Degradation Analysis of SOFC Performance for Long-Term Operation with High Fuel Utilization (2)

Abstract

Solid oxide fuel cells (SOFCs) are a power generation technology with its high efficiency and low environmental impact, and the most important issue for SOFC for practical use is to improve reliability as well as high efficiency. A national project on SOFC development in Japan, “Development of advanced evaluation and analysis technologies for the durability of Solid Oxide Fuel Cells stacks (2020-),” has been initiated as a NEDO project in order to clarify their long-term durability and find dominant degradation factor for each SOFC stacks. Central Research Institute of Electric Power Industry (CRIEPI) has operated three kinds of different SOFC cell/stacks (flat-tubular and two kinds of planer) for durability under NEDO’s project, which have been developed by KYOCERA, MORIMURA SOFC Technology, and DENSO.Long-term durability tests of 20,000 hours have been conducted under high fuel utilization of 80% and 85%, which is close to the operating limit of each SOFC cell/stack for high efficiency, to evaluate the effects on the performance and degradation behavior of the cell/stack. In previous projects, we have developed an electrode polarization model that can accurately represent SOFC performance, including cell voltage and each overvoltage, under a variety of conditions. The degradation factors for durability of each SOFC cell/stack have been analyzed by using this model. The analysis revealed that the dominant degradation factors were increased cathode overvoltage and IR loss, similar to the SOFC cell/stacks that were modified from the previous project to improve their long-term durability. On the other hand, the degradation rate of cell voltage was higher at 85% than at 80% fuel utilization in one cell/stack, and the performance degradation factor analysis revealed that this difference was due to an increase in anode overvoltage at 85% than at 80% fuel utilization, where anode overvoltage was not the primary degradation factor.This work has been carried out under the projects (JPNP13001 and JPNP20003) of the New Energy and Industrial Technology Development Organization (NEDO), Japan as contract research. We would like to express our gratitude to NEDO, many SOFC developers, as well as to university partners and National Institute of Advanced Industrial Science and Technology (AIST).