53 research outputs found
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 chelating and pH buffering properties. We discuss the remaining
challenges including the electrochemical stability of the electrolyte
components.Comment: 16 pages, 12 figure
Structural studies of apatite-type oxide ion conductors doped with Cobalt
A series of Co doped lanthanum silicate apatite-type phases, La9.83Si4.5Co1.5O26, La9.66Si5CoO26, La10Si5CoO26.5 and La8BaCoSi6O26, have been synthesised, and neutron diffraction, EXAFS and XANES used to investigate their structures in detail. All compositions were shown to possess the hexagonal apatite structure, and the results confirmed that cobalt can be doped onto both the La and Si sites within the structure depending on the starting composition. The Co doping is shown to cause considerable local distortions within the apatite structure. In the case of Si site doping two compositions showed anisotropic peak broadening, which has been attributed to incommensurate ordering of oxygen within the apatite channels.</p
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
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
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