Analysis of Key Factor of Higher Hydrogen Peroxide Production Performance of Diaphragm Discharge Plasma Based on Time-Resolved Observation

We have found that the diaphragm discharge plasma generates hydrogen peroxide (H₂O₂) at a markedly different rate and efficiency under different conditions of solution conductivity and applied voltage waveform. We can build some hypotheses on this characteristic, but its cause is not clear mainly because details of the discharge formation mechanism are unknown. In this paper, to elucidate the plasma generation process and the factor affecting the H₂O₂ generation rate and efficiency, we conducted time-resolved optical emission spectrum (OES) measurements on 10-parallel diaphragm discharge plasma. The electron temperature was much lower than the threshold energy of dissociation of water molecules, which starts reactions to generate H₂O₂. On the other hand, the rotation temperature of hydroxyl radical, an indicator of gas temperature, fluctuated around the threshold temperature of thermal dissociation of water molecules 3000–4000 K. The results of this study strongly suggest that thermal energy, rather than electrons, is responsible for the dissociation of water molecules and thus the formation of hydrogen peroxide. Furthermore, based on these results, we discuss the state of the discharge region and the mechanism of plasma formation and H₂O₂ production.