“Evolved Materials and Innovative Design for High Performance, Durable and Reliable SOFC Cell and Stack” Presentation and Status of the European Project EVOLVE

Beyond the state of the art, EVOLVE aims at the development of a new cell architecture for SOFC, combining benefits of existing Anode Supported (high power density, lifetime) and Metal Supported cell (redox stability) architectures, while limiting the issue of sulphur poisoning by using enhanced perovskite anode materials. The core component is based on a composite anode substrate made of porous Alumina forming alloy combined with an electron conducting oxide ceramic, without having Nickel as structural component. A first Anode/Electrolyte assembly based on a NiCrAl foam and La0,1Sr0,9TiO3-α has been produced by means of Vacuum Plasma Spraying, showing the feasibility of this cell concept. With a requirement of a low temperature process, the manufacturing of the electrolyte layer remains the key challenge. Work is under progress for the manufacturing and testing of the first full prototype

High Temperature Water Electrolysis Using Metal Supported Solid Oxide Electrolyser Cells (SOEC)

Metal supported cells as developed according to the DLR SOFC concept by applying plasma deposition technologies were investigated for use as solid oxide electrolyser cells (SOEC) for high temperature steam electrolysis. Cells consisting of a porous ferritic steel support, a diffusion barrier layer, a Ni/YSZ hydrogen electrode, a YSZ electrolyte and a LSCF oxygen electrode were electrochemically characterised by means of i-V characteristics and electrochemical impedance spectroscopy measurements including a long-term test over 2000 hours. The cell voltage during electrolysis operation at a current density of -1.0 A cm-2 was 1.28 V at an operating temperature of 850 °C and 1.4 V at 800 °C. A long-term test run over 2000 hours with a steam content of 43% at 800 °C and a current density of -0.3 A cm-2 showed a degradation rate of 3.2% per 1000 hours. The impedance spectra revealed a significantly enhanced polarisation resistance during electrolysis operation compared to fuel cell operation which was mainly attributed to the hydrogen electrode

The Solution Precursor Plasma Spraying Process for Making Zirconia Based Electrolytes

Ceramic layers, such as yttria-stabilized zirconia or scandia-stabilized zirconia, used for functional layers of solid oxide fuel cells, i.e. the gas tight oxygen ion conductive electrolyte or as ceramic component in the porous cermet anode, were obtained by the Solution Precursor Plasma Spray (SPPS) process. The influence of different solvent types on microstructure was analyzed by comparison of coatings sprayed with water-based solution to ethanol-based one. Use of solvent with low surface tension and low boiling point enhances splat formation, coating micro-structure and crystalline structure. Parameter adjustment to receive coatings from nitrate solutions with ethanol as solvent was carried out. Results of Raman spectroscopy indicate that an intermediate of both nitrates (zirconyl and scandium nitrate hydrate) was deposited

Superior septal approach versus left atrial approach for mitral valve replacement: a retrospective cohort study

Abstract OBJECTIVE: To compare the outcomes of superior septal approach and left atrial approach for mitral valve replacement. METHODS: This retrospective cohort study was conducted at the Aga Khan University Hospital, Karachi, and comprised records of patients who had undergone isolated mitral valve replacement from May 2003 to April 2012. Cases were reviewed for the outcomes [primary: loss of normal sinus rhythm; secondary: complications, residual defect and mortality]. Patients with prior history of dysrhythmia, low ejection fraction (\u3c30%), emergency/redo mitral valve replacement and concomitant coronary artery bypass grafting were excluded. SPSS 19 was used for data analysis. RESULTS: Of the 78 patients, 52(66.67%) were of superior septal approach and 26(33.33%) of left atrial approach. Both groups were comparable for baseline variables except cardiopulmonary bypass and cross-clamp times, which were significantly shorter in the superior septal approach group than the left septal approach group (p\u3c0.05). No residual atrial septal defect was found in any approach. Although loss of normal sinus rhythm was observed more frequent in superior septal approach 25(48%) compared to left septal approach 10(38.4%), but the difference was statistically insignificant (p=0.28). Age was the only significant variable affecting loss of normal sinus rhythm after adjusting for approaches. The difference of post-operative complications was also statistically insignificant between superior 9(17.3%) and left septal approach 4(15.38%) (p=1.0)]. CONCLUSIONS: The operative durations were significantly higher in left atrial approach compared to superior septal approach

e-XPlore: A High-Pressure Solid Oxide Cell Electrolyser in a Sea Container for Offshore Power-to-X Applications

Green hydrogen and synthesis gases are one of the main energy carriers in our attempts to combat global warming and to fulfill the transition of our fossil fuel-based society and industrial activities to carbon neutral alternatives. One of the promising technologies for the production of these gases is the high temperature electrolysis with solid oxide cells (SOCs). At the German Aerospace Center’s (DLR) Institute of Engineering Thermodynamics we experimentally investigate how SOC stacks1 and modules2 (up to 120 kW input) and use transient system simulations3 to develop operation strategies. Particularly when syngas is needed by downstream processes at elevated pressures, it can be advantageous to pressurize the electrolysis as well. Therefore, DLR is building up a transportable test environment called e-XPlore4 for an experimental analysis of a pressured electrolysis system. It comprises a system built in a 40 foot-sea container with an SOC module in a pressure vessel and includes almost all the required auxiliary components for nearly self-sufficient operation, such as cooling water, air supply, climate system, gas heaters, controls and safety system. The system only requires tap water, renewable electricity and some gases like hydrogen and nitrogen for heat-up or emergency cases. Steam electrolysis and co-electrolysis can be performed for hydrogen and syngas production with pressures up to 25 bar, an operating temperature of ca. 900 °C, and with a maximum electrical power input of 10 kW. This system supplies the synthesis gas for downstream processes, such as Fischer-Tropsch-synthesis to produce synthetic fuels within a Power-to-X context. This presentation will showcase the latest updates of planning and engineering of this system, as well as the relevant technical challenges. Operation strategies for different operating points will also be discussed. Furthermore, the off-shore application near a wind farm in the German North Sea as part of the H2Mare5 project will be presented

Palladium Membrane with High Density of Large-Angle Grain Boundaries to Promote Hydrogen Diffusivity

A higher density of large-angle grain boundaries in palladium membranes promotes hydrogen diffusion whereas small-angle grain boundaries suppress it. In this paper, the microstructure formation in 10 µm thick palladium membranes is tuned to achieve a submicronic grain size above 100 nm with a high density of large-angle grain boundaries. Moreover, changes in the grain boundaries’ structure is investigated after exposure to hydrogen at 300 and 500 °C. To attain large-angle grain boundaries in Pd, the coating was performed on yttria-stabilized zirconia/porous Crofer 22 APU substrates (intended for use later in an ultracompact membrane reactor). Two techniques of plasma sprayings were used: suspension plasma spraying using liquid nano-sized powder suspension and vacuum plasma spraying using microsized powder as feedstock. By controlling the process parameters in these two techniques, membranes with a comparable density of large-angle grain boundaries could be developed despite the differences in the fabrication methods and feedstocks. Analyses showed that a randomly oriented submicronic structure could be attained with a very similar grain sizes between 100 and 500 nm which could enhance hydrogen permeation. Exposure to hydrogen for 72 h at high temperatures revealed that the samples maintained their large-angle grain boundaries despite the increase in average grain size to around 536 and 720 nm for vacuum plasma spraying and suspension plasma spraying, respectively

TRANSIENT OPERATING STRATEGIES FOR SOLAR HEAT SUPPORTED SOLID OXIDE ELECTROLYSIS SYSTEMS FOR HYDROGEN PRODUCTION

Considering the transformation of the energy system, there are two main challenges. First, efficient and cost competitive long-term energy storage on a large scale. Second, making renewable energy accessible for hard-to-electrify sectors like transport and heavy industry. Converting renewable electricity into green hydrogen in Solid Oxide Electrolysis Cells (SOEC) is considered a viable solution for both challenges. Besides the high efficiency, SOEC offer the possibility to supply part of the energy demand by industrial waste heat or by renewable sources, such as solar thermal energy. The SOEC technology itself is mature but the integration within large systems and coupling with up- and downstream processes still requires research to be done on the SOEC's transient behaviour as well as identifying safe and efficient operating strategies. In this contribution, a solar-SOEC coupled system concept is introduced and analysed for its capability to cope with typical fluctuations in solar irradiance. The main focus is laid on the transient behaviour of the SOEC reactor during variation of different operating parameters, namely current, feed gas temperature and reactant conversion. Results show that the current variation has the strongest effect on the stacks’ temperature, yielding relevant temperature gradients, especially in endothermic operation. Whereas by increasing the reactant conversion during endothermic operation, it was possible to reduce thermal stress in the stacks, while increasing the hydrogen output as well as the system's efficiency. It is presented how these effects can be combined and utilized for the development of control and operating strategies that aim at improving system performance. This will be exemplary illustrated for improving system performance during a period of overcast and thus reduced heat supply

Operation of a Solid Oxide Fuel Cell Reactor with Multiple Stacks in a Pressured System with Fuel Gas Recirculation

Large-scale modular solid oxide fuel cell (SOFC) reactors composed of multiple stacks are regarded as an efficient form of power generation and important for the global energy transition. However, such an arrangement leads to several operational challenges, and methods are required for handling such challenges and understanding their sources. Hence, a test rig for the examination of a 30 kW SOFC reactor with multiple stacks, for operation near real system conditions, is built. The test rig, which allows operation at elevated pressure, is equipped with a high-temperature blower that recirculates the fuel gas at SOFC reactor temperature. In a measurement campaign, fuel gas, reactant conversion, and pressure are varied in stationary and transient experiments. The experimental results showed that the operating conditions of the individual stacks of large SOFC reactors vary largely due to flow distribution and heat losses. Methods for the investigation of these critical characteristic parameters are derived from the experimental results. Furthermore, the impact of pressurization and fuel gas recirculation on the SOFC reactor is analyzed. This publication shows the need to understand the behavior of large SOFC reactors with multiple stacks to increase the performance and robustness of complete process systems