Progress in Research and Development of Solid Oxide Cells, Stacks and Systems at Forschungszentrum Jülich
Authors: Kunz Felix , Peters Roland , Schäfer Dominik , Zhang Shidong , Kruse Nicolas , de Haart L.G.J. (Bert) , Vibhu Vaibhav , Eichel Rudiger-A , Menzler Norbert H. , Lenser Christian , Naumenko D. , Kadyk Thomas , Margaritis N. , Gross-Barsnick Sonja 
Published: September 2023

The defossilization of the energy sector requires the transfer of sustainable, carbon-neutral technologies and processes into application. Along with the development of a global hydrogen economy, technologies that generate, store, distribute and use hydrogen and derivatives are particularly relevant. Considerable potential in this sense is offered by the solid oxide cell (SOC), which can be operated as a fuel cell (SOFC), as an electrolysis cell (SOEC) and reversible (rSOC). Forschungszentrum Jülich has been involved in the research and development of SOCs for more than 30 years. In addition to material and cell development, stack and system development and understanding degradation effects are among the main topics today.

Recently, an rSOC system with an output power of 10kW in fuel cell mode and input power of 40kW in electrolysis mode was developed. Four SOC stacks, separated and surrounded by a total of five heating plates plus an air preheater at one end and a fuel preheater at the other end, form the Integrated Module of the system; each stack has 20 layers with an active cell area of 19x19 cm². A compact and optimized design could be realized, which achieves a system efficiency of 63.3 % and 71.1 % in fuel cell mode and electrolysis mode, respectively. The system has already been tested in stationary operation modes. Current developments focus on the operating strategy, in particular on the temperature control of the stack in fuel cell mode and during the transient operation of the system.

With a focus on the SOC stack, progress was made both in the area of actual stack development and in the area of clarification and optimization of performance and lifetime relevant processes. The role of contaminants, foremost silicon species and sulfur dioxide in feed gases, was investigated to support technical applications. Headway was also made in applying advanced measuring technology like fibre-optic sensors for temperature measurements in air channels. Degradation processes were investigated both experimentally and simulatively in fuel cells as well as in steam and co-electrolysis operation. On the one hand, machine learning approaches were pursued to analyze degradational patterns in SOC stacks, utilizing a specifically consolidated and curated set of long-term experiments and EIS measurements. On the other hand, a multiphysical stack model was developed that allows the relevant physical processes within the stack to be analyzed individually and coupled and thus to optimize the overall operation of the stack.

In the area of the development and investigation of cells and materials, the performance of the SOC in the fuel cell mode as well as in the electrolysis mode was in the focus. In addition to operation in steam and co-electrolysis modes, operation in pure CO2 electrolysis was also researched. On single cell level the degradation behavior in the different modes of electrolysis operation was investigated. Different alternative materials were examined both on the fuel side and on the air side as well. A hierarchical degradation model framework was developed that relates changes at the level of electrode particles to changes in electrode structure, resulting materials properties and overall lifetime-performance. Model-based diagnostic allows the extraction of model parameters from experimental data, model verification as well as identification and quantification of different degradation mechanisms.

Overall, therefore, significant progress can be observed in the field of cell as well as in the field of stack and system development of SOCs in fuel cell, electrolysis and reversible operation at Forschungszentrum Jülich.