Fabrication of PANI-coated ZnFe2O4 nanofibers with enhanced electrochemical performance for energy storage

Bimetal-organic framework-templated Zn-Fe-based transition metal oxide composites through heterostructure optimization to boost lithium storage

Transition metal oxides (TMOs), especially zinc- and iron-based materials, are known to be one of the most innovative anode materials based on their high theoretical capacity, low price and abundant natural reserves. However, the application of these materials is limited by poor electronic conductivity, slow ion mobility and large structural transformations during charging/discharging processes. To overcome these drawbacks, sacrificial template technology has been proposed as a promising strategy to optimize the electrochemical performance and structure stability of TMOs, showing its potential especially in the storage design of lithium-ion batteries (LIBs). In this paper, we successfully synthesized a series of ZnFe2O4/Fe2O3 compounds (named as ZFFO) with Zn/Fe-MOFs (metal-organic frameworks) as sacrificial templates, and then obtained single-component ZnFe2O4 contrast samples (named as ZFO) by etching ZFFO with NaOH. Density Functional Theory (DFT) calculations display that the bi-component ZFFO materials formed by the introduction of Fe2O3 exhibit a lower Li+ migration energy barrier compared to the single-component ZFO materials, indicating better ion diffusion kinetics of ZFFO. The bi-components of ZnFe2O4 and Fe2O3 in ZFFO electrodes can exert a synergistic effect to achieve mutual constraints on volume expansion and alleviate volume strain during charging/discharging processes, thus improving structural stability and electrochemical performance. Besides, the ZnFe2O4/Fe2O3 constructed with 2-methylimidazole as a ligand not only has the synergistic effect of bi-components, but also exhibits a uniformly distributed small-size particle morphology, so that the discharge capacity is 864.2 mAh g-1 after 200 cycles at 0.1 A g-1 when used as an anode for LIBs. This approach presents a feasible and efficient way to synthesize bi-component transition metal oxides with improved practical applications for LIBs.

Nanostructured Conducting Polymers and Their Applications in Energy Storage Devices

Due to the energy requirements for various human activities, and the need for a substantial change in the energy matrix, it is important to research and design new materials that allow the availability of appropriate technologies. In this sense, together with proposals that advocate a reduction in the conversion, storage, and feeding of clean energies, such as fuel cells and electrochemical capacitors energy consumption, there is an approach that is based on the development of better applications for and batteries. An alternative to commonly used inorganic materials is conducting polymers (CP). Strategies based on the formation of composite materials and nanostructures allow outstanding performances in electrochemical energy storage devices such as those mentioned. Particularly, the nanostructuring of CP stands out because, in the last two decades, there has been an important evolution in the design of various types of nanostructures, with a strong focus on their synergistic combination with other types of materials. This bibliographic compilation reviews state of the art in this area, with a special focus on how nanostructured CP would contribute to the search for new materials for the development of energy storage devices, based mainly on the morphology they present and on their versatility to be combined with other materials, which allows notable improvements in aspects such as reduction in ionic diffusion trajectories and electronic transport, optimization of spaces for ion penetration, a greater number of electrochemically active sites and better stability in charge/discharge cycles.

Investigation on In Situ Carbon-Coated ZnFe2O4 as Advanced Anode Material for Li-Ion Batteries

ZnFe₂O₄ as an anode that is believed to attractive. Due to its large theoretical capacity, this electrode is ideal for Lithium-ion batteries. However, the performance of ZnFe₂O₄ while charging and discharging is limited by its volume growth. In the present study, carbon-coated ZnFe₂O₄ is synthesized by the sol–gel method. Carbon is coated on the spherical surface of ZnFe₂O₄ by in situ coating. In situ carbon coating alleviates volume expansion during electrochemical performance and Lithium-ion mobility is accelerated, and electron transit is accelerated; thus, carbon-coated ZnFe₂O₄ show good electrochemical performance. After 50 cycles at a current density of 0.1 A·g⁻¹, the battery had a discharge capacity of 1312 mAh·g⁻¹ and a capacity of roughly 1220 mAh·g⁻¹. The performance of carbon-coated ZnFe₂O₄ as an improved anode is electrochemically used for Li-ion energy storage applications.

Polyaniline-wrapped MnMoO4 as an active catalyst for hydrogen production by electrochemical water splitting

Developing efficient, low-cost, and environment-friendly electrocatalysts for hydrogen generation is critical for lowering energy usage in electrochemical water splitting. Moreover, for commercialization, fabricating cost-efficient, earth-abundant electrocatalysts with superior characteristics is of urgent need. Towards this endeavor, we report the synthesis of PANI-MnMoO₄ nanocomposites using a hydrothermal approach and an in situ polymerization method with various concentrations of MnMoO₄. The fabricated nanocomposite electrocatalyst exhibits bifunctional electrocatalytic activity towards the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) at a lower overpotential of 410 mV at 30 mA cm^-2 and 155 mV at 10 mA cm^-2, respectively in an alkaline electrolyte. Furthermore, while showing overall water splitting (OWS) performance, the optimized PM-10 (PANI-MnMoO₄) electrode reveals the most outstanding OWS performance with a lower cell voltage of 1.65 V (vs. RHE) at a current density of 50 mA cm^-2 with an excellent long-term cell resilience of 24 h.

Polyaniline spinel particles with ultrahigh-performance liquid chromatography tandem mass spectrometry for rapid vitamin B9 determination in rice

Rice is an important crop that provides energy and nutrients to humans, which undergoes the aging process, the quality decline is related to the exogenous storage conditions and the change of own enzyme activity. However, due to the complex composition of rice and serious matrix interference, the ageing identification of rice is still challenging. Hence, a novel spinel particles ZnFe₂O₄@PANI was designed and synthesized for adsorption and determination of vitamin B₉, which can be used to distinguish rice in different years and analyze the degree of aging. The ZnFe₂O₄@PANI showed large specific surface area and fast mass transfer rate with good linear correlation coefficient (R² = 0.9965), satisfactory recoveries (85.1%-99.9%) and relative standard deviations (RSD, 9.3%). Moreover, the π-π electron-donor-acceptor (EDA) and intermolecular hydrogen-bonding interactions of polyaniline coating provided selective adsorption on vitamin B₉. Adsorption thermodynamics study suggested that the adsorption reactions were spontaneous, endothermic and thermodynamically favorable. Finally, ZnFe₂O₄@PANI was used to evaluate vitamin B₉ in rice from different years, which laid a theoretical foundation for exploring the relationship between vitamin changes and the aging degree of the rice.

Advanced materials and technologies for supercapacitors used in energy conversion and storage: a review

Supercapacitors are increasingly used for energy conversion and storage systems in sustainable nanotechnologies. Graphite is a conventional electrode utilized in Li-ion-based batteries, yet its specific capacitance of 372 mA h g−1 is not adequate for supercapacitor applications. Interest in supercapacitors is due to their high-energy capacity, storage for a shorter period and longer lifetime. This review compares the following materials used to fabricate supercapacitors: spinel ferrites, e.g., MFe2O4, MMoO4 and MCo2O4 where M denotes a transition metal ion; perovskite oxides; transition metals sulfides; carbon materials; and conducting polymers. The application window of perovskite can be controlled by cations in sublattice sites. Cations increase the specific capacitance because cations possess large orbital valence electrons which grow the oxygen vacancies. Electrodes made of transition metal sulfides, e.g., ZnCo2S4, display a high specific capacitance of 1269 F g−1, which is four times higher than those of transition metals oxides, e.g., Zn–Co ferrite, of 296 F g−1. This is explained by the low charge-transfer resistance and the high ion diffusion rate of transition metals sulfides. Composites made of magnetic oxides or transition metal sulfides with conducting polymers or carbon materials have the highest capacitance activity and cyclic stability. This is attributed to oxygen and sulfur active sites which foster electrolyte penetration during cycling, and, in turn, create new active sites.

Nitrogen-doped graphene fiber webs for multi-battery energy storage

Freestanding carbon-based electrodes with large surface areas and pore volumes are essential to fast ion transport and long-term energy storage. Many of the current porous carbon substrates are composed of particulates, making it difficult to form a self-supported structure. Herein, novel highly porous nitrogen-doped graphene fiber webs (N-GFWs) are prepared using a facile wet-spinning method. The wet chemical process facilitates simultaneous N-doping and surface wrinkling of graphene fibers in a one-pot process. The atomic structure and electrical conductivity of N-GFWs are tailored by tuning the degree of N-doping and thermal reduction for multi-battery charge storage in both lithium-oxygen batteries (LOBs) and lithium-sulfur batteries (LSBs). The N-GFW900 electrode presents an excellent electrocatalytic activity and the cathode with a high areal loading of 7.5 mg cm-2 delivers a remarkable areal capacity of 2 mA h cm-2 at 0.2 mA cm-2 for LOBs. The N-GFW700 interlayer with abundant oxygenated and nitrogen functional groups demonstrates effective entrapment of polysulfides in LSBs, delivering a much improved specific capacity after 200 cycles at 0.5C with a remarkable decay rate of 0.04%. The current approach paves the way for rational design of porous graphene-based electrodes, satisfying multifunctional requirements for high-energy storage applications.