Transition Metal Substitution Research Articles

Activation of efficient hydrogen evolution on 1T-VS2 nanoribbons by low-cost transition metals: A first-principles study

Electrocatalytic water splitting is a very important energy conversion technology that utilizes renewable energy sources to produce hydrogen for sustainable energy development. In this work, the catalytic performance of 1T-VS2 (1T phase of vanadium disulfide) nanoribbons in the hydrogen evolution reaction (HER) was investigated based on first-principles calculations. It was found that 1T-VS2 nanoribbons have a Gibbs free energy (ΔGH*) of 0.05 eV, demonstrating its excellent HER performance. Moreover, some transition metal substitutions can further improve this performance (e.g. the ΔGH* of the Ti/Fe-1T-VS2 are as low as −0.02/0.04 eV). The mechanism of the performance enhancement is thoroughly investigated. The improved catalytic performance of HER is mainly promoted by hybridization between the V-d and TM-d-orbitals. The crystal orbital Hamiltonian population (COHP) and integral crystal orbital Hamiltonian habitation (ICOHP) calculations show that the HER properties are closely related to the filling of bonding and antibonding states. The differential charge density indicates that the adsorption of H results in an effective charge transfer at the interface and an increase in the conductivity, leading to an increase in the HER. The HER activity of the TM-1T-VS2 (TM stands for transition metal) nanoribbons is also related to the proximity of the adsorption site to the edge. Our work suggests that the TM-1T-VS2 nanoribbons are expected to be low cost and highly efficient catalysts.

A comprehensive quantitative DFT procedure to evaluate rate-capability and electron conduction of intercalation electrode materials: Assessment of novel Li[Mi]1/3[Mj]1/3[Mk]1/3O2 electrodes as case studies

This paper uses comprehensive approach to propose quantitative evaluations of the electrode materials’ electronic rate-capability calculated by density functional theory (GGA/GGA + U). Here, a novel approach is introduced to evaluate electrical rate-capability by calculating electronic conductivity (σ) for the case studies. Application of the evaluated materials as electrodes of Li-ion battery is taken into account. Also, thermal conductivity and Seebeck coefficient for the materials are calculated. Here, three novel alternatives for LiNi1/3Co1/3Mn1/3O2 (NCM111), in which introduced by substitution of transition metals, are LiNi1/3Mn1/3Fe1/3O2(NMF), LiMn1/3Fe1/3Co1/3O2(MFC), and LiFe1/3Co1/3Ni1/3O2(FCN). The evaluated materials are compared with each other and other relevant electrodes, based on structural, electrochemical, and electrical properties. The voltage reaction of the cathode materials is calculated by two approaches, namely internal and Fermi energy methods. According to the obtained results, MFC and NMF have superior properties on NCM. It is concluded that the NMF can be the best alternative for NCM conditionally.

Boosted Light Alkane Deep Oxidation via Metal Bond Length Modulation-Induced C-C Bond Preferential Activation.

Light alkanes (LAs), typical VOCs existing in both stationary and mobile sources, pose significant environmental concerns. Although noble metal catalysts demonstrate strong C-H bond activation, their effectiveness in degrading LAs is hindered by inherent challenges, including poor chemical stability and water resistance. Here, from a new perspective, we propose a feasible strategy that adjusting the metal bond lengths within Pd clusters through partial substitution of smaller radius 3d transition metals (3dTMs) to prioritize the activation of low-energy C-C bonds within LAs. Benefiting from this, PdCo/CeO2 exhibits exceptional catalytic performance in propane degradation due to their high capacity for C-C cleavage stemming from the shorter Pd-Co length (2.51 Å) and lower coordination number (1.73), boosting the activation of α-H and β-H of propane simultaneously and accelerating the mobility of postactivated oxygen species to prevent Pd center deep oxidation. The presence of 3dTMs on Pd clusters improves the redox and charge transfer ability of catalysts, resulting in an amplified generation of oxygen vacancies and facilitating the adsorption and activation of reactants. Mechanistic studies and DFT calculations suggest that the substitution of 3dTMs significantly accelerate C-C bond cleavage within C3 intermediates to generate the subsequent C2 and C1 intermediates, suppressing the generation of harmful byproducts.

Pharmaceutical manifestation of Knoevenagel condensed metal (II) complexes through virtual, in vitro and in vivo assessments

Sulphur containing compounds possess a great deal of interest due to wide range of beneficial activities towards biotic species. This work also deals with the study of biological examination of newly synthesized sulphur containing Cu(II) and Zn(II) complexes derived from (E)-4-(phenylimino)-3-((E)-1-(phenylimino)ethyl)pent-2-ene-1-thiol Schiff bases. Moreover, the DNA nuclease efficiency of the synthesized metal complexes is studied by UV absorption studies, Fluorescence studies, Viscosity and CV titrations which confirm the intercalative mode of binding. Pharmacokinetic studies and drug like activity of these compounds are screened with the help of SWISS ADME online freeware. Their morphological nature is corroborated by various spectral techniques. Optimized geometry and biologically accessible nature of the synthesized compounds are investigated by Gaussian 09 W software. Interestingly, molecular docking studies are carried out against cancer DNA and 6J10 cancer cell. Anti–inflammatory and in vitro antioxidant activities have been studied to validate the theoretical prediction. Based on these preliminary pharmacological activities, the in vitro cytotoxicity and in vivo antitumor activities are examined using MCF-7, HeLa, Hep-2, HepG-2 and Ehrlich ascites carcinoma (EAC) cell lines. All the above examinations reveal that the nitro substituted transition metal complexes possess higher biological bustle. Communicated by Ramaswamy H. Sarma

STRUCTURES, ELECTRONIC PROPERTIES AND DIPOLE MAGNITUDES OF TMWn−1O3n AND TM2Wn−2O3n (TM = Ni, Pd AND Pt; n=2−6) CLUSTERS

Transition metal substitution can expand the applications of tungsten oxides in chemical sensors, catalysts, and other fields. In order to highlight the effect of TM substitution on the electronic properties of tungsten oxide clusters, the configurations, electronic properties and dipole magnitudes of [Formula: see text] and [Formula: see text] (TM = Ni, Pd and Pt; [Formula: see text]) clusters have been investigated via the density functional theory. The structures of [Formula: see text] and [Formula: see text] clusters inherit those of [Formula: see text] ([Formula: see text] = 2–6) clusters to some extent except for [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] clusters. [Formula: see text] clusters exhibit higher thermodynamic stability than the other [Formula: see text] and [Formula: see text] clusters. [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] clusters display more kinetically stable than adjacent [Formula: see text] and [Formula: see text] clusters. The Mülliken charge transfer amount of [Formula: see text] clusters is more than that of other [Formula: see text] and [Formula: see text] clusters except for [Formula: see text] clusters.

Modulation of the Band Gap and Redox Properties by Mixed Addenda in Sandwich Polyoxometalates.

Due to the wide range of applications of band-gap engineering in optoelectronics and photocatalysis, the rational design of polyoxometalate (POM) frameworks is highly desired. Here, we have successfully synthesized a series of mixed addenda (Mo and W) sandwich POMs by systematically varying pH, concentrations of salts, and counterions in Weakley-type sandwich POMs by incorporating Mo into the framework of tetrasubstituted sandwich POMs. Crystallographic analysis reveals the centrosymmetric structure; with variation in the Mo to W ratio, Mo preferentially binds to μ2 oxygen connected to transition metals in the sandwich position. UV-visible spectroscopy, electrochemical, and theoretical modeling rationalize the band-gap modulations. Theoretical studies and cyclic voltammograms indicate that during the reduction, the incoming electrons preferentially go to substituted transition metals followed by Mo. Flat band potential calculated from the Mott-Schottky enables tuning of the electronic properties of composites based on these sandwich POMs. Moreover, the dioxygen binding and activation studies of these polyoxometalates have been highlighted.

Enhancing the electrochemical properties of Na2Mn2P3O9N by partial substitution at Mn site: A first-principles study

Nitridophosphate materials have recently emerged as promising cathode materials for Na-ion batteries due to their excellent ionic conductivity, but their low electronic conductivity has limited their practical applications. In this study, the electrochemical properties of Na2Mn2P3O9N, a nitridophosphate material containing manganese was examined for the first time and the prevalent issue of low electronic conductivity in nitridophosphate-based materials was addressed through partial substitution of transition metal (TM) at the Mn site. The present work aims at improving the electronic conductivity of this material while maintaining desirable properties such as ionic conductivity, voltage, and structural stability. The study employed density functional theory (DFT) calculations to explore the role of TM substitutions in electronic conductivity and electrochemical properties. From the partial substitution of different electrochemical active and inactive elements at the Mn site, we found that the Cu/Ag substitutions improve the electronic conductivity while retaining other desirable electrochemical properties. The electronic and electrochemical properties of these materials were further studied in detail to reveal the redox mechanisms. Our DFT-assisted studies prove that the parent and Ag-substituted materials exhibit a stable O network even under a high state of charge. Furthermore, our nudged elastic band calculations revealed that Na2Mn2P3O9N, along with the Cu/Ag substituted variants, exhibit favourable Na-ion diffusion. The parent and Ag-substituted materials demonstrate exceptional ionic conductivities comparable to existing commercial cathodes used in Li-ion batteries. These findings suggest that partial substitution of copper/silver at the manganese site could be a promising strategy for improving the electronic conductivity of nitridophosphate materials without compromising their beneficial properties to use in higher energy density Na-ion batteries.

Effect of the Nature of Both Cation and Anion Substitution on the Structural Symmetry of Li‐Rich 3d‐Metal Chalcogenide Electrodes

AbstractLi‐rich layered chalcogenides have recently led to better understanding of the anionic redox process and its associated high capacity while providing ways to overcome its practical limitations of voltage fade and irreversibility. This study reports on the feasibility of triggering anionic activity in Li2TiS3, through anionic substitution (Se for S) or cationic substitution (Fe for Ti). Herein, the chalcogenide chemical space is further explored to prepare mono‐substituted Li1.7Ti0.85Mn0.45Ch3 (Ch = S/Se) and doubly substituted cationic and anionic phases (Li1.7Ti0.85Fe0.45S3‐zSez) which crystallize either in the O3‐ or O1‐type structures depending upon substituents. All series show a bell‐shape capacity variation as function of the transition metal (TM) substitution degree with values up to 240 mAh g−1. For specific compositions, a structural O3 to O1 phase transition is observed upon Li removal, which is not reversible upon Li re‐insertion due to kinetic limitations and negatively affects long‐term cycling performance. Density functional theory (DFT) calculations confirm the O3/O1 relative stability along the different series and point subtle electronic differences in the TM‐doping, rationalizing the structural and electrochemical behaviors of these phases upon cycling. These findings provide further insights into the link between structural and electronic stability, which is of key importance for designing chalcogenide‐based anionic redox compounds.

Regulating Oxygen Redox Chemistry through the Synergistic Effect of Transition-Metal Vacancy and Substitution Element for Layered Oxide Cathodes.

Reversible oxygen redox (OR) is considered as a paradigmatic avenue to boost the energy densities of layered oxide cathodes. However, its activation is largely coupled with the local coordination environment around oxygen, which is usually accompanied with irreversible oxygen release and unfavorable structure distortion. Herein, it is revealed that the synergistic effect of transition-metal (TM) vacancy and substitution element for modulating the OR activity and reversibility of layered Na0.67 MnO2 through multimodal operando synchrotron characterizations and electrochemical investigations. It is disclosed that TM vacancy can not only suppress the complicated phase transition but also stimulate the OR activity by creating nonbonding O 2p states via the Na─O─vacancy configurations. Notably, the substitution element plays a decisive role for regulating the reversibility of vacancy-boosted OR activity: the presence of strong Al─O bonds stabilizes the Mn-O motifs by sharing O with Al in the rigid Mn─O─Al frameworks, which mitigates TM migration and oxygen release induced by TM vacancy, leading to enhanced OR reversibility; while the introduction of weak Zn─O bonds exacerbates TM migration and irreversible oxygen release. This work clarifies the critical role of both TM vacancy and substitution element for regulating the OR chemistry, providing an effective avenue for designing high-performance cathodes employing anionic redox.

Magnetic, morphological, and photocatalytic studies of Cu2+ doped Mg-Zn ferrite nanoparticles

Due to their distinctive characteristics, including their optical, catalytic, electrical, and magnetic properties, spinel ferrite nanoparticles attract more interest. Also, the substitution of transition metals like copper in ferrites has the potential to control their physical characteristics and could improve their catalytic and magnetic capabilities. Cu2+ doped Mg-Zn ferrite samples show a change in behaviour from superparamagnetic to soft ferrimagnetic. The photocatalytic studies for the CuxMg0.5Zn0.5-xFe2O4 (x= 0.1 to 0.5, and Δx= 0.1) nano-ferrites are conducted in visible light to investigate the methylene blue photodecomposition capability. The Cu-Mg-Zn nano-ferrites displayed unique behaviour in terms of Magnetic, and photocatalytic activity. These outcomes show that the Cu-Mg-Zn ferrite samples are apply to water remediation.

Enhanced Cycling Performance by Transition Metal Substitution on Li2CuO2 Cathode Additive for Advanced Lithium-Ion Battery

Lithium-Ion batteries (LIBs) have made remarkable progress in the last decade and have been employed so far as the most popular power source for electric vehicles (EVs). However, the energy density issue still remains a drawback for LIBs on long-range driving of EVs for the reason of significant irreversible Li+ loss in the initial charging process of LIBs, induced by a spontaneous formation of solid electrolyte interphase (SEI) on the anode surface. Therefore, strategic studies are required to maximize the energy density of LIBs as compensation of the initial loss of Li+ during cell operation. The utilization of a Li-excess cathode additive in commercial cathodes is an ideal approach to minimize the loss of energy density of LIBs. Recently, Li2CuO2 has been proposed as a potential cathode additive with many advantages over other candidates, including the following: (i) high charge capacity (~ 490 mAh g-1), (ii) comparable operating voltage window (2.5 ~ 4.3 V vs. Li/Li+) to commercial cathode materials, and (iii) abundance of copper (Cu) on the earth. But, its practical use is still restricted by the structural instability and spontaneous oxygen (O2) evolution (> 3.8 V vs. Li/Li+), which results in loss of reversibility during subsequent cycling. It is thus crucial to reinforce the structure of Li2CuO2 to make it more reliable as a cathode additive for charge compensation. In a pursuit of improving the structural stability of Li2CuO2, herein, we demonstrate structural modification via co-substitution by heteroatoms, such as nickel (Ni) and manganese (Mn), for improving the structural stability and electrochemical performance of Li2CuO2. Such an approach effectively enhances the reversibility of Li2CuO2 by suppressing continuous structural degradation and O2 gas evolution during cycling. Our findings provide new conceptual pathways for developing advanced cathode additives for high-energy LIBs.

Impact of transition metal (Co and Mn) substitution on the structural and magnetic properties of BaFe12O19 nanoparticles towards permanent magnet application

Impact of transition metal (Co and Mn) substitution on the structural and magnetic properties of BaFe12O19 nanoparticles towards permanent magnet application

Role of Transition Metal Substitution on Nickel Sulfide toward Electrocatalytic Water Splitting

Role of Transition Metal Substitution on Nickel Sulfide toward Electrocatalytic Water Splitting

Effects of 3d Transition Metal Substitutions on the Phase Stability and Mechanical Properties of Ti-5.5Al-11.8[Mo]eq Alloys.

The phase stability, mechanical properties, and functional properties of Ti-5.5Al-11.8[Mo]eq alloys are focused on in this study by substituting 3d transition metal elements (V, Cr, Co, and Ni) for Mo as β-stabilizers to achieve similar β phase stability and room temperature (RT) superelasticity. The ternary alloy systems with the equivalent chemical compositions of Ti-5.5Al-17.7V, Ti-5.5Al-9.5Cr, Ti-5.5Al-7.0Co, and Ti-5.5Al-9.5Ni (mass%) alloys were selected as the target materials based on the Mo equivalent formula, which has been applied for the Ti-5.5Al-11.8Mo alloy in the literature. The fundamental mechanical properties and functionalities of the selected alloys were examined. The β phase was stabilized at RT in all alloys except for the Ti-Al-V alloy. Among all alloys, the Ti-Al-Ni alloy exhibited superelasticity in the cyclic loading-unloading tensile tests at RT. As a result, similar to the Ti-5.5Al-11.8Mo mother alloy, by utilizing the Mo equivalent formula to substitute 3d transition metal elements for Mo, a RT superelasticity was successfully imposed.

Electrochemical Performance of Spongy Snowballs of O3-NaFeO2@SnO: Cathodes for Sodium Ion Batteries

Electrode materials for large-scale applications from the earth-abundant material need to be developed in the energy storage system. Based on earth-abundant material, sodium-based batteries with Fe system-based positive electrodes seem attractive for a cost-effective system for large-scale storage applications. Instead of partial substitution of transition metals with Fe, in the present work, we choose surface coating to analyze the electrochemical performance of NaFeO2. SnO was coated on the NaFeO2 surface, and the electrochemical characteristic property is studied in detail. Spongy nanoball coating is confirmed on the surface of NaFeO2. The reversible capacity of SnO-coated NaFeO2 is about 158 mAh·g-1 at 0.25 C. The SnO coating greatly enhances electron transport during cycling, and 80% of capacity is retained after 1000 cycles. The enhanced electrode can be used as a cost-effective, eco-friendly natured electrode with high performance for large-scale energy storage applications.

Spin-orbital mechanisms for negative thermal expansion in Ca2RuO4

The phenomenon of negative thermal expansion (NTE) deals with the increase of the lattice parameters and the volume of the unit cell when the material is thermally cooled. The NTE is typically associated with thermal phonons and anomalous spin-lattice coupling at low temperatures. However, the underlying mechanisms in the presence of strong electron correlations in multiorbital systems are not yet fully established. Here, we investigate the role of Coulomb interaction in the presence of lattice distortions in setting out the NTE effect, by focusing on the physical case of layered ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$ with the ${d}^{4}$ configuration at each Ru ion site. We employ the Slater-Koster parametrization to describe the electron-lattice coupling through the dependence of the d-p hybridization on the Ru-O-Ru bond angle. The evaluation of the minimum of the free energy at finite temperature by fully solving the multiorbital many-body problem on a finite-size cluster allows us to identify the regime for which the system is prone to exhibit NTE effects. The analysis shows that the nature of the spin-orbital correlations is relevant to drive the reduction of the bond angle by cooling, and in turn the tendency toward a NTE. This is confirmed by the fact that a changeover of the electronic and orbital configuration from ${d}^{4}$ to ${d}^{3}$ by transition metal substitution is shown to favor the occurrence of a NTE in ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$. This finding is in agreement with the experimental observations of a NTE effect which is significantly dependent on the transition metal substitution in the ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$ compound.

Machine learning-based Curie temperature prediction for magnetic 14:2:1 phases

The TM14RE2B-based phases (TM = transition metal, RE = rare earth metal; hereafter called 14:2:1) enable permanent magnets with outstanding magnetic properties. Novel chemical compositions that represent new 14:2:1 phases necessitate that they do not demagnetize at application-specific operating temperatures. Therefore, an accurate knowledge of the Curie temperature (Tc) is important. For magnetic 14:2:1 phases, we present a machine learning model that predicts Tc by using merely chemical compositional features. Hyperparameter tuning on bagging and boosting models, as well as averaging predictions from individual models using the voting regressor, enables a low mean-absolute-error of 16 K on an unseen test set. The training set and a test set have been constructed by randomly splitting, in an 80:20 ratio, of a database that contains 449 phases (270 compositionally unique) mapped with their Tc, taken from distinct publications. The model correctly identifies the relative importance of key substitutional elements that influence Tc, especially in an Fe base such as Co, Mn, and Al. This paper is expected to serve as a basis for accurate Curie temperature predictions in the sought-after 14:2:1 permanent magnet family, particularly for transition metal substitution of within 20% in an Fe or Co base.

Tuning Discharge Behavior of Hollandite α-MnO2 in Hydrated Zinc Ion Battery by Transition Metal Substitution

The tunnel-type hollandite α-MnO2 is a promising cathode material for rechargeable aqueous zinc-ion batteries (ZIBs) due to its low cost in synthesis and high energy density. However, irreversible structural degradation upon continuous cycling prevents the cathode from being utilized commercially. Herein, density functional theory (DFT) was utilized to conduct a systematic study on tuning the behavior of α-MnO2 by substituting the Mn ions on the tunnel wall with a transition metal (V or Cr) during the H+-/Zn2+-intercalation in hydrated ZIB. Our study revealed that both substituents aid cyclability and capacity retention with Cr outperforming V. In term of discharge voltage, only the Cr-substitution displays clear promotion at the early stage of discharge. The superior performance of substituted Cr4+ comes from its unique atomic and electronic structures. Upon discharge, it can be reduced to Cr3+ more readily than Mn4+ and thereby limits the formation of unstable Mn3+ or Mn2+ centers; the formed Cr3+ is more stable than Mn3+ and Mn2+ from the reduction of Mn4+; and Cr3+ can also greatly stabilize the neighboring Mn ions. This study highlights the significant tuning effect of transition metal substitution on the electrochemical and physical performance of α-MnO2 as a cathode in hydrated ZIBs.

The effect of transition metal substitution on the structural, elastic, optical, electrical and dielectric properties of M0.5Fe2·5O4 (M=Co and Mg) synthesized by the auto combustion method

Spinel nanoparticles M0.5Fe2.5O4 (M = Co,Mg) were elaborated by the auto-combustion method using glycine as a fuel. X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy have been invested to investigate the structural and morphological properties of these compounds. The optical study reveals that these samples exhibit a strong absorption in the visible range. They possess intermediate gap energies 2.91 eV for Co0.5Fe2.5O4 and 3.16 eV for Mg0·5Fe2·5O4 which makes them good candidates in terms of photovoltaic applications. Electrical analysis demonstrates a semiconductor [300–520 K] - metallic [540–660 K] transition at 540 K. Correlated Barrier Hopping (CBH) and No Overlap Small Polaron Tunneling (NSPT) models dominate the conduction mechanisms in both compounds. The Nyquist diagrams are modelled by two series-connected circuits reflecting grain (Rg//Cg) and grain boundary effects (Rgb//CPEgb). Quantitative analysis of the dielectric constant is indicative that these compounds are promising at the level of electronic systems industry, LTCC devices and super capacitor applications.

A study of the antioxidant properties of Keggin-type polyoxometalates.

In this paper, we used extracellular reactive oxygen radical scavenging assay and cellular antioxidant assay to investigate the antioxidant ability of Keggin-type polyoxometalates on the inside and outside of cells influenced by three different factors: heteroatom substitution, transition metal substitution and the number of vanadium substitutions. The results showed that the IC50 values of heteroatomic (P, Si, Ga) polyoxometalates on superoxide anion radical scavenging were 1.32 ± 0.00047 mg mL-1, 17.49 ± 2.47500 mg mL-1, and 66.99 ± 20.0227 mg mL-1, respectively. In comparison, PMo12 had the best ability to scavenge free radicals, and the SOD activity of PMo12 at 12.5 μmol L-1 increased by 50% compared with that of the unspiked drug, which played an antioxidant role; the scavenging effect of superoxide anion radicals of PMo11Mn in transition metals (Fe, Mn, Cu) instead of polyoxometalate (IC50 value 1.18 ± 0.0008 mg mL-1) was lower than that of unsubstituted PMo12 (IC50 value 1.32 ± 0.00047 mg mL-1), where PMo11Mn was nearly 1.5 times higher than PMo11Cu administration to reduce the number of cells by half; the PMo11V, PMo10V2, PMo9V3, PMo8V4, PMo7V5 hydroxyl radical scavenging rates (IC50 values) were 0.19 ± 0.0011 mg mL-1, 0.22 ± 0.0027 mg mL-1, 0.03 ± 0.0014 mg mL-1, 0.04 ± 0.0008 mg mL-1, and 0.11 ± 0.0005 mg mL-1, respectively, and in comparison, scavenging of PMo9V3 radicals was more effective and they acted as an antioxidant. Therefore, they can be used as good antioxidants in biological and pharmaceutical applications and play an important role in the treatment of tumours, cancer, Alzheimer's disease and other diseases.