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Title: Processing microstructure property correlation of porous Ni-YSZ cermets anode for SOFC application

Abstract

The present paper investigates microstructural properties and electrical conductivity of cermets prepared by a solid-state technique, a liquid-dispersion technique and a novel electroless coating technique. The Ni-YSZ processed through different techniques shows varying temperature-conductivity behaviour. The cermets synthesised by electroless coating were found to be electronically conducting with 20 vol% nickel, which is substantially lower than that normally reported. The conductivity of Ni-YSZ cermets was found highest for the samples prepared by an electroless coating technique and lowest for the samples prepared by a solid-state technique, the samples prepared from liquid-dispersion show an intermediate value for a constant nickel content. The variation in electrical conductivity has been well explained from the microstructure of the samples.

Authors:
 [1];  [2];  [2]
  1. Department of Ceramic Engineering, National Institute of Technology, Rourkela 769008 (India). E-mail: skpratihar@nitrkl.ac.in
  2. Department of Ceramic Engineering, National Institute of Technology, Rourkela 769008 (India)
Publication Date:
OSTI Identifier:
20888110
Resource Type:
Journal Article
Resource Relation:
Journal Name: Materials Research Bulletin; Journal Volume: 40; Journal Issue: 11; Other Information: DOI: 10.1016/j.materresbull.2005.06.002; PII: S0025-5408(05)00215-1; Copyright (c) 2005 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ANODES; CERMETS; ELECTRIC CONDUCTIVITY; MICROSTRUCTURE; NICKEL; POROUS MATERIALS; SOLID OXIDE FUEL CELLS

Citation Formats

Pratihar, Swadesh K., Dassharma, A., and Maiti, H.S. Processing microstructure property correlation of porous Ni-YSZ cermets anode for SOFC application. United States: N. p., 2005. Web. doi:10.1016/j.materresbull.2005.06.002.
Pratihar, Swadesh K., Dassharma, A., & Maiti, H.S. Processing microstructure property correlation of porous Ni-YSZ cermets anode for SOFC application. United States. doi:10.1016/j.materresbull.2005.06.002.
Pratihar, Swadesh K., Dassharma, A., and Maiti, H.S. Thu . "Processing microstructure property correlation of porous Ni-YSZ cermets anode for SOFC application". United States. doi:10.1016/j.materresbull.2005.06.002.
@article{osti_20888110,
title = {Processing microstructure property correlation of porous Ni-YSZ cermets anode for SOFC application},
author = {Pratihar, Swadesh K. and Dassharma, A. and Maiti, H.S.},
abstractNote = {The present paper investigates microstructural properties and electrical conductivity of cermets prepared by a solid-state technique, a liquid-dispersion technique and a novel electroless coating technique. The Ni-YSZ processed through different techniques shows varying temperature-conductivity behaviour. The cermets synthesised by electroless coating were found to be electronically conducting with 20 vol% nickel, which is substantially lower than that normally reported. The conductivity of Ni-YSZ cermets was found highest for the samples prepared by an electroless coating technique and lowest for the samples prepared by a solid-state technique, the samples prepared from liquid-dispersion show an intermediate value for a constant nickel content. The variation in electrical conductivity has been well explained from the microstructure of the samples.},
doi = {10.1016/j.materresbull.2005.06.002},
journal = {Materials Research Bulletin},
number = 11,
volume = 40,
place = {United States},
year = {Thu Nov 03 00:00:00 EST 2005},
month = {Thu Nov 03 00:00:00 EST 2005}
}
  • The interaction of trace (ppm) phosphine with the nickel/yttria stabilized zirconia (YSZ) anode of commercial solid oxide fuel cells has been investigated and evaluated for both synthesis gas and hydrogen fuels in an effort to examine P–Y reactions. The Ni poisoning effects reported in literature were confirmed and degradation was examined by electrochemical methods and post-test microstructural and chemical analyses. The results indicate that P-induced degradation rates and mechanisms are fuel dependent and that degradation of cells operated in synthesis gas (syngas) with phosphine is more severe than that of cells operated in hydrogen with phosphine. As reported in publishedmore » literature, a cell operated in syngas containing 10 ppm phosphine demonstrated significant microstructural degradation within the Ni phase, including formation of Ni–P phases concentrated on the outer layer of the anode and significant pitting corrosion in the Ni grains. In this research, a previously undetected YPO{sub 4} phase is observed at the YSZ/YSZ/Ni triple grain junctions located at the interface with the YSZ electrolyte. Tetragonal YSZ (t-YSZ) and cubic-YSZ (c-YSZ) domains with sizes of several tens of nanometers are also newly observed along the Ni/YSZ interface. These observations contrast with data obtained for a cell operated in dry hydrogen with phosphine, where no YPO{sub 4} phase is observed and the alternating t-YSZ and c-YSZ domains at the Ni/YSZ interface are smaller with typical sizes of 5–10 nm. The data imply that electrolyte attack by P is a potentially debilitating mode of degradation in SOFC anodes, and that the associated reaction mechanisms and rates are worthy of further examination.« less
  • NiO-GDC, NiO-YSZ, NiO-Fe2O3-GDC, NiO-Fe2O3-YSZ anode tube supported tubular fuel cells was fabricated at the co-sintering temperature from 1250 C to 1400 C to investigate how the co-sintering temperature affect the open-circuit voltage. To focus on the changing of anode tube, all the tubular fuel cells support a ScSZ electrolyte layer and a LSCF cathode layer. The microstructure of the electrolyte layer sintered under 1300 C included pores inside it, and the densification of the electrolyte completed at the sintering temperatures above 1300 C. Furthermore, the shrinkage both in length and in diameter of a tubular fuel cell reaches as muchmore » as 20% at co-sintering temperature of 1400 C. The densification of ScSZ electrolyte layer and shrinkage of anode tube will result in the changing of open-circuit voltage of fuel cell from 1.0 V to 1.1 V.« less
  • Ni-YSZ cermet anode has been synthesized in one step using a simple and cost effective combustion synthesis process. The processed powder of NiO-YSZ is found to be nanocrystalline with crystallite sizes of 29 and 22 nm for NiO and YSZ respectively by X-ray diffraction and transmission electron microscopy analysis. X-ray diffraction analysis also shows that the precursor salts are converted to highly crystalline phases of NiO and YSZ (8 mol% Y{sub 2}O{sub 3}) without any intermediate calcination step and no undesirable phases are present. Comparison with the X-ray diffraction pattern of a commercial YSZ sample shows that the process ismore » also effective in maintaining a close compositional control. The microstructure of the sintered and reduced sample shows a well defined network of pores which is necessary for the effective functioning of the anode. The electrical conductivity as a function of temperature shows metallic behavior.« less
  • The activity of nickel-yttria stabilized zirconia (Ni-YSZ) solid oxide fuel cell (SOFC) cermet anodes for the steam reforming of methane has been investigated in the absence of electrochemical effects. The cermet was prepared by co-milling and sintering NiO and 5YSZ powders at 1375oC in air. During the high temperature sintering step, NiO dissolved into the YSZ particles to form a solid NiO-YSZ solution. During the subsequent catalyst reduction step, Ni exolved from the YSZ. As a result, many small Ni particles on the order of 10-20 nm formed at the surface of the YSZ. These small particles contribute significantly tomore » the overall reforming activity, along with the large bulk Ni particles within the Ni-YSZ cermet. We have observed high initial activity that decreases by as much as an order of magnitude with time on stream, until the anode catalyst reaches a stable steady state activity. The time to reach this stable activity is a function of the reaction conditions and feed gas composition. Higher temperature, hydrogen partial pressure, and space velocity all accelerated the deactivation rate at a constant steam-to-carbon ratio of 3. Initial and lined out activities and average turnover frequencies were obtained for both Ni-YSZ and bulk Ni, based on a rate expression that is first order in methane and zero order in steam. Comparative tests at 750oC show high initial activity on a per-Ni site basis with both materials, but these turnover rates decline over a period of a few hours. Following lineout, there appears to be a negligible effect of Ni particle size on turnover rate. These results indicate the presence of structure sensitivity for methane reforming, but only with freshly calcined and reduced catalysts that may contain highly coordinatively unsaturated sites. There is an apparent structure insensitivity with aged catalysts where Ni particle sizes are generally 50 nm and greater. Under reaction conditions that employ high space velocities and low methane conversions, the water-gas-shift reaction does not establish thermodynamic equilibrium.« less
  • Internal reforming of hydrocarbon fuels (e.g. methane or natural gas) can improve the thermal efficiency of solid oxide fuel cells (SOFC) by balancing exothermic electrochemical oxidation of H2 and CO at the anode/cathode interface with endothermic steam reforming reactions on the anode1. Generally the rate of reforming is much greater than the rate of H2 and CO oxidation leading to extensive thermal gradients across the cell that can compromise the physical integrity of the cell. Therefore, methods to control reformation activity and predict thermal gradients are needed. Computational modeling is used to predict thermal gradients and fuel conversion profiles acrossmore » the cell, thus accurate and predictable methane reforming kinetics are required. Significant discrepancies in activation energy, rate expressions, and rate constants for methane reforming over nickel-yttria stabilized zirconia (Ni-YSZ) are reported in the open literature1-4. The objective of this work is to provide clarity on factors leading to discrepancies in kinetic information reported in the literature and identify potential methods to control reforming rates over NiYSZ anodes. Effects of pretreatment and reforming on Ni microstructure and activity of NiYSZ anodes for methane reforming were examined under open-circuit conditions.« less