Sulfur Poisoning of Anode‐Supported SOFCs under Reformate Operation

Abstract

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.

The Influence of Sulfur Formation on Performance and Reforming Chemistry of SOFC Anodes Operating on Methane Containing Fuel

“…13,18 Several experimental studies have examined the sulfur poisoning of CO/H 2 /H 2 O gas mixtures in order to extract detailed information about the influence of sulfur on the water gas shift reaction, as a first step toward the elucidation of the poisoning of the methane steam reforming process. 14,16,22,23 The results of these studies show that the water gas shift reaction is also affected more strongly than the electrochemical oxidation of hydrogen, which entails a lack of hydrogen for gas phase mixtures with high CO contents.The magnitude of the performance drop has been found to be alleviated by increasing temperatures generally believed to be due to reduced surface sulfur coverage. 5,7,18,24 However, controversial interpretations of experimental studies exist regarding the influence of current density on the sulfur poisoning of Ni-based anodes.…”

“…[4][5][6][7][8][9][10] However, in recent years, a growing number of studies has been dedicated to the investigation of sulfur poisoning of Ni/YSZ SOFC anodes operating on hydrocarbon-containing fuels, such as methane, [11][12][13] reformates, 14 syn- 15,16 and biogas. 1 Regardless of the employed fuel gas mixture, in all experimental studies a rapid power output drop was observed already for H 2 S concentrations in the ppm range accompanied by a large increase in total anode resistance.…”

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

“…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.…”

Triode Solid Oxide Fuel Cell Operation Under Sulfur‐Poisoning Conditions

“…From the voltage history graph it is possible to observe how the AUX circuit (central electrode) is more directly exposed to the flow and experiences faster and more severe degradation (red curve Figure ) compared to the FC circuit (blue curve Figure ). The observed trend in conventional mode is in agreement with literature , where an initial voltage drop occurs in the range of a few hours (5 h in this case) with 2 ppm of H 2 S injection. Moreover, due to low H 2 S content and low polarization , just a small irreversible degradation is observed in the white area of Figure after 110 h. It has to be noted that when triode operation is applied, the higher voltage reached by the AUX circuit, that works in electrolysis mode, affects the voltage of the FC circuit as well.…”