Developing solid oxide electrolysis cells for CO2 conversion: A critical power-to-X approach

Excessive global greenhouse gas emissions have intensified climate change, posing serious threats to ecosystems and socio-economic systems. The Paris Agreement aims to limit global warming to below 2 ℃, which has accelerated the rapid development of renewable energy. However, the intermittent nature of renewable sources restricts large-scale applications. Power-to-X (P2X) technology, which converts electrical energy into chemical energy for storage, has emerged as a key pathway for accommodating renewable energy. Among these, high-temperature solid oxide electrolysis cells (SOECs) are regarded as an important technology for CO₂ conversion due to their high thermodynamic efficiency, lack of reliance on precious metal catalysts, and strong compatibility with downstream chemical processes. However, existing research lacks a systematic analysis of the diverse conversion pathways for integrating renewable energy with SOECs, and there has been no comprehensive review of the market status and key manufacturers of SOECs, which constitutes a significant bottleneck for their development.

Professor Jiujun Zhang et al. from Fuzhou University, Tsinghua University and Shandong Provincial Weifang Eco-environment Monitoring Center, providing a systematic review of the mechanisms by which SOECs reduce CO₂. The study summarizes two categories of CO₂ conversion pathways, analyzes the market landscape of SOECs, and identifies the main global manufacturers while discussing the challenges and directions for large-scale applications. The paper was published in Frontiers in Energy.

The research first categorizes and analyzes the working mechanisms of SOECs: they are divided into oxygen ion-conducting (O-SOECs) and proton-conducting (H-SOECs) based on the ionic conduction mechanisms of the electrolyte. O-SOECs require high temperatures (> 600 ℃) to facilitate oxygen ion migration but face challenges such as catalyst agglomeration and carbon deposition. In contrast, H-SOECs have lower activation energy for proton migration and can operate at 400-600 ℃, addressing some stability issues, but must contend with the degradation of the electrolyte in CO₂ environments.

Secondly, the study outlines two types of CO₂ conversion pathways: one involves direct conversion without additional steps, including the direct reduction of CO₂ to CO, co-electrolysis of CO₂ and H₂O to produce syngas, dry reforming of methane (DRM) to generate syngas, hydrogenation of CO₂ to produce methane, and oxidative dehydrogenation of alkanes to produce ethylene. The other type couples co-electrolysis with other processes (such as methanation, methanol synthesis, and Fischer-Tropsch synthesis) to enhance energy efficiency and product value.

Finally, the analysis of the market status of SOECs reveals that in 2023, SOECs accounted for only 2.17% of the global electrolysis market, primarily used for hydrogen production. North America dominates the market, while the Asia-Pacific region is experiencing rapid growth. Major global manufacturers include Bloom Energy (USA), Sunfire (Germany), and Ningbo SOFCMAN (China), focusing mainly on syngas production and system integration.

This research provides theoretical and practical references for the application of SOECs in CO₂ conversion. By efficiently converting CO₂ into syngas, methane, and ethylene, SOECs not only accommodate renewable energy but also facilitate carbon resource utilization, playing a significant role in promoting carbon neutrality and establishing a circular carbon economy. Despite facing challenges such as material degradation, high costs, and insufficient industrial demonstration, the advantages of high energy efficiency and independence from precious metals make SOECs one of the key technologies for future low-carbon energy systems.