Cathode material oxygen transport

The step change in pore structure can be fabricated in discrete steps. It also allows the use of dissimilar materials for the porous structure, as used in early Westinghouse SOFC cathode designs and discussed by Thorogood et al. for oxygen transport membranes [12]. 

Soils can be classified on the basis of particle size. Gravel contains the coarsest particles (> 2 mm) and clay the finest ones (< 0.002 mm), with sand and silt in between. Soils containing the finest particles, with ample distribution of small particle sizes are very dense and prevent supply of oxygen (but not of water), while gravel allows oxygen to be transported easily. Most metallic materials that are used in soils corrode under cathodic control, i.e. under control of oxygen transport. Thus, the density of the soil is important. The relationship is, however, somewhat... 

It should be noted that the type of cathode reaction has no direct effect on its surface chemistry. The most important aspects are the redox potentials, the particle size, and the level of reactivity of the surface oxygen atoms. Another important aspect relates to the ease of transition metal ion dissolution from the cathode material to the solution phase. In general, as the redox potential is lower, the cathode material is less reactive with the solution species. However, the redox potential is not the main important factor. The nucleophilicity and basicity of the oxygen atoms of the cathode compounds are also highly important. Li MOy compounds are much more basic and nucleophilic than LiMP04 compounds [13]. The phosphorous atoms at the 5+ oxidation state in the olivine compounds moderate the basic nature of the oxygen atoms. Thereby, olivine compounds are much less reactive to solution species than LLMOy compounds [ 14]. Consequently, they can be used as nanoparticles, which help to overcome their poor transport properties. The fluorine atoms in FeFs and its reduction product, LiF, are neither basic nor nucleophilic, and thereby this cathode material does not develop surface chemisfiy in conventional electrol)de solutions. Finally, as the particle size of cathode materials is smaller, they are supposed to be more surface reactive. 

The oxygen reduction reaction occurs at the cathode. Nearly all candidate cathode materials are based on perovskite oxides such as lanthanum strontium manganite (LSM). However, the oxygen reduction reaction is particularly affected by lower operating temperatures with kinetics and transport processes that are thermally activated. The development of materials with higher electrochemical activities for the oxygen reduction reaction is critical for the development of IT-SOFCs with higher efficiencies. 

Proton exchange membranes (PEMs) are one of the key materials in low-temperature fuel cells proton exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMECs). Especially, recent trend in the research and development of low-temperamre fuel cells focuses on PEMFCs for transportation (electric vehicle) applications due to the impact on economy and environment. The most important role of PEMs is to transport protons formed as a product of oxidation reaction of fuels at the anode to the cathode, where oxygen reduction reaction takes place to produce water. In addition to this, there are a number of requirements for PEM materials for the practical fuel cell applications, which include... 

The activity in oxygen reduction and transport properties of cathode materials were studied by oxygen isotope exchange, O2 TPD and H2TPR methods. 

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