High temperature X-ray diffraction and thermo-gravimetrical analysis of the cubic perovskite Ba0.5Sr0.5Co0.8Fe0.2O3-δ under different atmospheres

Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) with the cubic perovskite structure is known to be metastable at low temperature under an oxidizing atmosphere. Here, the thermal and chemical expansion of BSCF were studied by in situ high temperature powder X-ray diffraction and thermo-gravimetrical analysis (TGA) in partial pressure of oxygen ranging from an inert atmosphere (∼10−4 bar) to 10 bar O2. The BSCF powder, heat treated at 1000 °C and quenched to ambient temperature prior to the analysis, was shown to oxidize under an oxidizing atmosphere before thermal reduction took place. With decreasing partial pressure of oxygen the initial oxidation was suppressed and only reduction of Co/Fe and loss of oxygen were observed under an inert atmosphere. The thermal expansion of BSCF under different atmospheres was determined from the thermal evolution of the cubic unit cell parameter, demonstrating that the thermal expansion of BSCF depends on the atmosphere. Chemical expansion of BSCF was also estimated based on the diffraction data and thermo-gravimetrical analysis. A hexagonal perovskite phase, coexisting with the cubic BSCF polymorph, was observed to be formed above 600 °C during heating. The phase separation leading to the formation of the hexagonal polymorph was driven by oxidation, and the unit cell of the cubic BSCF was shown to decrease with increasing amounts of the hexagonal phase. The hexagonal phase disappeared upon further heating, accompanied with an expansion of the unit cell of the cubic BSCFAuthor preprin

Optimal particle parameters for CLC and CLR processes - predictions by intra-particle transport models and experimental validation

Validated models for predicting oxidation and reduction kinetics of multi-component porous particles in chemical looping combustion (CLC) and chemical looping reforming (CLR) processes are of key importance to identify the rate limiting step in these processes. Since particle properties (i.e., their composition, porosity, pore size, grain size, etc.) can be adjusted by modern synthesis techniques, there is an open question on the optimal set of these properties that would lead to the most economic process. We introduce a general open-source simulation environment, called ParScale that can be used to simulate models relevant for CLC and CLR processes, and hence can be used for their optimization. Most important, ParScale features a generalized one-dimensional spherical discretization which enables the user to predict an arbitrary number of reactions within non-isothermal porous particles consisting of multiple solid (reactive or inert) species. We perform an optimization study (constrained by typical process requirements like the maximum reaction time) for an isothermal first-order reaction, as well as for an n-th order reaction typical for hematite reduction. Finally, materials consisting of active nanoparticles embedded in a matrix of a different composition are synthesized and analyzed

Towards Rechargeable Zinc-Air Batteries with Aqueous Chloride Electrolytes

This paper presents a combined theoretical and experimental investigation of aqueous near-neutral electrolytes based on chloride salts for rechargeable zinc-air batteries (ZABs). The resilience of near-neutral chloride electrolytes in air could extend ZAB lifetime, but theory-based simulations predict that such electrolytes are vulnerable to other challenges including pH instability and the unwanted precipitation of mixed zinc hydroxide chloride products. In this work, we combine theory-based simulations with experimental methods such as full cell cycling, operando pH measurements, ex-situ XRD, SEM, and EDS characterization to investigate the performance of ZABs with aqueous chloride electrolytes. The experimental characterization of near-neutral ZAB cells observes the predicted pH instability and confirms the composition of the final discharge products. Steps to promote greater pH stability and control the precipitation of discharge products are proposed.Comment: 13 pages, 12 figure

A numerical homogenisation strategy for micromorphic continua

Cellular materials are of special interest according to their peculiar mechanical properties. In this paper, special attention is paid to the simulation of size-dependent microtopological effects. We introduce a numerical homogenisation scheme for a two-scale problem dealing with a micromorphic continuum theory on the macroscale and a classical Cauchy continuum on the microscale. The transitions between both scales are obtained by projection and homogenisation rules derived from an equivalence criterion for the strain energy, also known as the Hill-Mandel condition

Designing Aqueous Organic Electrolytes for Zinc-Air Batteries: Method, Simulation, and Validation

Aqueous zinc-air batteries (ZABs) are a low-cost, safe, and sustainable technology for stationary energy storage. ZABs with pH-buffered near-neutral electrolytes have the potential for longer lifetime compared to traditional alkaline ZABs due to the slower absorption of carbonates at non-alkaline pH values. However, existing near-neutral electrolytes often contain halide salts, which are corrosive and threaten the precipitation of ZnO as the dominant discharge product. This paper presents a method for designing halide-free aqueous ZAB electrolytes using thermodynamic descriptors to computationally screen components. The dynamic performance of a ZAB with one possible halide-free aqueous electrolyte based on organic salts is simulated using an advanced method of continuum modeling, and the results are validated by experiments. XRD, SEM, and EDS measurements of Zn electrodes show that ZnO is the dominant discharge product, and operando pH measurements confirm the stability of the electrolyte pH during cell cycling. Long-term full cell cycling tests are performed, and RRDE measurements elucidate the mechanism of ORR and OER. Our analysis shows that aqueous electrolytes containing organic salts could be a promising field of research for zinc-based batteries, due to their Zn$^{2+}$ chelating and pH buffering properties. We discuss the remaining challenges including the electrochemical stability of the electrolyte components.Comment: 16 pages, 12 figure

Cold Sintering as a Cost-Effective Process to Manufacture Porous Zinc Electrodes for Rechargeable Zinc-Air Batteries

Zinc-air batteries (ZABs) offer a sustainable and safe pathway to low-cost energy storage. Recent research shows that thermally-sintered porous Zn electrodes with a three-dimensional network structure can enhance the performance and lifetime of ZABs, but they are expensive and energy-intensive to manufacture. In this work, monolithic porous Zn electrodes fabricated through an efficient cold sintering process (CSP) were studied for rechargeable ZABs. Electrochemical studies and extended charge-discharge cycling show good Zn utilization with no observable performance degradation when compared to Zn foil. Post-mortem analysis after 152 h of cycling reveals that the cold-sintered electrodes retain their original structure. A techno-economic assessment of the cold sintering process confirms significant reductions in both the time and energy required to manufacture Zn electrodes compared to a comparable thermal sintering process.publishedVersio

Doping and defect association in AZrO3(A = Ca, Ba) and LaMO3(M = Sc, Ga) perovskite-type ionic conductors

Computer simulation techniques have been used to investigate the defect chemistry of perovskite-structured ionic conductors based upon AZrO3 (A = Ca, Ba) and LaMO3 (M = Sc, Ga). Our studies have examined dopant site-selectivity, oxide ion migration and dopant–defect association at the atomic level. The energetics of dopant incorporation in AZrO3 show strong correlation with ion size. We predict Y 3 to be one of the most favourable dopants for BaZrO3 on energetic grounds, which accords with experimental work where this cation is the commonly used acceptor dopant for effective proton conduction. Binding energies for hydroxy–dopant pairs in BaZrO3 are predicted to be favourable with the magnitude of the association increasing along the series Y < Yb < In < Sc. This suggests that proton mobility would be very sensitive to the type of acceptor dopant ion particularly at higher dopant levels. Oxygen vacancy migration in LaScO3 is via a curved pathway around the edge of the ScO6 octahedron. Dopant–vacancy clusters comprised of divalent dopants (Sr, Ca) at the La site have significant binding energies in LaScO3, but very low energies in LaGaO3. This points to greater trapping of the oxygen vacancies in doped LaScO3, perhaps leading to higher activation energies at increasing dopant levels in accord with the available conductivity data.

Gas Switching Reforming (GSR) for syngas production with integrated CO2 capture using iron-based oxygen carriers

The process behavior of a Gas Switching Reforming (GSR) reactor was studied using three different iron-based oxygen carrier materials: Iron-oxide on Alumina, Iron-Nickel oxide on Alumina and Iron-Ceria on Alumina. It was observed that, for all oxygen carriers, the fuel stage reaction occurs in two distinct sub-stages when feeding methane and steam to a bed of oxidized material, with methane combustion dominating the first and methane reforming dominating the second. This reflects a change in the catalytic activity of the oxygen carrier as it is reduced. The alumina support was observed to play a significant role in the reactions occurring, with the redox-active phases being hematite-structured Fe2O3 (oxidized form) and spinel-structured (FeNiAl)3O4 (reduced form). The Nickel-containing oxygen carrier outperformed the others in the reforming sub-stage, showing 40% improved methane conversion. The feed of dry methane only during the combustion sub-stage was found to improve methane conversion to syngas in the subsequent reforming sub-stage from 75% to 80% at 800 °C. Results also show that methane conversion improves with the increase in operating temperature and steam/carbon ratio. Autothermal operation of the reactor was achieved with repeatable performance over several redox cycles. The study therefore successfully demonstrated autothermal N2-free syngas production with integrated CO2 capture from the fuel combustion required to supply heat to the endothermic reforming reactions.publishedVersio

Improved cyclability of Nickel-rich layered oxides

This study compares the physico- and electro- chemical properties of LiNi0.8Mn0.10Co0.1O2 (NMC811) and LiNi0.83Mn0.06Co0.09Al0.1O2 (NMCA) prepared by an oxalic acid co-precipitation. Deposition of a SiO2 surface coating was attempted via reaction of the powder with an amino silane prior to the final heat treatment. It was found that either the presence of small amounts of Al3+, or the compositional gradient resulting from a two step co-precipitation, caused increased crystal growth of the NMCA in comparison to NMC811. This led to improved cyclability in LP40 electrolyte. However, the SiO2 coating appeared incomplete and negatively impacted performance. Crystal cleavage preferably on the {001} planes was observed after 100 charge-discharge cycles, Downloaded from https://www.cambridge.org/core. SINTEF, on 13 Jun 2020 at 10:36:09, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/adv.2020.90 with consequent cathode electrolyte interphase formation in the crystal cracks. This is believed to cause capacity decay via lithium loss, and increased charge transfer resistance. An FEC based electrolyte improved the cyclability in all cases and even under extreme conditions (45°C and upper cycling potential of 4.5 V) NMCA showed a capacity retention of 85% after 100 cyclespublishedVersio