Boosting the energy density of iron-cobalt oxide based hybrid supercapacitors by redox-additive electrolytes

Abstract

Due to the increasing requirement of small electronic devices for high energy output and long-term lifespan, hybrid supercapacitor device with ultrahigh energy density and long cycle stability has attracted great attention in recent decades. Herein, we constructed an aqueous FeCo2O4 needle-like array (NLA)/CC-based hybrid supercapacitor using K3[Fe(CN)6] as an electrolyte additive to enhance the pseudocapacitor performance. The extensive charge storage kinetics and the electron transport mechanism of the FeCo2O4-NLA in KOH+K3[Fe(CN)6] electrolyte are discussed. The FeCo2O4-NLA soaked in a 3 M KOH + 0.05 M K3[Fe(CN)6] mixed solution shows high specific capacitance (259.33 mA h g−1 at 2 A g−1), low charge transfer resistance and internal resistance, and long-term cycle stability (over 80.7% of capacitance retention at 10 A g−1 after 5000 cycles). An aqueous FeCo2O4-NLA//KOH+K3[Fe(CN)6]//AC hybrid supercapacitor device is assembled, which presents increased specific capacitance, long cycle stability (86.4% of the initial capacitance), and ultrahigh energy density (58.8 W h kg−1 @750.1 W kg−1). This work may provide a new approach to obtain high-performance energy storage devices.