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Winterthur, Switzerland

Bogolowski N.,Dechema Institute | Iwanschitz B.,Hexis AG | Drillet J.-F.,Dechema Institute
Fuel Cells | Year: 2015

The present work reports on the development of a coking-resistant NiSn-based membrane electrode assembly (MEA) for internal CH4 reforming in solid oxide fuel cells (SOFCs). Catalyst powder was prepared in a centrifugal casting oven by melting stoichiometric amounts of Ni and Sn under vacuum. The formation of Ni3Sn2 intermetallic phase was confirmed by XRD analysis. Catalytic activity for CH4 reforming and stability of the NiSn powder were first evaluated in a quartz glass reactor for 4 h at 600-1,000 °C. The main reaction products H2 and CO were detected by gas chromatography while no carbon formation was detected during the experiments. Then, 3YSZ electrolyte-supported MEAs were fabricated with a Ni3Sn2/YSZ anode and LSM/YSZ cathode and characterized under SOFC conditions. The MEA showed an excellent stability under CH4 atmosphere (3% H2O) at 850 °C over more than 650 h. No substantial decrease in cell potential was observed during this period. Copyright © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Marra D.,University of Salerno | Sorrentino M.,University of Salerno | Pianese C.,University of Salerno | Iwanschitz B.,Hexis AG
Journal of Power Sources | Year: 2013

The paper focuses on the experimental identification and validation of a neural network (NN) model of solid oxide fuel cells (SOFC) aimed at implementing on-field diagnosis of SOFC-based distributed power generators. The use of a black-box model is justified by the complexity and the incomplete knowledge of SOFC electrochemical processes, which may be awkward to simulate given the limited computational resources available on-board in SOFC systems deployed on-field. Suited training procedures and model input selection are proposed to improve NNs accuracy and generalization in predicting voltage variation due to degradation. Particularly, standing the interest in condition monitoring of SOFC performance throughout stack lifetime, input variables were selected in such a way as to account for the time evolution of SOFC stack performance. Different SOFC stacks outputs were tested to assess the generalization capabilities when extending NN prediction to those stacks for which no training data were gathered. The simulations performed on the test sets show the NN ability in simulating real voltage trajectory with satisfactory accuracy, thus confirming the high potential of the proposed model for real-time use on SOFC systems. © 2013 Elsevier B.V. All rights reserved.

Hexis AG | Date: 2011-02-01

A fuel cell system (

Terner M.R.,University of Zurich | Schuler J.A.,Hexis AG | Mai A.,Hexis AG | Penner D.,University of Zurich
Solid State Ionics | Year: 2014

The degradation of ionic conductivity in 6ScSZ and 3YSZ SOFC electrolytes was analysed via X-ray diffraction (XRD), 4-point conductivity and electrochemical impedance spectroscopy (EIS) and the results present a consistent story: in 6ScSZ subtle but reproducible changes to the phase assembly in the form of a shrinking "cubic shoulder" are obtained with ageing at 900 °C, which closely corresponds to the decrease in ionic conductivity. This appears to be the gradual transformation of the residual high-temperature c or t″ phase to t′. Both the shoulders and the conductivity return after "healing" at temperatures above the ageing temperature but below the sintering temperature, bringing the samples back to the as-sintered state. Evidence of a type of short-range ordering (SRO) acting in parallel with the phase changes was seen in the EIS. Distortions on the XRD peaks such as humps on the left shoulder were almost never seen and appear to be a polishing artefact unrelated to changes in the conductivity. © 2014 Elsevier B.V.

Verbraeken M.C.,University of St. Andrews | Iwanschitz B.,Hexis AG | Mai A.,Hexis AG | Irvine J.T.S.,University of St. Andrews
Journal of the Electrochemical Society | Year: 2012

Doped strontium titanates have been widely studied as potential anode materials in solid oxide fuel cells (SOFCs). The high n-type conductivity that can be achieved in these materials makes them well suited for use as the electronically conductive component in SOFC anodes. This makes them a potential alternative to nickel, the presence of which can be a major cause of degradation due to coking, sulfur poisoning and low tolerance to redox cycling. Here anode performance results are presented for an A-site deficient strontium titanate co-doped with lanthanum and calcium on the perovskite A-site, La 0.20Sr0.25Ca0.45TiO3 (LSCTA-). LSCTA- anodes and LSM cathodes were screen printed on 160 μm thick 6-ScSZ electrolyte supports. The LSCTA- anode backbone showed poor electrode performance, but its conductivity was sufficient to keep ohmic losses low. Upon impregnation with combinations of ceria and nickel, ohmic losses and polarization impedances are significantly reduced, resulting in a drastic improvement in anode performance. Unexpectedly, the performance of cells impregnated with both ceria and nickel showed an improvement upon redox cycling. A stable area specific resistance of 0.37 Ωcm2 was achieved after 20 redox cycles and 250 hours of operation at 900°C in H2 with 8% H2O, showing excellent redox stability. Copyright © 2012 The Electrochemical Society.

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