Influence of Active Layer Thickness of Reversible Solid Oxide Cells on the Electrochemical Performance of Water Electrolysis

Abstract

As energy storage becomes increasingly more important in contemporary and future energy solutions, the ability of a solid oxide cell (SOC) to work reversibly as an electrolyzer/fuel cell gives this technology great potential for use in large energy storage projects1,2. In theory, it is possible to use the state-of-the-art solid oxide cells in electrolysis operation to produce fuel (i.e. split water into oxygen and hydrogen) or generate electricity and heat using the so-called fuel cell regime. In addition, it is possible to produce syngas (H2 + CO)1,2 by co-electrolyzing water and CO2.While the performance and stability of the solid oxide fuel cell (SOFC) are in focus of most research regarding this technology, the technological possibilities of reversible solid oxide cells (RSOC) are far less studied. Although both technologies mostly share their device composition and main architecture, using the SOC in electrolysis mode creates new degradation mechanisms and technological problems3,4.In this work the authors focus on the electrolysis performance of the RSOC. The authors analyzed the influence of active layer thickness on SOC performance in electrolysis mode by using a commercial solid oxide cell (Ni-3YSZ|Ni-8YSZ|8YSZ|GDC|LSC). The study has been performed to establish the optimal active layer thickness and therefore to maximize the SOC performance in electrolysis mode.Electrochemical characterization of SOC button cells has been conducted using electrochemical impedance spectroscopy, cyclic voltammetry and galvanostatic methods at several operating conditions including different temperatures and different water vapor contents in the gas stream. The gas compositions have been exchanged to simulate working conditions at different locations in the RSOC stack during electrolysis work. The results of the electrochemical studies have been analyzed using equivalent circuit fitting method of Nyquist plots. Complex analysis of different porous architectures and chemical compositions at different operating conditions gave more information on how the structure of the SOC determines the electrochemical performance of the water electrolysis process.