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−Fe 2 O 3 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−Fe 2 O 3 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 Fe 3 O 4 nanoflake to a Au−Fe 2 O 3 nanorod. We have observed the superior chemical stability of the Au−Fe 2 O 3 nanocomposite in an acidic medium due to composite formation. The electrochemical measurement of the synthesized Au−Fe 2 O 3 nanocomposite exhibits specific capacitance of ∼570 F g −1 at the current density of 1 A g −1 in 0.5 M H 2 SO 4 electrolyte. The result is superior compared to the mother component, i.e., Fe 2 O 3 (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−Fe 2 O 3 nanocomposite compared to the mother compound, i.e., Fe 2 O 3 . 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−Fe 2 O 3 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.

Role of the Support in Gold-Containing Nanoparticles as Heterogeneous Catalysts

“…Interestingly, the energy required to create an oxygen vacancy in the oxidized part of the Au cluster was calculated to be 1.96 eV, indicating that the oxygen anions in the α-Fe 2 O 3 (0001) near to the cluster are more available for a MvK oxidation of CO than are the oxygen atoms introduced into the Au cluster by O 2 dissociation. Haruta has also considered the polymorph of the iron oxide support, producing an Au catalyst supported on mesoporous maghemite, γ-Fe 2 O 3 , nanoflakes 212 using a deposition− precipitation method. 213 The γ-Fe 2 O 3 appears to be a support, giving Au catalyst with higher CO oxidation activity than α-Fe 2 O 3 due to it being more easily reduced.…”

“…Haruta has also considered the polymorph of the iron oxide support, producing an Au catalyst supported on mesoporous maghemite, γ-Fe 2 O 3 , nanoflakes using a deposition–precipitation method . The γ-Fe 2 O 3 appears to be a support, giving Au catalyst with higher CO oxidation activity than α-Fe 2 O 3 due to it being more easily reduced .…”

One-Pot Synthesis of a Three-Dimensional Au-Decorated Cellulose Nanocomposite as a Surface-Enhanced Raman Scattering Sensor for Selective Detection and in Situ Monitoring

“…The HRTEM analysis (Figure C) of Au/RCF-4 illustrated that more spherical Au NPs with small particle size were embedded in the cellulose matrix. The 0.24 nm lattice fringes could be indexed to the (111) spacing of Au . Moreover, the SAED pattern (Figure D) showed diffraction spots corresponding to the (111), (220), and (311) lattice planes of the Au crystal.…”

“…The 0.24 nm lattice fringes could be indexed to the (111) spacing of Au. 44 Moreover, the SAED pattern (Figure 4D) showed diffraction spots corresponding to the (111), (220), and (311) lattice planes of the Au crystal. This further confirmed that the synthesized NPs mediated by cellulose were well crystallized, which was consistent with the XRD results.…”

Partially Graphitized Iron−Carbon Hybrid Composite as an Electrochemical Supercapacitor Material

“…reported Au‐Fe 2 O 3 composite nanorods having a gravimetric capacitance of ∼570 F/g at 1 A/g in 0.5 M aq. H 2 SO 4 in a three‐electrode system . Ishaq et al.…”