Tungsten-needle intensifies microwave-sustained plasma accelerating direct H₂S conversion to H₂

Direct sustainable conversion of hydrogen sulfide (H₂S) enables collaborative recovery of H and S resources via a metal-enhanced microwave plasma strategy, avoiding the hydrogen waste in the traditional Claus process. However, the metal size effect on microwave plasma property, the optimal process parameters, and the enhancement mechanism remain unclear in H₂S conversion. Herein, the optimal tungsten needle (diameter: 1 mm, length: 60 mm, and tip angle: 10°) is experimentally proven for intensifying microwave discharge in multi-mode cavities. Theoretical calculations and plasma distribution reveal that the optimized tungsten needle achieves the ideal coupling with the microwave field, exhibiting extreme electric field augmentation around the needle tip. Tungsten-needle intensifies microwave-sustained plasma, realizing 40.2 % (90.1 %) conversion of 100 % (10 %) concentration H₂S to H₂ at a low microwave power of 300 W with a good stability of 30 hrs. Low power, large flow rate, and high H₂S concentration are beneficial for improving energy efficiency. The excitation of microwave plasma is accompanied by a massive generation of highly energetic electrons. The direct high-energy electron-H₂S collision contributes a lot to H₂S splitting, especially for high-concentration H₂S. In-situ optical emission spectroscopy confirms the vital S and H radicals in the plasma. The free radical reactions triggered by electron collisions are responsible for the production of H₂ and S. This work opens an avenue to sustainable and low-carbon hydrogen production from the direct conversion and utilization of H₂S.