Comparison of SOFC cathode microstructure quantified using X-ray nanotomography and focused ion beam scanning electron microscopy

X-ray nanotomography and focused ion beans scanning electron microscopy (FIB-SEM) have been applied to investigate the complex 3D microstructure of solid oxide fuel cell (SOFC) electrodes at spatial resolutions of 45 nm and below. The application of near edge differential absorption for x-ray nanotomography and energy selected backscatter detection for FIB-SEM enable elemental mapping within the microstructure. Using these methods, non-destructive 3D x-ray imaging and FIB-SEM serial sectioning have been applied to compare three-dimensional elemental mapping of the LSM. YSZ, and pore phases in the SOFC cathode microstructure. The microstructural characterization of an SOFC cathode is reported based on these measurements. The results presented demonstrate the viability of x-ray nanotomography as a quantitative characterization technique and provide key insights into the SOFC cathode microstructure. (C) 2011 Elsevier B.V. All rights reserved.

Influence of Substrate on the Microstructure of Microcrystalline Silicon Layers and Cells

Julien Claude Bailat, Arvind Shah

Hydrogenated microcrystalline silicon i-layers were deposited with a fixed silane concentration on various substrates and incorporated into n-i-p solar cells. 'Average crystallinity' and detailed microstructure of layers and devices were evaluated by X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The role of the substrate is thereby shown to be very critical; a change in the substrate can cause a transition from amorphous to microcrystalline growth in micrometer-thick layers. When crystalline growth occurs, the layer microstructure is depth-dependent. © 2002 Elsevier Science B.V. All rights reserved.

2002

Segmented cell testing for cathode parameter investigation

Christos Comninellis, Josef Andreas Schuler, Pietro Tanasini, Jan Van Herle, Zacharie Wuillemin

The increasing quality and durability of solid oxide fuel cells (SOFCs) state-of-the-art materials renders the long-term testing of fuel cells difficult since considerably long equipment times are needed to obtain valuable results. Moreover, reproducibility issues are common due to the high sensitivity of the performance and degradation on the testing conditions. An original segmented cell configuration has been adopted in order to carry out four tests in parallel, thus decreasing the total experimental time and ensuring the same operating conditions for the four segments. The investigation has been performed on both anode-supported cells and symmetrical Lanthanum-Strontium Manganite-Yttria-stabilized Zirconia (LSM-YSZ) electrolyte-supported cells. In separate tests, the influence of variables like cathode thickness, current density and cathode composition on performance and degradation have been explored on anode-supported cells. Furthermore, the effect of chromium poisoning has been studied on electrolyte-supported symmetric cells by contacting one segment with a chromium-iron interconnect material. Long-term polarization of the segments is controlled with a multi-channel galvanostatic device designed in-house. Electrochemical characterization has been performed through electrochemical impedance spectroscopy (EIS) at different H-2 partial pressures, temperatures and bias current, effectively demonstrating the direct impact of each studied variable on the cell performance and degradation behavior. Segmented cell testing has been proven to be an effective strategy to achieve better reproducibility for SOFC measurements since it avoids the inevitable fluctuations found in a series of successively run tests. Moreover, simultaneous testing increased n-fold the data output per experiment, implying a considerable economy of time. (C) 2010 Elsevier B.V. All rights reserved.

Elsevier2011

Electrochemical model of solid oxide fuel cell for simulation at the stack scale. Part II: Implementation of degradation processes

Stefan Diethelm, Daniel Favrat, Arata Nakajo, Pietro Tanasini, Jan Van Herle

The degradation of the electrochemical performance of solid oxide fuel cell (SOFC) devices is a major hurdle to overcome before commercialisation. The interplay between the phenomena and the long testing times complicate the research, which highlights the relevance of modelling to propose mitigation approaches. This study comprises two parts. This Part II proposes approaches for the simulation of the degradation induced by: (i) interconnect corrosion, (ii) loss of ionic conductivity of the ion-conducting materials, (iii) nickel particle growth in the anode, (iv) chromium contamination and (v) formation of insulating phases in the cathode. The literature survey highlights the lack of data for a completely consistent calibration of the models, despite the simplifications. The support for the implementation is the electrochemical model validated in Part I and a two-dimensional model of the cell and interconnection system. The cathode largely contributes to the degradation. The local overpotential predominantly governs chromium contamination, which can promote the formation of insulating phases, as operation proceeds. The local electronic current density has comparatively a weak direct influence on the degradation. Qualitative agreement with experimental data from the literature could be achieved, without dedicated adjustments of the parameters. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3596435] All rights reserved.

2011

Segmented cell testing for cathode parameter investigation

Christos Comninellis, Josef Andreas Schuler, Pietro Tanasini, Jan Van Herle, Zacharie Wuillemin

Elsevier2011