Hydrogen sulfide poisoning in solid oxide fuel cells under accelerated testing conditions

The impact of sulfur‐poisoning on reforming chemistry and electrochemistry of anode‐supported solid oxide fuel cells is analyzed via electrochemical impedance spectroscopy. Different types of anode supported cells are operated in hydrogen/steam – as well as simulated reformate – (H2 + H2O + CO + CO2 + N2) fuels containing 0.1–15 ppm of H2S. A detailed analysis of impedance spectra by the distribution of relaxation times (DRT) and a subsequent complex nonlinear least squares (CLNS) fit separates the impedance changes taking place at the anode and the cathode. Two main features were detected in the DRT, a decreased reaction rate of the electrochemical hydrogen oxidation and a deactivation of the catalytic conversion of CO via the water‐gas shift reaction. During the first exposure of the cell to a H2S‐containing fuel, an enhanced degradation is observed. The degradation rate increases several hours after H2S was added to the fuel and decreases after the poisoning is completed. The polarization resistance increased by a factor of 2–10, depending on H2S‐content, fuel composition and cell type. Comparing the temporal characteristics of the polarization resistance of two different anode supported cells, it could be shown that the accumulated H2S‐amount divided by the Ni‐surface area inside the anode substrate and anode functional layer determine the onset of the degradation.

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“…is rather low. This supports the finding discussed above, that the impact of H 2 S-poisoning is decreased by polarizing the cell [22,23].…”

Section: Resultssupporting

confidence: 92%

Sulfur Poisoning of Anode‐Supported SOFCs under Reformate Operation

et al. 2013

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“…The vast literature refers and focusses on systems, which are fed with H 2 S in H 2 -containing fuels. They studied the deactivation mechanisms and materials application Zha et al, 2007;Li T. S. et al, 2009;Li et al, 2010;Hagen, 2009, 2010;Xu et al, 2010;Li and Wang, 2011a,b), summarized in several studies and reviews (Sasaki et al, 2006(Sasaki et al, , 2011Trembly et al, 2006;Gong et al, 2007;Goodenough and Huang, 2007;Sun and Stimming, 2007;Rasmussen and Hagen, 2009;Yang et al, 2010;Cheng et al, 2011;Hagen et al, 2011;Kromp et al, 2012;Hagen, 2013;Wang et al, 2013;Weber et al, 2013;Hauch et al, 2014). The effect of a sulfur-containing fuel is examined on the performance and durability of SOFCs through the variation of several factors, such as the: (i) operating temperature, (ii) applied current/voltage load, (iii) time on stream, (iv) H 2 S concentration and to a lesser extent the concentration of H 2 and H 2 O, and (v) the anodes materials.…”

Section: Introductionmentioning

confidence: 99%

Effect of Au and/or Mo Doping on the Development of Carbon and Sulfur Tolerant Anodes for SOFCs—A Short Review

Niakolas

Neofytidis

Neophytides

2017

Front. Environ. Sci.

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HIGHLIGHTS• The kinetics of CH 4 steam reforming and partial oxidation are determined by the oxidation rate of CH x adsorbed species • The modification of the Ni/YSZ and Ni/GDC with Au and/or Au-Mo results in differentiated structures of atomically dispersed Au and/or Au-Mo at the surface and the bulk of the Ni particles.• At lean S/C NiAu/YSZ selectively oxidizes electrochemically the catalytically produced H 2 and CO, while NiAu/GDC is selective to the direct partial electrochemical oxidation of CH 4 to CO and H 2.• The modified electrodes show significant tolerance to C formation.• Au-Mo modification enhances the intrinsic sulfur tolerance properties of Ni/GDC.The presented work is a short review of the research attempts from our group with collaborators, during the last 15 years, which had as main objective to study and improve the electrocatalytic performance of Ni-based electrode materials for the CH 4 Internal steam Reforming process (ISR.) in Solid Oxide Fuel Cells (SOFCs). In particular, NiO/YSZ and NiO/GDC anode powders were modified with Au and/or Mo nano-particles via different preparation methods. These efforts resulted in anode materials with high tolerance and improved electrocatalytic activity under both carbon forming and sulfur poisoning conditions. The most important findings are being reviewed and critical findings are being highlighted 50 as to stress the key differences in the electrocatalytic performance between Ni/YSZ and Ni/GDC. The possible effects of Au and/or Mo addition on the physicochemical and strucutral properties of the cermets are thoroughly discussed as well as active functional layers in the form of anode SOFC electrodes.

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“…Surface reconstruction of the metal may lead to a new surface on the electrode [5]; 3. A sulfide layer is formed on the electrode surface which increases the size of impedance arcs [9], impedes the transport of the reactant gas onto the electrode surface and transport of products away from the active sites [10], causes microstructure change and reduces the TPB area for electrochemical reactions [11], contaminates the anode surface and increases the interface resistances between electrode from the YSZ membrane [12]; 4. H 2 S may lead to an irreversible increase of the serial resistance due to a loss of percolation of the metal particles in the layers closest to the electrolyte [13].…”

Section: Introductionmentioning

confidence: 99%

“…Remove sulfur containing impurities, which may achieve completely recovery [4,14,15] or partial recovery [11,16,17]. Apply sulfur-tolerant electrodes.…”

Section: Introductionmentioning

confidence: 99%