Tuning transport mechanisms in solid oxide electrolysis cells for enhanced performance and product selectivity

Abstract

Solid oxide electrolysis cells offer a promising route for the electrochemical conversion of steam and carbon dioxide into valuable chemicals and feedstocks utilizing renewable and sustainable sources of energy. These cells also provide flexibility in their modes of operation, namely conventional, fuel-assisted, and co-electrolysis, in order to match the energy requirements and products desired by a particular application. However, significant challenges still persist in the development of these cells, which include mitigating oxygen concentration gradients and carbon deposition, determining the reaction pathways that contribute to the transport phenomena in the system and how they affect product selectivity, and making exact comparisons between cells of varying scale and operating conditions. Dimensional analysis can help address these problems, since it produces universal results that are relevant for a broad range of cell designs; reveals how performance metrics scale as a function of cell geometry and operation, thus presenting control strategies to improve performance and product selectivity; provides physical meaning for the interpretation of experimental and simulation data with order-of-magnitude estimates; and facilitates direct comparisons between different systems. Despite these benefits, dimensional analysis is seldom utilized when investigating solid oxide electrolysis cells, as well as other electrochemical energy conversion technologies. Therefore, the work presented in this thesis uses a combination of dimensional analysis, thermodynamics, transport phenomena, and numerical modelling to expand our understanding of the transport mechanisms that govern the performance, product selectivity, and longevity of solid oxide electrolysis cells that operate in conventional, fuel-assisted, and co-electrolysis modes. Design and operation strategies are proposed to address ongoing challenges in these systems, such as alleviating oxygen concentration gradients in the anode that can lead to electrode delamination, mitigating carbon deposition in the current collectors which has resulted in catalyst deactivation and electrode fracture, tuning the outlet product composition for a specific downstream application, and reducing electrical work input demands. The goal of this work is to promote the economic competitiveness of solid oxide electrolysis cells for the production of industrially relevant quantities of hydrogen and carbon monoxide, in order to help decouple the chemicals processing and transportation sectors from coal, natural gas, and oil.