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

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-Fe(2)O(3)nanorod. 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 similar to 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.