Low-crystalline mesoporous CoFe2O4/C composite with oxygen vacancies for high energy density asymmetric supercapacitors

Recently, nano/micro-scale Fe-based ferrites with high electrochemical performances have attracted extensive attention. However, almost all the mixed Fe-based oxide research paid close attention to the crystalline phase, despite the low-crystalline or amorphous phase possessing excellent electrochemical performance. Herein, a low-crystalline mesoporous cobalt ferrite and carbon composite (L-CoFe2O4/C) material with high surface area and superior electrical conductivity was prepared via a simple citric acid assisted sol-gel approach and calcination process. The L-CoFe2O4/C electrode exhibits an unprecedented specific capacitance (600 F g(-1) at 1 A g(-1)), which precedes some of the reported mixed Fe-based ferrite electrodes and their crystalline counterparts. The excellent electrochemical performance can mainly be attributed to the sufficient diffusion and reaction of electrolyte ions, more surface defects (e.g. oxygen vacancies) for redox reactions, and the predominant electro-conductivity of the composite during the charging/ discharging process. Moreover, an L-CoFe2O4/C-based asymmetric supercapacitor exhibited high energy density and power density, and outperformed most of the reported mixed Fe-based symmetric and asymmetric supercapacitors. These findings promote new opportunities for low-crystalline Fe-based metal oxides as high performance energy storage devices.