One-pot synthesis of CoFe2O4/rGO hybrid hydrogels with 3D networks for high capacity electrochemical energy storage devices

Enhanced electrocatalytic OER performance of Ba/CS-CoFe2O4 ternary heterostructure catalyst: Experimental and theoretical insights

Herein, a ternary heterostructure catalyst Ba/CS-CoFe2O4 (barium/chitosan-doped Cobalt ferrite) was developed by a straightforward co-precipitation technique to investigate oxygen evolution reaction (OER) activity. Varying quantities (2 and 4 wt %) of Ba and a fixed amount (3 wt %) of CS were doped to modify the surface area, porosity, crystallite size, and stability of CoFe2O4. Comprehensive characterizations revealed multiple phases, polycrystalline behavior, enhanced absorption, structural defects, and nanorods overlapping nanoparticles (NPs) like the morphology of Ba/CS-CoFe2O4. Furthermore, the experimental results revealed that 2 wt % of Ba/CS-CoFe2O4 exhibited superior electrocatalytic activity with the highest kinetics and ECSA (electrochemically active surface area) for the OER process in 1 M KOH. To further elucidate the OER performance, density functional theory (DFT) calculations were conducted. The optimized CoFe2O4 structure was confirmed to have a cubic Fd-3m symmetry, with a calculated bandgap energy (Eg) of 1.62 eV, closely matching experimental data. Adsorption energy calculations showed that Ba/CS doping significantly improved the binding strength of OH intermediates on the CoFe2O4 (100) surface, highlighting the role of dopants in enhancing surface reactivity. These findings demonstrate the potential of Ba/CS doping to optimize the electronic, structural, and surface properties of CoFe2O4 for efficient OER electrocatalysis, paving the way for novel electrochemical catalyst design.

Flexible and wearable electronic systems based on 2D hydrogel composites

Flexible electronics is a rapidly developing field of study, which integrates many other fields, including materials science, biology, chemistry, physics, and electrical engineering. Despite their vast potential, the widespread utilization of flexible electronics is hindered by several constraints, including elevated Young's modulus, inadequate biocompatibility, and diminished responsiveness. Therefore, it is necessary to develop innovative materials aimed at overcoming these hurdles and catalysing their practical implementation. In these materials, hydrogels are particularly promising owing to their three-dimensional crosslinked hydrated polymer networks and exceptional properties, positioning them as leading candidates for the development of future flexible electronics.

Biochar loaded with cobalt ferrate activated persulfate to degrade naphthalene

Considering the simple preparation of biochar and the excellent activation performance of cobalt ferrate material, a biochar supported cobalt ferrate composite was synthesized by a solvothermal method. The material was used to activate persulfate (PS) to degrade naphthalene (NAP) in water. The structure and morphology characterization showed that the composite (CoFe₂O₄-BC) was successfully prepared. Under the conditions of 0.25 g L^-1 CoFe₂O₄-BC and 1 mM PS, 90.6% NAP (the initial concentration was 0.1 mM) was degraded after 30 minutes. The degradation kinetics of NAP followed the pseudo-first-order kinetic model with a rate constant of 0.0645 min^-1. With the increase of the dosage of activator and PS, the removal rate of NAP could be increased to 99.5%. The coexistence of anions and humic acids inhibited the removal of NAP. The acid environment promoted the removal of NAP while the alkaline environment inhibited it. After four cycles of CoFe₂O₄-BC material, the removal rate of NAP decreased from 90.6% to 79.4%. The removal of TOC was about 45% after each cycle. After the first cycle, the concentration of leached cobalt ion and leached iron ion was about 310 μg L^-1 and 30 μg L^-1 respectively. The free radical quenching experiments showed that SO₄ ^-˙ and OH˙ were the main causes of NAP removal, and the possible degradation path of NAP was elucidated by DFT calculation.

Review on Hydrogel-Based Flexible Supercapacitors for Wearable Applications

Smart hydrogels with high electrical conductivity, which can be a real source of power while also collecting and storing the diverse sources of energy with ultrahigh stretchability, strong self-healability, low-temperature tolerance, and excellent mechanical properties, are great value for tailored wearable cloths. Considerable effort has been dedicated in both scientific and technological developments of electroconductive hydrogels for supercapacitor applications in the past few decades. The key to realize those functionalities depends on the processing of hydrogels with desirable electrochemical properties. The various hydrogel materials with such properties are now emerging and investigated by various scholars. The last decade has witnessed the development of high-performance supercapacitors using hydrogels. Here, in this review, the current status of different hydrogels for the production of flexible supercapacitors has been discussed. The electrochemical properties such as capacitance, energy density and cycling ability has been given attention. Diverse hydrogels, with their composites such as carbon-based hydrogels, cellulose-based hydrogels, conductive-polymer-based hydrogels and other hydrogels with excellent electromechanical properties are summarized. One could argue that hydrogels have played a central, starring role for the assembly of flexible supercapacitors for energy storage applications. This work stresses the importance of producing flexible supercapacitors for wearable clothing applications and the current challenges of hydrogel-based supercapacitors. The results of the review depicted that hydrogels are the next materials for the production of the flexible supercapacitor in a more sustainable way.

Synthesis and adsorption performance of three-dimensional gels assembled by carbon nanomaterials for heavy metal removal from water: A review

This review focuses on the removal of heavy metals from water by three-dimensional gels with carbon nanomaterials as the main building units. It highlights the fundamental knowledge, most recent advances, and future prospects of carbon nanomaterial-assembled gels (CNAGs) as effective adsorbents for heavy metals in water. Various synthesis methods of CNAGs including template-assisted, self-assembly and other methods are systematically summarized and evaluated. Adsorption performances of CNAGs to typical cationic and anionic heavy metals, especially lead, cadmium, mercury, chromium, and arsenic, are thoroughly examined and discussed in detail. These analyses bring out that composite CNAGs constructed from carbon nanomaterials with polymers or other engineered nanoparticles are the most promising adsorbents for heavy metal removal from water. Current challenges and future research directions that are critical to the applications of CNAGs in the removal of heavy metals from contaminated water are outlined at the end of the review.

CoFe2O4 Hollow Spheres-Decorated Three-Dimensional rGO Sponge for Highly Efficient Electrochemical Charge Storage Devices

The energy demand, the crisis of fossil fuels, and the increasing popularity of portable and wearable electronics in the global market have triggered the demand to develop high-performance flexible all-solid-state supercapacitors that are capable of delivering high energy at high power density as well as being safely entrenched in those electronics. Herein, we have designed a nanocomposite, 80CFhs-20rGOsp, which exhibits a high specific capacitance (C S) value of 1032 F g-1 at 3 A g-1. Utilizing this nanocomposite as the cathode and reduced graphene oxide sponge (rGOsp) as the anode, a flexible all-solid-state asymmetric device has been fabricated. In this device, poly(vinyl alcohol) (PVA) gel embedded with a mixture of 3 M KOH and 0.1 M K4[Fe(CN)6] was used as an electrolyte cum separator. The fabricated device showed the capability to deliver an energy density of 65.8 W h kg-1 at a power density of 1500 W kg-1 and retained its capability even after various physical deformations. The device also exhibited a long cycle life and retained ∼96% of its C S value after 5000 cycles. Moreover, the fabricated flexible all-solid-state device successfully illuminated light-emitting diodes, which proved its potential use in real-life supercapacitor applications. The obtained results revealed the excellent electrochemical performances of the fabricated device and rendered it a promising candidate in the energy sector.

Structural, Magnetic, and AC Measurements of Nanoferrites/Graphene Composites

As a contribution to the graphene-based nanoferrite composites, this article is intended to present Mn, Co, and Co-Mn nanoferrites for the preparation and investigation of such samples. Nanoparticles of Co ferrite, Mn ferrite, and Co-Mn ferrite were chemically synthesized by the coprecipitation method. The composites of ferrite/graphene were made by incorporating weight ratios of 25% graphene to 75% ferrite. Various structural and characterizing investigations of ferrite samples and ferrite/graphene composites were performed, including XRD, EDX, SEM, VSM hysteresis loops, AC conductivity, and dielectric behavior. The investigations ensured the formation of the intended nanoferrite powders, each having a single-phase crystal structure with no undesired phases or elements. All samples exhibit a soft magnetic behavior. They show a semiconducting behavior of AC electrical conductivity as well. This was proved by the temperature dependence of the AC's electrical conductivity. Whereas the dielectric function and loss tangent show an expected, well-explained behavior, the ferrite/graphene composite samples have lower saturation magnetization values, lower AC conductivity, and dielectric constant values than the pure ferrites but still have the same behavior trends as those of the pure ferrites. The values obtained may represent steps on developing new materials for expected applications, such as manufacturing supercapacitors and/or improved battery electrodes.

Electrochemical performance of transition metal based CoB2O4 (B = Co and Fe) oxides as an electrode material for energy storage devices

A high capacitance of 1039 F g−1 for Co3O4 as compared to 527 F g−1 for CoFe2O4 along with a capacity retention of 86% for up to GCD 5000 cycles, confirm it's potential to be used as an electrode for practical energy storage devices.

A reinforced concrete structure rGO/CNTs/Fe2O3/PEDOT:PSS paper electrode with excellent wettability and flexibility for supercapacitors

A paper electrode with a reinforced concrete structure using reduced rGO nanosheets, PEDOT:PSS, CNTs and Fe₂O₃ nanoparticles was formed by a facile and simple vacuum drying method. The assembled symmetrical supercapacitor exhibits excellent electrochemical performance.

A porous graphene-NiFe2O4 nanocomposite with high electrochemical performance and high cycling stability for energy storage applications

It is well agreed that supercapacitors form an important class of energy storage devices catering to a variety of needs. However, designing the same using eco-friendly and earth abundant materials with high performance is still the dire need of the day. Here, we report a facile solvothermal synthesis of a porous graphene-NiFe2O4 (PGNF) nanocomposite. Thorough elemental, diffraction, microscopic and spectroscopic studies confirmed the formation of the PGNF composite, in which the NF nanoparticles are covered over the PG surface. The obtained 10 PGNF composite showed a surface area of 107 m2 g-1, with large pore volume which is favorable for charge storage properties. When utilizing the material as an electrode for a supercapacitor in a 2 M KOH aqueous electrolyte, the electrode displayed an impressive specific capacitance value of 1465.0 F g-1 at a scan rate of 5 mV s-1 along with a high capacitance retention of 94% after 10 000 discharge cycles. The fabricated symmetrical supercapacitor device exhibited an energy density of 4.0 W h kg-1 and a power density of 3600.0 W kg-1 at a high applied current density of 14 A g-1. The superior electrochemical performance is attributed to the synergetic effect of the composite components which not only provided enough electroactive channels for the smooth passage of electrolyte ions but also maintained the hybrid structure intact in the ongoing electrochemical process. The obtained results underpin the promising utility of this material for future electrochemical energy storage devices.

A cabbage leaf like nanostructure of a NiS@ZnS composite on Ni foam with excellent electrochemical performance for supercapacitors

In the present study, a NiS@ZnS composite nanostructure was synthesized on a nickel foam substrate by a facile chemical bath deposition (CBD) method.

Synergistic bimetallic CoFe2O4 clusters supported on graphene for ambient electrocatalytic reduction of nitrogen to ammonia

Bimetallic CoFe₂O₄ clusters supported on graphene act as highly efficient and stable electrocatalysts for ambient electrocatalytic ammonia production.

N-doped graphene/CoFe2O4 catalysts for the selective catalytic reduction of NOx by NH3

In this paper, CoFe₂O₄/graphene catalysts and N-doped graphene/CoFe₂O₄ (CoFe₂O₄/graphene-_N) catalysts were prepared using the hydrothermal crystallization method for the selective catalytic reduction of NO_x by NH₃. The results of the test showed that CoFe₂O₄/graphene catalysts exhibited the best denitrification activity when the loading was at 4% and the conversion rate of NO_x reached 99% at 250–300 °C. CoFe₂O₄/graphene-_N catalysts presented a better denitrification activity at low temperature than CoFe₂O₄/graphene catalysts, and the conversion rate of NO_x reached more than 95% at 200–300 °C. The intrinsic mechanism of CoFe₂O₄/graphene-_N catalysts in promoting SCR activity was preliminarily explored. The physicochemical properties of the samples were characterized using XRD, TEM, N₂ adsorption, XPS, NH₃-TPD, and H₂-TPR. The results indicated that nitrogen doping can improve the dispersion of CoFe₂O₄, and it also increased the acidic sites and the redox performance conducive to improving the denitrification activity of the catalysts. In addition, CoFe₂O₄/graphene-_N catalysts demonstrated a better resistance to water and sulfur than CoFe₂O₄/graphene catalysts.

N-doped graphene/CoFe₂O₄ presented better denitrification activity than CoFe₂O₄/graphene due to the more uniform distribution of CoFe₂O₄ and acidic sites etc.