Oxide Solid Solutions Research Articles

Highly Durable Rh Single Atom Catalyst Modulated by Surface Defects on Fe-Ce Oxide Solid Solution.

Forming defect sites on catalyst supports and immobilizing precious metal atoms at these sites offers an efficient approach for preparing single-atom catalysts. In this study, we employed an Fe-Ce oxide solid solution (FC), which has surface oxygen that reduces more readily than that of ceria, to anchor Rh single atoms (Rh1). When utilized in the selective catalytic reduction of NO with CO (CO-SCR), Rh1/FC reduced at 500 °C-characterized by less oxidic Rh state induced by an oxygen-deficient coordination-exhibited superior activity and durability compared to Rh1/ceria and Rh1/FC reduced at 300 °C. This Rh single-atom structure was sustained after 100 hours of CO-SCR at 400 °C. Reaction intermediates formed on the catalyst surface were analyzed using in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) under NO and CO flow conditions. Additionally, the catalyst structure and the CO-SCR reaction mechanism were investigated using density functional theory (DFT). While Rh atoms located near surface Fe sites were found to be thermodynamically most stable, both NO and CO preferentially adsorbed on Rh sites. Fe plays a role in stabilizing Rh sites and facilitating oxygen transfer. This work provides valuable insights into the design of highly active and durable single-atom catalysts.

Design Strategies for High Voltage Spinel Cathode Materials to Enable Reversible Mg-Ion Intercalation

Reversible insertion of Mg2+ into metal oxide frameworks stands as a critical factor for facilitating the operation of a Mg-ion battery boasting high energy density, imperative for advancing energy storage technologies. While functional Mg-ion batteries have been achieved in frameworks featuring soft anions like S2– and Se2–, they fall short of meeting the energy density benchmarks to rival current rechargeable lithium-ion batteries due to their low insertion potentials. This underscores the need to pinpoint an oxide-based cathode capable of operating at elevated potentials. A leading theory posits that the limited availability of oxide Mg-ion cathodes stems from the sluggish diffusion kinetics of Mg2+ in oxides, attributed to robust electrostatic interactions between Mg2+ ions and oxide anions within the lattice. Consequently, it is hypothesized that rectifying these kinetic shortcomings could be achieved by tailoring an oxide framework to foster less stable Mg2+–O2– coordination.Drawing upon theoretical computations and preliminary experimental findings, oxide spinels emerge as promising candidates for cathodes, possessing storage capacity, insertion potential, and cation mobility that align with the requisites for a secondary Mg-ion battery. However, spinels featuring a single redox metal, such as MgCr2O4 or MgMn2O4, failed to exhibit adequately reversible Mg-ion intercalation at high redox potentials when paired with nonaqueous Mg-electrolytes. Consequently, a concerted effort in materials development was launched to conceive, synthesize, and assess a novel class of solid-solution oxide spinels designed to fulfill the requisite properties for a sustainable Mg-ion cathode. These materials were engineered by combining electrochemically active metals boasting stable redox potentials and charged states vis-a-vis the electrolyte, such as Mn3+, alongside a structural stabilization component, typically Cr3+. Additionally, common spinel structural defects known to compromise performance, such as antisite inversion, were managed to explore the relationship between structures and electrochemical overpotentials, thereby regulating overall hysteresis. Comprehensive structural characterization, encompassing both short- and long-range analyses in both ex-situ and in-situ settings, confirmed the nature of solid-solution and established a correlation between structural modifications and redox activity vis-a-vis electrochemical performance. Encouragingly, consistent and reproducible outcomes were noted, manifesting facile bulk Mg2+-ion activity sans phase transformations, thus bolstering energy storage capacity through reversible Mg2+ intercalation, facilitated by an understanding of the variables governing the electrochemical performance of spinel oxide. Leveraging these insights, it becomes conceivable to engineer an oxide cathode material boasting many of the desired attributes of a Li-ion intercalation cathode, marking a significant milestone in the pursuit of high energy density Mg-ion batteries.This study delineates strategies for designing and developing novel spinel oxide intercalation materials tailored for high-energy Mg-ion battery cathodes, leveraging a blend of theoretical and experimental methodologies. We discuss the key factors dictating the kinetics of Mg2+ diffusion in spinel oxides, elucidating how material complexity aligns with the electrochemical Mg2+ activity in oxides, bolstered by supplementary characterization. The insights gleaned from fundamental inquiries into cation diffusion in oxide cathodes are poised to benefit chemists and materials scientists engaged in the advancement of rechargeable batteries.Related publication: B. Kwon et al., Accounts of Chemical Research, 2024, 57, 1, 1–9 Figure 1

Regulation of Oxide Pathway Mechanism for Sustainable Acidic Water Oxidation.

The advancement of acid-stable oxygen evolution reaction (OER) electrocatalysts is crucial for efficient hydrogen production through proton exchange membrane (PEM) water electrolysis. Unfortunately, the activity of electrocatalysts is constrained by a linear scaling relationship in the adsorbed evolution mechanism, while the lattice-oxygen-mediated mechanism undermines stability. Here, we propose a heterogeneous dual-site oxide pathway mechanism (OPM) that avoids these limitations through direct dioxygen radical coupling. A combination of Lewis acid (Cr) and Ru to form solid solution oxides (CrxRu1-xO2) promotes OH adsorption and shortens the dual-site distance, which facilitates the formation of *O radical and promotes the coupling of dioxygen radical, thereby altering the OER mechanism to a Cr-Ru dual-site OPM. The Cr0.6Ru0.4O2 catalyst demonstrates a lower overpotential than that of RuO2 and maintains stable operation for over 350 h in a PEM water electrolyzer at 300 mA cm-2. This mechanism regulation strategy paves the way for an optimal catalytic pathway, essential for large-scale green hydrogen production.

Indium-Iron Oxide Nanosized Solid Solutions as Photocatalysts for the Degradation of Pollutants under Visible Radiation.

A series of solid solutions of indium and iron oxides with different In/Fe ratios (InxFeyO3, with x + y = 2) were synthesized in the form of nanoparticles (diameter of ca. 30-40 nm) with the purpose of generating enhanced photocatalysts with an intermediate band gap compared to those of the monometallic oxides, In2O3 and Fe2O3. The materials were prepared by co-precipitation from an aqueous solution of iron and indium nitrates and extensively characterized with a combination of techniques. XRD analysis proved the formation of the desired InxFeyO3 solid solutions for Fe content in the range 5-25 mol%. UV-Vis absorption analysis showed that the substitution of In with Fe in the crystalline structure led to the anticipated gradual decrease of the band gap values compared to In2O3. The obtained semiconductors were tested as photocatalysts for the degradation of model organic pollutants (phenol and methylene blue) in water. Among the InxFeyO3 solid solutions, In1.7Fe0.3O3 displayed the highest photocatalytic activity in the degradation of the selected probe molecules under UV and visible radiation. Remarkably, In1.7Fe0.3O3 showed a significantly enhanced activity under visible light compared to monometallic indium oxide and iron oxide, and to the benchmark TiO2 P25. This demonstrates that our strategy consisting in engineering the band gap by tuning the composition of InxFeyO3 solid solutions was successful in improving the photocatalytic performance under visible light. Additionally, In1.7Fe0.3O3 fully retained its photocatalytic activity upon reuse in four consecutive cycles.

Manufacturing and characterization of simulated fission product (FP)-doped uranium–plutonium mixed oxide solid solutions (FP = Zr, Nd, Sm, and Gd)

Seven uranium–plutonium mixed oxides (MOX) comprising 10 and 20 mol% of solid simulated fission products (FPs) were prepared via powder metallurgy. Zirconium, neodymium, samarium, and gadolinium were selected as the FPs owing to their high fission yields and solubility within the uranium–plutonium fluorite structure. A laboratory-scale manufacturing process was developed to prepare solid solutions that are prerequisites for thermodynamical investigations. The microstructure and crystal structure of the specimens were analyzed. Furthermore, a mechanistic approach toward cation interdiffusion is proposed. Finally, our hybrid crystallographic model was employed to re-evaluate the ionic radii of the species constituting the FP-MOX samples.

Ceramic Materials Based on a Complex Oxide Solid Solution of a Tetragonal Form of Zirconia: Application in Prosthetic Dentistry

Ceramic Materials Based on a Complex Oxide Solid Solution of a Tetragonal Form of Zirconia: Application in Prosthetic Dentistry

Preparation of uranium-plutonium oxide solid solution powder from ammonium uranyl-plutonyl carbonate in a laboratory microwave unit

The method of obtaining a solid solution powder of uranium-plutonium oxides (with 38% plutonium content) from the AUPuC pulp of the process (ammonium uranyl-plutonyl carbonate) using microwave radiation in reducing and atmospheric environments was proposed and tested at the laboratory level. For research purposes, the pulp obtained by coprecipitation of uranium and plutonium from nitrate solution (stripping product simulator) was prepared in advance. The process consists of three main stages: oxidation of Pu(IV) to Pu(VI), precipitation, and conversion in a laboratory microwave unit. According to the X-ray phase analysis, the powder obtained in a reducing atmosphere is a solid cubic solution (UxPu1–x)O2. The powder obtained in an atmospheric environment is a mixture of two oxides, PuO2 and U3O8. Scanning electron microscopy and electron probe microanalysis of the powder obtained in an atmospheric environment showed a fairly uniform distribution of U, Pu, and O in the solid phase.

Stepwise-Induced Synthesis and Excellent Corrosion Protection of Ce/Eu Codoped ZnO Solid Solution Materials.

Under purely inorganic conditions, a synthesis route was devised wherein elements were introduced stepwise via coprecipitation based on differences in compound solubility. This synthesis method can change the microscopic morphology of the material without relying on a templating agent, resulting in the formation of the multilayered lamellar Ce/Eu codoped zinc oxide solid solution (ZCEOSS) with a self-assembled nested imbrication structure. The study improves the critical matter of corrosion by focusing on the electron and energy transfer mechanisms. By introduction of the bandgap modulator cerium element and fluorescence enhancer europium element into the ZnO material, the anticorrosion material has been successfully endowed with both photocathodic protection and luminescent initiative/stress dual corrosion defense functions. Due to the energy level staircase protection mechanism synergistically generated by the 4f electron shell of rare-earth elements in concert with semiconductor zinc oxide, the energy band positions were modulated to progressively guide the direction of electron flow, thereby suppressing corrosion reactions. In particular, the ZCEOSS material synthesized by doping 1% cerium and 7% europium and adding rare-earth elements at pH 7 exhibited the best corrosion inhibition performance. After immersion in simulated seawater for 96 h, Tafel polarization test results showed that compared to epoxy resin and ZnO anticorrosion systems, the ZCEOSS anticorrosion system exhibited significantly improved corrosion inhibition efficiency with enhancements of 1028.3 and 402.9%, respectively. This study provides new insights into the development of highly efficient inorganic anticorrosion materials.

Molten salt method for preparing Mn0.3Ru0.7O2 nanosheets as a superior bifunctional catalyst for rechargeable zinc-air batteries

Integrating components for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) while optimizing their electronic structure is an effective strategy for developing excellent bifunctional catalysts for rechargeable zinc-air batteries (ZABs). In this study, we successfully fabricated Mn0.3Ru0.7O2 nanosheets based on a solid solution oxide using a simple molten salt method. The Mn0.3Ru0.7O2 nanosheets exhibits abundant Ru and Mn sites through the Ru-O-Mn structure, which serve as excellent OER and ORR active centers. Experimental and theoretical studies validate the coccurrence of charge transefer between the Ru-O-Mn bond, modulating the valence state and d-band center of the Mn and Ru, thereby subsequently improving their ORR/OER intrinsic activity. Remarkably, the Mn0.3Ru0.7O2 nanosheets displays superior electropcatalytic performance with a charge/discharge voltage gap (ΔE) of only 0.59 V, which is the best among all reported counterpart catalysts. A rechargeable ZAB utilizing Mn0.3Ru0.7O2 nanosheets achieved a power density of 154 mW cm−2 and a specific capacity of 821 mA h g−1, surpassing that of the commercial Pt/C + RuO2 mixing catalyst. This study offers a new strategy for preparing highly active and durable bifunctional catalysts for rechargeable ZABs.

Solid-liquid phase boundary of oxide solid solutions using neural network potentials

We propose a cost-effective computational approach for predicting the phase boundary of oxide solid solutions, i.e., melting point, by identifying the point where the free energies of the solid and liquid phases are equivalent. To evaluate the melting point, we computed the temperature-dependent free energies of both phases using the thermodynamic integration (TI) method. This was combined with the reverse-scaling technique, employing the Einstein model for the solid and the scaled Uhlenbeck–Ford model for the liquid as the reference systems. The change in free energy between the real and reference states in the present TI method was calculated as the ensemble average of the configurations sampled from molecular dynamics (MD) simulations using neural network potentials (NNPs) trained on first-principles density functional theory (DFT) data. Initially, we benchmarked copper (Cu) as a typical metal. Tungsten (W) and magnesium oxide (MgO) were then tested as typical high melting-point metals and oxides, respectively, achieving good agreement with both ab initio MD (AIMD) results and experimental data. We then applied our established approach to a BaO–CaO oxide solid solution, observing that the computed phase boundary aligns well with Calphad predictions from previous studies. The integration of NNPs into phase boundary prediction is essential for reducing computational costs while ensuring accuracy, compared with AIMD-based approaches.

Accelerated Proton Transfer in Asymmetric Active Units for Sustainable Acidic Oxygen Evolution Reaction.

The poor durability of Ru-based catalysts limits the practical application in proton exchange membrane water electrolysis (PEMWE). Here, we report that the asymmetric active units in Ru1-xMxO2 (M = Sb, In, and Sn) binary solid solution oxides are constructed by introducing acid-resistant p-block metal sites, breaking the activity and stability limitations of RuO2 in acidic oxygen evolution reaction (OER). Constructing highly asymmetric Ru-O-Sb units with a strong electron delocalization effect significantly shortens the spatial distance between Ru and Sb sites, improving the bonding strength of the overall structure. The unique two-electron redox couples at Sb sites in asymmetric active units trigger additional chemical steps at different OER stages, facilitating continuous proton transfer. The optimized Ru0.8Sb0.2O2 solid solution requires a superlow overpotential of 160 mV at 10 mA cm-2 and a record-breaking stability of 1100 h in an acidic electrolyte. Notably, the scale-prepared Ru0.8Sb0.2O2 achieves efficient PEMWE performance under industrial conditions. General mechanism analysis shows that the enhanced proton transport in the asymmetric Ru-O-M unit provides a new working pathway for acidic OER, breaking the scaling relationship without sacrificing stability.

Analysis of magnesia-carbon bricks erosion in vanadium extraction converters: Insights from dynamic experiments and interface characterization

This paper uses a rotary furnace to simulate the dynamic erosion behavior of various magnesia-carbon bricks within a vanadium extraction converter, focusing on the effects of carbon content and antioxidants on erosion. The results indicate that vanadium-rich slag primarily consists of oxide solid solutions, iron vanadium spinel, and metallic Fe. Adding aluminum and silicon powders to the bricks reduces apparent porosity, increases body density, and improves slag erosion resistance. However, an increase in carbon content (12.54 wt% to 18.59 wt%) within magnesia-carbon bricks correlates with decreased high-temperature strength, exacerbating the reaction propensity with slag and consequent structural damage. Analysis of the interface phase between magnesia-carbon bricks and vanadium slag reveals a predominance of metal phase, spinel phase, and liquid slag phase. Thermodynamic calculations suggest an initial reaction between MgO and C on the brick surface, yielding Mg vapor and CO gas, while C reacts with slag to produce Cr and V elements, leading to surface structure degradation. Subsequent slag encasement and dissolution of remaining MgO via decarburization channels further erode magnesia-carbon bricks. Cumulative erosion iterations ultimately culmi nate in performance failure of magnesia-carbon bricks.

Tuning the amount of Sn0 around Ru to promote hydrodeoxygenation of furfural

2-methylfuran (2-MF) is a high-performance gasoline additive due to its high-octane value and good explosion resistance. In this study, cerium tin oxide solid solutions were prepared by a co-precipitation method. The selectivity of 2-MF and the conversion of furfural significantly improved after doping CeO2 with SnO2. 95 % yield of 2-MF was obtained on 5 %Ru/Ce0.975Sn0.025O2, compared to only 40 % yield on 5 %Ru/CeO2. The reaction rate of furfural over 5 %Ru/Ce0.975Sn0.025O2 was 4.9 times higher than that with 5 %Ru/CeO2. Characterizations show an increased concentration of SnO2 around Ru, and the ratio of Ruδ+/Ru reaches a maximum on 5 %Ru/Ce0.975Sn0.025O2. The binding energy shift of Ru0, Sn0, O, and Ce3+ indicates that the introduction of Sn plays an important role in regulating the interface between Ru and CeO2. The increase of Ruδ+/Ru ratio benefits the hydrodeoxygenation of furfural and contributes to the high yield of 2-MF. This study provides a highly active catalyst for the hydrodeoxygenation of furfural.

Rutile‐Structured Ru0.48Mn0.52O2 Solid Solution for Highly Active and Stable Oxygen Evolution at Large Current Density in Acidic Media

AbstractThe development of active, stable, and cost‐effective electrocatalysts for the oxygen evolution reaction (OER) in acidic media is crucial for proton‐exchange‐membrane water electrolysis. Inspired by theoretical screening on a series of transition metal incorporated RuO2 systems, a low Ru‐content solid solution oxide (Ru0.48Mn0.52O2) achieved is fabricated by a simple two‐step synthesis method through the combination of rutile RuO2 and β‐MnO2. The Ru0.48Mn0.52O2 catalyst exhibits an exceptionally low overpotential of 154 mV at 10 mA cm−2 and maintains a high stability under a high current of 100 mA cm−2 for 50 h in 0.5 m H2SO4 electrolyte. Furthermore, the obtained catalyst exhibits sustained stability at a large current of 0.5 A cm−2 for at least 50 h when loaded onto a Ti felt. The in‐situ characterization results indicate that Ru0.48Mn0.52O2 preferably followed the adsorbate evolution mechanism rather than the lattice oxygen oxidation mechanism during the OER process, contributing to its high activity and stability at large current densities in acidic media.

Zn promoted GaZrOx Ternary Solid Solution Oxide Combined with SAPO-34 Effectively Converts CO2 to Light Olefins with Low CO Selectivity.

We proposed a new strategy for CO2 hydrogenation to prepare light olefins by introducing Zn into GaZrOx to construct ZnGaZrOx ternary oxides, which was combined with SAPO-34 to prepare a high-performance ZnGaZrOx/SAPO-34 tandem catalyst for CO2 hydrogenation to light olefins. By optimizing the Zn doping content, the ratio and mode of the two-phase composite, and the process conditions, the 3.5 %ZnGaZrOx/SAPO-34 tandem catalyst showed excellent catalytic performance and good high-temperature inhibition of the reverse water-gas shift (RWGS) reaction. The catalyst achieved 26.6 % CO2 conversion, 82.1 % C2 =-C4 = selectivity and 11.8 % light olefins yield. The ZnGaZrOx formed by introducing an appropriate amount of Zn into GaZrOx significantly enhanced the spillover H2 effect and also induced the generation of abundant oxygen vacancies to effectively promote the activation of CO2. Importantly, the RWGS reaction was also significantly suppressed at high temperatures, with the CO selectivity being only 46.1 % at 390 °C.

Cost-effective method for computational prediction of thermal conductivity in optical materials based on cubic oxides

In this paper we report on a computationally cost-effective method designed to estimate the thermal conductivity of optical materials based on cubic oxide including mixed ones, i.e. solid solutions of different oxides. The proposed methodology take advantage from Density Functional Theory (DFT) calculations to extract essential structural parameters and elastic constants which represent the inputs for revised versions of Slack and Klemens equations relating thermal conductivity to elastic constants. Slack equation is modified by the introduction of a corrective factor that incorporates the Grüneisen parameter γ, while in the revised Klemens equation a distortion parameter d\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d$$\\end{document} accounting for the impact of point defects on lattice symmetry is added, which is a critical factor in determining thermal conductivity in optical materials with mixed compositions. The theoretical results were found in good agreement with experimental data, showing the reliability of our proposed methodology.

Exploring microstructures of metal-doped oxides via simulated Raman spectrum

Solid solution of metal-doped oxide has been widely used in material industry and catalysis process. Its performance is highly correlated with the distribution of doped ions. Due to the complex distribution of doped ions in solid solution and its variation with temperatures, to obtain the microstructures of metal-doped ions in solid solution remains a substantial challenge. Taken Ce1-xZrxO2 as a model, the global structure searching, structures proportion with temperature determined by Boltzmann distribution, and the weighted simulation Raman spectra were integrated to explore the microstructures of metal-doped solid solution oxides. It was further verified by application into rutile and anatase TiO2 mixture, indicating that the present method is feasible to deduce the microstructure of metal composite oxides. We anticipate that it provides a powerful solution to explore microstructures of solid solution and complex metal oxides.

Comparative Analysis of Wear Behavior of High Entropy Alloy (TiVNbCrAl) and Ti-based Conventional Alloy (TiNbCrCoAl)

This research examined the relationships between processing, structure, and property at both room temperature and increased temperature for two BCC high entropy alloy (TiVNbCrAl) and Ti-based conventional alloy (TiNbCrCoAl) prepared using standard arc melting. Both alloys have been determined to have the BCC single-phase solid solution structure. To investigate the hardness and tribological behavior and processes at room temperature and above, microindentation and sliding wear experiments were undertaken. Both alloys display comparable friction behavior when sliding at room temperature, with an average steady-state coefficient of friction (COF) of 0.6. When sliding temperatures rise to 302 °C, the average COF for HEA (TiVNbCrAl) has decreased to a lowest value of ~0.4 due to the creation of a persistent tribochemical layer made of Nb and Cr oxides amid the sliding surfaces, which lowers COF. Whereas, COF for Ti-based conventional alloy remains at higher values of ~0.65. Mechanistic wear analyses revealed that the formation of tribofilms with low interfacial shear strength inside the wear tracks was the cause of this. The tribofilms were identified to be mostly constituted by multi-element solid solution oxides, such as Ni2O5, Cr2O3, and NiO2, according to Raman spectroscopy. The Vickers microharness values for Ti-based conventional alloy is about 365±4 HV. Whereas, for high entropy alloy is about 572±12 HV due to the solid solution strengthening.

Black paintings in the late Yocavil ceramics (11th–17th centuries): Applying micro X‐ray diffraction to the study of archaeological potteries in Northwest Argentina

AbstractThe black pigments used in Late Period (11th–17th centuries) painted pottery in the Yocavil Valley were characterized. Changes and continuities in the composition of this material over an extended span were evaluated. A regional sample of 47 potsherds from the Loma Rica, San José, and Santa María styles was collected, and for the first time micro wide‐angle X‐ray scattering was used in these ceramic styles. The results indicate the simultaneous presence of iron oxides (hematite) and solid solutions of manganese and iron oxides (jacobsite–magnetite). Besides, the paints were prepared by mixing the pigments with clay‐based binding materials.

Oxide Solid–Solution Catalysts with Good Redox Properties for Liquid–Phase Aerobic Additive–Free Oxidation: A Review

AbstractIn this review, we discuss liquid–phase redox reactions using oxide solid–solution catalysts. These oxide solid solutions are readily prepared by introducing various elements into the foundational metal oxide template. Doping with metal species leads to the formation of [MOx] clusters with unique coordination structures, which is a remarkable feature that deserves attention. Consequently, oxide solid solutions exhibit catalytic capabilities that extend beyond those of conventional metal–oxide catalysts. Notably, these [MOx] clusters occasionally exhibit exceptional redox activities that can be used to catalyze liquid–phase redox reactions. Hence, we conjecture that a connection exists between catalyst structure and activity. This review delves into oxide solid–solution catalysts through the lenses of organic chemistry, solid catalysts, and computational chemistry, thereby collectively shaping our understanding and prospects in this field.