Mixed Transition-Metal Oxides: Design, Synthesis, and Energy-Related Applications

Carbon Nanotube Intertwined Nano-Nested Heterojunction Cubes with Double Shell Layers FeSe2-CoSe2@NC for Efficient Lithium/Sodium Ion Storage Anode

Transition metal selenides (TMSes) have been extensively researched as anode materials of lithium/sodium-ion batteries (LIBs/SIBs). However, the serious volume expansion, unsatisfying initial coulombic efficiency (ICE), and ion diffusion extremely limited their further application. Therefore, nanostructure design and construction of heterogeneous structures can effectively alleviate the above problems. Herein, elaborately designed carbon nanotube-intertwined nano-nested heterojunction cubes, FeSe2-CoSe2@NC (FeSe2-CoSe2@NC/CNT), with unique double shell layers, are successfully prepared. Electrochemical tests and theoretical calculations show that the construction of double transition metal selenide heterostructures and CNTs inter-transfer networks promotes ion transport kinetics. Furthermore, the double-layer nested cubic structure contributes to alleviating the volume expansion over charging/discharging. Thanks to these merits, the FeSe2-CoSe2@NC/CNT composite exhibits enhanced Li+ storage capacity (1479.7 mAh g-1 after 500 cycles at a high current density of 2 A g-1), and outstanding rate capabilities. When used in SIB, the capacity is maintained at 300.1 mAh g-1 for 500 cycles at 1 A g-1. In addition, the FeSe2-CoSe2@NC/CNT as anode in the full cell displays a nice reversible capacity of 100.1 mAh g-1 at 0.5 C cycling for 115 cycles, demonstrating vast potential for feasible synthesis, superior performance, and efficient lithium/sodium ion storage anodes.

Structural Analysis of Deeply Charged Li(Ni0.95Co0.04Al0.01)O2 Cathode for Li-Ion Battery

LiNi0.95Co0.04Al0.01O2 (NCA95) is charged up to 4.6 V to study its structural stability at a highly delithiated state using transmission electron microscopy (TEM). The TEM analysis shows that the localized depletion of Li ions near the surface triggers the transition from the H3 phase to the H4 phase with the H4 phase with the O1 stacking appearing as a series of stacking faults even at 4.4 V. The H3→H4 transition appears irreversible and leads to the initial capacity loss. In addition, intraparticle cracks are observed when charged above 4.3 V. These intraparticle microcracks, unlike interparticle cracks that become sealed upon Li-uptake, likely remain during deintercalation, compromising the mechanical stability of the cathode and lead to fast deterioration of the cycling stability. The TEM analysis of the overcharged NCA95 cathode suggests a clear limit above which the cathode can be cycled without significant capacity loss. Introducing doping elements that promote the migration of Ni2+ ions into the Li layer would hinder the H3→H4 transition and help suppress the intraparticle cracks.

Triazine-containing Covalent Organic Polymer-derived Grid-Like Multilocular Spheres for Aqueous Supercapacitors

Triazine-containing covalent organic polymers (TCOPs) with unique structures and physicochemical properties are of great potential in energy storage and conversion applications, yet how to finely tune the morphology, and the accessible active sites, and to enhance capacitive activity remains a challenge. Here, the grid-like multilocular spheres derived from TCOP with abundant redox active sites and unique structures are fabricated via a molecular twist-induced regulation strategy, of which the number and size of cavities can be finely modulated by changing the conformers of the twisted unit and the Ostwald ripening time. The unique structure of the as-fabricated TCOP results in unprecedented high specific capacitance (8412 F g-1 at 1 A g-1) and enables the as-assembled supercapacitor with an ultra-high energy density of 675 Wh kg-1 in redox-active electrolyte (KI-mixed H2SO4), much better than all reported aqueous supercapacitors thus far. It is found that the high electro-activity is due to the synergistic effect of the enhanced accessibility of active sites and the enhanced interaction of the abundant active sites with the redox-active electrolytes. This approach may pave a new way to precise synthesis of COPs with tuned structure and properties for application-inspired cutting-edge electrochemical energy storage and beyond.

Robust Redox-Active Tetrathiafulvalene-Cobalt Metal-Organic Frameworks for Supercapatteries with Promoting Electrochemical Performances

Integrating abundant electroactive sites and redox reactions into stable metal-organic framework (MOF) electrodes is an effective and relatively unexplored approach to improve the performance of emerging supercapatteries. In this study, electroactive Co(II) was chosen to coordinate with a redox-active tetrathiafulvalene (TTF) ligand to construct a new MOF, formulated as [Co(TTF(py)4)(BDC)] (1) (TTF(py)4 is tetra(4-pyridyl)-TTF and H2BDC is terephthalic acid). Crystallographic characterization indicated that 1 possesses a three-dimensional 6-fold interpenetrating diamond-like topology with high crystal density. Isostructural [Zn(TTF(py)4)(BDC)] (2) was also synthesized to explore the effect of metal ions on the performance of supercapatteries. When directly used as an electrode material in a 3-electrode system, the iodine-treated MOFs 1 and 2 (namely 1-ox and 2-ox, respectively) electrodes exhibit battery-type performance and high capacities. The specific capacities are 1072.2 and 857.8 C g-1 at 1 A g-1 for 1-ox and 2-ox, respectively. The AC||1-ox supercapattery device presents a specific energy of 100.8 Wh kg-1 at a specific power of 0.975 kW kg-1. Ex situ characterizations and theoretical calculations revealed that the excellent performance of 1-ox originates from the synergistic effect of the robust topology, Co(II) metal centers, and ligand dominant mechanism.

Biomass-derived carbon dots: synthesis, modification and application in batteries

Biomass-derived carbon dots (BCDs) have attracted considerable attention for their promising attributes, including low toxicity, excellent solubility, biocompatibility, and eco-friendliness. Their rich surface chemistry and impressive photoluminescent properties have sparked widespread research interest, particularly in areas such as sensing and biomedicine. However, the potential applications of BCDs in the energy sector, especially in electrochemical energy storage batteries, have received scant review focus. This article systematically consolidates the selection of carbon sources, synthesis methods, modification strategies, and the corresponding characterization techniques for BCDs. Application strategies in energy storage batteries are explored, with the underlying connection between the role of BCDs in batteries and their structural properties being analyzed, providing comprehensive insights from synthesis and characterization to application. Furthermore, a preliminary discussion is initiated on the current limitations in material regulation and design within research, and potential avenues for enhancement are proposed.

Reconfigurable CMOS-Compatible Supercapacitor-Diode Empowering Computation Efficiency for Human-Machine Interaction

Biological system utilizes unidirectional ion flow to produce and transmit signals. To realize bioinspired artificial intelligence and thus seamless human-machine interaction, ion rectification devices should be developed. Here, a reconfigurable CMOS-compatible supercapacitor-diode (CAPode) is developed by resettling the pseudo-capacitive and electrochemical-double-layer-capacitive components of a lithium-ion pseudocapacitor into the positive and negative voltage regions respectively through engineering the redox peaks. This CAPode exhibits good ion rectification and charge-storage bifunction with high rectification ratio (RR) (RRI~20, RRII~0.83), large areal capacitance (17 mF cm-2) and long cycling stability (5000 cycles). More importantly, two main computing paradigms in the biological system are efficiently realized based on this CAPode by empowering the supercapacitor function into the diode: (I) multivalued ionic logic gates are constructed based on the tunable ion rectification characteristics induced by the bifunction of this CAPode for mimicking the dendritic computing; (II) all-CAPode based reservoir computing is implemented based on the reconfigurable volatile and nonvolatile charge-storage characteristics of this CAPode for mimicking the neuromorphic computing. This work paves a new way towards seamless and high-efficiency human-machine interaction.

Design and Application of Mesoporous Catalysts for Liquid-Phase Furfural Hydrogenation

Furfural (FAL), a platform molecule derived from biomass through acid-catalyzed processes, holds significant potential for producing various value-added chemicals. Its unique chemical structure, comprising a furan ring and an aldehyde functional group, enables diverse transformation pathways to yield products such as furfuryl alcohol, furan, tetrahydrofuran, and other industrially relevant compounds. Consequently, optimizing catalytic processes for FAL conversion has garnered substantial attention, particularly in selectivity and efficiency. The liquid-phase hydrogenation of FAL has demonstrated advantages, including enhanced catalyst stability and higher product yields. Among the catalysts investigated, mesoporous materials have emerged as promising candidates because of their high surface area, tunable pore structure, and ability to support highly dispersed active sites. These attributes are critical for maximizing the catalytic performance across various reactions, including FAL hydrogenation. This review provides a comprehensive overview of recent advances in mesoporous catalyst design for FAL hydrogenation, focusing on synthesis strategies, metal dispersion control, and structural optimization to enhance catalytic performance. It explores noble metal-based catalysts, particularly highly dispersed Pd systems, as well as transition-metal-based alternatives such as Co-, Cu-, and Ni-based mesoporous catalysts, highlighting their electronic structure, bimetallic interactions, and active site properties. Additionally, metal-organic frameworks are introduced as both catalysts and precursors for thermally derived materials. Finally, key challenges that require further investigation are discussed, including catalyst stability, deactivation mechanisms, strategies to reduce reliance on external hydrogen sources, and the impact of solvent effects on product selectivity. By integrating these insights, this review provides a comprehensive perspective on the development of efficient and sustainable catalytic systems for biomass valorization.

Recent Advances in Nanostructured Conversion-Type Cathodes: Fluorides and Sulfides

This review paper explores the emerging field of conversion cathode materials, which hold significant promises for advancing the performance of lithium-ion (LIBs) and lithium-sulfur batteries (LSBs). Traditional cathode materials of LIBs, such as lithium cobalt oxide, have reached their limits in terms of energy density and capacity, driving the search for alternatives that can meet the increasing demands of modern technology, including electric vehicles and renewable energy systems. Conversion cathodes operate through a mechanism involving complete redox reactions, transforming into different phases, which enables the storage of more lithium ions and results in higher theoretical capacities compared to conventional intercalation materials. This study examines various conversion materials, including metal oxides, sulfides, and fluorides, highlighting their potential to significantly enhance energy density. Despite their advantages, conversion cathodes face numerous challenges, such as poor conductivity, significant volume changes during cycling, and issues with reversibility and stability. This review discusses current nanoengineering strategies employed to address these challenges, including nano structuring, composite formulation, and electrolyte optimization. By assessing recent research and developments in conversion cathode technology, this paper aims to provide a comprehensive overview of their potential to revolutionize lithium-ion batteries and contribute to the future of energy storage solutions.

Solid-State Nuclear Magnetic Resonance Spectroscopy for Surface Characterization of Metal Oxide Nanoparticles: State of the Art and Perspectives

Metal oxide materials have found wide applications across diverse fields; in most cases, their functionalities are dictated by their surface structures and properties. A comprehensive understanding of the intricate surface features is critical for their further design, optimization, and applications, necessitating multi-faceted characterizations. Recent advances in solid-state nuclear magnetic resonance (ssNMR) spectroscopy have significantly extended its applications in the detailed analysis of multiple metal oxide nanoparticles, offering unparalleled atomic-level information on the surface structures, properties, and chemistries. Herein, we present an overview of the current state of the art from an NMR perspective. We begin with a brief introduction to contemporary ssNMR methodologies. Subsequently, we introduce and provide critical reviews on the applications of different ssNMR techniques in the detailed characterizations of the surface local structures, disorders, defects, active sites, and acidity on metal oxide nanoparticles, as well as the revelation of mechanisms behind some intriguing chemistries that occur on the surfaces, referencing representative recent studies. Finally, we address the challenges beyond the current status and provide perspectives on the future development and application of advanced ssNMR methodologies in this emerging field.

Euphorbia serpens extracts mediated synthesis of copper oxide nanoparticles and their biological applications

With the passage of time there is enormous development in the field of science and technology, however, human health remained the utmost concern. There are different strategies that helps us to treat various diseases but they have adverse reactions on our bodies. Nanobiotechnology is the advanced field consisting of new techniques and fabrication procedures for nanostructures for making drugs more effective against diseases in less time. These bio-nanoparticles easily target diseased cells, bind to them and damage the diseased tissue. Green synthesis of CuONPs is multi-purposed and can also be used for several bio-applications. The present study involves fabrication of economically viable copper oxide nanoparticles using aqueous plant extracts. The medicinal plants used in current study were Euphorbia serpens. The orchestrated nanoparticles were validated using several analytical techniques; Ultraviolet-Visible spectroscopy, XRD, SEM, FT-IR (Fourier-transform infrared), EDS, FT-IR and DLS (Dynamic light scattering). The average/mean size of the greenly fabricated nanoparticles was found to be 20.39 nm. Further, the biosynthesized NPs were evaluated for multiple biological activities. The bactericidal properties of green synthesized NPs were demonstrated using different bacterial strains revealing significant antibacterial potentials. The fungicidal properties were also demonstrated using different fungal strains showing significant antifungal potential. The minimum inhibitory concentration (MICs) values were calculated for different bacterial and fungal strains via disc-diffusion method. Further, our Euphorbia serpens orchestrated nanoparticles revealed excellent cytotoxic potentials against nascent brine shrimp larvae (IC50: 32.88 μg/mL) and have shown potential antioxidant properties. In conclusion, the asynthesized nanoparticles have shown significant in vitro bio-potentials. In future, different in vitro activities; antileishmanial, anticancer, enzyme degradation assays and different in vivo studies using animal models are recommended to further investigate the role of these NPs in different biomedical applications. Also, the formulations of multi-organic functional groups and biometallic NPs with regulated/balanced surface chemistry is worthy for the consideration.

M-Doped (M = Zn, Mn, Ni) Co-MOF-Derived Transition Metal Oxide Nanosheets on Carbon Fibers for Energy Storage Applications

Carbon fiber, with its strong mechanical properties and electrical conductivity, is ideal as a fiber electrode in wearable or structural energy storage devices. However, its energy storage capacity is limited, and coatings like transition metal oxides (TMOs) enhance its electrochemical performance. Metal-organic frameworks (MOFs) are commonly used to grow TMOs on carbon fibers, increasing the surface area for better energy storage. Despite this, TMOs have limited electrical conductivity, so ion exchange is often used to dope them with additional cations, improving both conductivity and energy storage capacity. This study compares different ion-exchange cations in ZIF-L-derived TMO coatings on carbon fiber. Testing both supercapacitor and Li-ion battery applications, Ni-doped samples showed superior results, attributed to their higher exchange ratio with cobalt. As a supercapacitor electrode, the Ni-doped material achieved 13.3 F/g at 50 mA/g-66% higher than undoped samples. For Li-ion battery anodes, it reached a specific capacity of 410.5 mAh/g at 25 mA/g, outperforming undoped samples by 21.4%.

A Machine Learning Assisted Non-Enzymatic Electrochemical Biosensor to Detect Urea Based on Multi-Walled Carbon Nanotube Functionalized with Copper Oxide Micro-Flowers

Detecting urea is crucial for diagnosing related health conditions and ensuring timely medical intervention. The addition of machine learning (ML) technologies has completely changed the field of biochemical sensing, providing enhanced accuracy and reliability. In the present work, an ML-assisted screen-printed, flexible, electrochemical, non-enzymatic biosensor was proposed to quantify urea concentrations. For the detection of urea, the biosensor was modified with a multi-walled carbon nanotube-zinc oxide (MWCNT-ZnO) nanocomposite functionalized with copper oxide (CuO) micro-flowers (MFs). Further, the CuO-MFs were synthesized using a standard sol-gel approach, and the obtained particles were subjected to various characterization techniques, including X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and Fourier transform infrared (FTIR) spectroscopy. The sensor's performance for urea detection was evaluated by assessing the dependence of peak currents on analyte concentration using cyclic voltammetry (CV) at different scan rates of 50, 75, and 100 mV/s. The designed non-enzymatic biosensor showed an acceptable linear range of operation of 0.5-8 mM, and the limit of detection (LoD) observed was 78.479 nM, which is well aligned with the urea concentration found in human blood and exhibits a good sensitivity of 117.98 mA mM-1 cm-2. Additionally, different regression-based ML models were applied to determine CV parameters to predict urea concentrations experimentally. ML significantly improves the accuracy and reliability of screen-printed biosensors, enabling accurate predictions of urea levels. Finally, the combination of ML and biosensor design emphasizes not only the high sensitivity and accuracy of the sensor but also its potential for complex non-enzymatic urea detection applications. Future advancements in accurate biochemical sensing technologies are made possible by this strong and dependable methodology.

The Alkynyl π Bond of sp-C Enhanced Rapid, Reversible Li-C Coupling to Accelerate Reaction Kinetics of Lithium Ions

Graphdiyne (GDY) is a promising anode for rechargeable batteries with high capacity, outstanding cyclic stability, and low diffusion energy. The unique structure of GDY endows distinctive mechanisms for metal-ion storage, and it is of great significance to further visualize the complex reaction kinetics of the redox process. Here, we systematically tracked the reaction kinetics and provided mechanistic insights into the lithium ions in the GDY to reveal the feature of the cation-π effect. It has been demonstrated that, unlike only one π bond in sp2-C, π electrons provided by one of the two alkynyl π bonds in sp-C can achieve proper interaction and speedy capture of lithium ions; thus, reversible Li-C coupling can be formed between electron-rich sp-C and lithium ions. In addition to interlayer intercalation in sp2-C regions, nanopores filling triangular-like cavities composed of highly conjugated sp-C contribute to the major capacity in flat voltage plateau regions. Therefore, a capture/pores filling-intercalation hybrid mechanism can be found in GDY. The coexistence of sp and sp2 carbon enables GDY electrodes with rapid Li+ diffusion, high capacity of over 1435 mAh g-1, extraordinary rate capability, and cyclic stability for more than 10000 cycles at 10A g-1. These results provide guidance for developing advanced carbon electrodes with optimized reaction kinetics for rechargeable batteries.

Screening Transition-Metal-Incorporated β-AgVO3 for Augmented Oxygen Reduction Activity

Exploring cost-effective alternatives to Pt-based catalysts for the oxygen reduction reaction (ORR) in fuel cells is crucial for their large-scale deployment in green energy applications. Silver vanadate (AgVO3) is a well-studied material for photocatalytic applications. Here, we investigate the electrocatalytic ORR activity of the thermodynamically stable β phase of AgVO3 through computational modeling based on DFT. It is found that β-AgVO3 exhibits weak catalytic activity for the ORR, with vanadium being the preferable active site. Incorporating single atoms of transition metals at surface-level vacancies in β-AgVO3 significantly modifies the ORR activity. We study the scaling of free energy changes for the ORR intermediates *OOH, *OH, and *O for various transition metals incorporated, which leads to an optimal overpotential for the system. The optimal overpotential thus obtained is remarkably lower than that of pristine β-AgVO3. For the transition metal atoms we consider here, Co-incorporated β-AgVO3 exhibits the best ORR catalytic activity due to its optimal binding of ORR species to the vanadium site. It is also observed that some of the transition metals considered like Re, Rh, Os, or Mn show weak activity, either due to strong or weak binding. Analysis of the electronic structure of the adsorbate-catalyst interface shows a strong correlation between optimal activity and evolution of midgap states in β-AgVO3, due to transition metal incorporation. Our study concludes that the ORR activity of a stable mixed transition metal oxide like β-AgVO3 can be enhanced with a minimal loading of transition metals, which could help in developing a novel series of ORR catalysts.

Tailoring surface morphology on anatase TiO2 supported Au nanoclusters: implications for O2 activation

Strong interaction between the support surface and metal clusters activates the adsorbed molecules at the metal cluster-support interface. Using plane-wave DFT calculations, we precisely model the interface between anatase TiO2 and small Au nanoclusters. Our study focusses on the adsorption and activation of oxygen molecules on anatase TiO2, considering the influence of oxygen vacancies and steps on the surface. We find that the plane (101) and the stepped (103) surfaces do not support O2 activation, but the presence of oxygen vacancies results in strong adsorption and O-O bond length elongation. Modifying the TiO2 surface with supported small Au n nanoclusters (n = 3-5) also significantly enhances O2 adsorption and stretches the O-O bond. We observe that manipulating the cluster orientation through discrete rotations results in improved O2 adsorption and promotes charge transfer from the surface to the molecule. We propose that the orientation of the supported cluster may be manipulated by making the cluster adsorb at the step-edge of (103) TiO2. This results in activated O2 at the cluster-support interface, with a peroxide-range bond length and a low barrier for dissociation. Our modeling demonstrates a straightforward means of exploiting the interface morphology for O2 activation under low precious metal loading, which has important implications for electrocatalytic oxidation reactions and the rational design of supported catalysts.

MOF-derived scaffolds as electrode materials: a mini-review

Metal-organic frameworks (MOFs) have unique properties but suffer from low conductivity and poor stability, limiting their use in energy storage. Transforming MOFs into other materials, like porous carbon or metal oxides/chalcogenides has been explored to overcome these limitations. However, these approaches still face issues such as dead volume and poor attachment due to insulating binders, causing high resistance and detachment. To address this, MOFs and their derived scaffolds directly on conductive substrates without binders have emerged. These electrodes offer simplified preparation, enhanced electron transfer, and improved interface contact. This mini-review focuses on MOF-derived scaffold electrodes using transition metal oxides, sulfides, selenides, and tellurides, which show promise in energy storage applications. Valuable insights, identified opportunities, and future suggestions in the field of MOF-derived scaffold electrodes and their applications in energy storage applications have been discussed.

Nanostructured Transition Metal Oxides on Carbon Fibers for Supercapacitor and Li-Ion Battery Electrodes: An Overview

Nowadays, owing to the new technological and industrial requirements for equipment, such as flexibility or multifunctionally, the development of all-solid-state supercapacitors and Li-ion batteries has become a goal for researchers. For these purposes, the composite material approach has been widely proposed due to the promising features of woven carbon fiber as a substrate material for this type of material. Carbon fiber displays excellent mechanical properties, flexibility, and high electrical conductivity, allowing it to act as a substrate and a collector at the same time. However, carbon fiber's energy-storage capability is limited. Several coatings have been proposed for this, with nanostructured transition metal oxides being one of the most popular due to their high theoretical capacity and surface area. In this overview, the main techniques used to achieve these coatings-such as solvothermal synthesis, MOF-derived obtention, and electrochemical deposition-are summarized, as well as the main strategies for alleviating the low electrical conductivity of transition metal oxides, which is the main drawback of these materials.

A Highly Robust and Conducting Ultramicroporous 3D Fe(II)-Based Metal-Organic Framework for Efficient Energy Storage

Exploitation of metal-organic framework (MOF) materials as active electrodes for energy storage or conversion is reasonably challenging owing to their poor robustness against various acidic/basic conditions and conventionally low electric conductivity. Keeping this in perspective, herein, a 3D ultramicroporous triazolate Fe-MOF (abbreviated as Fe-MET) is judiciously employed using cheap and commercially available starting materials. Fe-MET possesses ultra-stability against various chemical environments (pH-1 to pH-14 with varied organic solvents) and is highly electrically conductive (σ = 0.19 S m-1) in one fell swoop. By taking advantage of the properties mentioned above, Fe-MET electrodes give prominence to electrochemical capacitor (EC) performance by delivering an astounding gravimetric (304 F g-1) and areal (181 mF cm-2) capacitance at 0.5 A g-1 current density with exceptionally high cycling stability. Implementation of Fe-MET as an exclusive (by not using any conductive additives) EC electrode in solid-state energy storage devices outperforms most of the reported MOF-based EC materials and even surpasses certain porous carbon and graphene materials, showcasing superior capabilities and great promise compared to various other alternatives as energy storage materials.

Hierarchically Interconnected 3D Catalyst Structure of Porous Multi-Metal Oxide Nanofibers for High-Performance Li-O2 Batteries

Non-aqueous lithium-oxygen batteries (LOBs) have emerged as a promising candidate due to their high theoretical energy density and eco-friendly cathode reaction materials. However, LOBs still suffer from high overpotential and poor cycling stability resulting from difficulties in the decomposition of discharge reaction Li2O2 products. Here, a 3D open network catalyst structure is proposed based on highly-thin and porous multi-metal oxide nanofibers (MMONFs) developed by a facile electrospinning approach coupled with a heat treatment process. The developed hierarchically interconnected 3D porous MMONFs catalyst structure with high specific surface area and porosity shows the enhanced electrochemical reaction kinetics associated with Li2O2 formation and decomposition on the cathode surface during the charge and discharge processes. The uniquely assembled cathode materials with MMONFs exhibit excellent electrochemical performance with energy efficiency of 82% at a current density of 50 mA g-1 and a long-term cycling stability over 100 cycles at 200 mA g-1 with a cut-off capacity of 500 mAh g-1. Moreover, the optimized cathode materials exhibit a remarkable energy density of 1013 Wh kg-1 at the 100th discharge and charge cycle, which is nearly four times higher than that of C/NMC721, which has the highest energy density among the cathode materials currently used in electric vehicles.

Emerging Vanadium-Doped Cobalt Chloride Carbonate Hydroxide for Flexible Electrochromic Micro-Supercapacitor: Charged-State Prediction from RGB Input by ANN Model

Multifunctional devices integrated with electrochromic and supercapacitance properties are fascinating because of their extensive usage in modern electronic applications. In this work, vanadium-doped cobalt chloride carbonate hydroxide hydrate nanostructures (V-C3H NSs) are successfully synthesized and show unique electrochromic and supercapacitor properties. The V-C3H NSs material exhibits a high specific capacitance of 1219.9 F g-1 at 1 mV s-1 with a capacitance retention of 100% over 30 000 CV cycles. The electrochromic performance of the V-C3H NSs material is confirmed through in situ spectroelectrochemical measurements, where the switching time, coloration efficiency (CE), and optical modulation (∆T) are found to be 15.7 and 18.8 s, 65.85 cm2 C-1 and 69%, respectively. A coupled multilayer artificial neural network (ANN) model is framed to predict potential and current from red (R), green (G), and blue (B) color values. The optimized V-C3H NSs are used as the active materials in the fabrication of flexible/wearable electrochromic micro-supercapacitor devices (FEMSDs) through a cost-effective mask-assisted vacuum filtration method. The fabricated FEMSD exhibits an areal capacitance of 47.15 mF cm-2 at 1 mV s-1 and offers a maximum areal energy and power density of 104.78 Wh cm-2 and 0.04 mW cm-2, respectively. This material's interesting energy storage and electrochromic properties are promising in multifunctional electrochromic energy storage applications.

Voltage Control of Multiple Electrochemical Processes during Lithium Ion Migration in NiFe2O4 Ferrite

Li-ion-based electric field control has been attracting significant attention, since it is able to penetrate deep into materials to exhibit diverse and controllable electrochemical processes, which offer more degrees of freedom to design multifunctional devices with low power consumption. As opposed to previous studies that mainly focused on single lithiation/delithiation mechanisms, we reveal three Li-ion modulation mechanisms in the same NiFe2O4 spinel ferrite by in situ magnetometry, i.e., intercalation, conversion, and space charge, which are respectively demonstrated in high, medium, and low voltage range. During the intercalation stage, the spinel structure is preserved, and a reversible modulation of magnetization arises from the charge transfer-induced variation of Fe valence states (Fe2+/Fe3+). Conversion-driven change in magnetization is the largest up to 89 emu g-1, due to the structural and magnetic phase transitions. Although both intercalation and conversion exhibit sluggish kinetics and long response times, the space charge manifests a faster switching speed and superior durability due to its interface electrostatic effect. These results not only provide a clear and comprehensive understanding on Li-based modulation mechanisms but also facilitate multifunctional and multiscenario applications, such as multistate memory, micromagnetic actuation, artificial synapse, and energy storage.

Mesoporous Mn-substituted MnxZn1-xCo2O4 ternary spinel microspheres with enhanced electrochemical performance for supercapacitor applications

Extensive investigations have been carried out on spinel mixed transition metal oxide-based materials for high-performance electrochemical energy storage applications. In this study, mesoporous Mn-substituted MnxZn1-xCo2O4 (ZMC) ternary oxide microspheres (x = 0, 0.3, 0.5, 0.7, and 1) were fabricated as electrode materials for supercapacitors through a facile coprecipitation method. Electron microscopy analysis revealed the formation of microspheres comprising interconnected aggregates of nanoparticles. Furthermore, the substitution of Mn into ZnCo2O4 significantly improved the surface area of the synthesized samples. The electrochemical test results demonstrate that the ZMC3 oxide microspheres with an optimal Mn substitution exhibited enhanced performance, displaying the largest specific capacitance of 589.9 F g-1 at 1 A g-1. Additionally, the ZMC3 electrode maintained a capacitance retention of 92.1% after 1000 cycles and exhibited a significant rate capability at a current density of 10 A g-1. This improved performance can be ascribed to the synergistic effects of multiple metals resulting from Mn substitution, along with an increase in the surface area, which tailors the redox behavior of ZnCo2O4 (ZC) and facilitates charge transfer. These findings indicate that the incorporation of Mn into mixed transition metal oxides holds promise as an effective strategy for designing high-performance electrodes for energy storage applications.

In Situ Flash Synthesis of Ultra-High-Performance Metal Oxide Anode through Shunting Current-Based Electrothermal Shock

The synthesis of anode materials plays an important role in determining the production efficiency, cost, and performance of lithium-ion batteries (LIBs). However, a low-cost, high-speed, scalable manufacturing process of the anode with the desired structural feature for practical technology adoption remains elusive. In this study, we propose a novel method called in situ flash shunt-electrothermal shock (SETS) which is controllable, fast, and energy-saving for synthesizing metal oxide-based materials. By using the example of direct electrothermal decomposition of ZIF-67 precursor loaded onto copper foil support, we achieve rapid (0.1-0.3 s) pyrolysis and generate porous hollow cubic structure material consisting of carbon-coated ultrasmall (10-15 nm) subcrystalline CoO/Co nanoparticles with controllable morphology. It was shown that CoO/Co@N-C exhibits prominent electrochemical performance with a high reversible capacity up to 1503.7 mA h g-1 after 150 cycles at 0.2 A g-1and stable capacities up to 434.1 mA h g-1 after 400 cycles at a high current density of 6 A g-1. This fabrication technique integrates the synthesis of active materials and the formation of electrode sheets into one process, thus simplifying the preparation of electrodes. Due to the simplicity and scalability of this process, it can be envisaged to apply it to the synthesis of metal oxide-based materials and to achieve large-scale production in a nanomanufacturing process.

Confined Synthesis of Dual-Atoms Within Pores of Covalent Organic Frameworks for Oxygen Reduction Reaction

Dual-atom catalysts exhibit higher reactivity and selectivity than the single-atom catalysts. The pyrolysis of bimetal salt precursors is the most typical method for synthesizing dual-atomic catalysts; however, the finiteness of bimetal salts limits the variety of dual-atomic catalysts. In this study, a confined synthesis strategy for synthesizing dual-atomic catalysts is developed. Owing to the in situ synthesis of zeolitic imidazolate frameworks in the pores of covalent organic frameworks (COFs), the migration and aggregation of metal atoms are suppressed adequately during the pyrolysis process. The resultant catalyst contains abundant Zn─Co dual atomic sites with 2.8 wt.% Zn and 0.5 wt.% Co. The catalyst exhibits high reactivity toward oxygen reduction reaction with a half-wave potential of 0.86 V, which is superior to that of the commercial Pt/C catalyst. Theoretical calculations reveal that the Zn atoms in the Zn─Co dual atomic sites promote the formation of intermediate OOH*, and thus contribute to high catalytic performance. This study provides new insights into the design of dual-atom catalysts using COFs.

Structural Engineering of Anode Materials for Low-Temperature Lithium-Ion Batteries: Mechanisms, Strategies, and Prospects

The severe degradation of electrochemical performance for lithium-ion batteries (LIBs) at low temperatures poses a significant challenge to their practical applications. Consequently, extensive efforts have been contributed to explore novel anode materials with high electronic conductivity and rapid Li+ diffusion kinetics for achieving favorable low-temperature performance of LIBs. Herein, we try to review the recent reports on the synthesis and characterizations of low-temperature anode materials. First, we summarize the underlying mechanisms responsible for the performance degradation of anode materials at subzero temperatures. Second, detailed discussions concerning the key pathways (boosting electronic conductivity, enhancing Li+ diffusion kinetics, and inhibiting lithium dendrite) for improving the low-temperature performance of anode materials are presented. Third, several commonly used low-temperature anode materials are briefly introduced. Fourth, recent progress in the engineering of these low-temperature anode materials is summarized in terms of structural design, morphology control, surface & interface modifications, and multiphase materials. Finally, the challenges that remain to be solved in the field of low-temperature anode materials are discussed. This review was organized to offer valuable insights and guidance for next-generation LIBs with excellent low-temperature electrochemical performance.

Recent progress in electrode materials for micro-supercapacitors

Micro-supercapacitors (MSCs) stand out in the field of micro energy storage devices due to their high power density, long cycle life, and environmental friendliness. The key to improving the electrochemical performance of MSCs is the selection of appropriate electrode materials. To date, both the composition and structure of electrode materials in MSCs have become a hot research topic, and it is urgent to compose a review to highlight the most important research achievements, major challenges, opportunities, and encouraging perspectives in this field. In this review, research background of MSCs is first reviewed followed by their working principles, structural classifications, and physiochemical and electrochemical characterization techniques. Next, various materials and preparation methods are summarized, and the relationship between the MSC performance and structure and composition of materials are discussed in depth. Finally, this review provides a comprehensive suggestion on accelerating the development of electrode materials to facilitate the commercialization of MSCs.

Nitrogen-Doped Titanium Dioxide for Selective Photocatalytic Oxidation of Methane to Oxygenates

Photocatalytic conversion of methane (CH4) to value-added chemicals using H2O as the oxidant under mild conditions is a desired sustainable pathway for synthesizing commodity chemicals. However, controlling product selectivity while maintaining high product yields is greatly challenging. Herein, we develop a highly efficient strategy, based on the precise control of the types of nitrogen dopants, and the design of photocatalysts, to achieve high selectivity and productivity of oxygenates via CH4 photocatalytic conversion. The primary product (methanol) is obtained in a high yield of 159.8 μmol·g-1·h-1 and 47.7% selectivity, and the selectivity of oxygenate compounds reached 92.5%. The unique hollow porous structure and substituted nitrogen sites of nitrogen-doped TiO2 synergistically promote its photo-oxidation performance. Furthermore, in situ attenuated total reflectance Fourier transform infrared spectroscopy provides direct evidence of the key intermediates and their evolution for producing methanol and multicarbon oxygenates. This study provides insights into the mechanism of photocatalytic CH4 conversion.

Facile Synthesis of Ni-MgO/CNT Nanocomposite for Hydrogen Evolution Reaction

In this study, the pristine MgO, MgO/CNT and Ni-MgO/CNT nanocomposites were processed using the impregnation and chemical vapor deposition methods and analyzed for hydrogen evolution reaction (HER) using the electrochemical water splitting process. Furthermore, the effect of nickel on the deposited carbon was systematically elaborated in this study. The highly conductive carbon nanotubes (CNTs) deposited on the metal surface of the Ni-MgO nanocomposite heterostructure provides a robust stability and superior electrocatalytic activity. The optimized Ni-MgO/CNT nanocomposite exhibited hierarchical, helical-shaped carbon nanotubes adorned on the surface of the Ni-MgO flakes, forming a hybrid metal-carbon network structure. The catalytic HER was carried out in a 1M alkaline KOH electrolyte, and the optimized Ni-MgO/CNT nanocomposite achieved a low (117 mV) overpotential value (ɳ) at 10 mA cm-2 and needed a low (116 mV/dec) Tafel value, denotes the Volmer-Heyrovsky pathway. Also, the high electrochemical active surface area (ECSA) value of the Ni-MgO/CNT nanocomposite attained 515 cm2, which is favorable for the generation of abundant electroactive species, and the prepared electrocatalyst durability was also performed using a chronoamperometry test for the prolonged duration of 20 h at 10 mA cm-2 and exhibited good stability, with a 72% retention. Hence, the obtained results demonstrate that the optimized Ni-MgO/CNT nanocomposite is a highly active and cost-effective electrocatalyst for hydrogen energy production.

Two-stage confinement derived small-sized highly ordered L10-PtCoZn for effective oxygen reduction catalysis in PEM fuel cells

Intermetallic ordered PtCo is effective for high oxygen reduction reaction (ORR) activity and stability. However, preparing small-sized, highly ordered PtM alloys is still challenging. Herein, we report a controlled two-stage confinement strategy, in which highly ordered PtCoZn/NC nanoparticles of 5.3 nm size were prepared in a scalable process. The contradiction between the high ordering degree with the small particle size as well as the atomic migration with the space confinement was well resolved. An outstanding PEMFC performance was achieved for L10-PtCoZn/NC with a high mass activity (MA) of 1.21 A/mgPt at 0.9 ViR-free, 80.1 % MA retention after 30 k cycles in H2-O2 operation, and a high mass-specific power density of 8.24 W mg-1Pt in H2-Air operation with a slight loss of cell voltage@0.8 A cm-2 of 28 mV after 30 k cycles. The high performance can be ascribed to the high Pt area exposure, the enhanced Pt-Co coupling, and the prevented agglomeration in the mesoporous carbon wall. Overall, this strategy may contribute to the commercialization of fuel cells.

Towards engineering mitigation of leaching of Cd and Pb in co-contaminated soils using metal oxide-based aerogel composites and biochar

Applications of metal-based nanomaterials for the remediation of heavy metal (HM) contaminated environments are of great importance. The ability of metal oxide-based carbon aerogel composite to immobilize HMs in multi-metal contaminated soils has not yet been investigated, particularly under acidic conditions. Herein, we investigate the performance of metal oxides (Sr0.7 Mn0.3 Co0.5 Fe0.5O3-δ)-based carbon aerogel composite (MO-CAg) compared with coconut coil fiber biochar (CCFB) and carbon aerogel (CAg) for Cd and Pb immobilization in contaminated soil. The MO-CAg, applied at 2% (w/w), significantly decreased Pb leaching by 67-75% and Cd by 60-65%, CAg decreased Cd by 54% and Pb by 46%, while biochar decreased Cd by 40-44% and Pb by 43%. The addition of MO-CAg altered Cd and Pb geochemical fractions by increasing their residual fraction, i.e., stabilized both metals compared to the control. This presents a comprehensive elaboration on the probable reaction interactions between the MO-Cag and heavy metals, including a combination of (co)precipitation, and reduction-oxidation as the predominant mechanisms of metal stabilization with MO-CAg. Moreover, MO-CAg increased Pb and Cd stabilization in soils by strengthening the bonding between metal oxides and Cd/Pb. By imbedding MO into the CAg, in MO-CAg, the immobilization of Cd(II) and Pb(II) occurred through inner-sphere complexation, while with CCFB and CAg metals, immobilization occurred through outer-sphere complexation. MO-CAg is a promising and highly efficient material that could be recommended for the remediation of Cd- and Pb-contaminated soils in subsequent studies.

Molten salt synthesis of disordered spinel CoFe2O4 with improved electrochemical performance for sodium-ion batteries

Sodium-ion (Na-ion) batteries are currently being investigated as an attractive substitute for lithium-ion (Li-ion) batteries in large energy storage systems because of the more abundant and less expensive supply of Na than Li. However, the reversible capacity of Na-ions is limited because Na possesses a large ionic radius and has a higher standard electrode potential than that of Li, making it challenging to obtain electrode materials that are capable of storing large quantities of Na-ions. This study investigates the potential of CoFe2O4 synthesised via the molten salt method as an anode for Na-ion batteries. The obtained phase structure, morphology and charge and discharge properties of CoFe2O4 are thoroughly assessed. The synthesised CoFe2O4 has an octahedron morphology, with a particle size in the range of 1.1-3.6 μm and a crystallite size of ∼26 nm. Moreover, the CoFe2O4 (M800) electrodes can deliver a high discharge capacity of 839 mA h g-1 in the first cycle at a current density of 0.1 A g-1, reasonable cyclability of 98 mA h g-1 after 100 cycles and coulombic efficiency of ∼99%. The improved electrochemical performances of CoFe2O4 can be due to Na-ion-pathway shortening, wherein the homogeneity and small size of CoFe2O4 particles may enhance the Na-ion transportation. Therefore, this simple synthetic approach using molten salt favours the Na-ion diffusion and electron transport to a great extent and maximises the utilisation of CoFe2O4 as a potential anode material for Na-ion batteries.

Conformal Coverage of ZnO Nanowire Arrays by ZnMnO3 : Room-temperature Photodeposition from Aqueous Solution

Compositionally and structurally complex semiconductor oxide nanostructures gain importance in many energy-related applications. Simple and robust synthesis routes ideally complying with the principles of modern green chemistry are therefore urgently needed. Here we report on the one-step, room-temperature synthesis of a crystalline-amorphous biphasic ternary metal oxide at the ZnO surface using aqueous precursor solutions. More specifically, conformal and porous ZnMnO3 shells are photodeposited from KMnO4 solution onto immobilized ZnO nanowires acting not only as the substrate but also as the Zn precursor. This water-based, low temperature process yields ZnMnO3 /ZnO composite electrodes featuring in 1 M Na2 SO4 aqueous solution capacitance values of 80-160 F g-1 (as referred to the total mass of the porous film i. e. the electroactive ZnMnO3 phase and the ZnO nanowire array). Our results highlight the suitability of photodeposition as a simple and green route towards complex functional materials.

Polymorphs of Nb2O5 Compound and Their Electrical Energy Storage Applications

Niobium pentoxide (Nb2O5), as an important dielectric and semiconductor material, has numerous crystal polymorphs, higher chemical stability than water and oxygen, and a higher melt point than most metal oxides. Nb2O5 materials have been extensively studied in electrochemistry, lithium batteries, catalysts, ionic liquid gating, and microelectronics. Nb2O5 polymorphs provide a model system for studying structure-property relationships. For example, the T-Nb2O5 polymorph has two-dimensional layers with very low steric hindrance, allowing for rapid Li-ion migration. With the ever-increasing energy crisis, the excellent electrical properties of Nb2O5 polymorphs have made them a research hotspot for potential applications in lithium-ion batteries (LIBs) and supercapacitors (SCs). The basic properties, crystal structures, synthesis methods, and applications of Nb2O5 polymorphs are reviewed in this article. Future research directions related to this material are also briefly discussed.

Performance analysis of three distinct NixV2Oy single-phase nano self-assemblies for asymmetric supercapacitor fabrication and effective detection of low-concentration hazardous herbicide

Single-phase inorganic nanostructures with multiple applications are required for cost-effective, sustainable applications to save the environment from toxic activities. Nickel vanadate (NixV2Oy), possessing three phases, such as NiV2O6, Ni2V2O7, and Ni3V2O8, acts as an effective electrode material and potential electrochemical sensors. Nickel vanadate phases (NiV2O6, Ni2V2O7, and Ni3V2O8) were synthesized through the gel-matrix technique, and their phase purity, crystallinity, morphology, optical properties, etc., were evaluated and studied. Electrochemical studies infer that NiV2O6 exhibits the highest specific capacity of 251 C g-1 (69.7 mA h g-1) at 1 A g-1 compared to the other nickel vanadate phases and provides better cyclic stability of 80.19% for 5000 cycles. The asymmetric supercapacitor device fabricated from NiV2O6 results in a specific capacity of 189 C g-1 (52.5 mA h g-1), energy density of 59.06 W h kg-1, and a power density of 1125 W kg-1 with a capacitive retention rate of 74.91% and coulombic efficiency of 99.61% for 10 000 cycles. The electrochemical detection potential of NixV2Oy in bifenox herbicide has been studied with all the synthesized nanostructures. Among them, NiV2O6-based sensor probes demonstrated excellent characteristics, including high sensing current and low detection limits of 0.6 nM with a linear range of 1-57 nM. The real-time herbicide detection of NiV2O6 in live samples was checked with freshly harvested potatoes. This advancement further enhances the utilization of NixV2Oy materials for electrochemical applications.

Morphology Controlled Deposition of Vanadium Oxide (VOx) Nanoparticles on the Surface of Highly Reduced Graphene Oxide for the Photocatalytic Degradation of Hazardous Organic Dyes

Semiconducting nanomaterials based heterogeneous photocatalysis represent a low-cost, versatile technique for environmental remediation, including pollution mitigation, energy management and other environmental aspects. Herein, we demonstrate the syntheses of various heterogeneous photocatalysts based on highly reduced graphene oxide (HRG) and vanadium oxide (VOx)-based nanocomposites (HRG-VOx). Different shapes (rod, sheet and urchin forms) of VOx nanoparticles were successfully fabricated on the surface of HRG under solvo-/hydrothermal conditions by varying the amount of water and ethanol. The high concentration of water in the mixture resulted in the formation of rod-shaped VOx nanoparticles, whereas increasing the amount of ethanol led to the production of VOx sheets. The solvothermal condition using pure ethanol as solvent produced VOx nano-urchins on the surface of HRG. The as-prepared hybrid materials were characterized using various spectroscopic and microscopic techniques, including X-ray diffraction, UV-vis, FTIR, SEM and TEM analyses. The photocatalytic activities of different HRG-VOx nanocomposites were investigated for the photodegradation of methylene blue (MB) and methyl orange (MO). The experimental data revealed that all HRG-VOx composite-based photocatalysts demonstrated excellent performance toward the photocatalytic degradation of the organic dyes. Among all photocatalysts studied, the HRG-VOx nanocomposite consisting of urchin-shaped VOx nanoparticles (HRG-VOx-U) demonstrated superior photocatalytic properties towards the degradation of dyes.

Reconstructing 3d-Metal Electrocatalysts through Anionic Evolution in Zinc-Air Batteries

As one of the promising sustainable energy storage systems, academic research on rechargeable Zn-air batteries has recently been rejuvenated following development of various 3d-metal electrocatalysts and identification of their dynamic reconstruction toward (oxy)hydroxide, but performance disparity among catalysts remains unexplained. Here, this uncertainty is addressed through investigating the anionic contribution to regulate dynamic reconstruction and battery behavior of 3d-metal selenides. Comparing with the alloy counterpart, anionic chemistry is identified as a performance promoter and further exploited to empower Zn-air batteries. Based on theoretical modeling, Se-resolved operando spectroscopy, and advanced electron microscopy, a three-step Se evolution is established, consisting of oxidation, leaching, and recoordination. The process generates an amorphous (oxy)hydroxide with O-sharing bonded Se motifs that triggers charge redistribution at metal sites and lowers the energetic barrier of their current-driven redox. A pervasive concept of Se back-feeding is then proposed to describe the underlying chemistry for 3d-metal selenides with diversity in crystals or compositions, and the feasibility to fine-tune their behavior is also presented.

Three-dimensional Ni foam supported NiCoO2@Co3O4 nanowire-on-nanosheet arrays with rich oxygen vacancies as superior bifunctional catalytic electrodes for overall water splitting

Earth abundant transition metal oxide (EATMO)-based bifunctional catalysts for overall water splitting are highly desirable, but their performance is far from satisfactory due to low intrinsic activities of EATMOs toward electrocatalysis of both oxygen and hydrogen evolution reactions and poor electron transfer and transport capabilities. A three-dimensional (3-D) Ni-foam-supported NiCoO2@Co3O4 nanowire-on-nanosheet heterostructured array with rich oxygen vacancies has been synthesized, showing OER activity superior to most reported catalysts and even much higher than Ru and Ir-based ones and HER activity among the highest reported for non-noble-metal-based catalysts. The excellent activities are ascribed to the highly dense, ultrathin nanowire arrays epitaxially grown on an interconnected layered nanosheet array greatly facilitating electron transfer and providing numerous electrochemically accessible active sites and the high content of oxygen vacancies on nanowires greatly promoting OER and HER. When adopted as bifunctional electrodes for overall water splitting, this heterostructure shows an overvoltage (at 10 mA cm-2) lower than most reported electrolyzers and high stability. This work not only creates a 3-D EATMO-based integrated heterostructure as a low-cost, highly efficient bifunctional catalytic electrode for water splitting, but also provides a novel strategy to use unique heteronanostructures with rich surface defects for synergistically enhancing electrocatalytic activities.

Boosting Fe Cationic Vacancies with Graphdiyne to Enhance Exceptional Pseudocapacitive Lithium Intercalation

Modulating the electronic structure of electrode materials at atomic level is the key to controlling electrodes with outstanding rate capability. On the basis of modulating the iron cationic vacancies (IV) and electronic structure of materials, we proposed the method of preparing graphdiyne/ferroferric oxide heterostructure (IV-GDY-FO) as anode materials. The goal is to motivate lithium-ion batteries (LIBs) toward ultra-high capacity, superior cyclic stability, and excellent rate performance. The graphdiyne is used as carriers to disperse Fe3 O4 uniformly without agglomeration and induce high valence of Fe with reducing the energy in the system. The presence of Fe vacancy could regulate the charge distribution around vacancies and adjacent atoms, leading to facilitate electronic transportation, enlarge the lithium-ion diffusion, and decrease Li+ diffusion barriers, and thus displaying significant pseudocapacitive process and advantageous lithium-ion storage. The optimized electrode IV-GDY-FO reveals a capacity of 2084.1 mAh g-1 at 0.1 C, superior cycle stability and rate performance with a high specific capacity of 1057.4 mAh g-1 even at 10 C.

Coordination Engineering of Dual Co, Ni Active Sites in N-Doped Carbon Fostering Reversible Oxygen Electrocatalysis

The development of affordable and non-noble-metal-based reversible oxygen electrocatalysts is required for renewable energy conversion and storage systems like metal-air batteries (MABs). However, the nonbifunctionality of most of the catalysts impedes their use in rechargeable MAB applications. Moreover, the loss of active sites also affects the long-term performance of the electrocatalyst toward oxygen electrocatalysis. In this work, we report a simplistic yet controllable chemical approach for the synthesis of dual transitional metals such as cobalt, nickel, and nitrogen-doped carbon (CoNi-NC) as bifunctional electrode materials for rechargeable zinc-air batteries (ZABs). The spatially isolated Ni-N4 and Co-N4 active units were rendered for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), respectively. The individual efficacy of both reversible reactions enables an ΔE value of ∼0.72 V, which outperforms several bifunctional electrocatalysts reported in the literature. The half-wave potential (E1/2) and overpotential were achieved at 0.83 V and 330 mV (vs RHE) for ORR and OER, respectively. The peak power density of ZAB equipped with the CoNi-NC catalyst was calculated to be 194 mW cm-2. The present strategy for the synthesis of bifunctional electrocatalysts with dual active sites offers prospects for developing electrochemical energy storage and conversion systems.

A single step wet chemical approach to bifunctional ultrathin (ZnO)62(Fe2O3)38 dendritic nanosheets

At the ultrathin scale, nanomaterials exhibit interesting chemical and physical properties, like flexibility, and polymer-like rheology. However, to limit the dimensions of composite nanomaterials at the ultrathin level is still a challenging task. Herein, by adopting a new low temperature single step and single pot wet chemical approach, we have successfully fabricated two dimensional (2D) mixed oxide ZnO-Fe₂O₃ dendritic nanosheets (FZDNSs). Various control experimental outcomes demonstrate that precursor salts of both the metals are crucial for the formation of stable 2D FZDNSs. The obtained FZDNSs not only exhibit the best photoreduction performance but also much enhanced electrocatalytic performance. This work will provide a promising avenue for the synthesis of cost effective transition metal mixed oxide based 2D nanosheets having wide ranging applications.

Combination of Mn-Mo Oxide Nanoparticles on Carbon Nanotubes through Nitrogen Doping to Catalyze Oxygen Reduction

An efficient and low-cost oxygen catalyst for the oxygen reduction reaction (ORR) was developed by in situ growth of Mn-Mo oxide nanoparticles on nitrogen-doped carbon nanotubes (NCNTs). Doped nitrogen effectively increases the electron conductivity of the MnMoO₄@NCNT complex and the binding energy between the Mn-Mo oxide nanoparticles and carbon nanotubes (CNTs), leading to fast charge transfer and more catalytically active sites. Combining Mn and Mo with NCNTs improves the catalytic activity and promotes both electron and mass transfers, greatly enhancing the catalytic ability for ORR. As a result, MnMoO₄@NCNT exhibited a comparable half-wave potential to commercial Pt/C and superior durability, demonstrating great potential for application in renewable energy conversion systems.

Silver-functionalized bismuth oxide (AgBi2O3) nanoparticles for the superior electrochemical detection of glucose, NO2- and H2O2

In this study, silver-functionalized bismuth oxide (AgBi₂O₃) nanoparticles (SBO NPs) were successfully synthesized by a highly efficient hydrothermal method. The as-synthesized SBO nanoparticles were characterized using FT-IR, P-XRD, XPS, HR-SEM, and HR-TEM analytical methods. It was found that the NPs were in spherical shape and hexagonal crystal phase. The newly prepared SBO electrode was further utilized for the detection of glucose, NO₂^- and H₂O₂ by cyclic voltammetry (CV) and amperometric methods. The electrodes exhibited high sensitivity (2.153 μA mM^-1 cm^-2 for glucose, 22 μA mM^-1 cm^-2 for NO₂^- and 1.72 μA mM^-1 cm^-2 for H₂O₂), low LOD (0.87 μM for glucose, 2.8 μM for NO₂^- and 1.15 μM for H₂O₂) and quick response time (3 s for glucose, 2 s for both NO₂^- and H₂O₂ respectively). The sensor exhibited outstanding selectivity despite the presence of various interferences. The developed sensor exhibited good repeatability, reproducibility, and stability. In addition, the sensor was used to measure glucose, H₂O₂ in human serum, and NO₂^- in milk and river water samples, demonstrating its potential for use in the real sample.

High-Pressure-Stabilized Post-Spinel Phase of CdFe2O4 with Distinct Magnetism from Its Ambient-Pressure Spinel Phase

α-CdFe₂O₄ stabilizes its normal spinel structure due to the covalent Cd-O bond, in which all the connections between adjacent FeO₆ octahedral are edge-shared, forming a typical geometrically frustrated Fe³⁺ magnetic lattice. As the high-pressure methods were utilized, the post-spinel phase β-CdFe₂O₄ with a CaFe₂O₄-type structure was synthesized at 8 GPa and 1373 K. The new polymorph has an orthorhombic structure with the space group Pnma and an 11.5% higher density than that of its normal spinel polymorph (α-CdFe₂O₄) synthesized at ambient conditions. The edge-shared FeO₆ octahedra form zigzag S = 5/2 spin ladders along the b-axis dominating its low-dimensional magnetic properties at high temperatures and a long-range antiferromagnetic ordering with a high Néel temperature of T_N1 = 350 K. Further, the rearrangement of magnetic ordering was found to occur around T_N2 = 265 K, below which the competition of two phases or several couplings induce complex antiferromagnetic behaviors.

Effect of Indole-2-carboxylic Acid on the Self-Corrosion and Discharge Activity of Aluminum Alloy Anode in Alkaline Al-Air Battery

Al-air battery has been regarded as a promising new energy source. However, the self-corrosion of aluminum anode leads to a loss of battery capacity and a decrease in battery longevity, limiting its commercial applications. Herein, indole-2-carboxylic acid (ICA) has been added to 4 M NaOH as a corrosion inhibitor. Its impact on the self-corrosion of aluminum alloy and the enhancement of the functionality of Al-air batteries at various concentrations have been investigated. X-ray photoelectron spectroscopy (XPS), attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, atomic force microscopy (AFM), and scanning electron microscopy (SEM) techniques have been used to examine the compositional and morphological alterations of aluminum alloy surfaces. Electrochemical and hydrogen evolution tests showed that indole-2-carboxylic acid is an efficient corrosion inhibitor in alkaline solutions, and its impact grows with concentration. Our findings demonstrated that when the inhibitor concentration is 0.07 M, the inhibition efficiency is 54.0%, the anode utilization rises from 40.2% to 79.9%, the capacity density increases from 1197.6 to 2380.9 mAh g^-1, and the energy density increases from 1469.9 to 2951.8 Wh kg^-1. In addition, theoretical calculations have been performed to support the experimental results.

Understanding the origin of the improved sodium ion storage performance of the transition metal oxide@carbon nanocomposite anodes

Transition metal oxide (TMO) anodes show inferior sodium ion storage performance compared with that of lithium ion storage owing to the larger radium size and heavier elemental mass of Na+ than Li+. Effective strategies are highly desired to improve the Na+ storage performance of TMOs for applications. In this work, using ZnFe2O4@xC nanocomposites as model materials for investigation, we found that by manipulating the particle sizes of the inner TMOs core and the features of outer carbon coating, the Na+ storage performance can be significantly improved. The ZnFe2O4@1C with a diameter of the inner ZnFe2O4 core of around 200 nm coated by a thin carbon layer of around 3 nm shows a specific capacity of only 120 mA h g-1. The ZnFe2O4@6.5C with a diameter of the inner ZnFe2O4 core of around 110 nm embedding in a porous interconnected carbon matrix displays a significantly improved specific capacity of 420 mA h g-1 at the same specific current. Furthermore, the latter shows an excellent cycling stability of 1000 cycles with a capacity retention of 90% of the initial 220 mA h g-1 specific capacity at 1.0 A g-1. TEM, electrochemical impedance spectroscopy, and kinetic analysis show that the inner ZnFe2O4 core with reduced particle size and the outer thicker and interconnected carbon matrix synergistically improve the active reaction sites, integrity, electric conductivity, and pseudocapacitive-controlled contribution of ZnFe2O4@xC nanocomposites, thus leading to an overall enhanced Na+ storage performance. Our findings create a universal, facile, and effective method to enhance the Na+ storage performance of the TMO@C nanomaterials.

In Situ Construction of Zn2Mo3O8/ZnO Hierarchical Nanosheets on Graphene as Advanced Anode Materials for Lithium-Ion Batteries

Transition-metal oxides as anodes for lithium-ion batteries (LIBs) have attracted enormous interest because of their high theoretical capacity, low cost, and high reserve abundance. Unfortunately, they commonly suffer from poor electronic and ionic conductivity and relatively large volume expansion during discharge/charge processes, thereby triggering inferior cyclic performance and rate capability. Herein, a molybdenum-zinc bimetal oxide-based composite structure (Zn₂Mo₃O₈/ZnO/rGO) with rectangular Zn₂Mo₃O₈/ZnO nanosheets uniformly dispersed on reduced graphene oxide (rGO) has been prepared by using a simple and controllable cyanometallic framework template method. The Zn₂Mo₃O₈/ZnO rectangular nanosheets with desirable porous features are composed of nanocrystalline subunits, facilitating the exposure of abundant active sites and providing sufficient contact with the electrolyte. Benefiting from the composition and structural merits as well as the induced synergistic effects, the Zn₂Mo₃O₈/ZnO/rGO composite as LIB anodes delivers superior electrochemical properties, including high reversible capacity (960 mA h g^-1 after 100 cycles at 200 mA g^-1), outstanding rate performance (417 mA h g^-1 at 10,000 mA g^-1), and admirable long-term cyclic stability (862 mA h g^-1 after 400 cycles at 1000 mA g^-1). The mechanism of lithium storage and the formation of SEI film are systematically elucidated. This work provides an effective strategy for synthesizing promising Mo-cluster compound-based anodes for high-performance LIBs.

Development of Cellulose Nanofiber-SnO2 Supported Nanocomposite as Substrate Materials for High-Performance Lithium-Ion Batteries

The large volumetric expansion of conversion-type anode materials (CTAMs) based on transition-metal oxides is still a big challenge for lithium-ion batteries (LIBs). An obtained nanocomposite was established by tin oxide (SnO₂) nanoparticles embedding in cellulose nanofiber (SnO₂-CNFi), and was developed in our research to take advantage of the tin oxide's high theoretical specific capacity and the cellulose nanofiber support structure to restrain the volume expansion of transition-metal oxides. The nanocomposite utilized as electrodes in lithium-ion batteries not only inhibited volume growth but also contributed to enhancing electrode electrochemical performance, resulting in the good capacity maintainability of the LIBs electrode during the cycling process. The SnO₂-CNFi nanocomposite electrode delivered a specific discharge capacity of 619 mAh g^-1 after 200 working cycles at the current rate of 100 mA g^-1. Moreover, the coulombic efficiency remained above 99% after 200 cycles showing the good stability of the electrode, and promising potential for commercial activity of nanocomposites electrode.

Enhancing lithium storage performance of bimetallic oxides anode by synergistic effects

Spinel bimetallic transition metal oxide anode such as ZnMn₂O₄, has drawn increasing interest due to attractive bimetal interaction and high theoretical capacity. While it suffers from huge volume expansion and poor ionic/electronic conductivity. Nanosizing and carbon modification can alleviate these issues, while the optimal particle size within host is unclear yet. We here propose an in-situ confinement growth strategy to fabricate pomegranate-structured ZnMn₂O₄ nanocomposite with calculated optimal particle size in mesoporous carbon host. Theoretical calculations reveal favorable interatomic interactions between the metal atoms. By the synergistic effects of structural merits and bimetal interaction, the optimal ZnMn₂O₄ composite achieves greatly improved cycling stability (811 mAh g^-1 at 0.2 A g^-1 after 100 cycles), which can maintain its structural integrity upon cycling. X-ray absorption spectroscopy analysis further confirms delithiated Mn species (Mn₂O₃ but little MnO). Briefly, this strategy brings new opportunity to ZnMn₂O₄ anode, which could be adopted to other conversion/alloying-type electrodes.

Designing In Situ Grown Ternary Oxide/2D Ni-BDC MOF Nanocomposites on Nickel Foam as Efficient Electrocatalysts for Electrochemical Water Splitting

The security of future energy, hydrogen, is subject to designing high-performance, stable, and low-cost electrocatalysts for hydrogen and oxygen evolution reactions (HERs and OERs), for the realization of efficient overall water splitting. Two-dimensional (2D) metal-organic frameworks (MOFs) introduce a large family of materials with versatile chemical and structural features for a variety of applications, such as supercapacitors, gas storage, and water splitting. Herein, a series of nanocomposites based on NCM/Ni-BDC@NF (N=Ni, C=Co, M:F=Fe, C=Cu, and Z=Zn, BDC: benzene dicarboxylic acid, NF: nickel foam) were directly developed on NF using a facile yet scalable solvothermal method. After coupling, the electronic structure of metallic atoms was well-modulated. Based on the XPS results, for the NCF/Ni-BDC, cationic atoms shifted to higher oxidation states, favorable for the OER. Conversely, for the NCZ/Ni-BDC and NCC/Ni-BDC nanocomposites, cationic atoms shifted to lower oxidation states, advantageous for the HER. The as-prepared NCF/Ni-BDC demonstrated prominent OER performance, requiring only 1.35 and 1.68 V versus a reversible hydrogen electrode to afford 10 and 50 mA cm-2 current densities, respectively. On the cathodic side, NCZ/Ni-BDC exhibited the best HER activity with an overpotential of 170 and 350 mV to generate 10 and 50 mA cm-2, respectively, under 1.0 M KOH medium. In a two-electrode alkaline electrolyzer, the assembled NCZ/Ni-BDC (cathode) ∥ NCF/Ni-BDC (anode) couple demanded a cell voltage of only 1.58 V to produce 10 mA cm-2. The stability of NCF/Ni-BDC toward OER was also exemplary, experiencing a continuous operation at 10, 20, and 50 mA cm-2 for nearly 45 h. Surprisingly, the overpotential after OER stability at 50 mA cm-2 dropped drastically from 450 to 200 mV. Finally, the faradaic efficiencies for the overall water splitting revealed the respective values of 100 and 85% for the H2 and O2 production at a constant current density of 20 mA cm-2.