Microwave sintering slashes hydrogen cell production time and energy use

Solid oxide electrolysis cells (SOECs), a key technology for producing green hydrogen without carbon emissions, require a high-temperature “sintering” process to harden ceramic powders. Researchers at KAIST, led by Professor Kang Taek Lee from the Department of Mechanical Engineering, have successfully shortened this process from six hours to just 10 minutes, while also reducing the required temperature from 1,400°C to 1,200°C.

This innovation dramatically cuts both energy consumption and production time, marking a major step forward for the green hydrogen era. The study, titled “Ultra-Fast Microwave-Assisted Volumetric Heating Engineered Defect-Free Ceria/Zirconia Bilayer Electrolytes for Solid Oxide Electrochemical Cells,” is published in the journal Advanced Materials.

The core of this technology lies in sintering—a process in which ceramic powders are baked at high temperatures to form a dense, tightly bonded structure. Proper sintering is critical: It ensures that gases do not leak (as hydrogen and oxygen mixing could cause explosions), oxygen ions move efficiently, and the electrodes adhere firmly to the electrolyte to allow smooth current flow. In short, the precision of the sintering process directly determines the cell’s performance and lifetime.

To address these challenges, the team applied a “volumetric heating” technique that uses microwaves to heat the material uniformly from the inside out. This approach shortened the sintering process by more than thirtyfold compared to conventional methods. Whereas traditional sintering requires prolonged heating above 1,400°C, the new process uses microwaves to heat the material internally and evenly, achieving stable electrolyte formation at just 1,200°C within 10 minutes.

In conventional fabrication, the essential materials—ceria (CeO₂) and zirconia (ZrO₂)—tend to intermix at excessively high temperatures, degrading material quality. The new method allows these two materials to bond firmly at the right temperature without mixing, producing a dense, defect-free bilayer electrolyte.

The total “processing time” includes heating, holding, and cooling. The conventional sintering process required about 36.5 hours, whereas the team’s microwave-based technique completes the entire cycle in only 70 minutes—more than 30 times faster.

The resulting electrochemical cells demonstrated remarkable performance: They produced 23.7 mL of hydrogen per minute at 750°C, maintained stable operation for more than 250 hours, and exhibited excellent durability. Using 3D digital twin simulations, the team further revealed that ultra-fast microwave heating improves electrolyte density and suppresses abnormal grain growth of nickel oxide (NiO) particles within the fuel electrode, thereby enhancing hydrogen production efficiency.

Professor Lee stated, “This research introduces a new manufacturing paradigm that enables the rapid and efficient production of high-performance solid oxide electrolysis cells. Compared to conventional processes, our approach drastically reduces both energy consumption and production time, offering strong potential for commercialization.”