Transition Metal Elements Research Articles

Electron tailoring of thermal and magnetocaloric properties in Tb55TM17.5Al27.5 (TM = Fe, Co, and Ni) metallic glasses

Transition metal (TM) elements play a key role in determining properties of magnetocaloric materials. However, the effect of TM elements on the thermodynamic behavior and magnetocaloric effect (MCE) of metallic glasses (MGs) remains elusive. In this work, ternary Tb55TM17.5Al27.5 (TM = Fe, Co, and Ni) MGs without the complexities induced by high-entropy effects were designed. It is found that both the glass transition temperature (Tg) and the initial crystallization temperature (Tx) significantly increase with decreasing 3d electron number. It leads to the low values of Trg, γ, and γm for Tb55Fe17.5Al27.5, which is consistent with its poor glass forming ability (GFA) as evidenced by the obvious lattice fringes and structural order. Despite the mediocre value of magnetic entropy change (|ΔSMpk|) for Tb55Fe17.5Al27.5, its broader magnetic transition temperature of 110.4 K associated with ∼26% evident structural order yields the maximum relative cooling power (RCP) of 546.04 J kg−1 among three MGs. Moreover, a novel weighted method for evaluating 3d electron number by consideration of the concentration and species of TM elements was adopted to reveal an inverse correlation between the 3d electron number and Tg/Tx, as well as curie temperature (Tc), |ΔSMpk|, and RCP. It is found that with the decrease of the weighted 3d electron number of TM elements, the thermal stability of rare-earth-base MGs is effectively enhanced ascribed to the strong f - d orbital hybridization effect, along with the enhanced 3d - 3d exchange interaction that induces a high Tc. This work would help us more deeply understand the role of TM elements from the perspective of electronic structure, which is crucial for designing the novel MGs with a tunable MCE and GFA applied in various cryogenic refrigeration fields.

High temperature ferrimagnetic semiconductors by spin-dependent doping in high temperature antiferromagnets

To realize room temperature ferromagnetic (FM) semiconductors is still a challenge in spintronics. Many antiferromagnetic (AFM) insulators and semiconductors with high Neel temperature TN are obtained in experiments, such as LaFeO3, BiFeO3, etc. High concentrations of magnetic impurities can be doped into these AFM materials, but AFM state with very tiny net magnetic moments was obtained in experiments because the magnetic impurities were equally doped into the spin up and down sublattices of the AFM materials. Here, we propose that the effective magnetic field provided by a FM substrate could guarantee the spin-dependent doping in AFM materials, where the doped magnetic impurities prefer one sublattice of spins, and the ferrimagnetic (FIM) materials are obtained. To demonstrate this proposal, we study the Mn-doped AFM insulator LaFeO3 with FM substrate of Fe metal by the density functional theory (DFT) calculations. It is shown that the doped magnetic Mn impurities prefer to occupy one sublattice of the AFM insulator and introduce large magnetic moments in La(Fe, Mn)O3. For the AFM insulator LaFeO3 with high TN = 740 K, several FIM semiconductors with high Curie temperature TC > 300 K and the band gap less than 2 eV are obtained by DFT calculations when 1/8 or 1/4 Fe atoms in LaFeO3 are replaced by the other 3d, 4d transition metal elements. The large magneto-optical Kerr effect (MOKE) is obtained in these LaFeO3-based FIM semiconductors. In addition, the FIM semiconductors with high TC are also obtained by spin-dependent doping in some other AFM materials with high TN, including BiFeO3, SrTcO3, CaTcO3, etc. Our theoretical results propose a way to obtain high TC FIM semiconductors by spin-dependent doping in high TN AFM insulators and semiconductors.

Finding the best frequency dependent performance of 3d transition metals (Co, Ni, and Mn) substituted nano magnetite for miniaturizing device applications

Ferrite samples with enhanced magneto-dielectric properties are more essential in electromagnetic applications. Therefore, a parent composition of Fe3O4 has been modified by substituting 3d transition metal elements (Co, Ni, Mn) at a single Fe atom using the co-precipitation synthesis method. The structural properties of the synthesized Fe3O4, NiFe2O4, CoFe2O4, and MnFe2O4 samples have been evaluated from the X-ray diffraction patterns. The surface morphology and microstructures of the studied samples were studied by field emission scanning electron microscopy and the average grain size of all the studied samples varied from 60.11 to 106.03 nm. The magneto-dielectric properties were analyzed by frequency dependent permeability (μ) and permittivity (ε) measurements for the range of 100 Hz to 100 MHz. The conduction process for the synthesized ferrites has been noticed from the ac conductivity (σac). The localized relaxation mechanism for the studied ferrites has been observed from the variation of imaginary portion of the electric modulus (M") and the impedance (Z"). Moreover, the mismatch (Z/ηο) between the impedance of the antenna substrates (Z) made of the studied samples and air (ηο) has been evaluated from the permeability and permittivity. Finally, NiFe2O4 has been derived as a suitable ferrite for miniaturizing devices over a frequency range of 10 kHz-6.5 MHz.

Improved Alkaline Hydrogen Evolution Performance of Dealloying Fe75-xCoxSi12.5B12.5 Electrocatalyst.

The electrocatalytic performance of a Fe65Co10Si12.5B12.5 Fe-based compounds toward alkaline hydrogen evolution reaction (HER) is enhanced by dealloying. The dealloying process produced a large number of nanosheets on the surface of NS-Fe65Co10Si12.5B12.5, which greatly increased the specific surface area of the electrode. When the dealloying time is 3 h, the overpotential of NS-Fe65Co10Si12.5B12.5 is only 175.1 mV at 1.0 M KOH and 10 mA cm-2, while under the same conditions, the overpotential of Fe65Co10Si12.5B12.5 is 215 mV, which is reduced. In addition, dealloying treated electrodes also show better HER performance than un-dealloying treated electrodes. With the increase in Co doping amount, the overpotential of the hydrogen evolution reaction decreases, and the hydrogen evolution activity is the best when the addition amount of Co is 10%. This work not only provides a basic understanding of the relationship between surface activity and the dealloying of HER catalysts, but also paves a new way for doping transition metal elements in Fe-based electrocatalysts working in alkaline media.

The effects of refractory elements on the properties of quaternary high entropy carbides—A first-principles and experiment study

In this work, the effects of refractory transition metal elements on the properties of quaternary equimolar ratio high entropy carbides composed of ⅣB, ⅤB and ⅥB transition metals and C element were studied by first-principles calculations and experiments.The calculation results show that all 75 kinds of high entropy carbides were thermodynamically and mechanically stable and can be formed spontaneously. Among them, Hf can promote the synthesis of high entropy carbides, while Cr has the opposite effect. In addition, single phase solid solution structures can be formed for all 73 HECs except (TiZrHfCr)C and (ZrHfVCr)C. Thereafter, the mechanical properties of these 75 quaternary HECs were compared. The calculation results show that W, Mo, and Ta have a positive effect on improving the elastic modulus, fracture toughness, hardness and melting point of high entropy carbides, while Cr has the opposite effect. The calculation results of phonon spectra show that the six high entropy carbides represented by (TiHfNbTa)C, (TiVNbTa)C, (TiZrNbTa)C, (TiZrNbCr)C, (TiZrNbMo)C and (TiZrNbW)C have lattice dynamic stability. (TiHfNbTa)C, (TiVNbTa)C, (TiZrNbTa)C, (TiZrNbMo)C and (TiZrNbW)C face-centered cubic high entropy carbides were prepared by spark plasma sintering and the microstructure and properties were tested. The experimental results are basically consistent with the calculated results.

Computational Screening of Chalcogen-Terminated Inherent Multilayer MXenes and M2AX Precursors.

Sulfur-terminated single sheet (ss-)MXene was recently achieved by delamination of multilayered van der Waals bonded (vdW)-MXenes Nb2CS2 and Ta2CS2 synthesized through solid-state synthesis, rather than via the traditional way of selectively etching A-layers from the corresponding MAX phase. Inspired by this, we perform a computational screening study of vdW-MXenes M2CCh2 isotypical to Nb2CS2 and Ta2CS2, with M = Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Mo, or W and Ch = S, Se, or Te. The thermodynamic stability of each vdW-MXene M2CCh2 is assessed, and the dynamical stability of both vdW- and ss-MXene is considered through phonon dispersions. We predict seven stable vdW-MXenes, out of which four have not been reported previously, and one, V2CSe2, incorporates a new transition metal element into this family of materials. Electronic properties are presented for the vdW- and ss-forms of the stable vdW-MXenes, suggesting that the materials are either metallic, semimetallic, or semiconducting. In previous experimental reports the vdW-MXene Nb2CS2 is synthesized by manipulation of the corresponding M2AX phase Nb2SC. Therefore, we also evaluate the thermodynamic stability of the corresponding M2AX phases, identifying 15 potentially stable phases. Six of these are experimentally reported, leaving nine new M2AX phases for future experimental investigation.

A theoretical study on excited-state dynamical properties and laser cooling of zinc monohydride including spin-orbit couplings.

By means of highly accurate ab initio and dynamical calculations, we identify a suitable laser cooling candidate that contains a transition metal element, namely zinc monohydride (ZnH). The internally contracted multireference configuration interaction method is employed to compute the five lowest-lying Λ-S states of ZnH with the spin-orbit coupling effects included, and very good agreement is obtained between our calculated and experimental spectroscopic data. Our findings show that the position of crossing point of the A2Π and B2Σ+ states of ZnH is above the v' = 2 vibrational level of the A2Π state indicating that the crossings with higher electronic states will have no effect on laser cooling. Hence, we construct a feasible laser-cooling scheme for ZnH using five lasers based on the A2Π1/2 → X2Σ+ 1/2 transition, which features a large vibrational branching ratio R 00 (0.8458), a large number of scattered photons (9.8 × 103) and an extremely short radiative lifetime (64ns). The present work demonstrates the importance of electronic state crossings and spin-orbit couplings in the study of molecular laser cooling.

Cycloadditions of Diazoalkenes with P4 and tBuCP: Access to Diazaphospholes.

Diazoalkenes readily react with tert-butylphosphaalkyne (tBuCP) and white phosphorus (P4) to afford novel phosphorus heterocycles, 3H-1,2,4-diazamonophospholes and 1,2,3,4-diazadiphospholes. Both species represent rare examples of neutral heterophospholes. The mechanism of formation and the electronic structures of these formal (3+2) cycloaddition products were analyzed computationally. The new phospholes form structurally diverse coordination compounds with transition metal and main group elements. Given the growing number of stable diazoalkenes, this work offers a straightforward route to neutral aza(di-)phospholes as a new ligand class.

Cycloadditionen von Diazoalkenen mit P4 und tBuCP: Ein Zugang zu Diazaphospholen

AbstractReaktionen von Diazoalkenen mit tert‐Butylphosphaalkin (tBuCP) und weißem Phosphor (P4) führen zu neuen Phosphorheterocyclen, 3H‐1,2,4‐Diazamonophospholen und 1,2,3,4‐Diazadiphospholen. Die erhaltenen Verbindungen sind seltene Beispiele für neutrale Heterophosphole. Der Bildungsmechanismus der formalen (3+2)‐Cycloadditionsprodukte wurde quantenchemisch berechnet und die elektronischen Strukturen analysiert. Die neuen Phosphole bilden strukturell vielfältige Koordinationsverbindungen mit Übergangsmetallen und Hauptgruppenelementen. Angesichts der wachsenden Anzahl stabiler Diazoalkene bietet diese Arbeit einen unmittelbaren Zugang zu neutralen Aza(di‐)phospholen als neue Ligandenklasse.

A DFT investigation of Ti-substituted [formula omitted] for tailored photovoltaic properties

Transition Metal Chalcogenide Perovskites (TMCP) have been in the spotlight due to their exceptional optoelectronic properties. CaZrS3 is one among them with an experimental bandgap of 1.90 eV. If its bandgap is tuned to lower values, it can be employed in additional photovoltaic applications, such as solar cell absorbers. In this work, the transition metal element Zr in CaZrS3 is substituted with Ti atoms in different proportions and the optoelectronic properties are investigated using Density Functional Theory (DFT). The optoelectronic calculations are all done using the DFT+U method including the spin–orbit coupling. With substitutional alloying, we successfully tuned the energy gap from 1.91 eV to 1.18 eV and the photovoltaic properties were also observed to be modified. For the substituted CaZr1−xTixS3 samples, large birefringence is observed. This indicates enhancement in optical anisotropy via substitutional alloying which is significant in both linear and nonlinear optoelectronic applications like polarizers, wave plates etc.

Investigating interfacial segregation of [formula omitted]/Al in Al–Cu alloys: A comprehensive study using density functional theory and machine learning

Solute segregation at the interface between the aluminum (Al) matrix and the Ω (Al2Cu) phase decreases the interfacial energy, impedes the coarsening of precipitates, and enhances the thermal stability of such precipitates. In this study, we employ density functional theory to systematically calculate solute segregation energies of 42 solute elements at the coherent and semi-coherent interfaces between the two phases, as well as mixing energies of these elements within the Al and Cu sublattices of the Ω phase. Using correlation analysis and machine learning methods, we establish the relationship between the solute segregation energy and 20 selected atomic descriptors. Metalloid and late transition metal elements are predicted as potential candidates for enhancing the thermal stability of Al–Cu alloys. We observe that the solute segregation energy at the interfacial site of the semi-coherent interface correlates with the atomic size of solute atoms and their solubilities within the Ω phase. The developed machine learning models exhibit the potential to predict solute segregation energies at various sites of the coherent and semi-coherent interfaces. Overall, our study provides valuable insights into the stabilizing potential of individual elements at the Ω/Al interface in Al–Cu alloys.

Simple generic self-assembly fabrication of transition metal borates on polyaminophenylboric acid modified foam nickel for highly-efficient overall water splitting

Water electrocatalysis for hydrogen production as a prospect strategy to store renewable energy and reduce carbon emissions has attracted great attention, and exploring water electrolysis catalysts has become a research hotspot for widespread industrial water electrolysis application. Very recently, transition metal borates have been demonstrated great potential for electrocatalytic hydrogen or oxygen evolution in alkaline media. However, a generic method for fabricating transition metal borates as bifunctional oxygen catalysts are still challenging. Herein, through a two-step process including poly-aminophenylboronic acid electrodeposition and subsequent electrostatic self-assembly of transitional metal ions, for the first time, to our best knowledge, a simple and generic approach to fabricate polyaminophenylborate transition metal salt modified nickel foam electrodes (PAB-M/NF, M represents transition metal element) was developed for highly efficient water splitting. As a proof of concept, the obtained PAB-Ru/NF exhibited remarkable bifunctional HER and OER catalytic activities and stability in alkaline medium. To drive the HER and OER with a current density of 10 mA cm−2 in 1 M KOH electrolyte, PAB-Ru/NF only required an overpotential of 14 mV and 301 mV, respectively. Moreover, even at a great current density of 250 mA cm−2, PAB-Ru/NF can exhibit very favorable long-term stability for over 35 h. When assembled into an electrolyzer with PAB-Ru/NF as both the anode and cathode, a current density of 10 mA cm−2 can be achieved at a very low cell voltage of 1.50 V. In addition, the other PAB-M/NF catalysts (M including but not limited to Fe, Co and Ni) prepared by the same way also show excellent bifunctional HER and OER catalytic activities and durability. This study provides a prospective and economically feasible generic approach for developing practical bifunctional catalysts for industrial water electrolysis.

Intrinsic Activity and Ni-O-Fe Catalytic Active Site in Ni-Based (Oxy)Hydroxides for the Oxygen Evolution Reaction

NiFe layered double hydroxides (LDHs) and (oxy)hydroxides are among the most active electrocatalysts for the oxygen evolution reaction (OER) in alkaline electrolytes.1 However, they still show considerable overpotentials for the OER, i.e. 350 mV at 10 mA cm-2 in pH 13.1, 2 Understanding the nature of the catalytic active sites and the catalytic mechanism in NiFe LDHs are key challenges to develop better OER electrocatalysts.In this contribution, atomic-scale details of the catalytic active phase will be presented, showing that NiFe LDHs are oxidized under applied anodic potentials from as-prepared α-phase to activated γ-phase.2 The OER active γ-phase was characterized by operando wide angle X-ray scattering (WAXS) in alkaline electrolytes.2 The intrinsic activity was then obtained by an electrochemical impedance method through electrochemical surface area (ECSA) normalization.3 Comparison with other Ni- and Co- based LDHs revealed that NiFe LDH shows the highest intrinsic activity.4 Our density functional theory (DFT) calculations on a γ-phase atomic model showed that O-bridged Ni-Fe reaction centers (Ni-O-Fe) stabilize OER intermediates that are unfavourable on Ni-O-Ni centers and single Fe sites, fundamentally accounting for the high catalytic activity. Furthermore, our DFT calculations predicts that γ-NiFe LDH is close to, but not on, the top of the OER volcano.2,4 Strategies to modify the catalytic active site to approach the top of the volcano will be presented, together with preliminary experimental results. These strategies will involve the design of active sites involving subsurface metal sites and electronic modulation of the Ni-O-Fe sites by introduction of a third transition metal element. References F. Dionigi and P. Strasser, Advanced Energy Materials, 6, 1600621 (2016).F. Dionigi, Z. Zeng, I. Sinev, T. Merzdorf, S. Deshpande, M. B. Lopez, S. Kunze, I. Zegkinoglou, H. Sarodnik, D. Fan, A. Bergmann, J. Drnec, J. Ferreira de Araujo, M. Gliech, D. Teschner, J. Zhu, W.-X. Li, J. Greeley, B. Roldan Cuenya and P. Strasser, Nat. Commun., 11, 2522 (2020).S.S. Jeon, P.W. Kang, M. Klingenhof, H. Lee, F. Dionigi, P. Strasser, ACS Catal., 13, 1186-1196 (2023).F. Dionigi, J. Zhu, Z. Zeng, T. Merzdorf, H. Sarodnik, M. Gliech, L. Pan, W.-X. Li, J. Greeley, and P. Strasser, Angew. Chemie IE, 60, 14446 – 14457 (2021)

Tuning Oxygen Evolving Catalytic Activity of a Precious Metal-Free Nickel Boride by a Cost-Effective Method

The production of hydrogen (H2) by electrochemical water splitting [Green Hydrogen (Green H2)], if driven by green electricity, has attracted considerable interest as an alternative sustainable energy carrier, e.g., in fuel cells for electricity or power and heat generation [1]. However, the lack of satisfactory and cheap electrocatalysts (ECs) to drive the vital electrochemical reactions of hydrogen evolution (HER) and oxygen evolution (OER) in water splitting is the biggest challenge for this technology.Currently, the most advanced electrocatalysts for the two half-reactions of water electrolysis (HER and OER) are noble metal-based materials [2]. Despite the excellent catalytic properties of these noble metal catalysts, their high cost, and scarcity make their commercial use both uneconomical and impractical in low temperature water electrolysis (LT-WE) systems at industrial scale for green H2 as a clean energy alternative to cheaper fossil fuels[3]. In addition to addressing this issue by the development of precious-material-based with a low-loading of precious metal elements, the development of desirable and high-efficiency electrocatalysts (ECs) based on earth-abundant metal elements materials is paramount. However, their catalytic activity is often limited by poor electron transfer, low conductivity, low stability, and small surface area of these materials. Thus, it is crucial to develop earth-abundant metal elements-based materials that are more cost-effective to reduce the high cost of active catalysts for water electrolysis. Although several low-cost materials have already been designed, the potential required for the practical application of water splitting is still very high compared to the theoretical potential (1.23 V), which means that much energy is consumed, which theoretically could be reduced. Due to their remarkable advanced charge transfer and durability for water oxidation in alkaline media, electrocatalysts derived from metal borides-based materials have received a lot of attention as new high-performance catalysts for water oxidation.[4] These properties stem from the multi-dimensional covalent bonding of the metalloid with the surrounding metal atoms.We present here an approach to tune the OER of transition metal borides (TMBs) using the cost-effective and less energy-consuming method that is nevertheless a highly efficient material for OER (Fig. 1). We have developed a low-cost, rational and easily scalable method to enhance the catalytic activity of nickel boride (Ni–B), which requires an annealing process to optimize the catalytic activity. However, this method may have limited applicability on a large scale as it requires a highly inert environment and high-temperature treatment of Ni–B catalysts. We also elucidate a structure-activity relationship using scale-bridging techniques such as TEM and electrochemical characterization. The developed based on non-noble electrocatalysts are prepared by a simple method of chemical reduction of transition metal elements with boron in aqueous solution. The production is a one-step process and the material does not require any further treatment, yet this material shows comparable activity to the state of the art (precious metal-based materials) for OER in alkaline solution at a selected current density. This improved catalytic performance is further corroborated by the microstructural investigations in the TEM. The nanoparticles obtained have an improved porous structure compared to Ni–B and thus provide more available sites for the surface reactions and hence for the catalytic performance of the material. Furthermore, it is shown that activation enables the morphological and structural changes, while some transition metal elements act as sacrificial elements to provide more accessible and stable sites for oxygen-forming centers. This paves the way for a better understanding of metal boride-derived electrocatalysts for water oxidation, a crucial chemical reaction in water electrolysis and other electrochemical energy technologies. Acknowledgements: This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 945422. We acknowledge the use of the DFG-funded Micro-and Nanoanalytics Facility (MNaF) at the University of Siegen (INST 221/131-1).

(Invited) Extended Hubbard Functionals for Accurate Modeling of Li-Ion Battery Cathode Materials

Designing novel cathode materials for Li-ion batteries necessitates accurate first-principles predictions of their properties. Density-functional theory (DFT) employing standard (semi-)local functionals encounters challenges due to pronounced self-interaction errors within the partially filled d shells of transition-metal (TM) elements. Here, we demonstrate the efficacy of DFT with extended Hubbard functionals in accurately predicting the "digital" change in oxidation states of TM ions for mixed-valence phases at intermediate Li concentrations in phospho-olivine and spinel cathode materials. The resulting voltages exhibit remarkable agreement with experimental data [1,2].Our approach involves the use of onsite U and intersite V Hubbard parameters computed from density-functional perturbation theory with Lowdin-orthogonalized atomic orbitals, thus circumventing empirical factors [3,4]. Notably, the incorporation of intersite Hubbard V interactions proves indispensable for the precise prediction of thermodynamic quantities, particularly when electronic localization occurs amid inter-atomic orbital hybridization.Extending our investigation to vibrational spectroscopy, we calculate Raman spectra for these materials and find very good agreement with available experimental data [5]. Leveraging the robust and accurate computational framework based on extended Hubbard functionals, we embark on a high-throughput screening of Li-containing compounds, aiming to unveil novel and promising candidates for cathodes [6]. Our findings underscore the pivotal role of advanced DFT methodologies in advancing the discovery and design of high-performance battery materials.[1] I. Timrov, F. Aquilante, M. Cococcioni, N. Marzari, PRX Energy 1, 033003 (2022).[2] I. Timrov, M. Kotiuga, N. Marzari, Phys. Chem. Chem. Phys. 25, 9061 (2023).[3] I. Timrov, N. Marzari, M. Cococcioni, Phys. Rev. B 98, 045141 (2021).[4] I. Timrov, N. Marzari, M. Cococcioni, Phys. Rev. B 103, 085127 (2018).[5] L. Bastonero, N. Marzari, I. Timrov, in preparation.[6] C. Malica, L. Bastonero, M. Bercx, N. Marzari, I. Timrov, in preparation.

Electronic Structure Investigation of BSCF Catalysts during Electrochemical Water Electrolysis by Using Time Zero Analysis and Advanced Operando X-Ray Absorption Spectroscopy

The rapid increase in global energy demands and environmental awareness regarding the excessive use of fossil fuel has spurred significant academic interest in the development of alternative energy conversion and storage technologies that prioritize both efficiency and environmental sustainability. Among all kinds of renewable energy, hydrogen energy holds the potential to create a carbon free clean society, and a possible solution to the environmental issues.1 Electrochemical water splitting is considered as a greener approach for pure H2, which involved cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER). The anodic OER is kinetically sluggish and considered as a rate determining step of the water splitting reaction. Therefore, it is necessary to develop OER catalysts with high activities.Perovskite oxides knows as a promising oxygen electrode catalyst due to their low cost, flexibility, and tailorable properties. However, most perovskite oxides possess poor electrical conductivity at room temperatures, and this limits their oxygen catalytic activity. In our work Ba0.5Sr0.5CoxFe1-xO3-δ (BSCF) catalysts with different cobalt and iron amounts where X=0, 0.2, 0.8, 1 were synthesized and investigated by time zero analysis and flow rate infinitization analysis which are electrochemical testing method that uses pressure to remove generated oxygen gas bubbles and provides accurate activity of the catalyst.2We find the volcano plot of the Fe amount and the OER activities, showing samples with X=0.8 have the best OER activities as Figure 1. Electronic structure of B-Site transition metal elements, oxygen vacancies, crystal structures and electrical conductivity are the key factors for determining the activities of Perovskite catalysts in OER.3Also it is quite important to determine the real active sites during the OER process by using advance operando techniques.Therefore, in order to investigate the in-depth mechanism of OER activities of Perovskite catalysts, the newly designed operando soft X-ray Absorption Spectroscopy (XAS) cells was utilized to analyze the subtle change as shown in Figure 2 on the oxygen K-edge (531 eV - 532 eV). Ba0.5Sr0.5Co0.8Fe0.2O3-δ has the most obvious changes in integral surface area at the O K-edge pre-edge region, which leads to the best activity among other BSCF samples. According to the Energy Dispersive X-ray Spectroscopy and Lattice Oxygen Evolution Mechanism, ions on the A sites (Ba2+,Sr2+) tend to dissolve and ions on the B sites (Co, Fe) are forming hydroxides (BOOH).Keywords: oxygen evolution reaction, BSCF catalysts, Time zero analysis, operando X-ray absorption spectroscopy Acknowledgements This work is based on results obtained from a project (JPNP14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO) of Japan. Reference: (1) Rose, P. K.; Neumann, F. Hydrogen refueling station networks for heavy-duty vehicles in future power systems. Transportation Research Part D: Transport and Environment 2020, 83, 102358.(2) Nagasawa, K.; Matsuura, I.; Kuroda, Y.; Mitsushima, S. A Novel Evaluation Method of Powder Electrocatalyst for Gas Evolution Reaction. Electrochemistry 2022, 90 (1), 017012-017012.(3) Zhu, Y.; Zhou, W.; Shao, Z. Perovskite/carbon composites: applications in oxygen electrocatalysis. Small 2017, 13 (12), 1603793. Figure 1

High-Valence Ion Doped Compositionally Partitioned Li[Ni0.78Co0.10Mn0.12]O2 Cathode for Advanced Lithium-Ion Batteries

Numerous approaches have been employed to reduce the intrinsic instability of Ni-rich cathodes. Among them, the introduction of concentration gradient (CG), i.e., a strategy to protect the labile Ni-enriched compartment with a chemically protective Mn-rich shell, has proven successful in commercial applications.1 However, because the segmentation of transition metal (TM) constituents and the formation of unique geometric configurations are characteristics inherited from the CG hydroxide precursor; it is crucial to select the optimal calcination temperature and precisely control it.2 Excessive thermal energy input can result in concentration planarization because the CG of the hydroxide precursor is intrinsically susceptible to the interdiffusion of TM elements during lithiation. Moreover, the immoderate coarsening of the primary particles can eliminate the advantageous features of the CG design by producing equiaxed primary particles.2 In this study, we propose a strategy that can effectively ameliorate the deterioration of Ni-rich CG cathodes resulting from excessive thermal energy input and remarkably improve their electrochemical cycling performance. It was revealed that a trace amount of tungsten incorporation during the cathode calcination can effectively mitigate the high-temperature-induced cathode degeneration and maintain outstanding product quality over a wide range of temperatures. Thus, the proposed strategy opens new avenues for the facile synthesis of long-life Ni-rich CG cathodes. Reference s : [1] Y.-K. Sun, S.-T. Myung, B.-C. Park, J. Prakash, I. Belharouak, K. Amine, Nat. Mater. 8 (2009) 320-324.[2] G.-T. Park, H.-H. Ryu, T.-C. Noh, G.-C. Kang, Y.-K. Sun, Mater. Today 52 (2022) 9-18.

The impact of Ru and Gd dopants on the dielectric and conductive properties of NiO nanoparticles: A comparative study

This comparative study investigates the difference between the transition metal (Ru) and rare earth element (Gd) as dopants in NiO nanoparticles, to unveil their suitability in various applications. Pure, Ru- and Gd-doped NiO nanoparticles have been synthesized by the chemical co-precipitation method, in the presence of polyvinylpyrrolidone, as a capping agent. The EDX pattern revealed the purity, the un-stoichiometric nature of the synthesized nanoparticles, and the influence of the Ru- and Gd-dopants in generating advantageous structural imperfections, including oxygen and nickel vacancies. The dielectric and conductivity measurements have provided valuable insights into the electrical behavior of Ru- and Gd-doped NiO nanoparticles. The influence of the Ru- and Gd-dopants on the Debye model, universal dielectric model, and relaxation mechanism was implemented. The dielectric constant was affected by the dopants, where the Ru-dopants reduced it by a factor of 0.24, however, the Gd-dopants boosted it by a factor of 4. Moreover, the opposing influence of the Ru- and Gd-dopants on the nickel vacancies has tuned the ac conductivity of the NiO lattice, where it was reduced by 75 % with Ru-dopants due to the suppressed nickel vacancies and enhanced by 70 % with the Gd-dopants due to the augmented nickel vacancies. The dc conductivity was examined at ranging temperatures to explore the conduction mechanism and the effect of the dopants. The multi-functional ability of the pure, Ru- and Gd-doped NiO nanoparticles was tested by studying the complex power and temperature coefficient of resistance (TCR), from which the dominating capacitive and resistive nature is identified for the samples. Besides, NiO nanoparticles have attained a maximum TCR value of −10.41 %, rendering it a superior material for bolometric devices, even better than the used conventional materials. The studied dielectric and conductive properties unveiled the potential applicability of the samples in microelectronics, storage capacitor applications, and bolometric devices.

Electrochemical Behaviors and Doping Rules of NaRhO2 Cathode Materials for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) have great advantages for energy storage and conversion due to their low cost and large storage capacity. Currently, NaRhO2 is used as an electrode material for sodium-ion batteries. Doping first- and second-row transition metals has been carried out to comprehensively assess NaRhO2 as a cathode material. The geometric and electronic structures and electrochemical and doping behaviors of NaRhO2 cathode materials for SIBs have been investigated using density functional theory calculations. The results show that the bond lengths of Rh-O in NaRhO2 decrease during sodium deintercalation. The band gap of NaRhO2 with sodium extraction gradually reduces. The density of states of NaxRhO2 shows that the interaction between the Rh-4d and O-2p orbitals increases and the orbitals shift toward the right. The average intercalation voltage of NaxRhO2 cathode material increased from 2.7 to 3.9 eV. After doping with first- and second-row transition metal elements from Sc to Zn and Y to Cd, the changes in the band gaps of the doped NaRhO2 materials exhibit a W-type rule. In contrast, their magnetic moments show a reverse W-type rule. These findings on the pristine and doped NaRhO2 can provide theoretical guidance for the preparation of novel electrode materials suitable for sodium-ion batteries.

Alternating spin splitting of electronic and magnon bands in two-dimensional altermagnetic materials

Abstract Unconventional antiferromagnetism dubbed as altermagnetism was firstly discovered in rutile structured magnets, which is featured by spin splitting even without the spin-orbit coupling effect. This interesting phenomenon has led to the discovery of more altermagnetic materials. In this work, we explore two-dimensional altermagnetic materials by studying two series of two-dimensional magnets, including MF4 with M covering all 3d and 4d transition metal elements, as well as TS2 with T = V, Cr, Mn, Fe. Through the magnetic symmetry operation of the RuF4 and MnS2, it was verified that breaking the time inversion is a necessary condition for spin splitting. Based on symmetry analysis and first-principles calculations, we found that the electronic bands and magnon dispersion experience alternating spin splitting along the same path. This work paves the way for exploring altermagnetism in two-dimensional materials.