Influence of Fe Doping on the Electrochemical Performance of a ZnO-Nanostructure-Based Electrode for Supercapacitors.

ZnO is a potential candidate for providing an economic and environmentally friendly substitute for energy storage materials. Therefore, in this work, Fe-doped ZnO nanostructures prepared using the microwave irradiation procedure were investigated for structural, morphological, magnetic, electronic structural, specific surface area and electrochemical properties to be used as electrodes for supercapacitors. The X-ray diffraction, high-resolution transmission electron microscopy images, and selective-area electron diffraction pattern indicated that the nanocrystalline structures of Fe-doped ZnO were found to possess a hexagonal wurtzite structure. The effect of Fe doping in the ZnO matrix was observed on the lattice parameters, which were found to increase with the dopant concentration. Rods and a nanosheet-like morphology were observed via FESEM images. The ferromagnetic nature of samples is associated with the presence of bound magnetic polarons. The enhancement of saturation magnetization was observed due to Fe doping up to 3% in correspondence with the increase in the number of bound magnetic polarons with an Fe content of up to 3%. This behavior is observed as a result of the change in the oxidation state from +2 to +3, which was a consequence of Fe doping ranging from 3% to 5%. The electrode performance of Fe-doped ZnO nanostructures was studied using electrochemical measurements. The cyclic voltammetry (CV) results inferred that the specific capacitance increased with Fe doping and displayed a high specific capacitance of 286 F·g-1 at 10 mV/s for 3% Fe-doped ZnO nanostructures and decreased beyond that. Furthermore, the stability of the Zn0.97Fe0.03O electrode, which was examined by performing 2000 cycles, showed excellent cyclic stability (85.0% of value retained up to 2000 cycles) with the highest specific capacitance of 276.4 F·g-1, signifying its appropriateness as an electrode for energy storage applications.

Improvement of Supercapacitor Performance of In Situ Doped Laser-Induced Multilayer Graphene via NiO.

Herein, we have reported a novel strategy for improving the electrochemical performance of laser-induced graphene (LIG) supercapacitors (SCs). The LIG was prepared using a CO2 laser system. The polyimide polymer was the source material for the fabrication of the LIG. The doping process was performed in situ using the CO2 laser, which works as a rapid thermal treatment to combine graphene and NiO particles. NiO was used to improve the capacitance of graphene by combining an electric double-layer capacitor (EDLC) with the pseudo-capacitance effect. The high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, and Raman spectroscopy showed that the structure of the LIG is multilayered and waved. The HRTEM image proves the distribution of NiO fine particles with sizes of 5-10 nm into the graphene layers. The electrochemical performance of the as-prepared LIG was tested. The effect of the combination of the two materials (oxide and carbon) was investigated at different concentrations. The LIG showed a specific capacitance of 69 Fg-1, which increased up to 174 Fg-1 for the NiO-doped LIG. The stability investigations showed that the electrodes were very stable for more than 1000 cycles. This current study establishes an innovative method to improve the electrochemical properties of LIG.

Investigations of Structural, Magnetic, and Electrochemical Properties of NiFe2O4 Nanoparticles as Electrode Materials for Supercapacitor Applications.

Magnetic nanoparticles of NiFe2O4 were successfully prepared by utilizing the sol-gel techniques. The prepared samples were investigated through various techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), dielectric spectroscopy, DC magnetization and electrochemical measurements. XRD data analysed using Rietveld refinement procedure inferred that NiFe2O4 nanoparticles displayed a single-phase nature with face-centred cubic crystallinity with space group Fd-3m. Average crystallite size estimated using the XRD patterns was observed to be ~10 nm. The ring pattern observed in the selected area electron diffraction pattern (SAED) also confirmed the single-phase formation in NiFe2O4 nanoparticles. TEM micrographs confirmed the uniformly distributed nanoparticles with spherical shape and an average particle size of 9.7 nm. Raman spectroscopy showed characteristic bands corresponding to NiFe2O4 with a shift of the A1g mode, which may be due to possible development of oxygen vacancies. Dielectric constant, measured at different temperatures, increased with temperature and decreased with increase in frequency at all temperatures. The Havrilliak-Negami model used to study the dielectric spectroscopy indicated that a NiFe2O4 nanoparticles display non-Debye type relaxation. Jonscher's power law was utilized for the calculation of the exponent and DC conductivity. The exponent values clearly demonstrated the non-ohmic behaviour of NiFe2O4 nanoparticles. The dielectric constant of the nanoparticles was found to be >300, showing a normal dispersive behaviour. AC conductivity showed an increase with the rise in temperature with the highest value of 3.4 × 10-9 S/cm at 323 K. The M-H curves revealed the ferromagnetic behaviour of a NiFe2O4 nanoparticle. The ZFC and FC studies suggested a blocking temperature of ~64 K. The saturation of magnetization determined using the law of approach to saturation was ~61.4 emu/g at 10 K, corresponding to the magnetic anisotropy ~2.9 × 104 erg/cm3. Electrochemical studies showed that a specific capacitance of ~600 F g-1 was observed from the cyclic voltammetry and galvanostatic charge-discharge, which suggested its utilization as a potential electrode for supercapacitor applications.

Fabrication of High-Performance Asymmetric Supercapacitors Using Rice Husk-Activated Carbon and MnFe2O4 Nanostructures.

To meet the growing demand for efficient and sustainable power sources, it is crucial to develop high-performance energy storage systems. Additionally, they should be cost-effective and able to operate without any detrimental environmental side effects. In this study, rice husk-activated carbon (RHAC), which is known for its abundance, low cost, and excellent electrochemical performance, was combined with MnFe2O4 nanostructures to improve the overall capacitance of asymmetric supercapacitors (ASCs) and their energy density. A series of activation and carbonization steps are involved in the fabrication process for RHAC from rice husk. Furthermore, the BET surface area for RHAC was determined to be 980 m2 g-1 and superior porosities (average pore diameter of 7.2 nm) provide abundant active sites for charge storage. Additionally, MnFe2O4 nanostructures were effective pseudocapacitive electrode materials due to their combined Faradic and non-Faradic capacitances. In order to assess the electrochemical performance of ASCs extensively, several characterization techniques were employed, including galvanostatic charge -discharge, cyclic voltammetry, and electrochemical impedance spectroscopy. Comparatively, the ASC demonstrated a maximum specific capacitance of ~420 F/g at a current density of 0.5 A/g. The as-fabricated ASC possesses remarkable electrochemical characteristics, including high specific capacitance, superior rate capability, and long-term cycle stability. The developed asymmetric configuration retained 98% of its capacitance even after 12,000 cycles performed at a current density of 6A/g, demonstrating its stability and reliability for supercapacitors. The present study demonstrates the potential of synergistic combinations of RHAC and MnFe2O4 nanostructures in improving supercapacitor performance, as well as providing a sustainable method of using agricultural waste for energy storage.

Structural, Optical, Magnetic and Electrochemical Properties of CeXO2 (X: Fe, and Mn) Nanoparticles.

CeXO2 (X: Fe, Mn) nanoparticles, synthesized using the coprecipitation route, were investigated for their structural, morphological, magnetic, and electrochemical properties using X-ray diffraction (XRD), field emission transmission electron microscopy (FE-TEM), dc magnetization, and cyclic voltammetry methods. The single-phase formation of CeO2 nanoparticles with FCC fluorite structure was confirmed by the Rietveld refinement, indicating the successful incorporation of Fe and Mn in the CeO2 matrix with the reduced dimensions and band gap values. The Raman analysis supported the lowest band gap of Fe-doped CeO2 on account of oxygen non-stoichiometry. The samples exhibited weak room temperature ferromagnetism, which was found to be enhanced in the Fe doped CeO2. The NEXAFS analysis supported the results by revealing the oxidation state of Fe to be Fe2+/Fe3+ in Fe-doped CeO2 nanoparticles. Further, the room temperature electrochemical performance of CeXO2 (X: Fe, Mn) nanoparticles was measured with a scan rate of 10 mV s-1 using 1 M KCL electrolyte, which showed that the Ce0.95Fe0.05O2 electrode revealed excellent performance with a specific capacitance of 945 FÖ¼·g-1 for the application in energy storage devices.

Role of rare-earth oxides, conjugated with [Formula: see text], in the enhancement of power conversion efficiency of dye sensitized solar cells (DSSCs).

Different rare-earth (RE) metal-oxides nano-particles (NPs) viz. Samarium (III) oxide (Sm2O3), Neodymium (III) oxide (Nd2O3), and Gadolinium (III) oxide (Gd2O3) were synthesized using co-precipitation route, and investigated by structural, optical, and morphological studies. Findings and supporting studies were presented to understand the role of RE-metal-oxides NPs as photo-anode material for dye sensitized solar cells (DSSCs) applications. Structural analysis of prepared RE-metaloxides, by X-ray diffraction (XRD), reveals the crystalline nature of the particles ranging from 24 to 37 nm. Morphological study by field emission scanning electron microscopy (FESEM) supports the crystalline nature in the nano range of the prepared RE-metal oxides particles. The observed d values of each sample support the growth of Gd2O3, Nd2O3, and Sm2O3 material. The band-gap of prepared material was estimated from the UV-VIS absorption data and Tauc relation. The observed band gap values are 3.55 eV, 3.31 eV, and 3.52 eV for Gd2O3, Nd2O3, and Sm2O3 respectively. These values are reasonably high compare to the bulk values, indicates the nanostructure formation. Optimized RE-metal oxides NPs employed in the form of TiO2 photo anode for the fabrication of DSSCs. FESEM confirms that the Gd2O3-based photo-anode shows more uniform and decent coverage with more porosity on the TiO2. The EIS measurements of prepared DSSCs also supported the improvement in the photovoltaic output for the modified photo-anode devices as cells with modified photo-anode exhibited less charge recombination at the photo-anode/dye/electrolyte interface with increased electron lifetime leading to improved device performance as compared to the unmodified-based DSSCs. The highest efficiency 5.51% was demonstrated by [Formula: see text]/[Formula: see text] photo-anode-based DSSCs compare to Sm2O3, and Nd2O3 activated photo-anode.

Structural, Magnetic, and Electrical Properties of CoFe2O4 Nanostructures Synthesized Using Microwave-Assisted Hydrothermal Method.

Magnetic nanostructures of CoFe2O4 were synthesized via a microwave-assisted hydrothermal route. The prepared nanostructures were investigated using X-ray diffraction (XRD), field emission electron microscopy (FE-SEM), energy dispersive X-ray (EDX) spectroscopy, high-resolution transmission electron microscopy (HR-TEM), selective area electron diffraction (SAED) pattern, DC magnetization, and dielectric spectroscopy measurements. The crystal structure studied using HR-TEM, SAED, and XRD patterns revealed that the synthesized nanostructures had a single-phase nature and ruled out the possibility of any secondary phase. The lattice parameters and unit cell volume determined from the XRD data were found to be 8.4821 Å and 583.88 Å3. The average crystallite size (~7.0 nm) was determined using Scherrer's equation. The FE-SEM and TEM micrographs revealed that the prepared nanostructures had a spherical shape morphology. The EDX results showed that the major elements present in the samples were Co, Fe, and O. The magnetization (M) versus temperature (T) measurements specified that the CoFe2O4 nanostructures showed ferromagnetic ordering at room temperature. The blocking temperature (TB) determined using the M-T curve was found to be 315 K. The magnetic hysteresis (M-H) loop of the CoFe2O4 nanostructures recorded at different temperatures showed the ferromagnetic behavior of the CoFe2O4 nanostructures at temperatures of 200 K and 300 K, and a superparamagnetic behavior at 350 K. The dielectric spectroscopy studies revealed a dielectric constant (ε') and loss tangent (tanδ) decrease with the increase in the frequency, as well as demonstrating a normal dispersion behavior, which is due to the Maxwell-Wagner type of interfacial polarization. The values of ε' and tanδ were observed to increase with the increase in the temperature.

Structural, Morphological, Optical and Magnetic Studies of Cu-Doped ZnO Nanostructures.

In the present work, Cu-doped ZnO nanostructures (Cu% = 0, 1, 5) have been prepared using microwave-assisted chemical route synthesis. The synthesized nanostructures were investigated through structural, morphological, optical, and magnetic characterizations. The results of the X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), and selective area electron diffraction (SAED) patterns confirmed that all of the samples exhibit the single-phase polycrystalline hexagonal crystal structure. The XRD results infer a decrease in the lattice parameters (a/c) by increasing the Cu% doping into ZnO. The field emission scanning electron microscopy (FE-SEM) and energy dispersive x-ray (EDX) spectroscopic measurements revealed the formation of nanostructures, showing the major elemental presence of Zn and O in the samples. The photoluminescence (PL) spectra exhibited photoemission in the UV and blue-green regions. With the increase in the Cu%, the photoemission in the UV region is reduced, while it is enhanced in the blue-green region. Raman spectra of the Cu-doped ZnO nanostructures displayed a blue shift of the E2High mode and an increase in the peak intensity of E1(LO), indicating the doping of Cu ion in the ZnO lattice. The dc magnetization measurements demonstrated the ferromagnetic behavior of all of the samples with an enhanced ferromagnetic character with increasing Cu%.

Role of Cr Doping on the Structure, Electronic Structure, and Electrochemical Properties of BiFeO3 Nanoparticles.

BiFe1−xCrxO3, (0 ≤ x ≤ 10) nanoparticles were prepared through the sol−gel technique. The synthesized nanoparticles were characterized using various techniques, viz., X-ray diffraction, high-resolution field emission scanning electron microscopy (HRFESEM), energy dispersive spectroscopy (EDS), UV−Vis absorption spectroscopy, photoluminescence (PL), dc magnetization, near-edge X-ray absorption spectroscopy (NEXAFS) and cyclic voltammetry (CV) measurements, to investigate the structural, morphological, optical, magnetic and electrochemical properties. The structural analysis showed the formation of BiFeO3 with rhombohedral (R3c) as the primary phase and Bi25FeO39 as the secondary phase. The secondary phase percentage was found to reduce with increasing Cr content, along with reductions in crystallite sizes, lattice parameters and enhancement in strain. Nearly spherical shape morphology was observed via HRFESEM with Bi, Fe, Cr and O as the major contributing elements. The bandgap reduced from 1.91 to 1.74 eV with the increase in Cr concentration, and PL spectra revealed emissions in violet, blue and green regions. The investigation of magnetic field (H)-dependent magnetization (M) indicated a significant effect of Cr substitution on the magnetic properties of the nanoparticles. The ferromagnetic character of the samples was found to increase with the increase in the Cr concentration and the increase in the saturation magnetization. The Fe (+3/+4) was dissolved in mixed-valence states, as found through NEXAFS analysis. Electrochemical studies showed that 5%-Cr-doped BFO electrode demonstrated outstanding performance for supercapacitors through a specific capacitance of 421 F g−1 measured with a scan rate of 10 mV s−1. It also demonstrated remarkable cyclic stability through capacitance retention of >78% for 2000 cycles.

Influence of Fe and Cu Co-Doping on Structural, Magnetic and Electrochemical Properties of CeO2 Nanoparticles.

The nanoparticles of CeO2, Ce0.98Fe0.02O2, and Ce0.78Fe0.02Cu0.20O2 were synthesized using the co-precipitation-synthesis technique. The effect of co-doping of Fe and Cu on structural, optical, and magnetic properties as well as specific capacitance have been studied using X-ray diffraction (XRD), scanning-electron microscopy (SEM), UV-visible spectroscopy, Raman spectroscopy, dc magnetization, and electrochemical measurements at room temperature. The results of the XRD analysis infer that all the samples have a single-phase nature and exclude the formation of any extra phase. Particle size has been found to reduce as a result of doping and co-doping. The smallest particle size was obtained to be 5.59 nm for Ce0.78Fe0.02Cu0.20O2. The particles show a spherical-shape morphology. Raman active modes, corresponding to CeO2, were observed in the Raman spectra, with noticeable shifting with doping and co-doping indicating the presence of defect states. The bandgap, calculated using UV-Vis spectroscopy, showed relatively low bandgap energy (1.7 eV). The dc magnetization results indicate the enhancement of the magnetic moment in the samples, with doping and co-doping. The highest value of saturation magnetization (1.3 × 10-2 emu/g) has been found for Ce0.78Fe0.02Cu0.20O2 nanoparticles. The electrochemical behavior studied using cyclic-voltammetry (CV) measurements showed that the Ce0.98Fe0.02O2 electrode exhibits superior-specific capacitance (~532 F g-1) along with capacitance retention of ~94% for 1000 cycles.

Electronic Structure and Room Temperature Ferromagnetism in Gd-doped Cerium Oxide Nanoparticles for Hydrogen Generation via Photocatalytic Water Splitting.

Enhanced visible light photocatalytic activity of Gd-doped CeO2 nanoparticles (NPs) is experimentally demonstrated, whereas there are very few reports on this mechanism with rare earth doping. All-pure and Gd-doped CeO2 NPs are synthesized using a coprecipitation method and characterized using X-ray diffraction (XRD), absorption spectroscopy, surface-enhanced Raman Spectroscopy (SERS), X-ray photoelectron spectroscopy (XPS), and superconducting quantum interference device (SQUID). The effect of Gd-doping on properties of CeO2 is discussed along with defects and oxygen vacancies generation. The XRD confirms the incorporation of Gd3+ at the Ce3+/Ce4+ site by keeping the crystal structure same. The average particle size from transmission electron microscopy (TEM) images is in the range of 5-7 nm. The XPS spectra of Ce 3d, O 1s, and Gd 4d exhibits the formation of oxygen vacancies to maintain the charge neutrality when Ce4+ changes to Ce3+. The gradual increase in hydrogen production is observed with increasing Gd concentration. The observed results are in good correlation with the characterization results and a mechanism of water splitting is proposed on the basis of analyses. The absorption spectra reveal optical band gap (2.5-2.7 eV) of samples, showing band gap narrowing leads to desired optical absorbance and photoactivity of NPs.