Electrochemical Investigation of Nickel Pattern Electrodes in H[sub 2]/H[sub 2]O and CO/CO[sub 2] Atmospheres

Abstract

In this study, nickel pattern electrodes were electrochemically investigated in a three-electrode setup, operating both with H 2 /H 2 O and CO/CO 2 atmospheres. Heating introduced structural differences in the nickel layer among the pattern electrodes, which appear to affect the electrode performance. Both dense and porous nickel pattern electrodes were formed by heating. Holes appeared in the nickel layer of the porous pattern electrodes, where the open cavity triple phase boundaries exhibited different limiting processes than open triple phase boundary electrodes of the dense electrode. As the temperature was raised in the experiment, the electrodes stabilized, with a degraded behavior that seemed to be strongly coupled to the structural changes in the electrode. It was possible to compare literature results with high temperature impedance measurements in H 2 /H 2 O presented here, while new results at lower temperatures in H 2 /H 2 O are also presented. Impedance spectroscopy measurements were performed, and the gas dependence of the polarization resistance was observed as the mixture ratios and temperatures were varied in both atmospheres. A positive relation between the polarization resistance and the partial pressure of CO was determined for the dense nickel pattern electrode, which agrees with previous results using nickel point electrodes.Solid oxide fuel cells ͑SOFC͒ anodes operating with H 2 /H 2 O atmospheres have been studied using several types of electrode configurations such as point, 1-5 pattern, 6-12 and cermet electrodes. 13,14 The growing interest in the use of methane and syngas has motivated new electrochemical investigations both with methane 15 and CO/CO 2 atmospheres. 4,12 Previously, porous Pt-Ce 16 and Ni cermet 17 electrodes were used to compare the electrochemistry of both H 2 /H 2 O and CO/CO 2 . In the work by Sukeshini et al. 12 and the work reported here, Ni pattern anodes were used to compare both types of fuels.Interest in patterned electrodes is growing for several reasons. The possibility to examine the structure after heating is limited when using point electrodes, but patterning provides access to the triple phase boundary ͑TPB͒ for unambiguous ex situ detection of morphological changes [6][7][8][9][10][11][12]18,19 and potential impurity effects. 20 Furthermore, patterned electrodes allow one to isolate interfacial electrochemistry from other rate processes that complicate impedance spectra when using cermet electrodes ͑e.g., reactant diffusion, homogeneous gas phase reactions, heterogeneous nonredox reactions, etc. 12 ͒. The open access afforded by the patterned structures also allows one to apply spatially resolved measurement techniques in situ for unambiguous determination of species at the interface, 18 which is not straight forward using point electrodes. As an interesting extension of the patterned electrode concept, the work by Huang and co-workers 21 has demonstrated the ability to make nanostructured electrodes on very thin ͑submicrometer͒ yttria-stabilized zirconi...

Thin film cathodes in SOFC research: How to identify oxygen reduction pathways?

“…A likely explanation for the formation of these hillocks is a partial dewetting of the oxide by the Pt film-comparable structures were also reported for Ni thin films on YSZ. 57 Nonetheless, since the bubbles are gas tight, they are expected to not affect the faradaic reaction pathways. 56 Figures 2(c) and 2(d) depict circular Pt electrodes and a magnification of Pt deposited via the HT route.…”

Stability and electrochemical performance of Ni/YSZ pattern anodes in H2/H2O atmosphere

“…Ehn et al investigated the electrochemical behaviour of Ni pattern anodes in both H 2 /H 2 O and CO/CO 2 atmospheres. The effect of heat treatment on Ni pattern anode performance was also evaluated at different temperatures.…”

“…In the literature, stability studies of pattern anodes were only conducted by Utz et al and Ehn et al Utz et al focused on the effects of temperature, H 2 O content, and Ni thickness on Ni pattern anode stabilization, while Ehn et al mainly evaluated the effect of temperature (< 700 °C) on pattern anode stabilization. The influence of H 2 O on pattern anode performance was evaluated in a very small range, except in the study performed by Utz et al…”

“…Regarding activation energy, hydrogen, and water reaction orders, the results obtained by different research groups are different. Factors such as impurity level, Ni pattern thickness, Ni/YSZ pattern structure change, inaccurate estimation of active TPB length, or even the time at which data were collected may contribute to the difference of these studies …”

Investigation of H2, CO and Syngas Electrochemical Performance Using Ni/YSZ Pattern Anodes

“…Three groups studied CO electrochemical reaction mechanism experimentally by Ni/YSZ pattern anodes (6,6,7,12,17). But, different results were reported by these research groups.…”