Distribution Of Metal Cations Research Articles

Assessment of the concentration of toxic metals (aluminum, cadmium and manganese) in the soil and evergreen plant species at the Sastavci surface mine and its vicinity

The study aims to determine the concentration of Al+3, Cd+2 and Mn+2 in the soil and parts of evergreen plant species - juniper and white pine - at the surface mine Sastavci (Badanj) and its vicinity in order to determine the possibility of using evergreen plants as an ecological indicator or for phytoremediation. Globally, as a result of various anthropogenic activities such as traffic, agricultural activities, waste incineration, industrial production, mining, etc., it represents a serious problem leading to pollution with toxic and potentially toxic metal cations. One of the more innovative techniques used for the remediation of mining areas is phytoremediation. By applying phytoremediation, certain plant species in polluted areas have the ability to act as accumulators or hyperaccumulators, absorbing toxic metals from the soil through the plant roots and transporting them to the upper parts. This research has been conducted to determine the concentration of Al+3, Cd+2 and Mn+2 at the surface mine itself and its surroundings, as well as to monitor the distribution of metal cations in the system of roots, branches, needles, and fruits of the evergreen plant species - white pine and juniper. The results showed that the sampled soil was contaminated with Cd in zones I and II for both plant species, since the concentrations exceeded the limit values, while the concentration of Cd in zone III as well as in the control zone was below the determination limits for both plant species. The concentration of Mn in the soil from the white pine and juniper zone was above the world average in all three zones, as well as in the control zone itself. The soil was most enriched with the analyzed elements in the surface mine of zone I and zone II. According to the analysis of elements in the parts of white pine, roots, branches, needles and fruits, the highest concentration of Al was detected in the root in zone I, while the lowest concentration was recorded in the fruit (cones) in the control zone, an increased concentration of Cd was recorded in the branches in zones I and II, and the highest concentration of Mn was recorded in needles in zone II. The highest Al concentration was recorded in the juniper root in zone I and the lowest in the juniper fruit in the control zone, the Cd concentration was the highest in the juniper root zone I, and the lowest in the juniper fruit and the highest Mn concentration was recorded in the juniper needles in zone I. Based on the obtained values of the coefficient of biological absorption, it can be concluded that white pine is not suitable for phytoextraction or phytostabilization of the tested elements. The analysis of biological factors (bioconcentration, translocation and bioaccumulation factor) indicated possible usage of juniper in phytoextraction only for Cd.

Enhancing Water Oxidation Catalysis by Controlling Metal Cation Distribution in Layered Double Hydroxides (Adv. Funct. Mater. 2/2024)

Enhancing Water Oxidation Catalysis by Controlling Metal Cation Distribution in Layered Double Hydroxides (Adv. Funct. Mater. 2/2024)

Effect of Manganese-Doping on the chemical and optical properties of cobalt ferrite nanoparticles

We report on the effect of manganese (Mn) doping on the structural, chemical and optical properties of cobalt ferrite (CFO) nanoparticles (NPs). The Mn(II)-substituted CFO NPs with variable chemical composition (Co1-xMnxFe2O4; x = 0.0–0.5; CMFO) were synthesized by an eco-friendly hydrothermal route. The CMFO NPs produced were with a crystallite size varying in the range of 8–14 nm, where the chemical valence state, chemical bonding, electronic structure and optical properties are strongly influenced by the Mn-substitution. The X-ray diffraction (XRD) studies revealed the Mn-substitution induced changes in CFO crystal structure. The Mn-substitution in CFO causes the lattice parameter enhancement (a), crystallite size increase, and micro-strain (ε) as evident in the XRD studies. The chemical composition driven direct, functional relationship reflected in a-D-ε correlation, which suggests the Mn-substitution allows the ability to control the size and strain in CFMO NPs. Chemical bonding analyses using Fourier transform infrared spectroscopy (FTIR) corroborates with structural assessment made with XRD studies. The MTd–O (MTd = metal ions in tetrahedral locations) absorption bands shifting to higher wavenumbers in FTIR studies indicate that, Mn-substitution induce changes in the metal cation distribution between the tetrahedral and octahedral locations of the ferrite lattice. The X-ray photoelectron spectroscopic (XPS) analyses indicate the presence of iron as Fe+3, cobalt as Co+2, and manganese in Mn+2 chemical state. With increasing Mn-content, the XPS revealed that the binding energy (BE) separation of Fe, as well as Mn, does not change compared to Co, indicating the chemical stability and valence state of Fe+3 and Mn+2 cations maintained well in the CMFO samples. While the overall chemistry of CFO is maintained, and is not influenced by the increasing Mn-concentration, the remarkable effect of Mn-substitution is seen on the optical properties of CFO NPs. The optical studies indicate that the band gap of CFO NPs exhibits a direct, functional dependence on Mn-concentration; the band gap varies in a wide range of 2.38–3.12 eV. The analyses indicate the exponential dependence of CFO optical band gap with Mn-content which provide a roadmap to engineer the materials with tunable band gap for desired technological applications.

Enhancing Water Oxidation Catalysis by Controlling Metal Cation Distribution in Layered Double Hydroxides

AbstractThe sluggish kinetics of the oxygen evolution reaction (OER), the limiting step of the electrochemical water splitting process, hinders the eventual commercialization of this important renewable energy strategy. Hence, the development of efficient electrocatalysts for this reaction is crucial. Multi‐metal‐based (hydr)oxides are promising OER electrocatalysts because the electronic interactions between multiple constituent metal cations can potentially enhance electrochemical performances. However, complex compositions may not always lead to positive synergistic effects. The appropriate distribution of the cations is also critical. However, the high dispersibility of cations in these hydroxides renders the control of their distribution challenging. Herein, an approach is reported to control the metal cation distribution in layered double hydroxides (LDHs) to improve their OER performances. Restacking of exfoliated NiFe and CoAl LDH nanosheets leads to electrochemical synergistic effects between different nanosheets. As far as it is known, the restacked LDH described herein exhibits the lowest overpotential (224 mV) and Tafel slope (34.26 mV dec−1) among reported powder‐type (hydr)oxide and alloy OER electrocatalysts with more than three different metal cations. Thus, a new design approach is suggested to enhance the electrochemical performances of LDHs.

Enhanced Bacterial Growth by Polyelemental Glycerolate Particles.

While polyelemental alloys are shown to be promising for healthcare applications, their effectiveness in promoting bacterial growth remains unexplored. In the present work, we evaluated the interaction of polyelemental glycerolate particles (PGPs) with Escherichia coli (E. coli) bacteria. PGPs were synthesized using the solvothermal route, and nanoscale random distribution of metal cations in the glycerol matrix of PGPs was confirmed. We observed 7-fold growth of E. coli bacteria upon 4 h of interaction with quinary glycerolate (NiZnMnMgSr-Gly) particles in comparison to control E. coli bacteria. Nanoscale microscopic studies on bacteria interactions with PGPs showed the release of metal cations in the bacterium cytoplasm from PGPs. The electron microscopy imaging and chemical mapping indicated bacterial biofilm formation on PGPs without causing significant cell membrane damage. The data showed that the presence of glycerol in PGPs is effective in controlling the release of metal cations, thus preventing bacterial toxicity. The presence of multiple metal cations is expected to provide synergistic effects of nutrients needed for bacterial growth. The present work provides key microscopic insights of mechanisms by which PGPs enhance biofilm growth. This study opens the door for future applications of PGPs in areas where bacterial growth is essential including healthcare, clean energy, and the food industry.

Copper (II) anchored on layered double hydroxide functionalized guanidine as a heterogeneous catalyst for the synthesis of tetrazole derivatives

In this paper, a novel nanocomposite was prepared as a heterogeneous catalyst using layered double hydroxide (LDH), and copper(II) nanoparticles stabilized on guanidine (Mg-Al LDH@Guanidine-Cu(II)) (1). This nanocomposite was used in multi-component reactions for the synthesis of 2-(1H-tetrazole-5-yl) acrylonitrile derivatives with high yield in short reaction times. Identification of this nanocatalyst was performed by FT-IR, EDS, FE-SEM, TEM, XRD and TGA techniques. This nanocatalyst showed high thermal stability, high specific surface area, and good reusability up to 4 times without significant loss of activity. In addition, excellent activity, easy separation, and milder reaction conditions are among the factors that make this nanocomposite an excellent catalytic system for these reactions. In addition, synthesis of 2-(1H-tetrazole-5-yl) acrylonitrile derivatives under green chemistry conditions was performed using various benzaldehyde derivatives, malononitrile, sodium azide, and the optimal amount of nanocatalyst. The support used in this nanocatalyst was LDH which have become popular in the field of heterogeneous catalysts due to its very easy and low cost synthesis as well as excellent combination of structural features such as abundant hydroxyl groups on the surface, tunability of host layers, interlayer anions, regular distribution of metal cations, etc.

Low-Dimensional Magnetism in Multivariate Copper/Zinc MOF-74 Materials Formed via Different Mechanochemical Methods.

MOF-74 is an archetypal magnetic metal-organic framework (MOF) family, with metal nodes bridged by 2,5-dioxido-1,4-benzenedicarboxylic acid (H4dobdc) and arranged into one of the simplest representations of the 1D Ising magnetic model. Recently, a novel mechano-synthetic approach opened a pathway toward a series of bimetallic multivariate (1:1) M1M2-MOF-74 materials, with the uniform distribution of metal cations in the oxometallic chains, offering a unique opportunity to investigate low-dimensional magnetism in these heterometallic MOFs. We explore here how different mechanochemical procedures affect the interaction between the metal nodes of the model system of three multivariate copper(II)/zinc(II)-MOF-74 materials, two of which were obtained through a template-controlled procedure, and the third one was obtained by recently developed mechanical MOF-alloying combined with subsequent accelerated aging. While the three Cu/Zn-MOF-74 products have almost identical powder X-ray diffraction (PXRD) diffractograms and Fourier transform infrared spectra, they differ significantly in their magnetic properties, as revealed through detailed magnetization and X-band and multifrequency high-field electron spin resonance measurements. The magnetic results of the three multivariate Cu/Zn-MOF-74s were compared to the properties of the monometallic Cu-MOF-74, which shows antiferromagnetic intrachain and weaker ferromagnetic interchain interactions. Energy-dispersive X-ray spectroscopy/scanning electron microscopy and solid-state nuclear magnetic resonance spectroscopy helped rationalize the observed differences in magnetization, and in situ synchrotron PXRD monitoring of template-controlled MOF formation revealed different reaction pathways when using the zinc or copper intermediates, involving even the fleeting occurrence of a rare MOF-74 polymorph.

Soft Chemistry Synthesis and Characterization of CoFe1.8RE0.2O4 (RE3+ = Tb3+, Er3+) Ferrite

Nanosized CoFe1.8RE0.2O4 (RE3+ = Tb3+, Er3+) ferrites were obtained through wet ferritization method. These ferrites were characterized by X-ray diffraction (XRD), scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM/HR-TEM), Fourier transform infrared spectroscopy (FTIR), Mössbauer spectroscopy and magnetic measurements. The XRD results revealed that the average crystallite size is 5.77 nm for CoFe1.8Tb0.2O4 and 6.42 nm for CoFe1.8Er0.2O4. Distribution of metal cations in the spinel structure estimated from X-ray diffraction data showed that the Tb3+ and Er3+ ions occupy the octahedral sites. TEM images indicated the presence of polyhedral particles with average size 5.91 nm for CoFe1.8Tb0.2O4 and 6.80 nm for CoFe1.8Er0.2O4. Room temperature Mössbauer spectra exhibit typical nanoscaled cobalt ferrite spectra in good agreement with XRD and TEM data. The saturation magnetization value (Ms) is 60 emu/g for CoFe1.8Tb0.2O4 and 80 emu/g for CoFe1.8Er0.2O4. CoFe1.8RE0.2O4 nanoparticles showed similar antimicrobial efficacy against the five tested microbial strains, both in planktonic and biofilm state. The results highlight the promising potential of these types of nanoparticles for the development of novel anti-biofilm agents and materials.

Recent Advances in Constructing Interfacial Active Catalysts Based on Layered Double Hydroxides and Their Catalytic Mechanisms

The interaction between the metal and the support of supported metal catalysts, which are widely used in industry, is the primary focus of the study of such catalysts. With the developing understanding of the metal–support interaction, the intrinsic factor that influences the catalytic performance has been determined to be the structure of interfacial sites. Layered double hydroxides (LDHs, a class of two-dimensional layered anion clay) possess several unique characteristics, such as the following: (1) tunable elemental component, homogeneous distribution of metal cations. (2) anchoring effect. (3) multiple layered structure for exfoliation or intercalation and special memory effect; and (4) internal/external confinement effects during topological transformation. Taking LDHs and their derivatives as precursors or supports shows superior advantages in designing interfacial active catalysts with tunable properties. Therefore, this review is mainly focused on constructing interfacial active catalysts by LDHs and revealing the interfacial effects (including electronic, geometric, and bifunctional effects) on the catalytic performance that will provide new perspectives and approaches for the development of heterogeneous catalysis.

Hofmeister Series for Metal-Cation-RNA Interactions: The Interplay of Binding Affinity and Exchange Kinetics.

A large variety of physicochemical properties involving RNA depends on the type of metal cation present in solution. In order to gain microscopic insight into the origin of these ion specific effects, we apply molecular dynamics simulations to describe the interactions of metal cations and RNA. For the three most common ion binding sites on RNA, we calculate the binding affinities and exchange rates of eight different mono- and divalent metal cations. Our results reveal that binding sites involving phosphate groups preferentially bind metal cations with high charge density (such as Mg2+) in inner-sphere conformations while binding sites involving N7 or O6 atoms preferentially bind cations with low charge density (such as K+). The binding affinity therefore follows a direct Hofmeister series at the backbone but is reversed at the nucleobases leading to a high selectivity of ion binding sites on RNA. In addition, the exchange rates for cation binding cover almost 5 orders of magnitude, leading to a vastly different time scale for the lifetimes of contact pairs. Taken together, the site-specific binding affinities and the specific lifetime of contact pairs provide the microscopic explanation of ion specific effects observed in a wide variety of macroscopic RNA properties. Finally, combining the results from atomistic simulations with extended Poisson–Boltzmann theory allows us to predict the distribution of metal cations around double-stranded RNA at finite concentrations and to reproduce the results of ion counting experiments with good accuracy.

(Invited) Multiscale Chemical Complexities in Layered Oxides for Sodium Ion Batteries

Applications such as large-scale stationary energy storage call for significantly reduced cost of batteries. Sodium ion batteries offer one of the most feasible alternatives to meet these particular demands. Layered oxide materials are regarded as a technologically important class of cathode materials due to their excellent reversibility in cycling sodium ions and relatively smaller degree of lattice volume change. Various transition metal ions can be incorporated in the transition metal layer of sodium layered oxides giving considerable flexibility to the choice of the transition metals. The different choices of transition metals make it challenging to obtain the perfectly homogeneous distribution in multielemental sodium layered oxide materials because of their differences in the ionic size and electronic properties. However, how much does the homogeneous elemental distribution matter in the battery performance? What are the chemical and structural transformations of heterogeneous layered oxides during charging and discharging? In this presentation, we will discuss our recent progress in understanding the multiscale heterogeneity in sodium layered oxide materials. First, we will establish the relationship between the cathode surface chemistry and the sodium full-cell electrochemistry through a range of complementary advanced spectroscopic and imaging diagnostic techniques. Second, we will highlight our effort in decoupling the multiscale electrochemistry in sodium layered oxide materials. We will illustrate that engineering the three-dimensional distribution of metal cations in electrode particles can take advantage of the depth-dependent charging mechanisms thus empowering superior battery performance.

Effect of Cr3+ Substitution on the Structural, Electrical and Magnetic Properties of Ni0.7Zn0.2Cu0.1Fe2−xCrxO4 Ferrites

In this work, Ni0.7Zn0.2Cu0.1Fe2−xCrxO4 (x = 0.02, 0.04, 0.06, 0.08 and 0.1) ferrites were synthesized by using the solid state reaction method and how relevant properties of the samples were modified accordingly. The structural, morphological, magnetic and electrical features of the ferrites were evaluated by using X-ray diffraction, scanning electron microscopy, Fourier transmission infrared (FTIR) spectra, vibrating sample magnetometry, electron spin resonance and network analyser. The lattice constant decreases with increasing chromium concentration and the decrease in the lattice constant is attributed to the ionic radius of chromium being smaller than that of iron. The distribution of metal cations in the spinel structure was estimated from the X-ray diffraction data and showed that along with Ni2+ ions, most of the Zn2+ and the Cu2+ ions additionally occupied the octahedral [B] sites. The FTIR spectra revealed two prominent frequency bands in the wave number range 400–600 cm−1 which confirm the cubic spinel structure. The magnetic properties, such as the initial permeability, saturation magnetization and coercivity, were investigated at room temperature. The frequency-dependent dielectric constant was observed to decrease with increasing chromium concentration. This behavior was using Koops phenomenological theory.

Degradation Mechanisms and Accelerated Stress-Test Protocols for Polymer Electrolyte Water Electrolyzers

If polymer electrolyte water electrolysis (PEWE) is to be deployed to serve as an energy storage technology in the grid, the potential challenges related to the component durability need to be understood and addressed. The US Department of Energy (DOE) targets a cost of 2 $/kg H2 for the year 2020. Maintaining stack efficiency is key to a competitive end-cost of H2, as the main contribution is projected to come from the cost of electricity (1). The development of tailored PEWE components therefore needs to go hand-in-hand with the development of accelerated stress-tests that trigger specific degradation mechanisms. In this study, different degradation mechanisms were induced by subjecting commercial catalyst-coated membranes (CCMs) to specific operating conditions. PEWE cells were operated for 300 h to estimate the effects of the imposed stressors, and the cell performance was compared to the 300 h non-stressed benchmarks. The cell response was analyzed using electrochemical impedance spectroscopy (EIS). Individual catalyst layer (CL) characteristics were probed in the H2/N2 regime, and the cyclic voltamograms were recorded. Finally, samples were post-test investigated using scanning electron microscopy (SEM). The effect of the cell compression on the CL performance was stessed using cell assemblies with Ti-sintered porous transport layers (PTLs) of different morphological surface properties. Rigid PTL-surface features have induced local variation in CL porosity, and increased CL proton transport resistance (RCLa H+). In the case of PTLs with large voids, CCM creep led to the formation of thin spots and an increase in measured H2 in the O2 outlet. We have found that the increased gas crossover with mechanically stressed and locally thinned CCM results in a higher fluoride release rate over 300 h. The effects of start-stop operation on the CL stability were quantified over 300 h by periodically analyzing the anodic water using ICP-mass spectroscopy for traces of precious metals. Additionally, elemental mapping was done on the post-test CCM cross-sections to deterime if potentially dissolved species had deposited in the PEM (2). As water impurities are an important factor determining the electrolyzer lifetime (3), we have designed Ir2+ doping experiments to simulate the accelerated reverisble contamination of the CCM. A detalied overpotential analysis was done to determine the effect on the ohmic, activation and mass-transport overpotential. A specially designed cell was used to conduct operando neutron imaging of the contaminated CCM, and track the distribution of metal cations in the CCM cross-section under various operating conditions. EIS was done in paralell to correlate the impact of contaminants on the cell performance with their cross-sectional position. We established an comprehensive degradation matrix based on the PEWE degradation-inducing experiments, highlighting the stressors, degradation mechanisms and the affected aspects of PEWE performance.

Recent progress in functionalized layered double hydroxides and their application in efficient electrocatalytic water oxidation

Abstract Layered double hydroxides (LDHs), a class of anionic clays consisting of brucite-like host layers and interlayer anions, have been widely investigated in the last decade due to their promising applications in many areas such as catalysis, ion separation and adsorption. Owing to the highly tunable composition and uniform distribution of metal cations in the brucite-like layers, as well as the facile exchangeability of intercalated anions, LDHs can be modified and functionalized to form various nanostructures/composites through versatile processes such as anion intercalation and exfoliation, decoration of nanoparticles, self-assembly with other two-dimensional (2D) materials, and controlled growth on conductive supports (e.g., nanowire arrays, nanotubes, 3D foams). In this article, we briefly review the recent advances on both the LDH nanostructures and functionalized composites toward the applications in energy conversion, especially for water oxidation.

Use of Layered Double Hydroxides to Create New Environmental Technologies

This review surveys recent advances in the applications of layered double hydroxides [LDHs] in sorption processes. By virtue of the flexible tunability and uniform distribution of metal cations in the brucite-like layers and the facile exchangeability of intercalated anions, LDHs-both as directly prepared or after thermal treatment or rehydrated have found many applications as stable and recyclable sorbents for environmental protection in industrial regions. This paper presents data on the structure and properties of LDHs, the production of sorbents with fixed and labile dimensions of interplanar spaces. Technologies for the removal of organic and inorganic substances using LDHs sorbents have been developed. Keywords: layered double hydroxides; sorbent; environmental protection;

Polyoxometalate (POM)-Layered Double Hydroxides (LDH) Composite Materials: Design and Catalytic Applications

Layered double hydroxides (LDHs) are an important large class of two-dimensional (2D) anionic lamellar materials that possess flexible modular structure, facile exchangeability of inter-lamellar guest anions and uniform distribution of metal cations in the layer. Owing to the modular accessible gallery and unique inter-lamellar chemical environment, polyoxometalates (POMs) intercalated with LDHs has shown a vast array of physical properties with applications in environment, energy, catalysis, etc. Here we describe how polyoxometalate clusters can be used as building components for the construction of systems with important catalytic properties. This review article mainly focuses on the discussion of new synthetic approaches developed recently that allow the incorporation of the element of design in the construction of a fundamentally new class of materials with pre-defined functionalities in catalytic applications. Introducing the element of design and taking control over the finally observed functionality we demonstrate the unique opportunity for engineering materials with modular properties for specific catalytic applications.

Theoretical and experimental study on the topotactic transformation mechanism of Zn-Al layered double hydroxides

Layered double hydroxides (LDHs) are a class of minerals with nanoscale two-dimensional layered structure. The topotactic transformation of LDHs under calcination and the reconstruction behavior (memory effect) of the calcined LDHs in aqueous solution play a key role in the fabrication of high dispersed metal nanocatalysts. The thermal topotactic transformation mechanism of ZnAl-layered double hydroxides (LDHs) and memory effect of LDHs were investigated by density functional theory based molecular dynamics (MD) simulation, combined with thermogravimetric/differential thermal analysis (TG-DTA). TG-DTA results reveal that the LDH phase undergoes two key endothermic events at 273 and 800 °C. The results show that the anion in LDHs decomposes to CO2 and H2O via a monodentate intermediate at 273 °C, and H2O releases prior to CO2. After the decomposition of interlayer CO32− at 273 °C, the distribution of metal cations in LDH matrix changed heavily along both LDH(001) facet and the c -axis direction perpendicular to the (001) facet. The dehydrated products cannot reconstruct back to the hydroxide phase, showing no memory effect. At 800 °C, a complete collapse of layered structure occurs, resulting in a totally disordered cation distribution and plenty of holes in the final product. This work will be helpful for the design and preparation of highly dispersed nanocatalysts derived from LDHs precursors.

Recent progress in polyoxometalate-intercalated layered double hydroxides composite materials

Layered double hydroxides (LDHs) or hydrotalcite-like compounds are an important large family of two-dimensional (2D) anionic clay materials which possesses flexible tunability, uniform distribution of metal cations in the layers, and the facile exchangeability of intercalated anions. Polyoxometalates (POMs) are a class of V, Mo, and W-containing discrete anionic metal oxides that can be viewed as transferable building blocks. Owing to the modular accessible gallery and unique inter-lamellar chemical environment, the POMs intercalated LDHs have shown wide application in environment, energy, catalysis, etc . This review mainly focuses on the summary of synthetic strategy and recent development of the POM/LDHs composite materials.

Complexing Mechanistic Impacts on the Microstrucutre and Performances of LiFePO4 Synthesized Via Sol-Gel Approaches

Olivine structured LiFePO4 is an attractive cathode material for lithium ion batteries for its low cost, environmental benign, good cycling performance, safety, etc. It intrinsic low electronic conductivity and lithium-ion diffusion demands exquisite synthesis to produce small particles with surface electrical coating. Wet chemical sol-gel route have indisputable advantages over solid-state reactions for fabricating LiFePO4 fine particles with narrow size distribution, in addition to its ease of mass production and capabilities of in-situ carbon coating as well as flexible doping. Understanding of the influences of the key processing parameters like species of chelating agent and PH value of solution on the microstructure and performances of materials is fundamentally important. Here we report our studies on correlating the stability of complexing compounds on the mircrostructure of LiFePO4 products, carbon contents, and hence the electrochemical properties. LiOH.H2O and FeC2O4.2H2O were selected as the sources of lithium and iron. H3PO4 and/or NH4H2PO4 was the source of phosphate ions, which was also used to une the PH value of the sol. Basic complexing agents are citric acid (CA) and ethylene glycol (EG). In this work, individual complexing agent and the combination of the two with different ratios and their impacts on the product microstrucutre and electrochemical performances were investigated. The microstructure and composition of the LiFePO4/C products were investigated by means of X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS), and thermal graviemtric analyses (TGA) etc. For galvanostatic charge-discharge and electrochemical impedance spectroscopic analyses, the synthesized LiFePO4/C powders were mixed with conductive agent and binder at a certain mass ratio in solvent and coated on Al foil. Nanocrystalline LiFePO4/C materials with spherical particles of less than 500nm and appropriate amount of carbon coating were successfully obtained at the optimal synthesis parameters. It was found that carbon content remaining in the powder product after sintering varied from 10wt% and 1.2 wt%, depending on the chelating complex composition and the amount. A consistent trend was observed among the lithium-storage capacity, carbon content, and complex stability. The carbon content and the stability constants of the complex compounds are corroborative, while the Li-storage capacities of LiFePO4 products are inversely proportional to the stability constants of their corresponding complex compounds as well as the carbon content. It is well known that the types of central metallic ion and complex ligand have decisive influences on the stability of the formed complex compounds. The stability of complex compounds formed from Fe2+ are all small than that formed from Fe3+ with the same complex agent. The complex agent CA forms five or six-membered rings during the complex process, so the corresponding stability constants of the formed complex compounds are all relatively larger. Consequently, the product contains large amounts of carbon remnants. Excessive carbon on the surface of LiFePO4 will block the diffusion of Li into the LiFePO4 crystal structure, leading to the reduced lithium storage capacity and rate capability. The PH value of the precursor solution affects two main reactions, i.e. hydrolysis and polymerization, during the sol-gel process. Thereby, it affects the iorn valency and final particle size. Suitable PH environment is found to ensure uniform distribution of metal cations in the organic sol-gels leading to the uniformly fine and well dispersed LiFePO4 powders which are benefical to the high electrochemical performances.

Recent Advances in the Synthesis of Layered, Double‐Hydroxide‐Based Materials and Their Applications in Hydrogen and Oxygen Evolution

AbstractLayered double hydroxides (LDHs) consist of brucite‐like layers containing hydroxides of two or more different kinds of metal cations. These positively charged layers are neutralized by exchangeable anions in the interlayer galleries. LDH‐based materials have substantial potential in efficient energy (e.g., H2, O2) generation. Over the last few decades, tremendous progress has been made toward developing LDH‐based materials for H2 and O2 evolution, for which the performance of LDH‐based materials is closely related to the synthesis method. This minireview initially outlines the recent advances in the synthesis of LDH‐based materials. The advantages and challenges of the protocols in tuning the properties of the material are also discussed and highlighted. The application section concentrates on the most recent progress in photocatalytic H2 generation and photocatalytic and electrocatalytic O2 evolution. By taking advantage of the flexible tunability and uniform distribution of metal cations in the brucite‐like layers or the intercalated anions in the interlayer space, LDH‐based materials exhibit attractive properties in the generation of H2 and O2 with advantages such as improved light absorption, enhanced charge separation, better electron transfer, promoted electrode reaction kinetics, and high durability.