Scaling up syngas production with controllable H₂/CO ratio in a highly efficient, compact, and durable solid oxide coelectrolysis cell unit-bundle

High-temperature coelectrolysis of H₂O and CO₂ by using solid oxide coelectrolysis cells (SOC) is considered to be among the most efficient processes for CO₂ conversion as these SOCs can efficiently utilize both heat and renewable electrical energy. One of the key components is the development of highly efficient, modular SOC cells and stacks to further scale up the CO₂ conversion process towards industrial applications. In this study, we developed highly efficient and durable flat-tubular solid oxide coelectrolysis cells (FT-SOCs) and investigated the electrochemical performance (I-V, EIS, long-term galvanostatic test) of single cells and a 6-cell bundle for CO₂-H₂O coelectrolysis to produce syngas with controllable H₂/CO ratios. The FT-SOC with an active area of 40 cm² reached a maximum current density of −3.2A/cm² at 1.6 V at 800 °C and an H₂O/CO₂ ratio of 2. In the 6-cell FT-SOC bundle, 90% CO₂ conversion was achieved by producing high-quality syngas with flexible H₂/CO ratios and stable long-term operation for continuous 500 h. The results of this study show that by using an FT-SOC bundle, scalable and controllable syngas quality could be produced and integrated with the multitude of downstream processes.