Investigations on plasma parameters of diaphragm discharge plasma based on optical emission spectroscopy

As a plasma-based method, diaphragm discharge plasma, an underwater discharge, exhibits a relatively high production rate and efficiency of hydrogen peroxide (H 2 O 2 ). This study aimed to characterize the energetic state of plasma and the H 2 O 2 production mechanism by optical emission spectroscopy, evaluating the excitation temperature, gas temperature, electron density, and their temporal variations. The excitation temperature was approximately 3000 K, which was also presumed to almost coincide with the electron temperature in the plasma. The gas temperature was approximately 2500 K, and the electron density was approximately 6 × 10 22 m −3 at maximum. The electron density sustained higher values under the condition of better H 2 O 2 production performance, whereas the other two parameters exhibited almost no difference and variation. The reaction rate calculation based on the observation results indicated that the thermal dissociation of H 2 O is a more crucial reaction path for H 2 O 2 production in our plasma than expected.