Intrinsic electrochemical activity modulation of MOF-derived C/N-NiCoMn-LDH/Ag electrode for low temperature hybrid supercapacitors

Abstract

Layered double hydroxides (LDHs) are promising electrode candidates for supercapacitors. However, limitations like inferior cycling stability and unsatisfactory charge storage capability at low temperatures have exerted negative effects on their applications. Herein, a novel synthetic process has been elaborately designed and provided to have the composition and structure of the C/N-NiCoMn-LDH/Ag (C/N-CNMA) delicately regulated. Both the experimental and theoretical researches unveil that the incorporated manganese species and elemental silver could dramatically modulate the bandgap, crystallinity and surface electron structure of the LDH, leading to the remarkable improvement in its conductivity, exposed active sites and intrinsic electrochemical activity, and thus the OH* and O* adsorption free energy could be remarkably optimized, even at low temperatures. In addition, the low crystallinity C/N-CNMA is of great electrochemical compatibility with both the KOH aqueous electrolyte and the isobutyl alcohol (IPA) modulated organohydrogel electrolyte. By means of adjusting the solvation and hydrogen bonding in the electrolytes, the assembled hybrid supercapacitors deliver excellent energy density, power density and cycling stability in the temperature range of -30 to 25 °C. Specifically, the gel electrolyte with IPA as the anti-freezing functional additive displays high flexibility and ionic conductivity at low temperatures.