Catalytic Applications Research Articles

A Review on the Recent Progress of Layered Double Hydroxides (LDHs)-based Catalysts for Heterocyclic Synthesis

Abstract: Over the past decade, heterocyclic compounds and their derivatives have emerged as promising substances with potential pharmacological applications due to their interesting biological properties. The significance of heterocyclic compounds in drug discovery and development is evident from the fact that a majority of drugs in the pharmaceutical market incorporate heterocyclic compounds as active substances or ingredients. Various synthetic methods and advancements have been devised to prepare these heterocyclic compounds using diverse catalysts under mild conditions. Layered double hydroxides (LDHs)-based materials have gained considerable attention across different fields, and their usability can be significantly enhanced via the selection of metal cations, their molar ratios, surface complexation, and intercalation modifications. The synthesis and application of LDH-based materials as catalysts have garnered increasing interest due to their exceptional properties. Moreover, LDH-based materials have found extensive use as heterogeneous catalysts in the synthesis of numerous heterocyclic compounds. This review presents the latest developments in the catalytic application of LDH-based materials as solid heterogeneous catalysts in the synthesis of heterocyclic compounds, covering literature published from 2018 to 2023.

An Exceptional Valorization of CuO Nanoparticles in Ionic Liquids as an Efficient Medium for the Electrophilic Substitution of Indole Towards the Formation of Bis(indolyl)methanes

Aim: Ionic liquids are promising green solvents with simple but unique structure-related physical properties such as negligible vapour pressure, exceptional thermal conductivity, remarkable thermal stability and their suitability and inertness towards a broad range of catalytic applications. CuO NPs have been addressed as a cost-effective and a reagent of a choice that necessitates only mild reaction conditions to offer a high yield of the desired products with exceptional selectivity in a short duration of time. Therefore, in the present work, attempts have been made to explore the catalytic potentials of CuO NPs in an ionic liquid medium to synthesize biologically important bis(indolyl)methanes. Background: Catalytic explorations of metal oxide nanoparticles in ionic liquids offers a cooperative effect that has a significant impact on the kinetics as well as on the outcome of the reaction. Therefore, such catalytic systems in the present times have seized the scientific community's interest from the perspectives of sustainable development in synthetic organic chemistry. The combination of metal oxide nanoparticles with highly tunable ionic liquids is not only used to synthesize simple organic molecules but also explored in the synthesis of complex organic molecules of high commercial and biological relevance. Objectives: The current work offers a rapid and robust protocol for synthesizing bis(indolyl)methanes via electrophilic substitution reaction between indole and various aldehydes in the presence of a CuO nanoparticles-ionic liquid system. The discussion focuses on the high tolerance of different functionalities by the catalytic system leading to the synthesis of bis(indolyl)methanes. Methods: CuO NPs have been synthesized via the co-precipitation method using ionic liquid. The applicability of metal oxide nanoparticles-IL matrix was further investigated in synthesizing bis(indolyl)methanes. Results: The FT-IR absorption below 600 cm-1 and the XRD pattern showing all the peaks in the diffraction diagram revealed the formation of CuO NPs. FESEM images show the flake-shaped morphology of CuO NPs and are found to be separated from the agglomerated clusters Conclusion: Ionic liquid-CuO NPs matrix reveals good to exceptional catalytic properties, and their advancements as a catalytic system at room temperature open new avenues for synthetic organic chemists.

Hydrogen storage properties of MgH2 + Mg2NiH4–Co/C ternary nanocomposite

The application of ternary nanocomposite synergetic catalysis has proven to be an effective modification strategy for enhancing MgH2 hydrogen storage performance. The ternary magnesium-based hydrogen storage alloy, composed of MgH2+Mg2NiH4–Co/C, is successfully prepared and characterized. Through the optimized preparation process and the optimal ratio, it is observed that the catalyst Mg2NiH4–Co/C significantly reduces the reaction activation energy, resulting in a the initial hydrogen desorption temperature is approximately 60 °C lower than that of pure MgH2. The enhanced hydrogen storage properties are attributed to the synergistic catalytic effect of carbon (C) combined with the formation of Mg2Ni and Mg2Co facilitated by Ni and Co elements. Furthermore, the reversible phase transitions of Mg2Co/Mg2CoH5 and Mg2Ni/Mg2NiH4 serve as "hydrogen pumps" further aiding in hydrogen storage. This study extends the investigation of the synergistic catalytic effect of ternary nanocomposites to enhance the hydrogen storage performance of alloys.

A comparative study of the biosynthesis of CuNPs by Niallia circulans G9 and Paenibacillus sp. S4c strains: characterization and application as antimicrobial agents

BackgroundBiosynthesis of metallic nanoparticles using microorganisms are a fabulous and emerging eco-friendly science with well-defined sizes, shapes and controlled monodispersity. Copper nanoparticles, among other metal particles, have sparked increased attention due to their applications in electronics, optics, catalysis, and antimicrobial agents.ResultsThis investigation explains the biosynthesis and characterization of copper nanoparticles from soil strains, Niallia circulans G9 and Paenibacillus sp. S4c by an eco-friendly method. The maximum reduction of copper ions and maximum synthesis CuNPs was provided by these strains. Biogenic formation of CuNPs have been characterized by UV–visible absorption spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray analysis and transmission electron microscopy analysis. Using UV-visible spectrum scanning, the synthesised CuNPs’ SPR spectra showed maximum absorption peaks at λ304&308 nm. TEM investigation of the produced CuNPs revealed the development of spherical/hexagonal nanoparticles with a size range of 13–100 nm by the G9 strain and spherical nanoparticles with a size range of 5–40 nm by the S4c strain. Functional groups and chemical composition of CuONPs were also confirmed. The antimicrobial activity of the biosynthesized CuNPs were investigated against some human pathogens. CuNPs produced from the G9 strain had the highest activity against Candida albicans ATCC 10,231 and the lowest against Pseudomonas aeruginosa ATCC 9027. CuNPs from the S4c strain demonstrated the highest activity against Escherichia coli ATCC 10,231 and the lowest activity against Klebsiella pneumonia ATCC 13,883.ConclusionThe present work focused on increasing the CuNPs production by two isolates, Niallia circulans G9 and Paenibacillus sp. S4c, which were then characterized alongside. The used analytics and chemical composition techniques validated the existence of CuONPs in the G9 and S4c biosynthesized nano cupper. CuNPs of S4c are smaller and have a more varied shape than those of G9 strain, according to TEM images. In terms of antibacterial activity, the biosynthesized CuNPs from G9 and S4c were found to be more effective against Candida albicans ATCC 10,231 and E. coli ATCC 10,231, respectively.

Ni2MnAl Heusler Alloy Nanoparticles for Chemoselective Hydrogenation of Nitro Compounds

Despite immense interest for years in Heusler alloys as magnetoelastic materials, their application in heterogeneous catalysis has only recently been explored. We report the development of highly active, robust and magnetically separable Ni2MnAl Heusler alloy nanoparticles as a heterogeneous catalyst for hydrogenation of aliphatic and aromatic nitro compounds to the corresponding amines. The easily synthesizable Ni2MnAl nanoparticles are thermally and chemically robust and exhibited excellent chemoselectivity in the hydrogenation of a range of aliphatic and aromatic nitroarenes, including those bearing functional groups sensitive to reduction, such as alkene, bromo, iodo, carbonyl and cyano, yielding the respective functionalized amines in good yields. Moreover, this solid catalyst is magnetically separable from the reaction mixture and could be recycled and reused at least 10 times without any loss in catalytic activity. The mechanism of the Ni2MnAl Heusler alloy nanoparticles catalyzed nitro reduction was studied by various spectroscopy and control experiments and kinetics. Our work opens a new avenue of developing heterogeneous earth‐abundant metal catalysis for economic and environment‐friendly synthesis of fine chemicals owing to their straightforward synthesis and tunable composition from base‐metals and their diverse structure and properties with their high surface area, thermal and chemical stability, excellent chemoselectivity, magnetic separability and recyclability.

Prussian blue nanocubes with peroxidase-like activity for polyphenol detection in commercial beverages.

The present study describes an efficient method for the determination of polyphenol content in beverages based on a composite material of graphene oxide decorated with Prussian blue nanocubes (rGO/PBNCs). In this method, rGO/PBNCs act as a nanoenzyme with peroxidase-like catalytic activity and produce a colorimetric product in the presence of hydrogen peroxide and tetramethylbenzidine (TMB). To verify the effectiveness of the method, we used two model standards for antioxidants: gallic acid (GA) and tannic acid (TA). The method validation included a comparison of the performance of a natural enzyme and an artificial one (rGO/PBNCs) and two polyphenols in the analysis of commercial beverage samples. After optimization, a pH of 4, ambient temperature (22 °C), a reaction time of 2 minutes and an rGO/PBNCs concentration of 0.01 μg mL-1 were found to be the most favorable conditions. The detection limits obtained were 5.6 μmol L-1 for GA and 1.5 μmol L-1 for TA. Overall, rGO/PBNCs offer advantages over natural enzymes in terms of stability, versatility, scalability and durability, making them attractive candidates for a wide range of catalytic and sensory applications.

Recyclable Ag-Au bimetallic nanoparticles supported on acid functionalized multi walled carbon nanotubes for effective catalytic applications

In the present investigation, in situ green reduction approach is used to uniformly decorate the Ag-Au bimetallic nanoparticles (BNPs) on the surface of acid functionalised multi-walled carbon nanotubes (MWCNTs). The adsorbed Terminalia catappa aqueous leaf extract biopolymers on the surface of MWCNTs can increase the in situ reduction of Ag, Au ions to Ag-Au BNPs and stabilise them which can operate as a capper/stabiliser and reductant agent. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), scanning electron microscopy - energy dispersive x-ray spectroscopy (SEM-EDX), Fourier-transform infrared spectroscopy (FT-IR) and UV–visible spectroscopy techniques were employed to examine the structures, morphologies, composition, chemical bonds and optical properties of the functionalised MWCNTs and the nanohybrid. The results revealed that the spherical T.C-Ag-Au bimetallic nanoparticle with average size 12.4 nm was uniformly distributed on the surface of modified MWCNTs. Finally, evaluation of the catalytic activity of the T.C-Ag-Au BNPs decorated MWCNTs exhibited excellent catalytic performance for completing the reduction of 4-Nitrophenol (4-NP) and degradation of alizarin red (AR) dye at ambient temperature with a great rate constant and the degradation efficiency of 98.7% and 96.4%, respectively. The order of reaction, rate constant, half-life and mechanism of catalytic activity of the T.C-Ag-Au BNPs@COOH-MWCNTs nanohybrid were calculated using the Langmuir–Hinshelwood model. The catalyst can be retained and reapplied eight times without affecting its catalytic performance. The interaction between T.C-Ag-Au BNPs and MWCNTs has a synergistic effect, which is accountable for the enhanced catalytic activity.

Stabilization of halide perovskites with silicon compounds for optoelectronic, catalytic, and bioimaging applications

AbstractSilicon belongs to group 14 elements along with carbon, germanium, tin, and lead in the periodic table. Similar to carbon, silicon is capable of forming a wide range of stable compounds, including silicon hydrides, organosilicons, silicic acids, silicon oxides, and silicone polymers. These materials have been used extensively in optoelectronic devices, sensing, catalysis, and biomedical applications. In recent years, silicon compounds have also been shown to be suitable for stabilizing delicate halide perovskite structures. These composite materials are now receiving a lot of interest for their potential use in various real‐world applications. Despite exhibiting outstanding performance in various optoelectronic devices, halide perovskites are susceptible to breakdown in the presence of moisture, oxygen, heat, and UV light. Silicon compounds are thought to be excellent materials for improving both halide perovskite stability and the performance of perovskite‐based optoelectronic devices. In this work, a wide range of silicon compounds that have been used in halide perovskite research and their applications in various fields are discussed. The interfacial stability, structure–property correlations, and various application aspects of perovskite and silicon compounds are also analyzed at the molecular level. This study also explores the developments, difficulties, and potential future directions associated with the synthesis and application of perovskite‐silicon compounds.image

Equipment-Free Fabrication of Thiolated Reduced Graphene Oxide Langmuir–Blodgett Films: A Novel Approach for Versatile Surface Engineering

This research presents a novel method for the fabrication of mercapto reduced graphene oxide (m-RGO) Langmuir–Blodgett (LB) films without the need for specialized equipment. The conventional LB technique offers precise control over the deposition of thin films onto solid substrates, but its reliance on sophisticated instrumentation limits its accessibility. In this study, we demonstrate a simplified approach that circumvents the necessity for such equipment, thereby democratizing the production of m-RGO LB films. Thiolation of reduced graphene oxide (rGO) imparts enhanced stability and functionality to the resulting films, rendering them suitable for a wide range of applications in surface engineering, sensing, and catalysis. The fabricated m-RGO LB films exhibit favorable morphological, structural, and surface properties, as characterized by various analytical techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). Furthermore, the performance of the m-RGO LB films is evaluated in terms of their surface wettability, electrochemical behavior, and chemical reactivity. The equipment-free fabrication approach presented herein offers a cost-effective and scalable route for the production of functionalized graphene-based thin films, thus broadening the scope for their utilization in diverse technological applications.

Synthesis of Porous Connected Cryoaerogel Networks from Cadmium Chalcogenide Nanoplatelet Stacks

Cadmium chalcogenide nanoplatelets (NPLs) are not only known due to their unique optical properties but also because of their ability to self‐assemble into stacks with new collective properties. Only recently, a stacking process in an aqueous medium has been demonstrated, which opens up possible applications and methods such as gelation. Nanoparticle‐based aerogels gain a lot of attention due to their high relative surface areas and porosity and thus, high potential for catalytic applications. Herein, the positive properties of aerogels to the NPL‐stack system by cryoaerogelation of destabilized NPL dispersions are introduced. After the addition of an antisolvent to initiate the stacking, the dispersion is flash‐frozen with liquid nitrogen and freeze‐dried. By this method, porous cryoaerogel networks result in high surface areas and retained stacking of the NPLs. The formed stack‐gels are investigated by electron microscopy and physisorption measurements. Optical and photoelectrochemical measurements verify the charge carrier transport within the stack‐gel network.

Enhancement of methylene blue catalytic reduction by novel green synthesized metal decorated reduced graphene oxide: Sn@rGO and Ag@rGO

Carbon-based nanocomposites (NCs) attracted much attention in heterogeneous catalysis to remove organic dyes. Herein, a novel low-cost green approach was utilized to design a reduced graphene oxide (rGO) impregnated with Sn or Ag nanoparticles (NPs) using ginger extract as a green reducing agent. The synthesized NCs were characterized utilizing X-ray diffraction (XRD), Fourier transformation infrared (FTIR), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), Raman spectroscopy, and thermal gravimetric analysis (TGA). The synthesized NCs were assessed for their catalytic reduction activity towards methylene blue (MB) dye. XRD displayed the characteristic peaks of Sn- and Ag-NPs and the reduction of GO, referring to successful NC formation. FTIR and Raman confirmed the reduction of GO and the incorporation of Sn and Ag-NPs into the GO surfaces. TEM results proved that either Sn- or Ag-NPs was uniformly dispersed on rGO sheets with average sizes of 4.129 and 7.293 nm, respectively. EDX spectra of Sn@rGO- and Ag@rGO-NCs revealed the presence of C, O, Sn, and Ag. TGA confirmed the increased thermal stability of the NCs as compared to GO. Ag@rGO-NC exhibited stronger catalytic MB reduction (97% after 10 min) than Sn@rGO-NC (80% after 20 min). To the best of our knowledge, this is the first time Sn@rGO-NC has been designed for MB catalytic reduction, which gives rise to its promising capacity for future catalytic applications.

Non-Metal Doping as a First-Principles Study for Promoting the Hydrogen Evolution of Two-Dimensional Electride Y2C Electrocatalysts

The two-dimensional electrochemical Y2C’s low work function and strong charge transfer qualities limit its applicability in catalysis due to its poor catalytic activity. In this paper, based on density functional theory calculations, we use two techniques to increase the HER catalytic activity of the Y2C monolayer: substitution doping (XC) and adsorption doping (XT) of non-metal (X = N, P, O, S, and F). The results showed that the absolute values of hydrogen free energies (ΔGH*) of the substitutional dopants of PC, SC and adsorptive dopants of NT, OT, ST, and PT had increased catalytic activity compared with those of the pristine Y2C monolayer (−0.673 eV). It was highlighted that the adsorption doping of PT can further reduce the adsorption free energy of the pristine Y2C monolayer to −0.19 eV, which is close to the optimal zero value, and the binding energy of the hydrogen atoms on the Y2C surface significantly increased from −0.913 to −0.438 eV, which is more favorable for the desorption of hydrogen atoms. These results demonstrate that the doping of non-metals activates the adsorption of hydrogen atoms on monolayer Y2C and provides a feasible method for hydrogen generation.

Explosive Leidenfrost-Droplet-Mediated Synthesis of Monodispersed High-Entropy-Alloy Nanoparticles for Electrocatalysis.

High-entropy-alloy nanoparticles (HEA NPs) exhibit promising potential in various catalytic applications, yet a robust synthesis strategy has been elusive. Here, we introduce a straightforward and universal method, involving the microexplosion of Leidenfrost droplets housing carbon black and metal salt precursors, to fabricate PtRhPdIrRu HEA NPs with a size of ∼2.3 nm. The accumulated pressure within the Leidenfrost droplet triggers an intense explosion within milliseconds, propelling the carbon support and metal salt rapidly into the hot solvent through explosive force. The exceptionally quick temperature rise ensures the coreduction of metal salts, and the dilute local concentration of metal ions limits the final size of the HEA NPs. Additionally, the explosion process can be fine-tuned by selecting different solvents, enabling the harvesting of diverse HEA NPs with superior electrocatalytic activity for alcohol electrooxidation and hydrogen electrocatalysis compared to commercial Pt (Pd) unitary catalysts.

Organometallic Chirality Sensing via “Click”‐Like η6‐Arene Coordination with an Achiral Cp*Ru(II) Piano Stool Complex

AbstractPiano stool complexes have been studied over many years and found widespread applications in organic synthesis, catalysis, materials and drug development. We now report the first examples of quantitative chiroptical molecular recognition of chiral compounds through click‐like η6‐arene coordination with readily available half sandwich complexes. This conceptually new approach to chirality sensing is based on irreversible acetonitrile displacement of [Cp*Ru(CH3CN)3]PF6 by an aromatic target molecule, a process that is fast and complete within a few minutes at room temperature. The metal coordination coincides with characteristic circular dichroism inductions that can be easily correlated to the absolute configuration and enantiomeric ratio of the bound molecule. A relay assay that decouples the determination of the enantiomeric composition and of the total sample amount by a practical CD/UV measurement protocol was developed and successfully tested. The introduction of piano stool complexes to the chiroptical sensing realm is mechanistically unique and extends the scope of currently known methods with small‐molecule probes that require the presence of amino, alcohol, carboxylate or other privileged functional groups for binding of the target compound. A broad application range including pharmaceutically relevant multifunctional molecules and the use in chromatography‐free asymmetric reaction analysis are also demonstrated.

Strong Bases and beyond: The Prominent Contribution of Neutral Push–Pull Organic Molecules towards Superbases in the Gas Phase

In this review, the principles of gas-phase proton basicity measurements and theoretical calculations are recalled as a reminder of how the basicity PA/GB scale, based on Brønsted–Lowry theory, was constructed in the gas-phase (PA—proton affinity and/or GB—gas-phase basicity in the enthalpy and Gibbs energy scale, respectively). The origins of exceptionally strong gas-phase basicity of some organic nitrogen bases containing N-sp3 (amines), N-sp2 (imines, amidines, guanidines, polyguanides, phosphazenes), and N-sp (nitriles) are rationalized. In particular, the role of push–pull nitrogen bases in the development of the gas-phase basicity in the superbasicity region is emphasized. Some reasons for the difficulties in measurements for poly-functional nitrogen bases are highlighted. Various structural phenomena being in relation with gas-phase acid–base equilibria that should be considered in quantum-chemical calculations of PA/GB parameters are discussed. The preparation methods for strong organic push–pull bases containing a N-sp2 site of protonation are briefly reviewed. Finally, recent trends in research on neutral organic superbases, leaning toward catalytic and other remarkable applications, are underlined.

Ruthenium–Nickel Nanoparticles with Unconventional Face‐Centered Cubic Crystal Phase for Highly Active Electrocatalytic Hydrogen Evolution

AbstractRu‐based nanomaterials are promising alternatives to Pt electrocatalysts for green hydrogen energy generation, and crystal phase engineering holds the key to unlocking their catalytic potential to new heights. However, controllable phase regulation on Ru‐alloys remains a formidable challenge, and unraveling the crystal phase‐related electrocatalytic performance is of great significance. Herein, RuNi nanoparticles are successfully synthesized with an unconventional face‐centered cubic (fcc) phase via a facile route. Comprehensive transmission electron microscopy confirmed the structural characteristics of the fcc‐RuNi and electrochemical analyses indicate the impressive electrocatalytic hydrogen evolution reaction of fcc‐RuNi. Notably, the anomalous fcc‐RuNi nanoparticles possess an extraordinarily low overpotential of 16 mV in hydrogen evolution. Density functional theory calculations indicate that these nanoparticles are energetically conducive to intermediate desorption and H2O dissociation. This study enhances comprehension of phase regulation in Ru‐based nanostructures and will propel phase engineering in diverse catalytic applications.

Unraveling the Unique Strong Metal-Support Interaction in Titanium Dioxide Supported Platinum Clusters for the Hydrogen Evolution Reaction.

Strong metal-support interaction (SMSI) is crucial to modulating the nature of metal species, yet the SMSI behaviors of sub-nanometer metal clusters remain unknown due to the difficulties in constructing SMSI at cluster scale. Herein, we achieve the successful construction of the SMSI between Pt clusters and amorphous TiO2 nanosheets by vacuum annealing, which required a relatively low temperature that avoids the aggregation of small clusters. In situ scanning transmission electron microscopy observation is employed to explore the SMSI behaviors, and the results reveal the dynamic rearrangement of Pt atoms upon annealing for the first time. The originally disordered Pt atoms become ordered as the crystallizing of the amorphous TiO2 support, forming an epitaxial interface between Pt and TiO2. Such SMSI state can remain stable in oxidation environment even at 400 °C. Further investigations prove that the electron transfer from TiO2 to Pt occupies the Pt 5d orbitals, which is responsible for the disappeared CO adsorption ability of Pt/TiO2 after forming SMSI. This work not only opens a new avenue for constructing SMSI at cluster scale but also provides in-depth understanding on the unique SMSI behavior, which would stimulate the development of supported metal clusters for catalysis applications.

Unraveling the Unique Strong Metal‐Support Interaction in Titanium Dioxide Supported Platinum Clusters for the Hydrogen Evolution Reaction

Strong metal‐support interaction (SMSI) is crucial to modulating the nature of metal species, yet the SMSI behaviors of sub‐nanometer metal clusters remain unknown due to the difficulties in constructing SMSI at cluster scale. Herein, we achieve the successful construction of the SMSI between Pt clusters and amorphous TiO2 nanosheets by vacuum annealing, which required a relatively low temperature that avoids the aggregation of small clusters. In situ scanning transmission electron microscopy observation is employed to explore the SMSI behaviors, and the results reveal the dynamic rearrangement of Pt atoms upon annealing for the first time. The originally disordered Pt atoms become ordered as the crystallizing of the amorphous TiO2 support, forming an epitaxial interface between Pt and TiO2. Such SMSI state can remain stable in oxidation environment even at 400 °C. Further investigations prove that the electron transfer from TiO2 to Pt occupies the Pt 5d orbitals, which is responsible for the disappeared CO adsorption ability of Pt/TiO2 after forming SMSI. This work not only opens a new avenue for constructing SMSI at cluster scale but also provides in‐depth understanding on the unique SMSI behavior, which would stimulate the development of supported metal clusters for catalysis applications.

Novel High-Entropy FeCoNiMoZn-Layered Hydroxide as an Efficient Electrocatalyst for the Oxygen Evolution Reaction

The exploration of catalysts for the oxygen evolution reaction (OER) with high activity and acceptable price is essential for water splitting to hydrogen generation. High-entropy materials (HEMs) have aroused increasing interest in the field of electrocatalysis due to their unusual physicochemical properties. In this work, we reported a novel FeCoNiMoZn-OH high entropy hydroxide (HEH)/nickel foam (NF) synthesized by a facile pulsed electrochemical deposition method at room temperature. The FeCoNiMoZn-OH HEH displays a 3D porous nanosheet morphology and polycrystalline structure, which exhibits extraordinary OER activity in alkaline media, including much lower overpotential (248 mV at 10 mA cm−2) and Tafel slope (30 mV dec−1). Furthermore, FeCoNiMoZn-OH HEH demonstrates excellent OER catalytic stability. The enhanced catalytic performance of the FeCoNiMoZn-OH HEH primarily contributed to the porous morphology and the positive synergistic effect between Mo and Zn. This work provides a novel insight into the design of HEMs in catalytic application.

Facilitating Atom Probe Tomography of 2D MXene Films by In Situ Sputtering.

2D materials are emerging as promising nanomaterials for applications in energy storage and catalysis. In the wet chemical synthesis of MXenes, these 2D transition metal carbides and nitrides are terminated with a variety of functional groups, and cations such as Li+ are often used to intercalate into the structure to obtain exfoliated nanosheets. Given the various elements involved in their synthesis, it is crucial to determine the detailed chemical composition of the final product, in order to better assess and understand the relationships between composition and properties of these materials. To facilitate atom probe tomography analysis of these materials, a revised specimen preparation method is presented in this study. A colloidal Ti3C2Tz MXene solution was processed into an additive-free free-standing film and specimens were prepared using a dual beam scanning electron microscope/focused ion beam. To mechanically stabilize the fragile specimens, they were coated using an in situ sputtering technique. As various 2D material inks can be processed into such free-standing films, the presented approach is pivotal for enabling atom probe analysis of other 2D materials.