Redox-Mediated Shape Transformation of Fe₃O₄ Nanoflakes to Chemically Stable Au−Fe₂O₃ Composite Nanorods for a High-Performance Asymmetric Solid-State Supercapacitor Device

Abstract

Development of a stable and highly active metal oxide based electrochemical supercapacitor is a major challenge. Herein, we report a Au–Fe2O3 nanocomposite having tiny amount of gold (3 atomic % Au) by employing a simple redox-mediated synthetic methodology using a modified hydrothermal system. Structural and morphological studies of the synthesized Au–Fe2O3 nanocomposite have been performed both experimentally (XRD, IR, Raman, XPS, TEM, and FESEM analyses) and theoretically (WIEN2K). A probable dissolution–nucleation–recrystallization growth mechanism has been suggested to explain the morphological transformation from a Fe3O4 nanoflake to a Au–Fe2O3nanorod. We have observed the superior chemical stability of the Au–Fe2O3 nanocomposite in an acidic medium due to composite formation. The electrochemical measurement of the synthesized Au–Fe2O3 nanocomposite exhibits specific capacitance of ∼570 F g–1 at the current density of 1 A g–1 in 0.5 M H2SO4 electrolyte. The result is superior compared to the mother component, i.e., Fe2O3 (138 F g–1), under identical conditions. It is credited to its higher specific surface area and composite effect. Theoretically, a decrease in band gap associated with increase in conductivity supports the superiority of the Au–Fe2O3 nanocomposite compared to the mother compound, i.e., Fe2O3. In addition, electrochemical kinetic analysis showed that the charge-storage mechanism is mostly from a dominant capacitive process (78% at 1.5 mV s–1). A solid-state asymmetric supercapacitor device has been fabricated using a synthesized Au–Fe2O3 composite nanorod as the positive and activated carbon as the negative electrodes. The asymmetric solid-state device exhibits a maximum energy density of 34.2 Wh kg–1 and power density of 2.73 kW kg–1 at current densities 1 A g–1 and 10 A g–1, respectively. Thus, the synthesized nanocomposite shows excellent activity as a supercapacitor with long-term durability (91% capacitance retention) up to 5000 cycles even in an acidic medium.