Insight of synergistic effect of different active metal ions in layered double hydroxides on their electrochemical behaviors

Multimetal Layered Double Hydroxides: Synthesis, Characterization, and Synergic Effect in Mild Catalytic Oxidation of Alkanes

Layered double hydroxides (LDHs) represent a promising class of inexpensive and tunable inorganic materials with growing applications in diverse areas. In this study, we applied an aqueous miscible organic solvent treatment (AMOST) to prepare a novel series of highly dispersed LDHs containing up to four different metal centers (Mg, Cu, Al, and Fe). These AMO-LDHs were fully characterized and employed as precatalysts for the mild oxidative functionalization of cyclic and gaseous alkanes with aqueous H2O2 to give the corresponding alcohols, ketones, and carboxylic acids. Cyclohexane and propane were used as model substrates. The oxidation reactions, occurring under mild conditions (30-50 °C), demonstrated good efficiency with total product yields up to 40% and catalyst turnover numbers up to 370 when using a tetra-heterometallic AMO-LDH precatalyst (AMO-MgCuAlFe). Its enhanced catalytic activity is likely associated with the synergic effect of different metal centers (Cu, Fe, and Al─all having a recognized function in oxidation catalysis). Substrate scope, selectivity, and the influence of the reaction parameters were also investigated. This work offers a novel, easy, and more sustainable path to advance the application of AMO-LDHs in oxidation catalysis, opening up the use of this type of catalytic systems in the mild oxidation of alkanes.

Contribution of Active Surface of NiFe-Layered Double Hydroxide on the Removal of Methyl Orange

Layered double hydroxides (LDHs) have potential applications for pollutant removal. Enhancing their pollutant removal ability by fully utilizing the synergistic effects of physical adsorption and chemical catalysis has received widespread attention. In this study, a high methyl orange (MO) removal capacity was achieved by utilizing the synergistic effects of physical adsorption and chemical catalysis of NiFe-LDH. wNiFe-LDH showed a significant removal amount of MO, up to 506.30 mg/g due to its reserving of the active surface to the largest extent. Experiment and molecular simulation clarified the high removal capacity derived from surface adsorption and the degradation ability of the active surface. The presence of more -OH groups on the surface enhanced the removal of MO, and the vacancies in the surface were beneficial for the formation of •O2- and contributed to the degradation of MO. As K2S2O8 was introduced, the removal rate of MO improved to 100% from 60.67%. However, a deeper study showed that the degradation was incomplete, as K2S2O8 inhibited the formation of •O2-, and the active species in the system changed to holes. The degradation path of MO was also altered. Thus, this study gives new insight into the reactivity of the active surface of NiFe-LDH and affords a new path to preserve the active surface.

Coral-Inspired Terahertz-Infrared Bi-Stealth Electronic Skin

The development of electronic skin with dual stealth functionality is crucial for enabling devices to operate effectively in dynamic electromagnetic environments, thereby facilitating intelligent electromagnetic protection for autonomous perception. However, achieving compatibility between terahertz (THz) and infrared (IR) stealth technologies remains largely unexplored due to their inherent contradictions. Herein, inspired by natural corals, a novel coral-like multi-scale composite foam (CMSF) was proposed that ingeniously reconciles these contradictions. The design capitalizes on the conductive network and heat insulation properties of the foam skeleton, the loss effects and low infrared emission of metal particles, and the infrared transparency of magneto-optical materials. This approach leads to the realization of a THz-IR bi-stealth electronic skin concept. The CMSF exhibits a maximum reflection loss of 84.8 dB in the terahertz band, while its infrared stealth capability ensures environmental adaptability under varying temperatures. Furthermore, the electronic skin exhibits exceptional sensitivity and reliability as a wearable device for perceiving environmental changes. This advanced material, combining multispectral stealth with sensing capabilities, holds immense potential for applications ranging from camouflage technology to smart wearables.

Synthesis of High-Entropy Alloys with a Tailored Composition and Phase Structure Using a Single Configurable Target

Previously, refractory high-entropy alloys (HEAs) with high crystallinity were synthesized using a configurable target without heat treatment. This study builds upon prior investigations to develop nonrefractory elemental HEAs with low crystallinity using a novel target system. Different targets with various elemental compositions, i.e., Co20Cr20Ni20Mn20Mo20 (target 1), Co30Cr15Ni25Mn15Mo15 (target 2), and Co15Cr25Cu20Mn20Ni20 (target 3), are designed to modify the phase structure. The elemental composition is varied to ensure face-centered cubic (FCC) or body-centered cubic (BCC) phase stabilization. In target 1, the FCC and BCC phases coexist, whereas targets 2 and 3 are characterized by a single FCC phase. Thin films based on targets 1 and 2 exhibit crystalline phases followed by annealing, as indicated by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. In contrast, target 3 yields crystalline thin films without any heat treatment. The thin-film coatings are classified based on the atomic size difference (δ). The δ value for the target with the elemental composition CoCrMoMnNi is 9.7, i.e., ≥6.6, corresponding to an HEA with an amorphous phase. However, the annealed thin film is considered a multiprincipal elemental alloy. In contrast, δ for the CoCrCuMnNi HEA is 5, i.e., ≤6.6, upon the substitution of Mo with Cu, and a solid solution phase is formed without any heat treatment. Thus, the degree of crystallinity can be controlled through heat treatment and the manipulation of δ in the absence of heat treatment. The XRD results clarify the crystallinity and phase structure, indicating the presence of FCC or a combination of FCC and BCC phases. The outcomes are consistent with those obtained through the analysis of the valence electron concentration based on X-ray photoelectron spectroscopy. Furthermore, a selected area electron diffraction analysis confirms the presence of both amorphous and crystalline structures in the HEA thin films. Additionally, phase evolution and segregation are observed at 500 °C.

ECL resonance energy transfer-regulated "off-on" mode biosensor for the detection of miRNA-150-5p in triple negative breast cancer

MiRNAs played critical roles in triple negative breast cancer (TNBC) as potential biomarkers. Herein, an efficient signal "off-on" mode-biosensor based on electrochemiluminescence resonance energy transfer (ECL-RET) was successfully constructed for the miRNA-150-5p determination in TNBC. The ECL-RET regulated-sensing platform consisted of NiMn-LDHs nanoflowers, the artificially assembled phospholipid bilayers and hairpin DNA-labeled Eu-doped MoS2 QDs. Firstly, Eu-doped MoS2 QDs with high quantum efficiency were prepared as the ECL-RET donors. And NiMn-layer double hydroxides (LDHs) nanoflowers with wide UV-vis absorption spectra as the ECL-RET acceptors. Secondly, due to the hairpin DNA structure, the closed distance between ECL-RET donor-acceptor pair can quench the luminescence signal of Eu-doped MoS2 QDs. When miRNA-150-5p was captured, the hairpin DNA structure changed to a rodlike configuration and enlarged the distance between Eu-doped MoS2 QDs and NiMn-LDHs. As a result, the recovery of ECL signal can be observed as a signal "turn off-on" mode. Furthermore, the hydrophilicity of the lipid bilayer can reduce the nonspecific adsorption and improve the flexibility of the hairpin DNA efficiently. Therefore, based on the ECL-RET regulation strategy, the biosensor was employed to detect miRNA-150-5p from 10 fM to 1 nM with a detection limit of 1.5 fM. The constructed biosensor can effectively differentiate TNBC patient tumor and healthy breast fibroadenoma. The ECL-RET regulation strategy provided a new biosensing pathway for ultrasensitive detection of biomolecules and promoted the development of diagnosis and treatment of TNBC.

Microenvironment-responsive electrocution of tumor and bacteria by implants modified with degenerate semiconductor film

Implantable biomaterials are widely used in the curative resection and palliative treatment of various types of cancers. However, cancer residue around the implants usually leads to treatment failure with cancer reoccurrence. Postoperation chemotherapy and radiation therapy are widely applied to clear the residual cancer cells but induce serious side effects. It is urgent to develop advanced therapy to minimize systemic toxicity while maintaining efficient cancer-killing ability. Herein, we report a degenerate layered double hydroxide (LDH) film modified implant, which realizes microenvironment-responsive electrotherapy. The film can gradually transform into a nondegenerate state and release holes. When in contact with tumor cells or bacteria, the film quickly transforms into a nondegenerate state and releases holes at a high rate, rendering the "electrocution" of tumor cells and bacteria. However, when placed in normal tissue, the hole release rate of the film is much slower, thus, causing little harm to normal cells. Therefore, the constructed film can intelligently identify and meet the physiological requirements promptly. In addition, the transformation between degenerate and nondegenerate states of LDH films can be cycled by electrical charging, so their selective and dynamic physiological functions can be artificially adjusted according to demand.

Design of a high-performance ternary LDHs containing Ni, Co and Mn for arsenate removal

To cope with the current serious arsenate pollution problem, a new ternary layered double hydroxides (LDHs) containing Ni, Co and Mn with good performance was developed, guiding by DFT calculations. First, Ni, Co and Mn were screened as the metal sources to constitute the LDHs, due to their high ionic charge density. Then, Ni(II), Co(II) and Mn(III)-O octahedra were selected as the primary units for structuring the LDHs, because of their good chemical activity. Meanwhile, the ratio of metals in the ternary LDHs, favoring for arsenate removal, was optimized at 1:2:1. In addition, the synergistic effect among various metals in the LDHs was considered. The results suggested that in the case of single doping, all three metals can act as the center to promote chemical activity independently. On the contrary, when combined together, there is only one unilateral active center. Moreover, the existence of ligand covalent bonds between arsenate and LDHs was confirmed. Finally, a promising new NiCo₂Mn-LDHs with the maximum adsorption capacity of 407.23 mg/g for arsenate removal had been prepared.

Solid-state synthesis of single-phase nickel monophosphosulfide for the oxygen evolution reaction

High-performance and cost-effective nonprecious-metal catalysts are essential for the next-generation oxygen evolution reaction (OER). However, the electrocatalysis of the OER during water splitting is often carried out by using noble metal catalysts, such as RuO₂ or IrO₂ with high-cost and limited stability. Herein, we reported a successful synthesis of a ternary nickel monophosphosulfide (NiPS) compound via a simple solid-state route and further investigated its electrocatalytic performances for water oxidation. It is found that the NiPS electrocatalyst exhibits good OER performance in 1.0 M KOH solution, i.e., achieving a current density of 20 mA cm^-2 at an overpotential of 400 mV and a Tafel slope of 126 mV dec^-1, comparable to commercial benchmark RuO₂. The ternary NiPS electrocatalyst for the OER is superior to its binary counterparts, i.e., Ni₂P and NiS. Density functional theory (DFT) calculations combined with ex situ XPS were performed to obtain further insights into the intrinsic catalytic mechanism of NiPS, and their results clearly revealed that the instability of the NiO intermediate during the OH* → O* process and the easy oxidation of the (PS)^3- anion favoring the formation of hydroxyl-based species (i.e., Ni(OH)₂/NiOOH) on the surface of the catalyst, which plays a crucial role in facilitating the OER activity. Furthermore, we creatively extended this method to the fabrication of heteroatom substituted catalysts and a new quaternary CoNiP₂S₂ compound was successfully synthesized for the first time in the same way. The structural properties and electrocatalytic performance towards the OER for CoNiP₂S₂ (e.g., 20 mA cm^-2 at 376 mV) are also systematically investigated in this work.

Facile Synthesis of MPS3/C (M = Ni and Sn) Hybrid Materials and Their Application in Lithium-Ion Batteries

Herein, we successfully synthesized two novel metal thiophosphites (MTPs) hybridized with carbon, that is, NiPS3/C and SnPS3/C composites, via an environment-friendly and cost-effective approach without harsh reaction conditions. Subsequently, the electrochemical performances of NiPS3/C and SnPS3/C composites have been investigated in coin-cells, and it is revealed that MTPs/C have a significantly higher Li-storage capacity and better stability compared to the MTPs without carbon. Moreover, the SnPS3/C electrode shows a lower internal resistance and a better rate performance compared to NiPS3/C. We employed extensive ex situ experiments to characterize the materials and interpreted the remarkably improved performance of MTPs/C.

Effective toluene oxidation under ozone over mesoporous MnOx/γ-Al2O3 catalyst prepared by solvent deficient method: Effect of Mn precursors on catalytic activity

In this study, the role of manganese precursors in mesoporous (meso) MnOx/γ-Al₂O₃ catalysts was examined systematically for toluene oxidation under ozone at ambient temperature (20 °C). The meso MnOx/γ-Al₂O₃ catalysts developed with Mn(CH₃COO)_2, MnCl₂, Mn(NO₃)₂.4H₂O and MnSO₄ were prepared by an innovative single step solvent-deficient method (SDM); the catalysts were labeled as MnO_x/Al₂O₃(A), MnO_x/Al₂O₃(C), MnO_x/Al₂O₃(N), and MnOx/Al₂O₃(S), respectively. Among all, MnO_x/Al₂O₃(C) showed superior performance both in toluene removal (95%) as well as ozone decomposition (88%) followed by acetate, nitrate and sulphated precursor MnO_x/Al₂O₃. The superior performance of MnO_x/Al₂O₃(C) in the oxidation of toluene to CO_x is associated with the ozone decomposition over highly dispersed MnO_x in which extremely active oxygen radicals (O^2-, O₂^2- and O^-) are generated to enhance the oxidation ability of the catalysts greatly. In addition, toluene adsorption over acid support played a vital role in this reaction. Hence, the properties such as optimum Mn³⁺/Mn⁴⁺ ratio, acidic sites, and smaller particle size (≤2 nm) examined by XPS, TPD of NH₃, and TEM results are playing vital role in the present study. In summary, the MnO_x/Al₂O₃ (C) catalyst has great potential in environmental applications particularly for the elimination of volatile organic compounds with low loading of manganese developed by SDM.

Surface site density and utilization of platinum group metal (PGM)-free Fe-NC and FeNi-NC electrocatalysts for the oxygen reduction reaction

Pyrolyzed iron-based platinum group metal (PGM)-free nitrogen-doped single site carbon catalysts (Fe-NC) are possible alternatives to platinum-based carbon catalysts for the oxygen reduction reaction (ORR). Bimetallic PGM-free M1M2-NC catalysts and their active sites, however, have been poorly studied to date. The present study explores the active accessible sites of mono- and bimetallic Fe-NC and FeNi-NC catalysts. Combining CO cryo chemisorption, X-ray absorption and 57Fe Mössbauer spectroscopy, we evaluate the number and chemical state of metal sites at the surface of the catalysts along with an estimate of their dispersion and utilization. Fe L3,2-edge X-ray adsorption spectra, Mössbauer spectra and CO desorption all suggested an essentially identical nature of Fe sites in both monometallic Fe-NC and bimetallic FeNi-NC; however, Ni blocks the formation of active sites during the pyrolysis and thus causes a sharp reduction in the accessible metal site density, while with only a minor direct participation as a catalytic site in the final catalyst. We also use the site density utilization factor, ϕ SDsurface/bulk , as a measure of the metal site dispersion in PGM-free ORR catalysts. ϕ SDsurface/bulk enables a quantitative evaluation and comparison of distinct catalyst synthesis routes in terms of their ratio of accessible metal sites. It gives guidance for further optimization of the accessible site density of M-NC catalysts.

Enhanced Electrochemical Properties and OER Performances by Cu Substitution in NiCo2O4 Spinel Structure

In order to improve the electrochemical performance of the NiCo2O4 material, Ni ions were partially substituted with Cu2+ ions having excellent reducing ability. All of the electrodes were fabricated by growing the Ni1-xCuxCo2O4 electrode spinel-structural active materials onto the graphite felt (GF). Five types of electrodes, NiCo2O4/GF, Ni0.875Cu0.125Co2O4/GF, Ni0.75Cu0.25Co2O4/GF, Ni0.625Cu0.375Co2O4/GF, and Ni0.5Cu0.5Co2O4/GF, were prepared for application to the oxygen evolution reaction (OER). As Cu2+ ions were substituted, the electrochemical performances of the NiCo2O4-based structures were improved, and eventually the OER activities were also greatly increased. In particular, the Ni0.75Cu0.25Co2O4/GF electrode exhibited the best OER activity in a 1.0 M KOH alkaline electrolyte: the cell voltage required to reach a current density of 10 mA cm-2 was only 1.74 V (η = 509 mV), and a low Tafel slope of 119 mV dec-1 was obtained. X-ray photoelectron spectroscopy (XPS) analysis of Ni1-xCuxCo2O4/GF before and after OER revealed that oxygen vacancies are formed around active metals by the insertion of Cu ions, which act as OH-adsorption sites, resulting in high OER activity. Additionally, the stability of the Ni0.75Cu0.25Co2O4/GF electrode was demonstrated through 1000th repeated OER acceleration stability tests with a high faradaic efficiency of 94.3%.

Z-scheme binary 1D ZnWO4 nanorods decorated 2D NiFe2O4 nanoplates as photocatalysts for high efficiency photocatalytic degradation of toxic organic pollutants from wastewater

In this study, dimensionally coupled Z-scheme binary nanocomposites from two-dimensional (2D) NiFe₂O₄ nanoplates and one-dimensional (1D) ZnWO₄ nanorods are prepared for efficient degradation of an antibiotic tetracycline (TC) and organic dye rhodamine B (RhB) under solar illumination. NiFe₂O₄/ZnWO₄ nanocomposites were synthesized by a simple and ecological in-situ hydrothermal method without the use of surfactants. Structural and morphological studies revealed the formation of heterostructure and 1D ZnWO₄ nanorods were uniformly distributed over the surface of NiFe₂O₄ nanoplates. Light-harvesting capability was improved and optimized by loading with different amounts of ZnWO₄. Photoluminescence analysis demonstrated inhibited nature of the recombination of photo-excited charge carriers in the nanocomposites. Photocatalytic experiments revealed that the nanocomposite exhibited improved Z-scheme electron-transfer for the degradation of TC under solar illumination. In particular, NFZW-20 nanocomposite demonstrated superior photocatalytic degradation of TC of approximately 98% within 105 min. Furthermore, their photocatalytic performance was investigated by RhB dye under the solar irradiation to achieve 98% of degradation of RhB in 70 min. Improved photocatalytic activities are attributed to the Z-scheme electron-transfer mechanism, which could enhance the superior ability of light absorption and reduced recombination rate of the photogenerated charge carriers.

PtSn Nanoalloy Thin Films as Anode Catalysts in Methanol Fuel Cells

Reactions of SnX₂ (X = Cl, Br) with [PtMe₂(bipy)], 1, (bipy = 2,2'-bipyridine), followed by NaBH₄ reduction at the toluene/water interface in the presence or absence of graphene oxide support rendered PtSn nanoalloy thin films. They were characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. The electrocatalytical activity of the PtSn thin films was investigated in the methanol oxidation reaction. Our studies showed that the PtSn/reduced-graphene oxide (RGO) thin film gave better catalytic results for MOR in comparison to bare PtSn or Pt thin films. A maximum j_f/j_b ratio (j_f and j_b are the maximum current densities in the forward and backward scans, respectively) of 6.77 was obtained for the PtSn/RGO thin film deriving from the 1 + SnBr₂ + NaBH₄ sequence.

Nitrogen-doped carbon integrated nickel–cobalt metal phosphide marigold flowers as a high capacity electrode for hybrid supercapacitors

The fabrication of advanced MOF-derived multicomponent NiCoP/NC marigold flowers electrode for high-performance hybrid supercapacitors.

Visible-light-driven photo-enhanced zinc–air batteries using synergistic effect of different types of MnO2 nanostructures

Solar light enhanced the charge generation which leads to better O redox reactions.

Recent advances in flexible aqueous zinc-based rechargeable batteries

Flexible aqueous Zn battery has exhibited great potential as a power source for flexible and wearable electronic devices due to its unique features, such as high safety, low cost, and eco-friendliness. Numerous studies on flexible Zn batteries have been reported and exciting achievements have been obtained in the past few years. However, there are still many problems in the electrode design and the assembly process to acquire desirable flexibility without sacrificing the capacity. This review summarizes the up-to-date advances in flexible Zn batteries. We first introduce the recent progresses in anodes, cathodes and solid-state electrolytes. Special emphases are then put on the discussions of differences between various flexible current collectors or substrates. Electrode preparation techniques and flexible battery assembly technologies are also compared and discussed. Finally, challenges toward further developments of flexible Zn batteries with high capacity, excellent flexibility and cycling stability are proposed. Future research trends and highlights are suggested as well.

Electrochemical Synergies of Heterostructured Fe2O3-MnO Catalyst for Oxygen Evolution Reaction in Alkaline Water Splitting

For efficient electrode development in an electrolysis system, Fe₂O₃, MnO, and heterojunction Fe₂O₃-MnO materials were synthesized via a simple sol-gel method. These particles were coated on a Ni-foam (NF) electrode, and the resulting material was used as an electrode to be used during an oxygen evolution reaction (OER). A 1000-cycle OER test in a KOH alkaline electrolyte indicated that the heterojunction Fe₂O₃-MnO/NF electrode exhibited the most stable and highest OER activity: it exhibited a low overvoltage (n) of 370 mV and a small Tafel slope of 66 mV/dec. X-ray photoelectron spectroscopy indicated that the excellent redox performance contributed to the synergy of Mn and Fe, which enhanced the OER performance of the Fe₂O₃-MnO/NF electrode. Furthermore, the effective redox reaction of Mn and Fe indicated that the structure maintained stability even under 1000 repeated OER cycles.

Tunable preparation of highly dispersed Ni x Mn-LDO catalysts derived from Ni x Mn-LDHs precursors and application in low-temperature NH3-SCR reactions

A series of Ni x Mn bimixed metal oxides (Ni x Mn-LDO) were prepared via calcining Ni x Mn layered double hydroxides (Ni x Mn-LDHs) precursors at 400 °C and applied as catalysts in the selective catalytic reduction (SCR) of NO x with NH3. The DeNO x performance of catalysts was optimized by adjusting the Ni/Mn molar ratios of Ni x Mn-LDO precursors, in which Ni5Mn-LDO exhibited above 90% NO x conversion and N2 selectivity at a temperature zone of 180-360 °C. Besides, Ni5Mn-LDO possessed considerable SO2 & H2O resistance and outstanding stability. Multiple characterization techniques were used to analyze the physicochemical properties of the catalysts. The analysis results indicated that all catalysts had the same active species Ni6MnO8, while their particle sizes showed significant differences. Notably, the uniform distribution of active species particles in the Ni5Mn-LDO catalyst provided the rich surface acidity and suitable redox ability which were the primary causes for its desirable DeNO x property.

Oxo-bridged trinuclear and tetranuclear manganese complexes supported with nitrogen donor ligands: syntheses, structures and properties

This work illustrates syntheses, structures, redox and magnetic properties as well as catalase activities of rare μ₃-oxo bridged mixed-valent trinuclear Mn^IIMn^III complexes (1 and 2) and a μ₄-oxo bridged tetranuclear MnII4 complex (3) supported with nitrogen donor ligands.

Research Progress of NiMn Layered Double Hydroxides for Supercapacitors: A Review

The research on supercapacitors has been attractive due to their large power density, fast charge/discharge speed and long lifespan. The electrode materials for supercapacitors are thus intensively investigated to improve the electrochemical performances. Various transition metal layered double hydroxides (LDHs) with a hydrotalcite-like structure have been developed to be promising electrode materials. Earth-abundant metal hydroxides are very suitable electrode materials due to the low cost and high specific capacity. This is a review paper on NiMn LDHs for supercapacitor application. We focus particularly on the recent published papers using NiMn LDHs as electrode materials for supercapacitors. The preparation methods for NiMn LDHs are introduced first. Then, the structural design and chemical modification of NiMn LDH materials, as well as the composites and films derived from NiMn LDHs are discussed. These approaches are proven to be effective to enhance the performance of supercapacitor. Finally, the reports related to NiMn LDH-based asymmetric supercapacitors are summarized. A brief discussion of the future development of NiMn LDHs is also provided.