The hybrid sulfur cycle (HyS cycle) is a promising clean hydrogen production method that is expected to be efficiently coupled with a high-temperature reactor (HTR). SO2 depolarized electrolysis (SDE) is the hydrogen-producing step of the HyS cycle, and the electrolyzer is its core equipment. The Institute of Nuclear and New Energy Technology (INET), Tsinghua University, has paid great attention to the design and scale-up of SDE electrolyzers. Based on these efforts and the progress in membrane electrode assembly preparation, the fabrication of a three-dimensional electrode, etc. the performance of the SDE cell has been greatly improved.

Using SDE cells with a small membrane area (50  mm × 50 mm), the cell structure and flow field have been compared and optimized. With the optimized configuration, the scale-up of the electrolyzer was conducted, aiming for industrial applications. Single-cell electrolyzers with a 187 cm2 (170 mm  × 110 mm) effective membrane area and multiple-unit SDE stacks with cell areas of 226 cm2 (112  mm × 202 mm) and 218 cm2 (109  mm × 200 mm) were designed and tested with the help of computational fluid dynamics.

By applying novel electrodes, the stacks were optimized again, and the stacks consisting of two, four, or eight cells with an active cell area of 246 cm2 (120  mm × 205 mm) were secured. On the eight-cell stack, a hydrogen-producing rate close to 500 NL/h was achieved. At present, INET is assembling larger SDE stacks, aiming at a 1 Nm3/h or higher hydrogen product. The work is expected to be conducted in synergy and collaboration with nternational programs, effectively promoting the research on nuclear hydrogen production and process heat utilization of a HTR.