Synthesis and electrochemical investigation of spinel cobalt ferrite magnetic nanoparticles for supercapacitor application

Structural modulation of tin nickelate nanostructures embedded in reduced graphene oxide for high-performance asymmetric supercapacitors

Development of a new, cost-effective, advanced energy storage material via a simple method is a great challenge among researchers. In this study, we have synthesized efficient spinel tin nickelate nano-popcorns, SnNi2O4 (SNNPs), via a solvothermal process. Furthermore, to enhance their charge transfer characteristics, SNNPs were impregnated on reduced graphene oxide (rGO) nanosheets through ultrasonication to obtain SnNi2O4@rGO (SNNPR). By varying the percentage load ratio of SNNPs and rGO, six different nanocomposites, namely, SNNPR-1, SNNPR-2, SNNPR-3, SNNPR-4, SNNPR-5 and SNNPR-6, were produced. They were thoroughly characterized using spectroscopic and microscopic techniques. The electrochemical analysis of all the SNNP-based electrode materials was performed using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). Among these six electrode materials, SNNPR-3 produces a maximum specific capacitance (Csp) of 225 mA h g-1 (1624 F g-1) in a three-electrode assembly at 1 A g-1 and retains a cycle stability of 94% up to 1000 cycles. Based on the superiority of SNNPR-3, an asymmetric supercapacitor (ASC) was fabricated with SNNPR-3 as the cathode and activated carbon (AC) as the anode (SNNPR-3//AC). Exhibiting a thorough electrochemical performance, the present ASC yielded a specific capacitance, Csp of 264 F g-1, high energy density of 62.3 W h kg-1 and power density of 2600 W kg-1. The device exhibited 80.02% of retention capacitance even after 5000 cycles. Also, SNNPR-3//AC was able to illuminate a green light emitting diode. Therefore, this asymmetric energy storage device has enormous potential for practical applications in the future.

Electrochemically engineered zinc(iron)oxyhydroxide/zinc ferrite heterostructure with interfacial microstructure and hydrophilicity ideal for supercapacitors

Zinc ferrite@nickel foam (ZF@Nf) is a potential commercial supercapacitor electrode due to its large theoretical capacity, abundant elemental composition, excellent conductivity, and stability. However, deficient active sites limit its specific capacitance (SC). Herein, we demonstrate that engineering ZF's interfacial microstructure and hydrophilicity mitigate this limitation. ZF@Nf is used as the working electrode in a 3-electrode cell and subjected to multiple oxygen evolution reaction cycles in potassium hydroxide. Systematic changes in ZF's porosity, crystallinity, hydrophilicity, and composition after each cycle were characterised using spectroscopy, sorption isotherm, microscopy and photography techniques. During cycling, the edges of ZF partially phase-transform into a dense polycrystalline zinc(iron)oxyhydroxide film via semi-reversible oxidation resulting in zinc(iron)oxyhydroxide/ZF interface formation. The maximum ion-accessible zinc(iron)oxyhydroxide film density is obtained after 1000 cycles. Strong ionic interaction at the interface induces high hydrophilicity, this together with the 3-dimensional diffusion channels of the zinc(iron)oxyhydroxide significantly increase electroactive surface area and decrease ion diffusion resistance. Consequently, the SC, energy density, and rate-capability of the interface compare favourably with state-of-the-art electrodes. The strong interfacial interaction and polycrystallinity also ensure long-term electrochemical stability. This study proves the direct correlation between interfacial microstructure and hydrophilicity, and SC which provides a blueprint for future energy-storage electrode design.

Synthesis and Characterisation of Cobalt Ferrite Coatings for Oxygen Evolution Reaction

In this paper, two novel procedures based on powder sedimentation, thermal treatment, and galvanostatic deposition were proposed for the preparation of porous cobalt ferrite (CoFe2O4) coatings with a metallic and organic binder for use as catalysts in the oxygen evolution reaction (OER). The electrochemical properties of the obtained electrode materials were determined as well, using both dc and ac methods. It was found that cobalt ferrite coatings show excellent electrocatalytic properties towards the oxygen evolution reaction (OER) with overpotential measured at a current density of 10 mAcm−2 from 287 to 295 mV and a Tafel slope of 35–45 mVdec−1. It was shown that the increase in the apparent activity of the CoFe2O4 coatings with an organic binder results mainly from a large electrochemically active area. Incorporation of the nickel binder between the CoFe2O4 particles causes an increase in both the conductivity and the electrochemically active area. The Tafel slopes indicate that the same rate-determining step controls the OER for all obtained coatings. Furthermore, it was shown that the CoFe2O4 electrodes exhibit no significant activity decrease after 28 h of oxygen evolution. The proposed coating preparation procedures open a new path to develop high-performance OER electrocatalysts.

Pulsed laser deposited CoFe2O4 thin films as supercapacitor electrodes

The influence of the substrate temperature on pulsed laser deposited (PLD) CoFe2O4 thin films for supercapacitor electrodes was thoroughly investigated. X-ray diffractometry and Raman spectroscopic analyses confirmed the formation of CoFe2O4 phase for films deposited at a substrate temperature of 450 °C. Topography and surface smoothness was measured using atomic force microscopy. We observed that the films deposited at room temperature showed improved electrochemical performance and supercapacitive properties compared to those of films deposited at 450 °C. Specific capacitances of about 777.4 F g-1 and 258.5 F g-1 were obtained for electrodes deposited at RT and 450 °C, respectively, at 0.5 mA cm-2 current density. The CoFe2O4 films deposited at room temperature exhibited an excellent power density (3277 W kg-1) and energy density (17 W h kg-1). Using electrochemical impedance spectroscopy, the series resistance and charge transfer resistance were found to be 1.1 Ω and 1.5 Ω, respectively. The cyclic stability was increased up to 125% after 1500 cycles due to the increasing electroactive surface of CoFe2O4 along with the fast electron and ion transport at the surface.

Synthesis of Spinel Ferrite MFe2O4 (M = Co, Cu, Mn, and Zn) for Persulfate Activation to Remove Aqueous Organics: Effects of M-Site Metal and Synthetic Method

Metal species and synthetic method determine the characteristics of spinel ferrite MFe₂O₄. Herein, a series of MFe₂O₄ (M = Co, Cu, Mn, Zn) were synthesized to investigate the effect of M-site metal on persulfate activation for the removal of organics from aqueous solution. Results showed that M-site metal of MFe₂O₄ significantly influenced the catalytic persulfate oxidation of organics. The efficiency of the removal of organics using different MFe₂O₄ + persulfate systems followed the order of CuFe₂O₄ > CoFe₂O₄ > MnFe₂O₄ > ZnFe₂O₄. Temperature-programmed oxidation and cyclic voltammetry analyses indicated that M-site metal affected the catalyst reducibility, reversibility of M²⁺/M³⁺ redox couple, and electron transfer, and the strengths of these capacities were consistent with the catalytic performance. Besides, it was found that surface hydroxyl group was not the main factor affecting the reactivity of MFe₂O₄ in persulfate solution. Moreover, synthetic methods (sol–gel, solvothermal, and coprecipitation) for MFe₂O₄ were further compared. Characterization showed that sol–gel induced good purity, porous structure, large surface area, and favorable element chemical states for ferrite. Consequently, the as-synthesized CuFe₂O₄ showed better catalytic performance in the removal of organics (96.8% for acid orange 7 and 62.7% for diclofenac) along with good reusability compared with those obtained by solvothermal and coprecipitation routes. This work provides a deeper understanding of spinel ferrite MFe₂O₄ synthesis and persulfate activation.

A facile synthesis of nanostructured CoFe2O4 for the electrochemical sensing of bisphenol A

This work reports a novel, highly sensitive and cost-effective electrochemical sensor for the detection of bisphenol A in environmental water samples. Attractive non-noble transition metal oxide CoFe₂O₄ nanoparticles were successfully synthesized using a sol–gel combustion method and further characterized by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. Under optimal conditions, the CoFe₂O₄ nanoparticle modified glassy carbon electrode exhibits high electrochemical activity and good catalytic performance for the detection of bisphenol A. The linear calibration curves are obtained within a wide concentration range from 0.05 μmol L⁻¹ to 10 μmol L⁻¹, and the limit of detection is 3.6 nmol L⁻¹ for bisphenol A. Moreover, this sensor also demonstrates excellent reproducibility, stability, and good anti-interference ability. The sensor was successfully applied to determine bisphenol A in practical samples, and the satisfactory recovery rate was between 95.5% and 102.0%. Based on the great electrochemical properties and practical application results, this electrochemical sensor has broad application prospects in the sensing of bisphenol A.

A new electrochemical sensor for bisphenol A is reported. CoFe₂O₄ nanoparticles were synthesized by a sol–gel combustion method. A nanoparticle-modified glassy carbon electrode exhibited outstanding electrochemical performance for the detection of bisphenol A.

Graphitic carbon nitride decorated with FeNi3 nanoparticles for flexible planar micro-supercapacitor with ultrahigh energy density and quantum storage capacity

Schematic description of graphitic-C₃N₄@FeNi₃ (pseudocapacitive FeNi₃ and electrochemical double layer g-C₃N₄) heterostructure having energy density and quantum storage capacity for in-plane micro-supercapacitor application.