A review of high temperature co-electrolysis of HO and CO to produce sustainable fuels using solid oxide electrolysis cells (SOECs): advanced materials and technology.

High-temperature solid oxide electrolysis cells (SOECs) are advanced electrochemical energy storage and conversion devices with high conversion/energy efficiencies. They offer attractive high-temperature co-electrolysis routes that reduce extra CO emissions, enable large-scale energy storage/conversion and facilitate the integration of renewable energies into the electric grid. Exciting new research has focused on CO electrochemical activation/conversion through a co-electrolysis process based on the assumption that difficult C[double bond, length as m-dash]O double bonds can be activated effectively through this electrochemical method. Based on existing investigations, this paper puts forth a comprehensive overview of recent and past developments in co-electrolysis with SOECs for CO conversion and utilization. Here, we discuss in detail the approaches of CO conversion, the developmental history, the basic principles, the economic feasibility of CO/HO co-electrolysis, and the diverse range of fuel electrodes as well as oxygen electrode materials. SOEC performance measurements, characterization and simulations are classified and presented in this paper. SOEC cell and stack designs, fabrications and scale-ups are also summarized and described. In particular, insights into CO electrochemical conversions, solid oxide cell material behaviors and degradation mechanisms are highlighted to obtain a better understanding of the high temperature electrolysis process in SOECs. Proposed research directions are also outlined to provide guidelines for future research.