Alkaline anion exchange membrane water electrolysis (AEMWE) is considered to be an alternative to proton exchange membrane water electrolysis (PEMWE) and conventional alkaline water electrolysis (AWE), owing to the use of non-precious metal and avoiding high alkaline concentration electrolyte, respectively. Here, we report a highly efficient AEMWE design using the fabrication of membrane-electrode assembly (MEA) by simply sandwiching anion exchange membrane between electrodes developed by plasma spraying of NiMoAl for cathode and NiAl for anode in various low concentrated KOH solutions (0.1 to 1.0M). The first impression from the electrochemical characterization is that a higher KOH concentration has positive effects on the overall cell performance. However, this effect is limited at higher KOH concentration. The cell operated in 1.0M KOH exhibits the highest current density of 0.44 A/cm² at 1.80 V, which is very close the one, 0.5 A/cm² at 1.80 V, in 6.0M KOH achieved in AWE.
The current paper attempts to use equivalent circuit diagrams to simulate impedance spectra of metal supported SOFCs. Measured electrical impedance spectroscopy data on full cells was fitted to an equivalent circuit with the aim to evaluate the contribution of each functional layer towards the ASR of the cell separately. Further, the suitability of equivalent circuit diagrams to predict changes in cell behavior due to alteration in electrodes was investigated. For that purpose, two approaches were opted. First one consisted of replacing LSM cathode with LSCF cathode whereas the second comprised of redox cycling of cells provoking degradation in anodes and overall performance of the cells. Not only was the break down of the losses underlined, but also the limiting factors in the performance of metal supported cells were studied.
Metal supported cells as developed at DLR for use as solid oxide fuel cells by applying plasma deposition technologies were investigated in operation of high temperature steam electrolysis. The cells consisted of a porous ferritic steel support, a diffusion barrier layer, a Ni/YSZ fuel electrode, a YSZ electrolyte and a LSCF oxygen electrode. During fuel cell and electrolysis operation the cells were electrochemically characterised by means of i-V characteristics and electrochemical impedance spectroscopy measurements including a long-term test over 2000 hours. The results of electrochemical performance and long-term durability tests of both single cells and single repeating units (cell including metallic interconnect) are reported. During electrolysis operation at an operating temperature of 850 °C a cell voltage of 1.28 V was achieved at a current density of -1.0 A cm-2; at 800 °C the cell voltage was 1.40 V at the same operating conditions. 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. During a long-term test run of a single cell over 2000 hours a degradation rate of 3.2% per 1000 hours was observed for operation with steam content of 43% at 800 °C and a current density of -0.3 Acm-2. Testing of a single repeating unit proved that a good contacting of cell and metallic interconnect is of major importance to achieve good performance. A test run over nearly 1000 hours showed a remarkably low degradation rate.
In the metal supported SOFCs (MS-SOFCs), conventional sintering route for cathode layer appears unfeasible due to excessive oxidation of metal support in air at sintering temperatures and degradation of perovkites during sintering in low oxygen partial pressures. The novel process of suspension plasma spraying (SPS), capable of producing a wide variety of coating structures and compositions without any post-deposition sintering, is developed and evaluated in detail for the fabrication of cathode layers for MS-SOFCs. Composite cathodes of LSCF and CGO were developed and the influence of different cathode microstructures on fuel cell performance was examined. Four exemplary cathode coatings have been created, ranging from partially dense with small pores to highly porous layers preserving submicronic agglomerated structures. These cathode coatings have been tested on equal half-cells made of the same anode and electrolyte. The best performing microstructure had a powder density of 798 mW/cm² at 800°C. Microstructural differences could be attributed to different behavior and performance of the coatings.
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.
Reducing emission of greenhouses gases represents a huge societal challenge, Among the portfolio of technologies, High Temperature Solid Oxide Cells (SOC) present key advantages in term of efficiency to be used either for power generation or energy storage.
From cells to system, research activities at German Aerospace Center activities are covering the whole technological chain.
Over the last decades continuous improvement in materials, architecture and manufacturing processes have been achieved to improve performance durability and lifetime. The advanced concept of a metal-supported SOC where the functional ceramic layers are deposited onto a mechanically stable porous metal support is the most advanced approach for mobile application as auxiliary power units (APU). This application requires low volume, limited weight and improved ability for rapid start-up and thermal cycling. At DLR, functional layers are consecutively deposited by plasma spray technology onto a metal substrate. Recently, further research efforts have started to develop a metal-supported cell with thin-film electrolyte applied through PVD technology preparing the next generation of SOCs.
The German Aerospace Center (DLR) aims to build and operate a hybrid power plant with an electrical power output of 30 kW which can be operated at higher efficiency than conventional plants. This hybrid power plants consists of a gas turbine coupled with solid oxide fuel cells. Theoretical studies suggest electrical efficiencies of up to 70%. The system concept and design of the power plant have been finalized and the specification of all major system components has been carried out. Currently, different system components are being purchased and tested.
The presentation provides first an overview of the metal-supported cell development including materials aspects, stack technology and electrochemical performance. In a second part, an overview of the current status of the project of hybrid power plant will be given, illustrating the general concept of the power plant. Important specifications characteristics and test results of the components will be presented.
Abstract Interconnect coatings are extremely important to ensure an optimal performance of a solid oxide fuel cell (SOFC) stack. Nowadays the most common material used to produce SOFC interconnects is a ferritic stainless steel (FSS) rich in chromium which is much less expensive than the previously used ceramic interconnects. Nevertheless interconnects have to be coated in order to provide protection from the aggressive environment that surrounds them and reduce chromium species migration to the cell's cathode. In this work three different coatings were applied to Crofer ® 22 H substrates via atmospheric plasma spraying (APS): two different stoichiometries of copper manganese oxide (Cu x Mn 3–x O 4 , where x = 1.4 and 1.5) and one of cobalt manganese oxide (Co x Mn 3–x O 4 , where x = 1.5), considered the state of the art coating for SOFC interconnects. X‐ray diffraction (XRD) was used to check the composition of deposited layers. Area specific resistance (ASR) of samples has been characterized for different samples in the range 673–1,073 K and during a 100 hours ageing test at 1,073 K. Microstructural changes and Cr‐barrier properties have been characterized by SEM‐EDX analyses.
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