Electrochemical behaviour of Fe x Co3−x O4 with (x = 0, 1, 2 and 3) oxides thin film electrodes in alkaline medium

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.

Controlled synthesis of MnO2 nanosheets vertically covered FeCo2O4 nanoflakes as a binder-free electrode for a high-power and durable asymmetric supercapacitor

We developed a simple and controlled method to synthesize FeCo₂O₄@MnO₂ core-sheath nanoarchitecture (CSN) grown on Ni foam. Ultrathin FeCo₂O₄ nanoflakes with an average thickness of 10 nm served as the scaffold to deposit the MnO₂ nanosheets. The MnO₂ nanosheets were able to vertically grow on FeCo₂O₄ nanoflakes to form a sheath via a hydrothermal reaction. The nanocomposites' thickness could be tailored from 80 nm-550 nm by changing the reaction times. Electrochemical measurements demonstrated that FeCo₂O₄@MnO₂ CSN with an optimal thickness of about 400 nm achieved an areal capacitance of 3.077 F cm^-2 at 2 mA cm^-2, which is much higher than individual FeCo₂O₄ nanoflakes (0.295 F cm^-2) and MnO₂ nanosheets (1.065 F cm^-2). An aqueous asymmetric supercapacitor (ASC) was assembled using FeCo₂O₄@MnO₂ CSN as its positive electrode and activated carbon (AC) as its negative electrode. The FeCo₂O₄@MnO₂⫽AC ASC exhibited a capacitance of 0.538 F cm^-2 at 5 mA cm^-2 with a potential window of 1.65 V, and an excellent cycling stability (99.1% retention even after 5000 cycles). Furthermore, the maximum energy density and power density of FeCo₂O₄@MnO₂⫽AC ASC was 0.203 mWh cm^-2 at 3.44 mW cm^-2 and 28.6 mW cm^-2 at 0.061 mWh cm^-2, respectively.

High-performance lithium-ion battery and symmetric supercapacitors based on FeCo₂O₄ nanoflakes electrodes

A successive preparation of FeCo2O4 nanoflakes arrays on nickel foam substrates is achieved by a simple hydrothermal synthesis method. After 170 cycles, a high capacity of 905 mAh g(-1) at 200 mA g(-1) current density and very good rate capabilities are obtained for lithium-ion battery because of the 2D porous structures of the nanoflakes arrays. The distinctive structural features provide the battery with excellent electrochemical performance. The symmetric supercapacitor on nonaqueous electrolyte demonstrates high specific capacitance of 433 F g(-1) at 0.1 A g(-1) and 16.7 F g(-1) at high scan rate of 5 V s(-1) and excellent cyclic performance of 2500 cycles of charge-discharge cycling at 2 A g(-1) current density, revealing excellent long-term cyclability of the electrode even under rapid charge-discharge conditions.

Biohydrogels with magnetic nanoparticles as crosslinker: characteristics and potential use for controlled antitumor drug-delivery

Hybrid magnetic hydrogels are of interest for applications in biomedical science as controlled drug-delivery systems. We have developed a strategy to obtain novel hybrid hydrogels with magnetic nanoparticles (NPs) of CoFe(2)O(3) and Fe(3)O(4) as crosslinker agents of carboxymethylcellulose (CMC) or hyaluronic acid (HYAL) polymers and we have tested these systems for controlled doxorubicin release. The magnetic NPs are functionalized with (3-aminopropyl)trimethoxysilane (APTMS) in order to introduce amino groups on the surface. The amino coating is determined and quantified by standard Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy methods, and by cyclic voltammetry, a novel approach that permits us to look at the solution properties of the functionalized NPs. The gel formation involves the creation of an amide bond between the carboxylic groups of CMC or HYAL and the amine groups of functionalized NPs, which work as crosslinking agents of the polymer chains. The hybrid hydrogels are chemically and morphologically characterized. The rheological and the water uptake properties of the hydrogels are also investigated. Under the application of an alternating magnetic field, the CMC-HYAL hybrid hydrogel previously loaded with doxorubicin shows a drug release greater than that showed by the CMC-HYAL hydrogel crosslinked with 1,3-diaminopropane. In conclusion, the presence of magnetic NPs makes the synthesized hybrid hydrogels suitable for application as a drug-delivery system by means of alternating magnetic fields.