Effects of Oxygen Content during Heat Treatment on Properties of Solution-Processed Cu2O-αFe2O3 Composite for Supercapacitor Application

Abstract

The Cu2O-αFe2O3 composite film was heated in air (FC-A), O2 (FC-O) and vacuum (FC-V) respectively to investigate the effects of heat-treated conditions on the material and electrochemical characteristics. As a result, the heat treatment did not significantly affect the morphology but the grain size and crystal phase of the materials. In accordance with the oxygen content in the heat treatment environment, the heat-treated composite films performed as a mixed phase containing mainly CuFe2O4, parts of αFe2O3 (relatively high O2 content) and Cu-Sn alloy (low O2 content). With tuning the oxygen content in/on the crystal lattice of CuFe2O4 and αFe2O3, the energy storage mechanism of the composite electrode could be modified from the comprehensively capacitive and pseudocapacitive effects to an independent EDLC behavior. Compared with the FC-O and FC-V electrodes, the FC-A electrode presented a better capacitance retention (1.8% capacitance loss up to 2,000 cycles) and the highest specific capacitance (176.2 F·g−1 at 0.5 mA·cm−2). The outstanding performance can be ascribed to its lower charge transfer resistance, the porous feature having faster ion transportation efficiency and the additional pseudocapacitance provided by the Faradaic redox reaction.