A Critical Review of Models of the H2/H2O/Ni/SZ Electrode Kinetics

Abstract

Various models of the H 2 /H 2 O/Ni/SZ (SZ = stabilized zirconia) electrode kinetics have been presented in the literature in order to explain the reported experimental data. However, there has been a strong tendency of using a limited set of data to "verify" a given model, disregarding other data sets, which do not fit the model. We have inspected some models in the literature, and problems (e.g. no quantitative model has explained the large variation in reported values of apparent activation energy of the electrode kinetics) as well as strengths of the models are discussed. We point out experimental findings that a useful model must be able to explain such as difference in sensitivity to poisoning by H 2 S due to differences in the detailed composition of the SZ and large change in apparent activation energy by change in cermet preparation. Finally, we will point out some elements, which seem important for any realistic and useful mathematical model of the H 2 /H 2 O/Ni/SZ electrode.

Dealing with fuel contaminants in biogas-fed solid oxide fuel cell (SOFC) and molten carbonate fuel cell (MCFC) plants: Degradation of catalytic and electro-catalytic active surfaces and related gas purification methods

“…Adsorption/desorption, surface diffusion, and charge-transfer reactions having all been suggested as plausible mechanisms [132]. In the conventional Ni-YSZ anode, the more likely mechanism is H2 adsorption on the Ni surface.…”

Tailoring Ni and Sr2Mg0.25Ni0.75MoO6−δ Cermet Compositions for Designing the Fuel Electrodes of Solid Oxide Electrochemical Cells

“…Although typical Ni-based cermets are commonly used for SOFC anodes due to their excellent electrocatalytic properties [11][12][13], they have significant disadvantages associated with reduction-oxidation (redox) cycling instability and degradation due to the agglomeration of Ni particles occurring at high temperatures. Moreover, sulphur poisoning and carbon coking on the Ni-based anode surface are serious problems when SOFCs are used with hydrocarbon fuels [14].…”

Lanthanum strontium vanadate in solid oxide fuel cells.

“…The reaction mechanisms can thus be fairly complicated. Some reaction paths have been proposed but the underlying mechanisms are hitherto still unclear (Raz et al, 2001;Mogensen et al, 2007). Surprisingly, little attention has been paid to the double layer of anode/electrolyte interfaces.…”

“…Further work on the effects of dielectric mismatch (Jho et al, 2008;Wang and Ma, 2010b), temperature, and fuel atmosphere will be considered in future to establish a complete understanding of SOFC anode/electrolyte interfaces. however, are still in controversy (Mogensen et al, 2007;Bessler et al, 2010). One of the reasons may be the insufficient understanding on the double layer under SOFC operating conditions.…”