Study of Surface Discharges in capillary size reactors for Hydrogen Production*

H₂ production from natural gas typically uses steam reforming or partial oxidation, which generate significant CO₂ emissions and require high temperatures and active catalysts. An efficient and eco-friendly alternative is methane cracking, producing H₂ and solid carbon. Non-thermal plasma technology, particularly Dielectric Barrier Discharges (DBDs), offers a low-temperature reactive environment for this process. However, DBDs face challenges as a non-uniform discharge but it can be mitigated by using capillary reactors sized to the filaments. This study investigates the properties of pulsed surface discharges in a 1 mm diameter capillary DBD reactor. This setup ensures fast and linear energy deposition in methane plasma. Time-resolved imaging, optical emission spectra, and electrical measurements were used to analyze the plasma. A glass capillary (1 mm outer diameter, 0.6 mm inner diameter, 150 mm length) served as the reactor where Ar-CH₄ and CH₄ gas mixtures were tested. Results show the presence of H, C₂ and CH species with rotational and vibrational temperatures of approximately 3620 K and 4900 K, respectively at atmospheric pressure. Filament widths range from 100 to 200 µm. The effect of pressure, applied voltage and frequency on these parameters was investigated.