Composition-structure Relationship Research Articles

Exploring a Facile Synthetic Procedure of Iron-Based Platinum Group Metal-Free Electrocatalyst for Polymer Electrolyte Fuel Cells

The transportation sector, mainly powered by fossil fuels, is responsible for approximately 14% of all greenhouse gas emissions1. Polymer electrolyte fuel cells (PEFCs) are promising candidates for sustainable transport as they only emit water, can be refilled fast, and enable long ranges with a single refill. Their current costs and dependence on scarce materials challenge their broad implementation in heavy-duty vehicles and maritime transportation 2. Another challenge is the catalyst degradation during operation, therefore the goal of at least 35,000 lifetime hours for heavy-duty transportation is ambitious as existing fuel cell vehicles have been engineered for ca. 5,000 hours3. The state-of-the-art catalyst layers are based on platinum nanoparticles supported on carbon and global efforts have been made to develop high-activity catalysts with reduced platinum contents, including platinum alloys such as Pt-Ni4 and Pt-Co5, alternative supports such as nanotubes6, or a combination aforementioned methods. While platinum-based materials remain the most active for the oxygen reduction reaction, their elevated cost and instability during operation motivate the exploration of alternative materials.Platinum group metal (PGM)-free catalysts have gained prominence in the PEFCs field, where Fe-N-C based catalysts have shown high oxygen reduction reaction activity in acidic media7, approaching that of platinum-based catalyst layers, yet their practical application is hindered by insufficient stability under operating conditions8. Inspired by recent efforts7,8, our goal is to develop stable, active, and low-cost catalyst layers using earth-abundant materials. In this poster presentation, I will discuss my efforts in the synthesis of Fe-N-C catalysts by the incorporation of iron in a calcinated nitrogen-doped zeolitic imidazolate framework (ZIF). ZIFs are excellent supports due to their high porosity of approximately 60% and a surface area of 1600 m2/g, leading to a high density of active sites9. After the incorporation of iron, post-treatments are applied including leaching and the utilization of secondary nitrogen precursors, where efforts are made to develop non-hazardous activation approaches. The incorporation of secondary nitrogen precursors such as cyanamide have been shown to promote the formation of metal-N-C bonds and increase the performance towards the oxygen reduction reaction10,11. We employ microscopic, spectroscopic and electrochemical techniques, such as the rotating disc electrode, to correlate the catalyst composition with electrochemical performance and durability. With this work, we hope to gain an understanding of composition-structure relationships to enhance the performance of iron-based platinum-free catalysts for PEFCs. Acknowledgements SH2IPDRIVE has received funding from the Ministry of Economic Affairs and Climate Policy, RDM regulation, carried out by the Netherlands Enterprise Agency. References W.F. Lamb et al., 2021, Environmental Research Letters vol. 16.S.T. Thompson et al., 2018, Solid State Ion 319, 68–76.D.A. Cullen et al., 2021, Nature Energy vol. 6 462–474.S.I. Choi et al., 2013, Nano letters 13(7), 3420-3425.P.R. Kumar et al., 2018, Surfaces and Interfaces 12,116-123.D. Schonvogel et al., 2017, Journal of the Electrochemical Society 164(9), F995.A. Mehmood et al., 2022, Nature Catalysis 5(4), 311-323.X. Wan, and J. Shui, 2022, ACS Energy Letters 7(5), 1696-1705.J.C.Tan et al, 2010, Proceedings of the National Academy of Sciences 107(22), 9938-9943.X. Wu et al., 2022, Journal of The Electrochemical Society 169.1, 016507.N.D. Leonard et al., 2018, ACS Catalysis 8(3), 1640-1647.

Ultralow-Overpotential Acidic Oxygen Evolution Reaction Over Bismuth Telluride-Carbon Nanotube Heterostructure with Organic Framework.

The state-of-the-art iridium and ruthenium oxides-based materials are best known for high efficiency and stability in acidic oxygen evolution reaction (OER). However, the development of economically feasible catalysts for water-splitting technologies is challenging by the requirements of low overpotential, high stability, and resistance of catalysts to dissolution during the acidic oxygen evolution reaction . Herein, an organometallic core-shell heterostructure composed of a carbon nanotube core (CNT) and bismuth telluride (Bi2Te3) shell (denoted as nC-Bi2Te3) is designed and use it as a catalyst for the acidic OER. The proposed catalyst achieves an ultralow overpotential of 160mV at 10mAcm-2 (geometrical), thereby outperforming most of the state-of-the-art precious-metal-based catalysts. The low Tafel slope of 30mVdec-1 and charge transfer resistance (RCT)of 1.5Ω demonstrate its excellent electrocatalytic activity. The morphological and chemical compositions of nC-Bi2Te3 enable the generation of ─OH functional group in the Bi─Te sections formed via a ligand support, which enhances the absorption capacity of H+ ions and increases the intrinsic catalytic activity. The presented insights regarding the material composition-structure relationship can help expand the application scope of high-performance catalysts.

CoFeNiTix and CrFeNiTix high entropy alloy thin films microstructure formation

High entropy alloys (HEA) composition-structure relationships are crucial for guiding their design and applications. Here, we use a combined experimental and molecular dynamics (MD) approach to investigate phase formation during physical vapor deposition (PVD) of CoFeNiTix and CrFeNiTix HEA thin films. We vary titanium molar ratio from 0 to 1 to understand the role of a larger element in the alloy mixture. The experiments show that a high titanium content favors amorphous phase formation in the samples produced by magnetron co-sputtering. In contrast, a low titanium content results in the formation of a face-centered cubic (FCC) structure in both HEA families. This effect of titanium content on the stability of the amorphous and FCC phases is reproduced in PVD MD simulations. The threshold titanium molar ratio is identified to be ∼0.53 and ∼0.16 for the CoFeNiTix and CrFeNiTix films in the experiments, and ∼0.53 and ∼0.53 in the MD simulations. In addition, the atomistic modeling allows for energy versus volume calculations with increasing titanium content, which demonstrate the stabilization of the amorphous phase with respect to crystalline structures. To isolate the effect of atomic sizes, additional simulations are performed using an average-atom model, which disregards differences in atomic radii while preserving the average properties of the alloy. In these simulations, the energetic stability of the amorphous phase disappears. The combined experimental and simulation results demonstrate that the formation of the amorphous phase in HEA thin films generated by PVD is directly caused by the atomic size difference.

Insight into the medium-long-medium structured lipids made from Camellia oil: Composition-structure relationship.

Medium-long-medium (MLM) structured lipid (SL) as a new SL is a potential functional ingredient in food and nutraceutical products, but its composition-structure-physicochemical properties relationship has not been revealed in food industry. MLM type of medium-long chain triacylglycerol (MLCT) was synthesized from Camellia oil by combi-lipase; its physicochemical properties and composition-structure relationship were investigated in this research. The higher MLCT (67.24%±0.09) and MLM (52.71%±0.53) productivities were achieved after parameter optimization. The physicochemical characterization of SLs exhibited mild thermal property, intermediate Fourier transform infrared spectroscopy absorption intensity, and better crystal morphology. Joint characterizations identified that MLM and long-medium-long type SL were rich in 1,3-dioctanoyl-2-linoleoyl glyceride (CaLCa), 1,3-dioctanoyl-2-oleoyl glyceride (CaOCa), 1,3-dilinoleoyl-2-octanoyl glyceride (LCaL), and 1,3-dilinoleoyl-2-decanoyl glyceride (LCL) components, respectively. This is ascribed to the higher proportion of caprylic and linoleic acid in 1,3-specific enzyme. The 3D structural analysis further demonstrated that the CaLCa, CaOCa, LCaL, and LCL molecules had lower steric energy to form symmetrical structure at 1,3-position. This research provides a practical method to produce MLM-type SL from edible oils and fats in food industry.

Toward Understanding the Composition–Structure Relationship of Hybrid Organic Lead Iodide Compounds: Impact from Secondary Structures of Organic Cations

Toward Understanding the Composition–Structure Relationship of Hybrid Organic Lead Iodide Compounds: Impact from Secondary Structures of Organic Cations

CALPHAD-Based Modelling of the Temperature–Composition–Structure Relationship during Physical Vapor Deposition of Mg-Ca Thin Films

The temperature-dependent composition and phase formation during the physical vapor deposition (PVD) of Mg-Ca thin films is modeled using a CALPHAD-based approach. Considering the Mg and Ca sublimation fluxes calculated based on the vapor pressure obtained by employing thermochemical equilibrium calculations, the experimentally observed synthesis-temperature trends in the thin-film composition and phase formation were reproduced. The model is a significant step towards understanding how synthesis parameters control composition and, therefore, phase formation in the PVD of metals with high vapor pressures.

Crystal Structure and Bond-Valence Investigation of Nitrogen-Stabilized LiAl5O8 Spinels.

An in-depth insight into the effect of nitrogen substitution on structural stabilization is important for the design of new spinel-type oxynitride materials with tailored properties. In this work, the crystal structures of ordered and disordered LiAl5O8 obtained by slow cooling and rapid quenching, respectively, were analyzed by a X-ray diffraction (XRD) Rietveld refinement and OccQP program. The variation in the bonding state of atoms in the two compounds was explored by the bond valence model, which revealed that the instability of spinel-type LiAl5O8 crystal structure at room temperature is mainly due to the severe under-bonding of the tetrahedrally coordinated Al cations. With the partial substitution of oxygen with nitrogen in LiAl5O8, a series of the nitrogen-stabilized spinel LiyAl(16+x-y)/3O8-xNx (0 < x < 0.5, 0 < y < 1) was successfully prepared. The crystal structures were systematically investigated by the powder XRD structural refinement combined with 7Li and 27Al magic-angle spinning nuclear magnetic resonance. All the Li+ ions entered the octahedra, while the Al resonances may be composed of multiple non-equivalent Al sites. The structural stability of spinel LiyAl(16+x-y)/3O8-xNx at ambient temperature was attributed to the cationic vacancies and high valence generated by the N ions, which alleviated the under-bonding state of the tetrahedral Al-O bond. This work provides a new perspective for understanding the composition-structure relationship in spinel compounds with multiple disorders.

Hollow platinum-gold and palladium-gold nanoparticles: synthesis and characterization of composition-structure relationship

Hollow palladium-gold (PdAu) and platinum-gold (PtAu) alloy nanoparticles (NPs) were synthesized through galvanic replacement reactions. PdAu NPs denoted PdAu-99.99 and PdAu-98 were produced using palladium precursors with different purity degree: Na2PdCl4 ≥ 99.99% and Na2PdCl4 98%, respectively. The effect of the addition time of the gold palladium precursor solution on the size of the generated NPs was evaluated. Two types of particles, with a rough and a smooth surface, were identified in the suspensions of PtAu and PdAu NPs by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM). The atomic percentage of gold, platinum, palladium, and cobalt (atomic %) in the nanoparticles was determined by energy dispersive X-ray spectroscopy (EDX). PtAu NPs (26–42 nm) contain Pt (41 at%), Au (36 at%), and Co (23 at%). Two groups of hollow palladium gold NPs (30–50 nm) with a different residual cobalt content were produced. PdAu-99.99 NPs consisted of Pd (68 at%), Au (26 at%), and Co (6 at%), whereas PdAu-98 NPs were composed of Pd (70 at%), Au (22 at%), and Co (8 at%). The hollow structure of the NPs was confirmed by EDX line scanning. Selected area electron diffraction analysis (SAED) revealed the formation of PtAu and PdAu alloys and it was used in estimating the lattice parameters, too.

Physics in the Machine: Integrating Physical Knowledge in Autonomous Phase-Mapping

Application of artificial intelligence (AI), and more specifically machine learning, to the physical sciences has expanded significantly over the past decades. In particular, science-informed AI, also known as scientific AI or inductive bias AI, has grown from a focus on data analysis to now controlling experiment design, simulation, execution and analysis in closed-loop autonomous systems. The CAMEO (closed-loop autonomous materials exploration and optimization) algorithm employs scientific AI to address two tasks: learning a material system’s composition-structure relationship and identifying materials compositions with optimal functional properties. By integrating these, accelerated materials screening across compositional phase diagrams was demonstrated, resulting in the discovery of a best-in-class phase change memory material. Key to this success is the ability to guide subsequent measurements to maximize knowledge of the composition-structure relationship, or phase map. In this work we investigate the benefits of incorporating varying levels of prior physical knowledge into CAMEO’s autonomous phase-mapping. This includes the use of ab-initio phase boundary data from the AFLOW repositories, which has been shown to optimize CAMEO’s search when used as a prior.

Composition-Structure Relationship for the Skeletal-Dendritic Ferrospheres Isolated from Fly Ash formed in Combustion of Pulverized Ekibastuz Coal

Composition-Structure Relationship for the Skeletal-Dendritic Ferrospheres Isolated from Fly Ash formed in Combustion of Pulverized Ekibastuz Coal

Composition-Structure Relationship for the Skeletal-Dendritic Ferrospheres Isolated from Fly Ash formed in Combustion of Pulverized Ekibastuz Coal

Composition-Structure Relationship for the Skeletal-Dendritic Ferrospheres Isolated from Fly Ash formed in Combustion of Pulverized Ekibastuz Coal

Statistical mechanical model for the formation of octahedral silicon in phosphosilicate glasses

AbstractUnlike ambient pressure silicate glasses, some phosphosilicate glasses contain sixfold‐coordinated silicon (Si6) units even when prepared at ambient pressure. The variation in the fraction of Si6 with composition remains a topic of interest, both for technological applications of phosphosilicate glasses and for fundamental understanding of the glass structure. In this work, we use statistical mechanical modeling to predict the composition–structure relationships in Na2O–P2O5–SiO2 and CaO–P2O5–SiO2 glasses. This is achieved by accounting for the enthalpic and entropic contributions to the interactions between each pairwise modifier ion and structural unit. The initial enthalpy parameters are obtained based on experimental structural data for binary Na2O–SiO2, CaO–SiO2, Na2O–P2O5, and CaO–P2O5 glasses, which can then be transferred to predict the structure of mixed former glasses. This approach has previously been used to predict the short‐range structure of borosilicate and aluminoborate glass systems. However, here we show that the formation of Si6 must be specifically included to make accurate predictions of the composition–structure relationships in phosphosilicate glasses. After incorporating the formation mechanism of Si6 in the statistical mechanics model, we find an excellent agreement between model predictions and experimental structure data for Na2O–P2O5–SiO2 and CaO–P2O5–SiO2 glasses.

Influence of Magnesium on the Structure of Complex Multicomponent Silicates: Insights from Molecular Simulations and Neutron Scattering Experiments.

A series of multicomponent glasses containing up to five oxides are studied using classical molecular dynamics simulations and neutron scattering experiments. The focus is on the role of magnesium in determining the structural properties of these glasses and the possible mixed effect during a sodium/magnesium substitution. Calculated structure functions (pair correlation function and structure factor) rather accurately reproduce their experimental counterpart, and we show that more fine structural features are qualitatively reproduced well, despite some discrepancies in the preferential spatial distribution between sodium and magnesium to aluminum and boron, as well as the nonbridging oxygen, distribution. The simulated systems offer a solid basis to support previous experimental findings on the composition-structure relationship, allowing for further analysis and property calculation. It is confirmed that the substitution of sodium by magnesium leads to the decrease of four-fold boron and a modification of the alkali coordinations with a significant change of the network structure. Specifically, magnesium coordination extracted from numerical simulations highlights a potential dissociation from penta- to tetra- and hexahedral units with increasing MgO contents along the glass series, which could not be resolved experimentally.

Composition-Structure Relationship and Routes of Formation of Blocklike Ferrospheres Produced by Pulverized Combustion of Two Coal Types.

The composition–structure relationship of blocklike ferrospheres (FSs) isolated from fly ash produced during the combustion of two different types of coal was studied systematically by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. Monoblock globules were shown to consist of large sintered crystallites of Mg, Mn ferrospinel, which are formed from excluded siderite particles containing isomorphic impurities of magnesium and manganese carbonates. The common groups of globules for which the gross composition of polished sections corresponds to the general equations for the relationship of the concentrations SiO2 = f(Al2O3) and CaO = f(SiO2) were highlighted from FSs of two series. These globules are formed during the thermochemical transformation of associates of siderite, quartz, calcite, and anorthite, which have a silicate modulus of SiO2/Al2O3 equal to 1.18, which corresponds to the coefficients in the general equations of the relationship SiO2 = f(Al2O3). SEM analysis of polished cross-sections of the globules of selected FS groups demonstrates that the crystallite size of ferrospinel decreases, while the content of the glass phase increases with the declining FeO concentration in individual globules. The crystallite size and shape are found to depend on the size of the local melt area where the concentration of spinel-forming oxides is >85 wt %. The observed increase in the glass-phase content is attributed to the broadening of the liquation zone in the FeO–Fe2O3–SiO2 system as the oxidative potential increases and to the higher content of [Fe3+O2]− and [Fe3+2O5]4– ferrite complexes in calcium-rich melts.

Exotic structural motifs in aluminosilicate glasses quantified by solid-state NMR and molecular dynamics simulations

Conventional structural models of aluminosilicate (AS) glasses assume that there are no direct bonds between four-coordinated Al (Al[4]) species and non-bridging oxygen (NBO) anions, along with the (near) absence of Al[4]–O–Al[4] linkages (the “Loewenstein Al avoidance rule”). Yet, accumulating evidence from advanced solid-state NMR experiments on AS glasses that incorporate (moderately) high field-strength cations, notably so those of rare-earth metals (RE3+), reveal significant Al[4]–NBO and Al[4]–O–Al[4] populations. Here we review such NMR experimentation that enable a direct probing of these “exotic” structural motifs. We also re-analyze and discuss previously presented experimental and modeling results of a large set of RE2O3–Al2O3–SiO2 glasses with RE={La, Y, Lu, Sc}, where the structure/composition-related parameters that dictate the degrees of Al[4]–NBO and Al[4]–O–Al[4] bonding in AS glasses are identified, leading to new quantitative composition–structure relationships. Moreover, for a given AS composition, criteria are presented for whenever Al[4]–O–Al[4] linkages must exit in its glass structure.

Balancing Cost and Accuracy in Quantum Mechanical Simulations on Collagen Protein Models.

Collagen proteins are spread in almost every vertebrate's tissue with mechanical function. The defining feature of this fundamental family of proteins is its well-known collagen triple-helical domain. This helical domain can have different geometries, varying in helical elongation and interstrands contact, as a function of the amino acidic composition. The helical geometrical features play an important role in the interaction of the collagen protein with cell receptors, but for the vast majority of collagen compositions, these geometrical features are unknown. Quantum mechanical (QM) simulations based on the density functional theory (DFT) provide a robust approach to characterize the scenario on the collagen composition-structure relationships. In this work, we analyze the role of the adopted computational method in predicting the collagen structure for two purposes. First, we look for a cost-effective computational approach to apply to a large-scale composition-structure analysis. Second, we attempt to assess the robustness of the predictions by varying the QM methods. Therefore, we have run geometry optimization on periodic models of the collagen protein using a variety of approaches based on the most commonly used DFT functionals (PBE, HSE06, and B3LYP) with and without dispersion correction (D3ABC). We have coupled these methods with several different basis sets, looking for the highest accuracy/cost ratio. Furthermore, we have studied the performance of the composite HF-3c method and the semiempirical GFN1-xTB method. Our results identify a computational recipe that is potentially capable of predicting collagen structural features in line with DFT simulations, with orders of magnitude reduced computational cost, encouraging further investigations on the topic.

Structural Study of MgyAl(8+x-2y)/3O4-xNx (0 < x < 0.5, 0 < y < 1) Spinel Probed by X-ray Diffraction, 27Al MAS NMR, and First-Principles Calculations.

The deep understanding of the crystal structure and composition-structure relationship is important for modifying and designing solids to obtain functional materials with customized properties. However, because of multiple compositions and complex structures in some spinel solid solutions, the composition-structure relationship is unknown, or becomes very complicated and difficult to be controlled. In this work, the solid-state magic-angle spinning nuclear magnetic resonance (MAS NMR) technique and powder X-ray diffraction (XRD) Rietveld refinement were combined to characterize the crystal structure of quaternary disordered MgyAl(8+x-2y)/3O4-xNx solid solutions in detail, which was supported by the first-principles density functional theory calculations. Diffraction data indicate that Mg ions preferentially enter the tetrahedron structure in MgyAl(8+x-2y)/3O4-xNx solid solutions because the sum of the bond valence in tetrahedron is closer to the atomic valence of Mg. With the compositional change, the coordination polyhedra in the crystal structure will also adjust the volume according to the changes in lattice parameter, anion parameter, and inversion parameter. In addition, the populations, chemical shifts, and quadrupole coupling constants of Al located in different coordinated environments of the solid solutions were detected through the simulation and integration of 27Al MAS NMR spectra, which were related to the structural parameters by the bond valence method. It turns out that 27Al MAS NMR parameters are highly sensitive to the subtle changes in the local environment of Al caused by the preferential occupation of Mg in the tetrahedron. These results provide deep insights into the crystal structural details of novel spinel materials with multiple disorders.

Mixed Alkali Effect in Silicate Glass Structure: Viewpoint of 29Si Nuclear Magnetic Resonance and Statistical Mechanics

The mixed alkali effect in glasses is the deviation from linear property changes when alkali cations are mixed. The extent of this effect and its structural origin remain topics of interest. In this work, we use a statistical mechanics approach to predict the composition-structure relationship in mixed modifier Na2O-K2O-SiO2 glasses. This is achieved by accounting for the enthalpy between each pairwise alkali ion and silicate unit interaction. The initial enthalpy parameters are obtained based on experimental structural data for binary Na2O-SiO2 and K2O-SiO2 glasses, which can be transferred to predict the short-range order structure of mixed modifier glasses without additional free parameters. To this end, we have performed 29Si magic angle spinning NMR spectroscopy measurements on y(xNa2O-(1 - x)K2O)-(100 - y)SiO2 glasses with x = 0, 0.25, 0.5, 0.75, and 1 and y = 34, 42, and 50. Good agreement between experimental data and model predictions are observed. Finally, we use this information to discuss the relative entropic and enthalpic contributions to the mixed modifier effect in silicate glass structure.

Predicting Cation Interactions in Alkali Aluminoborate Glasses using Statistical Mechanics

• We use a statistical mechanics model to predict network former speciation in alkali aluminoborate glasses. • Different structural assumptions regarding the role of aluminum species are considered. • The model is trained on experimental data for sodium aluminoborate glasses. • The model is validated on experimental data for lithium and caesium aluminoborate glasses. In this work, we attempt to predict the composition-structure relationship in alkali aluminoborate glasses by using a recent statistical mechanics-based model that has previously been applied to predict the structure of binary modifier-former and ternary modifier-former-former oxide glasses. However, the structure of glasses with network intermediates such as Al 2 O 3 has not yet been predicted with this approach. We thus extend the statistical mechanics-based model to predict composition-structure relations in Na 2 O-Al 2 O 3 -B 2 O 3 glasses with different structural assumptions regarding the role of high-coordinated aluminum species. This ternary glass system was chosen since its structure has been thoroughly investigated in literature and is thus the best system for training the statistical mechanics-based model. To test and validate the model parameters established in the Na 2 O-Al 2 O 3 -B 2 O 3 glass system, we accurately predict the structural speciation in Cs 2 O-Al 2 O 3 -B 2 O 3 and Li 2 O-Al 2 O 3 -B 2 O 3 glasses with the same parameters for Al-B interactions.

Boron Carbide Secrets

The issues of the composition-structure relationship of boron carbide are discussed. A new hypothesis based on the presence of channels with a diameter of 2.7–2.9 A in crystals, into which C or B atoms can be intruded, has been proposed. The intrusion has been confirmed by the data of quantum-chemical simulation using VASP program. It has been shown that the introduction of atoms into the channels changes the cell parameters and deforms the structural fragments. The latter may cause the formation of monoclinic crystals of boron carbide. According to the quantum chemical simulattions, the cell parameters of boron carbide crystals of the same composition depend on the site of intrusion of the C atoms into the channels.