Isothermal Cycling Research Articles

Thermal life assessment of laser powder-directed energy deposited NiCrAlY/CuCrZr bimetallic clad for rocket nozzle applications

To enhance the thermal life of rocket exhaust nozzles, the hot side of copper liners is coated with thermal barrier coatings (TBCs) to provide thermal insulation and oxidation resistance. However, interface failures often occur between M-CrAlY bond coats and nozzle liners due to significant differences in their thermal expansion coefficients (CTE). This study explores the use of Laser Powder-Directed Energy Deposition (LP-DED) to clad NiCrAlY onto a CuCrZr substrate, as the process offers localized heating which can offer better bond strength. Optimization trials were conducted using single and multi-track studies to identify optimal parameters. Due to the low energy absorption of the CuCrZr substrate to 1070 nm laser sources, cladding was performed at a high energy density of 135 J/mm2 with a 1.2 g/min feed rate to achieve defect-free clads with sufficient diffusion. The bulk of the NiCrAlY clads showed γ′-Ni3Al, β-NiAl, and γ-Ni phases, while Y4Al2O9 and Y2O3 oxides formed on the top surface due to aluminum and yttrium depletion at high temperatures. The clads exhibited cellular dendritic microstructures at the bulk region, and planar microstructures were observed at the dilution zone. EBSD-KAM maps showed higher dislocation density near the interface due to CTE mismatch across substrate and clad. Scratch tests confirmed strong adhesion with no interface cracks, though crack propagation was observed from the edges after 50 isothermal cycles, driven by copper erosion. With Cu diffusion, interface region exhibited a graded microstructure which could enhance CTE, improving compatibility compared to standard NiCrAlY alloys.

Shrinkage and deformation of material extrusion 3D printed parts during sintering: Numerical simulation and experimental validation

Material extrusion 3D printing (ME3DP) combined with sintering is a low-cost additive manufacturing technique for fabricating components of difficult-to-print metals, such as copper, aluminum, and ceramics. However, the sintering process includes complex material science, such as volumetric shrinkage and free structural bending, to identify the relative density and deformation of a 3D printed sample. The prediction of the relative density and deformations during the sintering process provides information to the design engineer to optimize the design of the CAD model before sintering. In this study, a phenomenological model based on constitutive equations was developed to predict the density and structural deformation during the sintering process of pure copper components fabricated by ME3DP using metal injection molding feedstock. The densification rate was determined using shrinkage estimation with an isothermal stairway heating cycle in a vertical dilatometer. Furthermore, different sets of experiments were performed with a load on the probe with long isothermal heating cycles at 850, 900, 950, 1000, and 1050 °C in a vertical dilatometer to estimate the axial viscosity of the copper. The constitutive equations were solved using the solid mechanics module with user-defined creep in COMSOL Multiphysics by considering isotropic assumptions. Two types of geometries, cube and overhanging I section, were used to predict shrinkage and deformation during the sintering process. The developed model successfully predicted the relative density based on shrinkage and structural deformation owing to gravity during the sintering process.

Preliminary Study of Stone Sawing Sludges-based Alkali Activated Materials (AAMs) for the Conservation of Archaeological Ceramics

This paper presents research into the feasibility of using stone sawing sludge-based Alkali Activated Materials (AAMs) for conservation of Cultural Heritage. Sawing sludges are a stone processing waste product resulting from the mixing of rock powder with the water used to cool down the cutting blades. The chemical composition of the sawing sludges, when aluminosilicatic, is suitable for acting as a precursor to produce AAMs. AAMs are known for their low environmental impact and versatility since their existence is drawn from recycling waste materials. One of their possible applications is in the conservation of Cultural Heritage objects. This work presents a preliminary investigation into three sawing sludge-based AAMs with different mineralogical compositions and contributes to formulating guidelines for applying them as fillers on modern and archaeological ceramic pottery based on the evaluation of their workability, appearance and physical properties over time from the moment of application and up to 30 days. Dynamic Vapor Sorption and X-Ray Diffraction results provided an overview of the structural and mineralogical changes under high RH conditions, where the tested AAMs showed a type II isotherm curve, as expected for concrete-like materials, as well as disappearance of thermonatrite after one isothermal cycle. Ultrasonic Pulse Velocity test demonstrated the general homogeneity of the AAMs despite the lower velocity exhibited by one of the formulations, probably due to its internal pore distribution and possible presence of microstratification. The Oddy tests, application tests and colourimetric measurements evidenced the advantages and weaknesses of the AAMs, with overall encouraging results ensuing investment in further in-depth studies of these innovative conservation materials in view of their future use in the field of conservation of Cultural Heritage as a result of a circular economy model.

Unlocking thermochemical CO2/H2O splitting by understanding the solid-state enthalpy and entropy of material reduction process

Two-step redox thermochemical cycles, capable of directly converting CO2 and H2O respectively into CO and H2, offer a promising synthesis route towards green carbon-neutral fuels. The performance of such two-step cycles depends highly on the thermodynamic properties of splitting materials, particularly the solid-state enthalpy (Δhsolid) and entropy (Δssolid) changes during the reduction process. Here, we report an investigation into the roles of the Δhsolid and Δssolid. We shall show that a high Δssolid relaxes both reduction temperature and oxygen pressure, but increases oxidant consumption. Conversely, an increase in Δhsolid enhances reduction resistance while promotes oxidation reactions. There are therefore no perfect materials, and a trade-off is needed for an optimal solution. We also defined a thermodynamic region based on Δhsolid and Δssolid and typical operating conditions, and showed that higher values of both Δhsolid and Δssolid provided a larger reaction space. While lower Δhsolid and negative Δssolid may be more suitable for isothermal cycles. Our analyses also suggest future efforts in searching for splitting materials with a high Δssolid within an appropriate range of Δhsolid (280–460 kJ/mol).

Feasibility of continuous water and carbon dioxide splitting via a pressure-swing, isothermal redox cycle using iron aluminates

Efficient solar thermochemical fuel production has been hindered by either solid–solid heat recuperation and material stability challenges associated with conventional temperature swing operation or low reactant conversion associated with isothermal operation. Increasing the oxidation pressure has emerged as a method for achieving efficient and practical solar-to-fuel conversion with certain redox mediators. When coupled with isothermal operation, pressure-swing redox cycling with iron aluminates eliminates irreversible heating penalties associated with large temperature swings while simultaneously enabling greater reactant conversion. However, remaining questions persist regarding 1) kinetics, 2) co-splitting capabilities, and 3) continuous processing prior to implementation beyond the lab scale. Here, we provide mechanistic insight on how pressure impacts the oxidation kinetics of iron aluminates, demonstrate syngas production with H2:CO ratios ranging from 1.3 ± 0.05 to 3.2 ± 0.25, and produce fuel continuously over an eight-hour period using dual fluidized bed reactors to evaluate the key considerations for large scale implementation. This work demonstrates the feasibility of a continuous solar thermochemical fuel production process via pressure-swing, isothermal redox cycling.

Study on the Corrosion Behavior of inconel 625 deposited metal against molten nitrate

In order to investigate the corrosion resistance of Inconel 625 deposited metal under two conditions of isothermal and thermal cycling in nitrate molten salt, this paper conducted nitrate molten salt tests on its alloy at alternating temperatures between 565 ℃ and 290 ℃-565 ℃. By using SEM, XPS and other methods to characterize the corroded samples, it was found that the corrosion amount of the deposited metal under isothermal conditions was higher than that under thermal cycling conditions. The results showed that compared to corrosion under isothermal conditions, the corrosion weight loss of Inconel 625 deposited metal under thermal cycling conditions was 0.536×10−3 mg/mm2, 0.714×10−3 mg/mm2, 0.1429×10−2 mg/mm2, and 0.232×10−2 mg/mm2, respectively, which were smaller than those under isothermal conditions of 0.1×10−2 mg/mm2, 0.13×10−2 mg/mm2, 0.2×10−2 mg/mm2, and 0.35×10−2 mg/mm2. The corrosion rate under thermal cycling conditions was maintained at approximately 0.228×10−3 μm/h, while under isothermal conditions, the corrosion rate ranged from a minimum of 0.427×10−3 μm/h to a maximum of 0.1458×10−2 μm/h. Through observation, layers of Cr2O3, NiO, and Fe2O3 were identified. The intermediate layer of Fe2O3 plays a protective role against potential dissolution triggered by the molten salt in the inner Cr2O3 and NiO layers.

Gas-phase surface modification to control catalyst structure and yields in methane dehydroaromatization

Methane dehydroaromatization (MDA) is a promising approach for direct methane transformation to aromatics and hydrogen. The benchmark catalyst Mo/H-ZSM-5 struggles to find commercial adoption because of thermodynamically-limited yields and rapid coking on Brønsted acid and molybdenum carbide species, especially on zeolite external surfaces. Here, gas-phase atomic layer deposition (ALD) overcoats H-ZSM-5 external surfaces with SiO2 or Al2O3. NH3-TPD, HRTEM, and textural properties show that these overcoats exclusively passivate zeolite external surfaces. Under MDA conditions, SiO2 gives softer coke and increases cumulative benzene yields by 25 %, while Al2O3 strongly decreases yields. H2-TPR and UV–visible and Raman spectroscopy show how the overcoats redisperse the MoOx precatalysts, especially over multiple deactivation and isothermal oxidative regeneration cycles. Combined with 27Al-MAS NMR, MoOx redistribution and dealumination are seen as the causes of long-term deactivation over multiple regeneration cycles, and this process continues to occur regardless of the overcoat. Overall, the deposition of a small amount of silica on the outer surface of Mo/H-ZSM-5 reduces the formation of hard coke, which could be regenerated by milder methods such as hydrogen treatment.

Out-of-phase thermomechanical fatigue of a single crystal Ni-base superalloy

The present work studies the out-of-phase thermomechanical fatigue (OP-TMF) behavior of the precisely oriented [001] single crystal Ni-base superalloy ERBO/1 (CMSX-4 type). The OP-TMF tests are performed between minimum and maximum temperatures of 1023 and 1223 K and a cyclic mechanical strain amplitude of ±0.5 %. In accordance with previous findings, the present study confirmed that isothermal low cycle fatigue (LCF) tests at 1023 and 1223 K show significantly longer fatigue lives than the OP-TMF tests, specimens with rougher surfaces fail earlier than polished specimens and deformation bands and cracks form in the specimen surface. Two new results were obtained: First, when comparing OP-TMF cycles with fast cooling (tensile part of cycle) and fast vs. slow heating (compressive part of cycle) one finds that the slower heating/compressive cycle is more damaging. Second, analytical scanning electron microscopy of the flanks of an OP-TMF crack allows to study the diffusion-controlled growth kinetics of the oxide and the underlying zone, which is depleted by the oxide forming elements. These results are discussed in the light of the microstructural, mechanical and chemical results of the present study considering previous work on OP-TMF of superalloy single crystals (SXs).

Comparison of non-isothermal and isothermal cycles in a novel methane-assisted two-step thermochemical process

As driven by thermodynamics and reaction kinetics considerations, conventional two-step solar thermochemical processes typically rely on non-isothermal cycling conditions to effectively couple the endothermic reduction and exothermic oxidation reactions. Nevertheless, recent discussions on isothermal cycles based on thermodynamics simulation and material characterization have sparked dissenting opinions, as certain reaction processes operating under isothermal cycling conditions have demonstrated the possibility of achieving higher energy conversion efficiency. To delve further into such phenomenon and potentially unveil the underlying scientific principles, this study conducts a reaction kinetic analysis and lab-scale systematic experiments on a novel methane-assisted two-step thermochemical process using iron-based oxygen carriers. Despite the fact that the reaction kinetics analysis of iron oxides indicates that isothermal cycles at reaction temperatures of 573–1173 K do not provide significant advantages in terms of energy conversion efficiency, surprisingly, the experiments conducted with the prepared cobalt–nickel ferrite materials conclude oppositely. More specifically, the observed increase in material reactivity with rising oxidation temperature contributes to an approximately two-fold enhancement in the CO yield under isothermal conditions, as well as a noteworthy improvement of about 15% in solar-to-fuel efficiency. This energy efficiency improvement could be attributed, at least in part, to the stable reaction temperature during isothermal cycling, which effectively mitigates the challenges associated with solid-phase sensible heat recovery caused by significant temperature fluctuations, particularly when operating at high feed flow rates. Accordingly, the applicability of isothermal cycles is linked to two crucial factors: the reactivity of the oxygen carrier and the specific operating conditions employed. The experiments herein conducted showed that the catalytic activity of the material reached a relatively stable state after 24 h of reaction, resulting in a peak CO yield of 20.5 mL min−1 g−1 and a CO2 conversion exceeding 90%. Thorough analyses reveal several optimization measures for enhancing efficiency under the setting of the reaction system.

A nickel-modified perovskite-supported iron oxide oxygen carrier for chemical looping dry reforming of methane for syngas production

The chemical looping dry reforming of methane (CLDRM) process, which converts methane and carbon dioxide into syngas, is an environmentally friendly greenhouse gas utilization strategy. In this work, it is demonstrated that a nickel-modified perovskite-supported iron-based oxygen carrier (Ni-Fe2O3/La0.8Sr0.2FeO3) significantly enhances the reactivity of CLDRM in the temperature range of 770–800 °C while maintaining high CO selectivity and oxygen capacity, as well as good carbon deposition resistance. With the addition of nickel, the methane conversion is 52 % higher than that without nickel at 800 °C. Rational coupling of the oxygen carrier components achieves over 99 % CO selectivity. 160 consecutive isothermal cycles confirm the outstanding stability of Ni-Fe2O3/La0.8Sr0.2FeO3. Based on the experimental results and characterizations, the evolution scheme and synergistic effects between the components of the Ni-Fe2O3/La0.8Sr0.2FeO3 oxygen carrier for CLDRM reaction are proposed. The results provide a pathway for oxygen carrier design to decrease the reforming temperature while maintaining excellent reaction performance in iron-based chemical looping systems.

Active metal-free CaO-based dual-function materials for integrated CO2 capture and reverse water–gas shift

Integrated CO2 capture and conversion into CO via the reverse water–gas shift reaction (ICCC-RWGS) using CaO-based dual-function materials (DFMs) offers an attractive avenue for mitigating anthropogenic CO2 emissions. Active metal-free CaO-based DFMs have advantages such as no CO formation at the CO2 capture stage and high CO selectivity across a broad temperature range at the CO2 conversion stage, yet they face challenges with low CO yield. Herein, we report the enhanced performance of CaO-based DFMs co-doped with gallium (Ga) and zirconium (Zr) oxides in the ICCC-RWGS process. This improvement can be attributed to the synergistic interaction among Ca, Ga and Zr oxides, resulting in reduced CaO crystallites, enhanced surface basicity, and increased concentration of oxygen vacancies. The most promising DFM consists of 90 wt% CaO, 4.5 wt% Ca3Ga4O9 and 5.5 wt% CaZrO3 (with a Ga/Zr molar ratio of 1). When exposed to a simulated flue gas (5 % O2, 10 % H2O, 15 % CO2, and 70 % N2), this DFM exhibits a stable CO2 capture capacity of 11.90 mmol/gDFM over 20 consecutive isothermal ICCC-RWGS cycles at 650 °C. Meanwhile, its CO2 conversion and CO yield are maintained at 83.4 % and 10.26 mmol/gDFM, respectively. This study highlights the significance of a multi-metal oxide synergistic strategy in CaO-based DFMs to achieve superior performance in the ICCC-RWGS process.

Failure-mode dependence on the formation of deformation twinning in the fourth-generation single crystal Ni-based superalloy at high temperatures

In this work, the twinning-related deformation mechanisms under different failure modes of a fourth-generation single crystal (SX) superalloy at high temperatures were investigated. Notably, the twinnability of alloy increased in the sequence as follows: pure tension, in-phase (IP) thermal mechanical fatigue (TMF), isothermal low cycle fatigue (LCF), hot compression, out-of-phase (OP) TMF. High-temperature compressive loading which facilitated the successive operation of {111}〈1 1 2〉 viscous slipping, was indispensable for the nucleation of micro-twins. However, this stimulative effect could be markedly offset by the co-existence of high-temperature tensile loading. Moreover, the activation of different {111}〈1 1 2〉 slipping systems as well as potential interactions between stacking faults played a significant role in the formation and thickening processes of deformation twins. In the experimental alloy system, the presence of deformation twins was attested to impair the fatigue resistance of the specimen. These findings provided new insights for ensuring the safe service of the fourth-generation SX superalloys.

High Temperature Oxidation of Additively and Traditionally Manufactured Inconel 718

Abstract Additively manufactured nickel-based superalloys are now being considered as a replacement for traditionally manufactured components on commercial and military aircraft. While the potential of additive manufacturing for gas turbine engines is promising, the quality and performance of additive manufactured components still need extensive study. Coupon-sized test specimens comprised of as-printed additively and traditionally manufactured Inconel 718 with and without yttria-stabilized zirconia thermal barrier coating were tested under simulated isothermal and thermal cycling combustion conditions that were representative of gas turbine environments. Pre-test scanning electron microscopy indicated that traditionally manufactured coupons had a smooth surface finish with minor imperfections while additive manufactured coupons had a rough surface finish. Post-test scanning electron microscopy exhibited differences in oxide scale between the isothermal and thermal cycling conditions. The thermal cycling condition increased the amount of oxide scale for both additively manufactured and traditionally manufactured Inconel 718. The size of the oxide islands on traditionally manufactured coupons was significantly larger than the additively manufactured coupons. The results indicated that differences in surface roughness may affect the growth of the oxidation scale in a high-temperature combustion environment. The benefits of yttria-stabilized zirconia thermal barrier coating were characterized. The substrate of the coupons experienced little to no formation of oxide scales compared to the uncoated additive and traditionally manufactured coupons. The results further suggested that yttria-stabilized zirconia thermal barrier coating can be utilized to provide both insulation and oxidation protection when desired. Post-test energy-dispersive X-ray spectrometry results corresponded well with known elemental compositions and oxidation mechanisms.

Prospects of Hydrogen Application as a Fuel for Large-Scale Compressed-Air Energy Storages

A promising method of energy storage is the combination of hydrogen and compressed-air energy storage (CAES) systems. CAES systems are divided into diabatic, adiabatic, and isothermal cycles. In the diabatic cycle, thermal energy after air compression is discharged into the environment, and the scheme implies the use of organic fuel. Taking into account the prospects of the decarbonization of the energy industry, it is advisable to replace natural gas in the diabatic CAES scheme with hydrogen obtained by electrolysis using power-to-gas technology. In this article, the SENECA-1A project is considered as a high-power hybrid unit, using hydrogen instead of natural gas. The results show that while keeping the 214 MW turbines powered, the transition to hydrogen reduces carbon dioxide emissions from 8.8 to 0.0 kg/s, while the formation of water vapor will increase from 17.6 to 27.4 kg/s. It is shown that the adiabatic CAES SENECA-1A mode, compared to the diabatic, has 0.0 carbon dioxide and water vapor emission with relatively higher efficiency (71.5 vs. 62.1%). At the same time, the main advantage of the diabatic CAES is the possibility to produce more power in the turbine block (214 vs. 131.6 MW), having fewer capital costs. Thus, choosing the technology is a subject of complex technical, economic, and ecological study.

Synergistic promotions between high purity H2 production and CO2 capture via sorption enhanced chemical looping reforming

Hydrogen energy, a promising clean source, holds potential to combat global warming. To achieve efficient and low-carbon H2 production, we proposed an isothermal sorption-enhanced chemical looping reforming (SE-CLR) process to realize the high-purity hydrogen production and in-situ CO2 capture at mild temperatures (550–650 °C). For practical application, the process is characterized to use Fe-Ni double metal oxide particles as steam methane reforming oxygen carriers, and K2CO3-promoted Li4SiO4 particles as CO2 sorbent. The oxygen transfer capacity of metal oxide matintained high at 57.4%, and the K-Li4SiO4 absorbents remained at 22.5% CO2 absorption capacity over 200 isothermal absorption-regeneration cycles. Conducting a synergistic conversion mechanism within double metal oxides and absorbents, and adjusting the absorbent-to-metal oxide mass ratio to 7:4, enhanced hydrogen purity to 92% and CO2 uptake to 95%. Furthermore, in-situ CO2 removal in CLR processes achieved methane conversion and H2 production rates equivalent to conventional CLR processes under the same reaction conditions, but at temperatures ∼60 °C lower. The effects of the reaction temperature, pressure, steam-to-methane and methane-to-solid ratios on SE-CLR performance were studied systematically. Finally, stable hydrogen production with a purity of 91%–89% and CO2 uptake of 94%–91% were obtained over 25 CLR cycles, with minimal changes in mechanical strength of particles.

Design a novel Ca-Mn perovskite oxygen carrier with balanced performance in chemical looping combustion

The cornerstone of chemical looping combustion (CLC) is oxygen carriers (OCs), and most OCs have one or more ever-present problems with performance, cost, stability, and service life. It is vital to develop OCs with balanced performance. A novel CM0.625TF-Mg OC is proposed in this study via B-site elemental substitution of CaMnO3 perovskite. Systematic experiments using a thermogravimetric analyzer (TGA), a batch fluidized bed reactor, a fixed bed reactor, and an air jet attrition apparatus are performed to evaluate various aspects of the performance of the OC manufactured by the hydraulic molding method. First, in isothermal TGA redox cycles, CM0.625TF-Mg OC exhibits a high oxygen donation ratio (∼5.0 wt.%) and excellent cyclic stability. Mg substitution eliminates the activation effect and promotes lattice oxygen release. Then, the CH4-fueled CLC experiments on a batch fluidized bed demonstrate that Mg B-site substitution promotes oxygen uncoupling (0.2 wt.% gaseous oxygen) and significantly improves its reactivity with CH4. Following that, an agglomeration resistance test on a packed bed reveals that CM0.625TF-Mg OC particles expand slightly yet exhibit remarkable agglomeration resistance. Further characterization results from SEM, EDS, and XRD analysis show that the perovskite phase is formed in fresh CM0.625TF-Mg OC via solid-phase synthesis at 1350 °C, and OC has high thermal and chemical stability during the multiple redox cycles. According to the attrition test results, CM0.625TF-Mg OC has an 8333-hour service life. Last, CM0.625TF-Mg OC has a material cost of $0.892/kg and a use cost of 0.00217 ($/kg[O]/h). In summary, this CM0.625TF-Mg OC has excellent and balanced performance in reactivity, stability, agglomeration resistance, attrition resistance, and cost, which is of great value for industrial demonstration of CLC in the later stage.

An APE1-mediated isothermal target cycling amplification for label-free and rapid detection of miRNA

Developing simple, rapid and sensitive strategies for miRNA analysis is extremely important for diseases early diagnosis. Herein, an APE1-mediated isothermal target cycling amplification system combined with magnetic separation was established for label-free and rapid detection of miRNA. As a proof-of-concept, miR-1246 was selected as research model. In the detection system, when the miR-1246 is present, it hybridizes with AP probes of AP-MBs to form a double-stranded, in which the APE1 recognizes specific AP site of double-stranded and cleaves the AP probes, releasing a sequence containing a G-quadruplex (G4). After the cleavage, target miR-1246 can be released to hybridize with another AP of AP-MBs, triggering a continues cleavage reaction. After magnetic separation, label-free analysis of miRNA was achieved by measuring the fluorescence of G4/ThT. Due to the high efficiency and specificity of APE1 toward AP sites in dsDNAs, this method exhibits high specificity and sensitivity with the capability of distinguishing miRNAs with single-base mismatch. The system could detect miRNA with high sensitivity within 2 h, and the limit of detection (LOD) was calculated as 25.6 fM. Furthermore, high accuracy has been achieved through recovery experiments and successful attempts has been made in applying the approach to detect miR-1246 in serum samples from breast cancer patients and normal people. This method is expected to be an effective tool for miRNA-related research and clinical early diagnosis.

Effect of Mg on elevated-temperature low cycle fatigue and thermo-mechanical fatigue behaviors of Al-Cu cast alloys

The effects of Mg addition on the cyclic deformation and fatigue life behaviors of Al-Cu 224 cast alloys were investigated under isothermal low cycle fatigue (LCF) at 300 °C and out-of-phase thermo-mechanical fatigue (OP-TMF) in the temperature range 60–300 °C. The results show that all tested alloys experienced cyclic softening during both LCF and OP-TMF, whereas the softening ratio of Mg-containing alloys was lower than that of the base alloy free of Mg because of the lower coarsening rate of θ'-Al2Cu precipitates. Under both LCF and TMF, near-surface porosity and brittle intermetallic particles were considered sources of crack initiation. TMF lives were inferior to LCF lives under the same strain amplitude because of the combined damage effect of the cyclic mechanical and thermal loadings. Under LCF, the addition of Mg enhanced the fatigue performance because of the co-existing θʹ and θʺ precipitates and the higher thermal resistance of θʹ; under TMF, it led to a slight reduction in fatigue performance. The hysteresis energy model was successfully applied to predict the LCF and TMF lifetimes. The predicted results agree well with the experimentally measured LCF and TMF lifetimes.

Superior synergistic effect derived from MnTiO3 nanodiscs for the reversible hydrogen storage properties of MgH2

Herein, nanodisc-like MnTiO3 was successfully prepared via a hydrothermal method, and for the first time, the MnTiO3 nanodiscs were doped into magnesium hydride (MgH2) for the study. In the first dehydrogenation cycle, MgH2-8 wt% MnTiO3 showed a low onset hydrogen release temperature of 202 °C, while MnTiO3 was transformed into Mg6MnO8 and TiOx by reaction with MgH2, which played a real catalyst in the subsequent reaction. The composite system could instantly absorb 4.79 wt% H2 in 100 s at 150 °C and rapidly release about 5.71 wt% H2 in 500 s at 300 °C. The Kissinger plot revealed that the dehydrogenation activation energy dropped to 72.06 kJ/mol, which was significantly lower than that of as-milled MgH2. Moreover, after 50 isothermal cycles, the composite system still has an excellent capacity retention rate of 94.4 %. Compositional and structural analysis indicated that the in situ formation of TiOx and Mg6MnO8 during dehydrogenation provided a multivalent multielement catalytic surrounding that accelerated the H atoms adsorption and dissociation, yielding a better kinetic property of MgH2.

Hydrogen production by isothermal thermochemical cycles using La0.8Ca0.2MeO3±δ (Me = Co, Ni, Fe and Cu) perovskites

Solar-driven thermochemical water splitting has the potential to transform concentrated solar energy into green hydrogen and other solar fuels. In this work, La0.8Ca0.2MeO3±δ (Me = Co, Ni, Fe and Cu) perovskites have been synthesised by a modified Pechini method and evaluated as materials for hydrogen production by two step thermochemical water splitting cycles. Performing the thermal reduction at temperatures of 1200 and 1000 °C, while the oxidation is done at 800 °C, allows a remarkable and stable hydrogen production after 5 consecutive cycles. However, the perovskites suffer changes in the structure after each redox cycle, with potential effects in the long-term cyclic operation. On the contrary, the isothermal thermochemical cycles at 800 °C produce a stable amount of hydrogen with each consecutive cycle maintaining the perovskite structure. This hydrogen production ranges from 3.60 cm3 STP/gmaterial·cycle for the material with the lowest productivity (La0.8Ca0.2FeO3±δ) to 5.02 cm3 STP/gmaterial·cycle for the one with the highest activity (La0.8Ca0.2NiO3±δ). Particularly the Ni-based material shows the highest H2 productivity accompanied by very good material stability after 15 consecutive cycles, being possible to combine with current solar thermal facilities based on concentrated solar power technologies like plants with central receivers.