Advancement in Solid Oxide and Protonic Ceramic Electrolysis Cells: A Review

Hydrogen gas is a crucial fuel for the green energy transition as its combustion yields energy and water. However, it is mainly produced through fossil fuels, hindering its potential for environmental benefits. Therefore, the trend is shifting toward green hydrogen produced through renewable sources. Electrolysis by solid oxide electrolysis cells (SOECs) is one of the most promising methods for green hydrogen production due to its high efficiency and chemical conversion flexibility. In addition to producing hydrogen and oxygen by steam electrolysis, SOECs can also produce other electro-fuels such as syngas and ammonia by co-electrolysis of steam and carbon dioxide and co-electrolysis of steam and air, respectively. Conventional SOECs utilize oxide ionic conductor ceramic electrolytes such as zirconia; however, proton-conducting ceramic electrolytes have recently emerged due to their efficient electrochemical cell designs and improved performance at low operating temperatures. This review presents the status of the oxide ion conductor (SOEC) and proton conductor (PCEC) cell configurations. For this purpose, we summarize the most used materials, fabrication methods, and characterization techniques. Furthermore, we critically investigated the issues related to cell performance and stability by performing a systematic analysis of the degradation mechanisms for both oxide ion conductor and proton conductor electrolysis cells. The recommendations provided in this work would help researchers identify the key issues hindering the commercialization of promising SOEC technology.