Competitive Adsorption Reaction Mechanism of Ni/Yttria-Stabilized Zirconia Cermet Anodes in H[sub 2]-H[sub 2]O Solid Oxide Fuel Cells

Abstract

The reaction mechanism of the most commonly used anode material, Ni/yttria-stabilized zirconia ͑YSZ͒ cermets, in H 2 -H 2 O solid oxide fuel cells ͑SOFCs͒ was investigated. Because the reaction mechanism for the Ni/YSZ anode in H 2 has not been conclusively determined, we investigated the detailed dependence of dc polarization and interfacial conductivity of Ni/YSZ cermet anode on the partial pressure of hydrogen (p H 2 ). Based on our experimental results, we developed a model that links the chemical reactions on the anode with the electrical characteristics of the anode such as the dc polarization and the interfacial conductivity. In our model, we assumed competitive adsorption equilibrium of H 2 , H 2 O, and O on Ni surfaces at the three-phase boundary, and assumed the rate-determining step to be Langmuir-type reactions of H with O. In SOFCs with Ni/YSZ anodes, reported dependencies of the current and interfacial conductivity on p H and p H 2 O differ among previous studies. Both our measured dependencies and previously published dependencies were successfully reproduced by our Langmuir reaction model. Furthermore, possible reasons for these different observed dependencies include the different adsorption equilibrium constants.

Fundamentals of electro- and thermochemistry in the anode of solid-oxide fuel cells with hydrocarbon and syngas fuels

“…In fact, from all of the possible reaction pathways, the competitive adsorption of gas species on the electrode or electrolyte surface, as well as the following surface diffusion processes, are candidates for rate-limiting steps. Ihara et al 87 investigated the detailed dependence of DC-polarization and interfacial conductivity of Ni-YSZ cermet anodes on the partial pressure of hydrogen. They developed a Langmuir reaction model, which links the chemical reactions on the anode with the electrical characteristics of the anode, such as the DC-polarization and the interfacial conductivity.…”

Recent anode advances in solid oxide fuel cells

“…Ihara et al [116] investigated the detailed dependence of dc polarization and interfacial conductivity of Ni/YSZ cermet anode on the partial pressure of hydrogen, p(H 2 ). Based on the experimental results, they developed a Langmuir reaction model as shown schematically in Fig.…”

Power generation characteristics of a SOFC with a Ni/YSZ anode incorporating a SrZr_0.95Y_0.05O_3-α proton conductor

“…Near the triple phase boundary at the anode, adsorbed oxygen reacts with adsorbed hydrogen to produce adsorbed water, as described by the following chemical reaction (Ihara et al, 2001):…”