitor application

Two chromite spinel-based composite materials, (MnCr2O4)-Cr-II-O-III/(MnMn2O4)-Mn-II-O-III/C and CoCr2O4/C are successfully synthesized by a solid-state conversion process via annealing Mn-Cr-coordination compound and Co-Cr-coordination compound at 350 degrees C in air for 1 h, respectively. The two composite materials both show the morphology of nanoparticles, in which the spinels are embedded in carbon matrix into a continuous phase. The as-prepared composite materials are used as supercapacitor electrodes in basic electrolyte. The (MnCr2O4)-Cr-II-O-III/(MnMn2O4)-Mn-II-O-III/C composite material possesses a high specific capacity of 184.0 mAh g(-1) at a current density of 0.5 A g(-1) with a superior rate capability of 138.3 mAh g(-1) (75.2% retention) at 20 A g(-1). Meanwhile, CoCr2O4/C nanoparticles also deliver a high specific capacity of 158.8mAh g(-1) at a current density of 0.5 A g(-1) with a superior rate capability of 125.0mAh g(-1) (78.7% retention) at 20 A g(-1). The good supercapacitive behaviors of the two composite materials are probably attributed to the characteristics of bimetallic compound and the presence of multiple valence states in the samples, giving rise to obvious redox responses. And the (MnCr2O4)-Cr-II-O-III/(MnMn2O4)-Mn-II-O-III/C and CoCr2O4/C composites possess reversible electrochromism. (C) 2018 Elsevier Ltd. All rights reserved.