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1. Comparative Thermal Insulation Nature of Ca ₂ FeMnO _6−δ and Sr ₂ FeMnO _6−δ

   https://doi.org/10.1149/2754-2734/ad27dc  

   Schultz, Ebony; Guinn, Mandy; Azure, Alexa D; Hona, Ram Krishna (February 2024, ECS Advances)

   unknown (Ed.)

   In this study, we investigate the utility of Ca₂FeMnO_6-δand Sr₂FeMnO_6-δas materials with low thermal conductivity, finding potential applications in thermoelectrics, electronics, solar devices, and gas turbines for land and aerospace use. These compounds, characterized as oxygen-deficient perovskites, feature distinct vacancy arrangements. Ca₂FeMnO_6-δadopts a brownmillerite-type orthorhombic structure with ordered vacancy arrangement, while Sr₂FeMnO_6-δadopts a perovskite cubic structure with disordered vacancy distribution. Notably, both compounds exhibit remarkably low thermal conductivity, measuring below 0.50 Wm⁻¹K⁻¹. This places them among the materials with the lowest thermal conductivity reported for perovskites. The observed low thermal conductivity is attributed to oxygen vacancies and phonon scattering. Interestingly as SEM images show the smaller grain size, our findings suggest that creating vacancies and lowering the grain size or increasing the grain boundaries play a crucial role in achieving such low thermal conductivity values. This characteristic enhances the potential of these materials for applications where efficient heat dissipation, safety, and equipment longevity are paramount. 

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2. Earth abundant perovskite oxides for low temperature CO ₂ conversion

   https://doi.org/10.1039/C7EE03383D  

   Maiti, Debtanu; Hare, Bryan J.; Daza, Yolanda A.; Ramos, Adela E.; Kuhn, John N.; Bhethanabotla, Venkat R. (January 2018, Energy & Environmental Science)

   Conversion of CO 2 in a scalable technology has the potential for enormous energy and environmental impact but remains a challenge. We present several stable, earth abundant perovskite oxide materials for the reverse water gas shift chemical looping (RWGS-CL) process as a potential solution for this CO 2 mitigation problem. This material and process combination circumvents issues plaguing other emerging technologies, viz. poor rates of CO 2 conversion, high operation temperatures, use of precious metal catalysts, or combinations thereof. Using DFT-calculated oxygen vacancy formation energy, a key descriptor for the RWGS-CL process, we have successfully predicted several earth abundant perovskite oxides with high CO 2 conversion capability. We simultaneously achieved 100% selective CO generation from CO 2 at the highest known rates (∼160 μmoles per min per gram perovskite oxide) at record low process temperatures of 450–500 °C using lanthanum and calcium based perovskite oxides. These materials are stable over several RWGS-CL cycles, enabling industrial implementation. 

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3. Ru-promoted perovskites as effective redox catalysts for CO ₂ splitting and methane partial oxidation in a cyclic redox scheme

   https://doi.org/10.1039/D2NR04437D  

   Iftikhar, Sherafghan; Martin, William; Wang, Xijun; Liu, Junchen; Gao, Yunfei; Li, Fanxing (July 2022, Nanoscale)

   The current study reports AxA’1-xByB’1-yO3-𝛿 perovskite redox catalysts (RCs) for CO2-splitting and methane partial oxidation (POx) in a cyclic redox scheme. Strontium (Sr) and iron (Fe) were chosen as A and B site elements with A’ being lanthanum (La), samarium (Sm) or yttrium (Y), and B’ being manganese (Mn), or titanium (Ti) to tailor their equilibrium oxygen partial pressures (P_(O_2 ) s) for CO2-splitting and methane partial oxidation. DFT calculations were performed for predictive optimization of the oxide materials whereas experimental investigation confirmed the DFT predicted redox performance. The redox kinetics of the RCs improved significantly by 1 wt.% ruthenium (Ru) impregnation without affecting their redox thermodynamics. Ru impregnated LaFe0.375Mn0.625O3 (A=0, A’=La, B=Fe, and B’=Mn) was the most promising RC in terms of its superior redox performance (CH4/CO2 conversion >90% and CO selectivity~ 95%) at 800oC. Long-term redox testing over Ru impregnated LaFe0.375Mn0.625O3 indicated stable performance during the first 30 cycles following with a ~25% decrease in the activity during the last 70 cycles. Air treatment was effective to reactivate the redox catalyst. Detailed characterizations revealed the underlying mechanism for redox catalyst deactivation and reactivation. This study not only validated a DFT guided mixed oxide design strategy for CO2 utilization but also provides potentially effective approaches to enhance redox kinetics as well as long-term redox catalyst performance. 

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4. Mechanisms of Hysteresis and Reversibility across the Voltage-Driven Perovskite–Brownmillerite Transformation in Electrolyte-Gated Ultrathin La _0.5 Sr _0.5 CoO _3−δ

   https://doi.org/10.1021/acsami.4c01336  

   Postiglione, William M.; Yu, Guichuan; Chaturvedi, Vipul; Zhou, Hua; Heltemes, Kei; Jacobson, Andrew; Greven, Martin; Leighton, Chris (April 2024, ACS Applied Materials & Interfaces)

   ABSTRACT: Perovskite cobaltites have emerged as archetypes for electrochemical control of materials properties in electrolytegate devices. Voltage-driven redox cycling can be performed between fully oxygenated perovskite and oxygen-vacancy-ordered brownmillerite phases, enabling exceptional modulation of the crystal structure, electronic transport, thermal transport, magnetism, and optical properties. The vast majority of studies, however, have focused heavily on the perovskite and brownmillerite end points. In contrast, here we focus on hysteresis and reversibility across the entire perovskite ↔ brownmillerite topotactic transformation, combining gate-voltage hysteresis loops, minor hysteresis loops, quantitative operando synchrotron X-ray diffraction, and temperature-dependent (magneto)transport, on ion-gel-gated ultrathin (10-unit-cell) epitaxial La0.5Sr0.5CoO3−δ films. Gate-voltage hysteresis loops combined with operando diffraction reveal a wealth of new mechanistic findings, including asymmetric redox kinetics due to differing oxygen diffusivities in the two phases, nonmonotonic transformation rates due to the first-order nature of the transformation, and limits on reversibility due to first-cycle structural degradation. Minor loops additionally enable the first rational design of an optimal gate-voltage cycle. Combining this knowledge, we demonstrate state-of-the-art nonvolatile cycling of electronic and magnetic properties, encompassing >105 transport ON/OFF ratios at room temperature, and reversible metal−insulator−metal and ferromagnet−nonferromagnet−ferromagnet cycling, all at 10-unit-cell thickness with high room-temperature stability. This paves the way for future work to establish the ultimate cycling frequency and endurance of such devices. KEYWORDS: electrolyte gating, magnetoionics, complex oxides, perovskite−brownmillerite transformation, hysteresis, reversibility 

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5. Roundtrip Energy Efficiency Optimization of an Energy Storage System Using Products of Iron Combustion

   https://doi.org/10.1115/1.4071808  

   You, Dongchuan; Metghalchi, Hameed; Levendis, Yiannis (January 2026, ASME Open Journal of Engineering)

   Hamidzedeh, Hamid (Ed.)

   Iron has attracted increasing attention as a cyclic energy carrier for large-scale, long-duration, and transportable energy storage. In this study, an integrated iron-based energy storage system is presented and thermodynamically analyzed by coupling an iron reduction cycle with a power generation cycle. The reduction cycle is designed as an energy-recovery process to convert Fe2O3 into iron fuel for power generation, where hydrogen serves as the reducing agent and thermal energy is recovered through a series of energy exchangers. The power generation cycle is configured as a combined cycle consisting of a closed air Brayton topping cycle and a reheat steam Rankine bottoming cycle, where the chemical energy stored in iron is released through combustion for electricity generation. Since hydrogen is used as the reducing agent and iron is combusted with oxygen rather than air, NOx formation in the main reactive processes is avoided. The reduction and combustion processes are modeled using Reaktoro/NASA-CEA thermodynamic data, while the air and steam properties in the power cycle are obtained from REFPROP. A comprehensive parametric study and optimization were performed to evaluate the effects of reactor hydrogen inlet temperature, air cycle pressure, steam cycle pressure, and air turbine inlet temperature on system performance. The results show that the minimum fresh hydrogen requirement is achieved at a reactor hydrogen inlet temperature of 1233 K, corresponding to approximately 4.36 mol H2 per mol Fe2O3. In the power cycle, parametric studies have been made to determine the air cycle high pressure and steam cycle high pressure. The results indicate that when air turbine inlet temperature is either 1500 K or 1600 K, the higher the steam cycle pressure and air cycle pressure, the higher the power cycle efficiency. However, when air turbine inlet temperature is 1400 K, while the power cycle efficiency still increases when steam cycle pressure increases, the air cycle pressure reaches the maximum efficiency at about 1750 kPa. The maximum power cycle efficiency reaches about 61–64% when air turbine inlet temperature ranges from 1400 K to 1600 K. For hydrogen production electricity consumption ranging from 42 kWh/kg-H2 to 55 kWh/kg-H2, the overall roundtrip energy efficiency of the integrated system ranges from about 26% to 34%, with the best performance obtained at the optimized reduction condition, higher turbine inlet temperatures, air cycle pressure, and steam cycle pressure. These results demonstrate the thermodynamic potential of iron-based energy storage systems with hydrogen and combined-cycle power generation. 

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