In situ tailored nickel nano-catalyst layer for internal reforming hydrocarbon fueled SOFCs

The authors gratefully thank the Engineering and Physical Sciences Research Council (EPSRC) SuperGen Hydrogen Fuel Cells Challenges Flame SOFC Project (Grant No EP/K021036/1) for financial supportConventional Ni cermet anodes suffer from carbon deposition when they are directly used with hydrocarbon fuels due to the negative effects of pyrolysis and Boudouard reactions. In this work, the use of a non-stoichiometric perovskite, La0.8Ce0.1Ni0.4Ti0.6O3, as a reforming layer in reducing atmospheres led to the surface being highly populated with homogeneously exsolved Ni nano particles. This catalyst layer was applied to Ni-GDC anode supported and ScSZ electrolyte supported cells to prevent carbon deposition and to stabilize operation with dry methane. The catalyst layer showed both excellent attachment to the Ni-GDC anode and resistance to carbon deposition. The performance of the Ni-GDC anode-supported cells with the catalyst layer was about 1.1 W/cm2 in hydrogen fuel which is similar to that seen without the use of a catalyst layer. For the ScSZ electrolyte supported cells, the catalyst layer improved the power density and stability when in operation with dry methane.Publisher PD

Alkaline modified A-site deficient perovskite catalyst surface with exsolved nanoparticles and functionality in biomass valorisation

The authors would like to thank the Petroleum Technology Development Fund (Nigeria) for funding this research and University of St Andrews (Scotland, UK) for the opportunity to carry out the research.Environmental problems associated with the use of fossil fuels and increase in energy demands due to rise in population and rapid industrialisation, are the driving forces for energy. Catalytic conversion of biomass to renewable energies is among the promising approaches to materialize the above. This requires development of robust catalysts to suppress deactivation due to carbon deposition and agglomeration. In this work, surface properties and chemistry such as exsolution of B-site metal catalyst nanoparticles, particle size and distribution, as well as catalyst-support interactions were tailored through the use of alkaline dopants to enhance catalytic behaviour in valorisation of glycerol. The incorporation of alkaline metals into the lattice of an A-site deficient perovskite modified the surface basic properties and morphology with a consequent robust catalyst-support interaction. This resulted in promising catalytic behaviour of the materials where hydrogen selectivity of over 30% and CO selectivity of over 60% were observed. The catalyst ability to reduce fouling of the catalyst surface as a result of carbon deposition during operation was also profound due to the robust catalyst-support interaction occurring at the exsolved nanoparticles due to their socketing and the synergy between the dopant metals in the alloy in perovskite catalyst systems. In particular, one of the designed systems, La0.4Sr0.2Ca0.3Ni0.1Ti0.9O3±δ, displayed almost 100% resistance to carbon deposition. Therefore, lattice rearrangement using exsolution and choice of suitable dopant could be tailored to improve catalytic performance.Publisher PDFPeer reviewe

Combining exsolution and infiltration for redox, low temperature CH4 conversion to syngas

Exsolution of surface and bulk nanoparticles in perovskites has been recently employed in chemical looping methane partial oxidation because of the emergent materials’ properties such as oxygen capacity, redox stability, durability, coke resistance and enhanced activity. Here we attempt to further lower the temperature of methane conversion by complementing exsolution with infiltration. We prepare an endo/exo-particle system using exsolution and infiltrate it with minimal amount of Rh (0.1 wt%) in order to functionalize the surface and induce low temperature activity. We achieve a temperature decrease by almost 220 °C and an increase of the activity up to 40%. We also show that the initial microstructure of the perovskite plays a key role in controlling nanoparticle anchorage and carbon deposition. Our results demonstrate that microstructure tuning and surface functionalization are important aspects to consider when designing materials for redox cycling applications

A model for modulating oxide ion transport with endo-particles for application in energy conversion

Certain energy conversion processes are underpinned by the transport of oxide ions across materials, components or interfaces. Examples include solid oxide fuel cells for power generation from hydrogen, but also chemical looping for hydrogen and syngas generation. Identifying new ways of enhancing oxide ion transport is thus required for advancing such technologies. Traditionally, this is achieved by doping or crystal lattice engineering but recent reports in these fields suggest a new approach, where oxide ion transport is potentially modulated through embedded (endo-) nanoparticles. This is assumed to occur due to the strain that endo-particles induce throughout the material. Here we propose a model to rationalize this effect, by constructing corresponding visual and numerical models of these experimental systems and calculating their respective volumetric strain and resulting conductivity enhancement. Our model indicates a strong correlation between ion conductivity enhancement and observed experimental data in these two different applications. This result demonstrates how nanoparticles may be harnessed within materials, to modulate oxide ion transport properties, beyond their traditional role as catalytic centers, which could inspire the design of new nanostructured oxide ion conductors for energy conversion applications

A brief review of the literature on the malignant ureteral obstruction

Malignant ureteral obstruction (MUO) caused by a primarily urological tumor or secondary to a late-stage malignancy can be difficult for the urologist to manage. Due to a lack of clinical data on the management of MUO, every case is particular and should be aborted individually. Lack of specific treatment, either palliative or definitive, can severely damage renal function and lifetime expectancy in patients, causing even more damage that could otherwise be avoided. Prompt management directed at the recovery of renal function is the main goal in such cases. Even after urinary flow is restored, life threatening post-obstructive diuresis needs to be managed

Exsolved nickel nanoparticles acting as oxygen storage reservoirs and active sites for redox CH4 conversion

The growing demand for H2 and syngas requires the development of new, more efficient processes and materials for their production, especially from CH4 that is a widely available resource. One process that has recently received increased attention is chemical looping CH4 partial oxidation, which, however, poses stringent requirements on material design, including fast oxygen exchange and high storage capacity, high reactivity toward CH4 activation, and resistance to carbon deposition, often only met by composite materials. Here we design a catalytically active material for this process, on the basis of exsolution from a porous titanate. The exsolved Ni particles act as both oxygen storage centers and as active sites for CH4 conversion under redox conditions. We control the extent of exsolution, particle size, and population of Ni particles in order to tune the oxygen capacity, reactivity, and stability of the system and, at the same time, obtain insights into parameters affecting and controlling exsolution

Towards efficient use of noble metals : via exsolution exemplified for CO oxidation

Many catalysts and in particular automotive exhaust catalysts usually consist of noble metal nanoparticles dispersed on metal oxide supports. While highly active, such catalysts are expensive and prone to deactivation by sintering and thus alternative methods for their production are being sought to ensure more efficient use of noble metals. Exsolution has been shown to be an approach to produce confined nanoparticles, which in turn are more stable against agglomeration, and, at the same time strained, displaying enhanced activity. While exsolution has been extensively investigated for relatively high metal loadings, it has yet to be explored for dilute loadings which is expected to be more challenging but more suitable for application of noble metals. Here we explore the substitution of Rh into an A-site deficient perovskite titante aiming to investigate the possibility of exsolving from dilute amounts of noble metal substituted perovskites. We show that this is possible and in spite of certain limitations, they still compete well against conventionally prepared samples with higher apparent surface loading when applied for CO oxidation

The effects of sulphur poisoning on the microstructure, composition and oxygen transport properties of perovskite membranes coated with nanoscale alumina layers

Perovskite oxides displaying mixed ionic and electronic conductivity have attracted a lot of interest for application in oxygen separation membranes. Such membranes could be used for a range of processes, including the conversion of natural gas to hydrogen or syngas. A major limitation of these materials is their tendency to segregate into simpler oxides under operating conditions, reacting with sulphur-based species often found in natural gas and leading to irreversible membrane degradation over time. Here we aim to delay or prevent this process by coating La0.6Sr0.4Co0.2Fe0.8O3-δ membranes with Alumina (Al2O3) layers of 1–100 nm thickness by using atomic layer deposition. We show that coatings of about 30 nm have negligible negative effect on O2 transport flux across the membrane and display good flux recovery when H2S is removed from the stream. Coatings thinner than this critical value provide little protection against irreversible poisoning while thicker coatings dramatically decrease overall O2 permeation fluxes. We also show that the irreversible sulphur poisoning under O2 permeation conditions is linked to microstructural and composition changes at the membrane surface caused predominantly by the formation of SrSO4 particles at the perovskite grain boundaries

Evolution of the electrochemical interface in high-temperature fuel cells and electrolysers

C.C. acknowledges financial support from ECoProbe (DFF – 4005-00129) funded by the Danish Independent Research Council. C.G. and M.B.M. acknowledge financial support from Energinet.dk through the ForskEL programme Solid Oxide Fuel Cells for the Renewable Energy Transition contract no. 2014-1-12231. J.T.S.I., M.C.V. and D.N. acknowledge support from EPSRC Platform Grant EP/K015540/1, EPSRC Tailoring of microstructural evolution in impregnated SOFC electrodes EP/M014304/1 and Royal Society Wolfson Merit Award WRMA 2012/R2.The critical region determining the performance and lifetime of solid oxide electrochemical systems is normally at the electrode side of the electrode/electrolyte interface. Typically this electrochemically active region only extends a few micrometres and for best performance involves intricate structures and nanocomposites. Much of the most exciting recent research involves understanding processes occurring at this interface and in developing new means of controlling the structure at this interface on the nanoscale. Here we consider in detail the diverse range of materials architectures that may be involved, describe the evolution of these interface structures and finally explore the new chemistries that allow control and manipulation of these architectures to optimize both performance and durability.PostprintPeer reviewe