Influence of Experimental Conditions on Reliability of Carbon Tolerance Studies on Ni/YSZ SOFC Anodes Operated with Methane

Abstract

The effect of experimental parameters on carbon accumulation in the Ni/YSZ anode of SOFC operated at 1,073 K with CH4, has been described in this paper. Experimental parameters including sealing of the cell to the cell holder, operating current, surface coverage by current collector paste on the surface of the anode, and the configuration of the current collector were evaluated in terms of carbon accumulation at the Ni/YSZ anode. The carbon accumulation was quantified using temperature‐programmed oxidation and cells were examined using scanning electron microscopy. The results suggested that variations in any of these experimental parameters could significantly increase or decrease the amount of carbon accumulation on Ni/YSZ anodes, and hence, the reliability of the carbon tolerance studies. In particular, the higher the air leakage rate, the less carbon that accumulated on equivalent anodes. The extent of surface coverage by current collector paste and the configuration of current collector also impacted the amount of carbon accumulation. Less carbon accumulated directly below and near the areas of current collector paste than on the anode areas directly exposed to CH4 and far from the current collector paste. Additionally, variations in the fuel humidity and current levels also significantly influenced the carbon accumulation.

Strategies for Carbon and Sulfur Tolerant Solid Oxide Fuel Cell Materials, Incorporating Lessons from Heterogeneous Catalysis

“…The paper referred to above also showed that the coverage of silver current collector paste can have a large effect on carbon deposition, even completely preventing it if the electrode is completely covered. 473 Presumably, this works in a similar way to the barrier layer concept discussed in section 6.2. There has also been considerable controversy over the use of platinum current collectors, with claimed high power densities in dry methane for some MIECs being shown to be almost entirely due to the use of platinum current collectors and doped ceria electrolytes.…”

“…It has been shown that leaks causing an increase in measured OCV of less than 0.02 V from 1.223 to 1.239 V in dry methane results in a decrease in implied water content (as calculated from the H 2 /O 2 equilibrium) of 30% from 0.24% to 0.17%. 473 This is enough to result in a dramatic decrease by over half in the amount of carbon deposition over a period of 1 h. Likewise, many groups using 10−50 μm CGO and CSO electrolytes report OCVs below 0.9 V, which implies a substantial oxygen flux at OCV through the electrolyte caused by the electronic conductivity of doped ceria (or through a slightly permeable electrolyte). This oxygen flux or leakage should be extremely effective at preventing carbon deposition and improving sulfur tolerance, but if the aim is to study the carbon and sulfur tolerance of the electrode materials then care should be taken to account for this.…”

Carbon deposition behaviour in metal-infiltrated gadolinia doped ceria electrodes for simulated biogas upgrading in solid oxide electrolysis cells

“…[52] Delamination of the electrode due to carbon deposits promoted by cell polarisation in (co-) electrolysis conditions has been reported previously. [17,55] Structural differences on the interface between the electrode and the electrolyte are examined in Fig.…”

“…The effects of the current collector configuration on the carbon formation when the cell is operated with methane has been reported previously. [52] It is important to note that the non-porous region of the current collection may affect the partial pressures of the gases on the electrode and hence the tendency for carbon formation in these places.…”

Carbon deposition thresholds on nickel-based solid oxide fuel cell anodes I. Fuel utilization

“…The OCV was measured with dry H 2 in step 7 for the purpose of checking for cell failure. Finally, note that N 2 was used at the cathode during steps 4e6 to prevent unintended carbon removal via O 2 crossover [39,40]. In this work, cell failure was defined by conditions that indicate combustion: a drop in OCV with dry H 2 and an increase in the cell temperature.…”