Effects of Current Collector on Internal Visualization of Solid Oxide Cells

Abstract

Introduction Visualization of spatial distribution in solid oxide fuel cells (SOFCs) operating under high temperature is difficult to use various measurement equipment and sensors due to their recommended operating temperature. Therefore, it is difficult to reveal the distributions of gas species and reactions in the cell, as well as the loading current, using only electrochemical measurement methods. Simulation technology can be used to visualize various distributions in the cell and predict cell performance. While many simulation studies have revealed various spatial distributions in the SOFCs such as current density, they have also indicated that it is essential to accurately reflect the cell shape and multiphysics to simulate the cell performance1, 2.In our previous study, simulation and experimental thermal imaging combined temperature visualization method was developed. It was suggested that the temperature distribution under actual operating conditions is affected by Joule heating due to loading current distribution depending on the current collector geometry. Therefore, in order to evaluate the influence of the collector shape on the spatial temperature distribution, the influences of Joule heating and the collector geometry on the temperature distribution are evaluated. Then, we also analyze the influence of the current collector on the SOFC performance and propose a current collection method suitable for visualizing the reaction in an SOFC. Simulation Method In this study, the calculation was performed using a three-dimensional model that simulates the actual cell geometry used in the experiments. The simulated 3-D model was based on an electrolyte-supported plate cell with Scandia-stabilized Zirconia (ScSZ, 5 cm × 5 cm in size) as the support, LSM ((La0.8Sr0.2)0.98MnO3) and LSM-ScSZ composite material for the air electrode, and Ni-ScSZ cermet for the fuel electrode, respectively. The electrode area was 4 cm × 4 cm (16 cm2), and a platinum mesh and wire were used as a current collector. A schematic diagram of one of these examples is shown in Fig. 1. COMSOL Multiphysics (Ver. 6.0) was used as the 3-D simulation software to calculate the I-V characteristics and cell temperature distribution.The cell operating conditions were set to 800 ℃ for the operating temperature, 100 ml min-1 of 3 % humidified hydrogen as the incoming fuel, and the air electrode side opened to the atmosphere. I-V characteristics and cell temperature distributions were calculated under current density loading conditions ranging from 0.01 A cm-2 to 0.15 A cm-2. Based on each result, the relationship between current density and cell temperature distribution was evaluated. Results and Discussion As a result of numerical analysis and experiments focusing on the effect of the current collector shape, it was confirmed that the influence of the current collector shape appeared significantly in the cell temperature distribution as shown in Fig. 2. In addition, it was found that the visualization of the spatial distribution may be difficult because the effect of the heat generated by the Pt wire used as the current collector appears in the results of the temperature distribution on the surface. Based on these findings, we improved the current collector shape. Although the effect of the improvement on the Joule heating at Pt wire appeared in the temperature distribution result, the temperature distribution change was confirmed due to the loading current flow pattern, which depends on the shape of the current collector. The simulation results of the further improved collector shape showed that the temperature distribution change depending on the collector shape became smaller, suggesting that this collector shape is promising as a current collecting method suitable for visualizing the cell inside. In this presentation, we report the simulation results and discussion on the changes in current density distribution, gas distribution, and I-V characteristics, in addition to the changes in temperature distribution. References (1) M. Andersson, H. Paradis, J. Yuan, and B. Sundén, Electrochimica Acta, 109, 881 (2013).(2) A. Li, C. Song, and Z. Lin, Applied Energy, 190, 1234 (2017). Figure 1