Abstract
Exsolution is a novel technology for attaching metal catalyst particles onto ceramic anodes in the solid oxide fuel cells (SOFCs). The exsolved metal particles in the anode exhibit unique properties for reaction and have demonstrated remarkable stabilities under conditions that normally lead to coking. Despite extensive investigations, the underlying principles behind exsolution are still under investigation. In this review, the present status of exsolution materials for SOFC applications is reported, including a description of the fundamental concepts behind metal incorporation in oxide lattices, a listing of proposed mechanisms and thermodynamics of the exsolution process and a discussion on the catalytic properties of the resulting materials. Prospects and opportunities to use materials produced by exsolution for SOFC are discussed.
Highlights
The most commonly used material for the fuel electrodes (the anode in Solid Oxide Fuel Cells (SOFCs) and the cathode in Solid Oxide Electrolysis Cells (SOECs)) in Solid Oxide Cells (SOCs) is a physical mixture of metallic Ni and the electrolyte material, typically either Yttria-Stabilized Zirconia (YSZ) [1] or Gd-doped Ceria (GDC) [2]
We provide a brief review of this l2i.teTroawtuarred.s an Optimal Anode for SOFC
Substitution of cations into the lattice of a host oxide is specific to the composition of both the metal cations and the host oxide, and not all metal cations can be incorporated into all ceramics, including those with perovskite structures. This was demonstrated by Tanaka et al [10], who reported this specificity in a study of Pd, Pt and Rh in a series of simple perovskites using X-Ray Absorption Spectroscopy (XAS)
Summary
The most commonly used material for the fuel electrodes (the anode in Solid Oxide Fuel Cells (SOFCs) and the cathode in Solid Oxide Electrolysis Cells (SOECs)) in Solid Oxide Cells (SOCs) is a physical mixture of metallic Ni and the electrolyte material, typically either Yttria-Stabilized Zirconia (YSZ) [1] or Gd-doped Ceria (GDC) [2] These Ni-based ceramic–metallic (cermet) composites are used because they exhibit excellent performances in syngas, a mixture of CO and H2. In an attempt to address sintering issues, Tanaka and his co-workers at Daihatsu Motor Company developed the concept of “intelligent” catalysts [10,27,28,29,30] In their studies of Pd-doped perovskites, it was observed that, upon high-temperature reduction, Pd could be reduced to its metallic form and “ex-solved” to the surface of the perovskite (see Figure 1). We only consider cases where the cations of the catalytic metal can be definitely shown to be part of the crystalline lattice of the host oxide in the oxidized form of the material
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