Out there omega edition pc torrent1/9/2024 ![]() It is thus not easy to predict how microstructure degradation affects the distribution of current densities and electrochemical activity. Microstructure degradation usually leads to a decrease of both ionic transport as well as charge transfer properties. In contrast, if the ionic conductivity is relatively low, then the active zone tends to be restricted in a narrow active layer close to the electrolyte-anode interface. For example, if TPB and associated charge transfer kinetics are rate limiting then the electrochemical reaction tends to spread over a relatively thick active layer. Thereby the charge transfer and the associated ionic and electronic current densities may spread over the anode in different ways, depending on the microstructure and materials properties. The complexity of this topic is mainly due to the fact that the anode performance results from coupled transfer and transport processes. The aim of this study is to unravel the complex relationships among microstructure, anode performance, and degradation behavior upon redox cycling, with a strong focus on the influence from variations in TPB density. Schematic representation of Ni-YSZ cermet anode and the mechanism of charge transport and charge transfer processes. ![]() The anode performance can be predicted reliably if the volume-averaged properties (TPB active, effective ionic conductivity) are corrected for the so-called short-range effect, which is particularly important in cases with a narrow active layer. The observed loss of YSZ percolation in the coarse anode is not detrimental because the electrochemical activity is concentrated in a narrow active layer. The mechanistic scenarios describe the microstructure influence on current distributions, which explains the observed complex relationship between TPB lengths and anode performances. These scenarios are based on a model for coupled charge transfer and transport, which allows using TPB and effective properties as input. Mechanistic scenarios are discussed for different anode microstructures. Surprisingly, this severe microstructure degradation did not lead to electrochemical failure. The coarse anode suffers from complete loss of YSZ connectivity and associated drop of TPB active by 93%. The latter is attributed to weak bottlenecks associated with lower sintering activity of the coarse YSZ. In fine microstructures, TPB loss is found to be due to Ni coarsening, while in coarse microstructures reduction of active TPB results mainly from loss of YSZ percolation. Finer microstructures exhibit lower degradation rates of TPB and R pol. The degradation mechanism strongly depends on the initial microstructure. However, the quantitative results also show that there is no simplistic relationship between TPB and R pol. In general the TPB lengths correlate with anode performance. ![]() Three different Ni-YSZ anodes of varying microstructure are subjected to eight reduction-oxidation (redox) cycles at 950 ☌. 3D microstructure-performance relationships in Ni-YSZ anodes for electrolyte-supported cells are investigated in terms of the correlation between the triple phase boundary (TPB) length and polarization resistance ( R pol).
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