(De)lithiation of spinel ferrites Fe3O4, MgFe2O4, and ZnFe2O4: a combined spectroscopic, diffraction and theory study
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99 GENERAL AND MISCELLANEOUS↗
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Advances and Prospects of High-Voltage Spinel Cathodes for Lithium-Based Batteries
Abstract not provided.
Chemistry↗
Topotactic Phase Transformation of Lithiated Spinel to Layered LiMn0.5Ni0.5O2: The Interaction of 3-D and 2-D Li-ion Diffusion
This study investigates the structural evolution of LiMn0.5Ni0.5O2 cathode materials for Li-ion batteries as a function of synthesis temperature and its effect on electrochemical performance. It is demonstrated that, as the synthesis temperature increases from 400 to 900 ?C, a gradual topotactic transformation occurs between a lithiated spinel structure, denoted herein as “lithium-excess spinel” LxS-LiMn0.5Ni0.5O2 (or LxS-LMNO), and the well-known layered LiMn0.5Ni0.5O2 structure prepared at high temperature, HT-LiMn0.5Ni0.5O2 (HT-LMNO). The electrochemical capacity of the LiMn0.5Ni0.5O2 electrodes follows a parabolic trend with increasing synthesis temperature, which is attributed primarily to the gradual transformation of 3-dimensional (3-D) to 2-dimensional (2-D) diffusion pathways for the Li ions. When synthesized at 400 °C, LxS-LiMn0.5Ni0.5O2 electrodes perform well, benefitting from the 3-D network of channels within the LxS structure. By contrast, when prepared at 500-700 °C, LiMn0.5Ni0.5O2 electrodes operate poorly, which is attributed to the formation of locally disordered structural arrangements that impede Li-ion diffusion. Such an increase in local disorder in the mid-temperature synthesis range is attributed to the structural frustration between the lithium-excess spinal and layered end-members. The transformation from the locally disordered to more ordered layered components between 700 °C and 900 °C enhances electrochemical performance. The study opens new avenues for designing next-generation Mn-rich cathode materials by fine-tuning the synthesis conditions as well as the composition and structure of LxS-LMNO electrodes.
energy storage↗
Oxidation kinetics of hercynite spinels for solar thermochemical fuel production
Not Available
Millican, Samantha L.↗
Controlling Infrared Plasmon Resonances in Inverse-Spinel Cadmium Stannate Nanocrystals via Site-Selective Cation-Exchange Reactions
Doped metal oxide nanocrystals (NCs) exhibit tunable localized surface plasmon resonances (LSPRs) in the infrared spectral region. Compared to the binary oxides commonly studied, plasmonic NCs derived from ternary oxides remain far less explored primarily due to the difficulty of controlling NC phase-purity and stoichiometry. Here, we report the synthesis of inverse spinel-type cadmium stannate (Cd 2 SnO 4 ) NCs, for which cation-exchange reactions were developed to tailor their composition and LSPR properties. X-ray absorption spectroscopy studies revealed that the inequivalent tetrahedrally and octahedrally coordinated Cd 2+ can be selectively exchanged for Cu + and In 3+ ions, respectively, enabling broadband tunable LSPR and Cu-mediated cation-exchange with lanthanide ions that are otherwise difficult to incorporate. Here, our work paves the way for systematic compositional engineering to accelerate the design of complex metal oxide NCs with emerging plasmonic, electronic, and magnetic properties.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Magnetic Texture in Insulating Single Crystal High Entropy Oxide Spinel Films
Magnetic insulators are important materials for a range of next-generation memory and spintronic applications. Structural constraints in this class of devices generally require a clean heterointerface that allows effective magnetic coupling between the insulating layer and the conducting layer. However, there are relatively few examples of magnetic insulators that can be synthesized with surface qualities that would allow these smooth interfaces and precisely tuned interfacial magnetic exchange coupling, which might be applicable at room temperature. In this work, we demonstrate an example of how the configurational complexity in the magnetic insulator layer can be used to realize these properties. The entropy-assisted synthesis is used to create single-crystal (Mg 0.2 Ni 0.2 Fe 0.2 Co 0.2 Cu 0.2 )Fe 2 O 4 films on substrates spanning a range of strain states. These films show smooth surfaces, high resistivity, and strong magnetic responses at room temperature. Furthermore, local and global magnetic measurements further demonstrate how strain can be used to manipulate the magnetic texture and anisotropy. These findings provide insight into how precise magnetic responses can be designed using compositionally complex materials that may find application in next-generation magnetic devices.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Hall–Petch effect in binary and ternary alumina / zirconia / spinel composites
Not provided.
Materials Science↗
Crystal structures and electrical properties of cobalt manganese spinel oxides
Not Available
Park, Kyoung Ryeol↗
High-throughput investigation of the formation of double spinels
Spinel compounds, with the general chemical formula AB 2 O 4 , are a wide class of materials, where A and B can be a variety of cations, providing this structure with a great deal of functional flexibility and giving rise to its considerable scientific interest. Recently, a spinel with the general formula ABB'O 4 has been predicted, increasing the possible usability of the spinels due to the higher cation diversity in the so-called double spinel structure. In this study, we use density functional theory calculations to predict if double spinels can be formed between experimentally synthesized normal and inverse single spinels. Our computations reveal that 49 double spinels have negative mixing enthalpies and are thus thermodynamically stable, with most of the stable compounds being formed from one of two distinct cation orderings. We show that the 17 different cations that form the different double spinels have a preferred site, tetrahedral or octahedral, except for Mn, Fe and Co which can occupy both sites interchangeably. We also study the relation between mixing enthalpies and cation-specific properties, as well as ways to classify the double spinels into distinct types and spinel groups depending on the cation ordering and cation oxidation states, respectively. Furthermore, by applying the Sure Independence Screening and Sparsifying Operator (SISSO) approach on the coordination-dependent ionic radii of the elemental constituents, we show that an interplay of local strain and electrostatic dominated terms can be used to separate the double spinels into distinct structural types depending on the cation order and their oxidation states.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Coupled methane and NO x conversion on Pt + Pd/Al 2 O 3 monolith: Conversion enhancement through feed modulation and Mn 0.5 Fe 2.5 O 4 spinel addition
The performance of a dual-layer Pt-Pd/Al 2 O 3 washcoated monolith promoted by an Al 2 O 3 -supported Mn 0.5 Fe 2.5 O 4 spinel base layer was evaluated with the objective to develop a catalyst with a lower loading of Platinum group metal (PGM) for stoichiometric natural gas vehicle (NGV) emission control. Flow reactor results show that a combination of a lean/rich modulated feed and spinel addition gives enhanced methane and NO conversions compared to a steady-state feed having the same overall composition. Washcoated catalysts – PGM-only, spinel-only, PGM + spinel – were compared over a wide range of operating conditions. The results show a decrease in the methane conversion light-off temperature of up to 85 °C for an application-relevant feed (CH 4 + NO + H 2 + CO + O 2 + H 2 O + CO 2 ) while a moderate 40 °C decrease was observed for a simple feed (CH 4 + O 2 + H 2 O + CO 2 ). In the absence of spinel the modulation enhancement is negatively impacted at high methane conversion (> 80 %). The data show that the O 2 storage and release property of the spinel is needed to fully exploit the modulation enhancement. The mechanism responsible for the enhancement is linked to suppression of O 2 inhibition on the methane oxidation rate near the stoichiometric neutral point (λ = 1). Sufficiently fast cycling achieves a balance between a metallic and oxidic precious metal crystallites favorable for methane activation. The addition of spinel moves this balance closer to the λ = 1 feed, enabling a high oxidation efficiency with lower byproduct NH 3 selectivity. Enhancement in the NO conversion follows the methane conversion due to an easier NO reduction under the slightly rich of stoichiometric feed. Comparison of the PGM + spinel catalysts to PGM-only catalysts shows that the addition of spinel in combination with modulation can achieve the same activity with a lower PGM loading.
03 NATURAL GAS↗
Lithium Manganese Spinel Cathodes for Lithium-Ion Batteries
Spinel LiMn 2 O 4 , whose electrochemical activity was first reported by Professor John B. Goodenough’s group at Oxford in 1983, is an important cathode material for lithium-ion batteries, which attracts continuous academic and industrial interests. It is cheap and environmentally friendly, and has excellent rate performance with 3-dimensional (3D) Li + diffusion channels. However, it suffers from severe degradations, especially under extreme voltages and during high-temperature operations. In this review, the current understanding and future trends of the spinel cathode and its derivatives with cubic lattice symmetry (LiNi 0.5 Mn 1.5 O 4 that shows high-voltage stability, and Li-rich spinels that show reversible hybrid anion- and cation-redox activities) shall be discussed. Special attention is given to the degradation mechanisms, further development of spinel cathodes, and concepts of utilizing the cubic spinel structure to stabilize high-capacity layered cathodes and as robust framework for high-rate electrodes. Lastly, “Good spinel” surface phases like LiNi 0.5 Mn 1.5 O 4 are distinguished from “bad spinel” surface phases like Mn 3 O 4 .
25 ENERGY STORAGE↗
Prediction of structure and cation ordering in an ordered normal-inverse double spinel
Abstract Spinels represent an important class of technologically relevant materials, used in diverse applications ranging from dielectrics, sensors and energy materials. While solid solutions combining two “single spinels” have been explored in a number of past studies, no ordered “double” spinels have been reported. Based on our first principles computations, here we predict the existence of such a double spinel compound MgAlGaO 4 , formed by an equimolar mixing of MgAl 2 O 4 normal and MgGa 2 O 4 inverse spinels. After studying the details of its atomic and electronic structure, we use a cluster expansion based effective Hamiltonian approach with Monte Carlo simulations to study the thermodynamic behavior and cation distribution as a function of temperature. Our simulations provide strong evidence for short-ranged cation order in the double spinel structure, even at significantly elevated temperatures. Finally, an attempt was made to synthesize the predicted double spinel compound. Energy Dispersive X-ray Spectrometry and X-ray diffraction Rietveld refinements were performed to characterize the single-phase chemical composition and local configurational environments, which showed a favorable agreement with the theoretical predictions. These findings suggest that a much larger number of compounds can potentially be realized within this chemical space, opening new avenues for the design of spinel-structured materials with tailored functionality.
36 MATERIALS SCIENCE↗
Facile Electrochemical Mg-Ion Transport in a Defect-Free Spinel Oxide
Inversion, i.e. Mg/Mn antisite disorder, in a spinel oxide simultaneously causes blockage of favorable Mg 2+ migration paths, raising activation barriers for diffusion, and it reduces the number of redox-active metals, limiting the maximum capacity in the spinel. Here, an inversion-free spinel, MgCr 1.5 Mn 0.5 O 4 , was synthesized by exploiting the different intrinsic crystal field stabilization of redox-active Cr and Mn in the form of a solid-solution. The capability of the tailored spinel to reversibly (de)intercalate Mg 2+ at high redox potentials was investigated. The decrease in inversion dramatically lowered the electrochemical overpotential and hysteresis, and enabled utilization of high potentials at ~2.9 V (vs. Mg/Mg 2+ ) upon re-intercalation of Mg 2+ . A combination of characterization techniques reveals that the structural, compositional, and redox changes within the spinel oxide were consistent with the observed electrochemical Mg 2+ activity. Quantification of selective solely to lattice Mg 2+ upon the electrochemical reaction was investigated by monitoring NMR signals in isotope 25 Mg-enriched spinel oxides. Our findings enhance the understanding of Mg 2+ transport within spinel oxide frameworks and provide conclusive evidence for bulk Mg migration in oxide lattices at high redox potentials with minimized electrochemical hysteresis.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Demonstration of MgCr 2– x Mn x O 4 Spinel Oxide Cathodes in High-Voltage Mg Batteries
Solid-solution oxide spinels with high redox voltages and facile Mg 2+ mobility have been identified as promising candidates for practical, high-voltage cathodes in Mg batteries. In this work, we discuss the development of MgCr 2-x Mn x O 4 [x = 0.5, 1, 1.2] solid-solution spinel oxides as a cathode material and their electrochemical performance paired with an Mg anode in a full cell. This work presents the first demonstration of full cells with these materials. Mg-Cr-Mn spinel oxides with varying Cr and Mn contents were synthesized using alternative synthetic routes for optimal electrochemical performance. High-resolution synchrotron powder X-ray diffraction (PXRD), solid-state nuclear magnetic resonance (NMR) spectroscopy, and electron microscopy showed that these different synthetic routes resulted in changes in structures and particle morphologies, which in turn affect the electrochemical performance. Particularly, the urea coprecipitation synthetic route resulted in high-surface-area particles that enabled lower overpotentials and increased discharge capacity. The high surface area also resulted in expedited structural degradation caused by the irreversible migration of Mg 2+ into normally vacant 16c sites in the spinel lattice. This structural degradation was lessened by using a hydrosauna-urea synthesis method, which decreased the Mg/Mn inversion ratio while retaining high-surface-area particles with good cycling performance. Furthermore, our findings highlight the necessity for high surface area or nanostructured spinel oxide cathodes with minimized Mg-Mn inversion to enable spinel oxide cathodes in Mg full cells.
Mg anode↗
CH 4 steam reforming on Pt + Pd/Al 2 O 3 monolith: impact of Mn 0.5 Fe 2.5 O 4 spinel addition
The performance of Pt + Pd/Al 2 O 3 monolith catalysts was analyzed under a feed (H 2 + CO + CH 4 + NO + O 2 + H 2 O + CO 2 ) simulating the exhaust gas of stoichiometric natural gas vehicles (NGVs). The flow reactor results show enhanced low temperature (<400 °C) CH 4 oxidation activity under cyclic lean/rich feed modulation and with Mn 0.5 Fe 2.5 O 4 (MFO) spinel addition to the platinum group metal (PGM) catalyst. In the absence of the MFO spinel, the PGM catalyst can achieve full CH 4 conversion, but the presence of spinel in the catalyst limits the high temperature (>500 °C) CH 4 conversion. The depletion of gas phase O 2 , as indicated by the detection of products CO and H 2 in the reactor effluent at higher temperature and CH 4 conversion, portends the emergence of steam reforming of CH 4 (SRM). To investigate the cause of the detrimental impact of spinel under the high temperature, net rich regime, we show through a combination of SRM experiments and post-reaction catalyst characterization that SRM is negatively impacted by the accumulation of Mn and Fe spinel species on the PGM catalyst. This is due to the migration of the base metal species and potential encapsulation and blockage of PGM active sites. The latter is supported by density functional theory (DFT) calculations that indicate favorable metal oxide decoration of active Pt step sites. Lastly, a zoned catalyst design is developed that mitigates the detrimental metals migration while exploiting the methane conversion enhancement afforded by spinel oxides under oxygen rich conditions.
03 NATURAL GAS↗
Development & Validation of Low-Cost, Highly-Durable, Spinel-Based Materials for SOFC Cathode-Side Contact (Final Report)
A cathode-side contact layer is required to provide and maintain stable electrical conduction paths between the interconnect and cathode in a solid oxide fuel cell (SOFC) stack assembly and thus minimize the ohmic resistance and stack power loss. Current cathode-interconnect contact materials are based on noble metals, electrically-conductive perovskites, their composite materials, etc. These materials are either too expensive or do not possess the overall balanced performance required for the cathode-side contact application. To achieve the DOE SOFC system cost and performance stability goals, a new generation of low-cost, high-performance contact materials needs to be developed. In this project, spinel-based materials thermally converted from the Fe-Ni and Co-Mn based alloy precursors were developed and validated for the cathode-side contact application. The precursor alloy compositions were optimized via a combination of composition screening in the (Ni,Fe) 3 O 4 and (Mn,Co) 3 O 4 spinel system, alloy design using physical metallurgy principles, and cost considerations. The alloy powders with the desired composition and particle size were manufactured via gas atomization. The optimal process parameters for thermal conversion of these alloy precursor layers to a spinel-based layer were identified, i.e., 900°C x 2h in air, which is close to the initial stack firing condition. The area-specific resistances (ASRs) of the interconnect/contact/cathode test assemblies with the developed contact layer were determined for various durations (up to 5000 h) under simulated cathodic operation conditions. Some of the alloy-derived spinel contacts exhibited the lowest ASR and ASR degradation rate. The in-stack performance of the most promising alloy-derived contact layer is currently being evaluated via stack testing. To reduce the stack cost, the Co-Mn based alloy powders were utilized as the precursor for synthesis of dense spinel-based interconnect coating. By optimizing both the initial powder size/distribution and the alloy powder composition, a dense (Mn,Co) 3 O 4 -based spinel coating was achieved. Furthermore, co-sintering of the coating/contact dual-layer structure under the initial stack firing condition was realized by utilizing the tailored Co-Mn alloy precursors. Cost analysis of the developed technology indicated a total stack cost reduction of around 10.6% with the implementation of co-sintering of the interconnect coating and the contact layer during initial stack firing. Since low-cost processes such as screen printing is utilized in the precursor application and no reduction heat treatment is needed for the coating formation, the developed technology can be readily implemented at the industrial partner’s manufacturing facilities with no additional capital investment needed.
08 HYDROGEN↗
The Effects of Mixing Multi-Component HLW Glasses on Spinel Crystal Size
The Hanford Waste Treatment and Immobilization Plant will vitrify radioactive waste into borosilicate glass. The high-level waste (HLW) glass formulations are constrained by processing and property requirements, including restrictions aimed at avoiding detrimental impacts of spinel crystallization in the melter. To understand the impact of glass chemistry on crystallization, two HLW glasses precipitating small (?5 µm) spinel crystals were individually mixed with a glass that precipitated large (?45 µm) spinel crystals in ratios of 25, 50, and 75 wt%. The size of spinel crystals in the mixed glasses varied from 5 to 20 µm. Small crystal size was attributed to: (1) high concentrations of nuclei due to the presence of ruthenium oxide and (2) chromium oxide aiding high rates of nucleation. Results indicate that the spinel crystal size can be controlled using chromium oxide and/or noble metal concentrations in the melt, even in complex mixtures like HLW glasses. Small crystals tend to settle slowly, so they are acceptable in the melter without a risk of failure. Allowing higher concentrations of spinel-forming waste components in the waste glass enables glass compositions with higher waste loading, thus increasing plant operational flexibility. An additional benefit to the presence of chromium oxide in the glass composition is the potential for the oxide to protect melter walls against corrosion.
Lonergan, Charmayne E.↗