Modeling and comparison to literature data of composite solid oxide fuel cell electrode–electrolyte interface conductivity

Abstract

a b s t r a c tA Monte Carlo percolation model previously used to characterize Triple Phase Boundary (TPB) formation in composite SOFC electrode-electrolyte interfaces has been augmented to allow for investigation of the effects of composition, gas-phase percolation, and surface exchange and transport phenomena on the overall conductivity of these electrode-electrolyte interfaces. The model has been utilized to replicate the results of a previous modeling effort, with similar assumptions and application to an SOFC electrode electrolyte interface. Although the models are similar in many aspects, their key differences allow equivalent predictions of the behavior of overall electrode conductivity as a function of electrode composition, thereby verifying the assumptions and overall approach of the current model. The validity of omitting charge-transfer and activation resistances when comparing overall interfacial conductivity trends is confirmed. The current model is then used to simulate several experimental results. The comparisons among these results show the importance of including gas-phase percolation physics and surface exchange and transport phenomena features in the model. Including gas-phase percolation and these surface phenomena can significantly alter the predictions of conductivity behavior and better predicts experimental observations, particularly at low and high electronic conductor volume fractions.

Monte Carlo Investigation of Particle Properties Affecting TPB Formation and Conductivity in Composite Solid Oxide Fuel Cell Electrode-Electrolyte Interfaces

“…In addition, it was of interest to study the disagreement in results between Sasaki et al and others. Finally, it has been noticed that electronic and ionic phases do not behave equivalently with respect to percolation of the phases and the effect this has on performance [3,4]. Thus, distributions that reflect contrasts between these two phases are desirable in this investigation.…”

“…The model was used to study how threephase percolation in representative geometries influences the formation of TPBs [3] and the overall conductivity of the electrode [4]. Although the details of the model have been discussed previously, certain capabilities of the model were not fully utilized in the previous studies, particularly those features imparted by the properties of the specific materials used to build the electrode.…”

“…This investigation focuses upon these particle-based properties and their contributions to electrode performance within the context of the simulation results previously presented. The full details of the electrode simulation software have been discussed [3,4], but a brief summary description is provided below.…”

“…Common practices, as followed by researchers such as Sunde and Costamagna et al, have therefore modeled the electrode structure as comprised of two phases and followed with assumptions that the materials are themselves porous enough (implying porosity only on a dimensional scale smaller than an individual conducting particle) to allow gaseous diffusion without any limitations throughout the electrode [1,2]. However, it has been shown through the use of a similarly formulated Monte Carlo model, which includes gas phase percolation, that the development of large pore structures in the electrode plays a critical role in the formation of the TPBs, especially as it interacts with the electronic phase [3,4]. In spite of overlooking the gaseous phase, the prior modeling efforts have made useful observations of the basic percolation properties and identified key factors in the optimization of electrode microstructure.…”

“…Previous investigations by the authors [3,4] have explored the fundamentals of these TPB-forming interactions with the inclusion of the gas phase structure as well as novel considerations such as the structure of the current collector and its effect on percolation and conductivity in the electrode. In order to complement the findings of this previous work, the current work attempts to provide more detailed information about these processes by investigating the ways in which they depend upon the properties of the materials included in electrode manufacture.…”