Parameters affecting the H2 production and frequency gaps in Ar moisture dielectric barrier discharge

Dependency of H2 production and frequency gaps with working frequency, applied electric fields, discharge gas-gap (GG), and central electrode materials in Ar-moisture dielectric barrier discharge (DBD) non-thermal plasma is presented. H2 production during the transformation of moisture in an Ar carrier having 100% relative humidity employing DBD is monitored by gas chromatography with a thermal conductivity detector. Coaxial cylindrical reactors with an outer Pyrex tube (common for all reactors) accompanied by two different categories of central electrodes [Pyrex in double dielectric (DD) and bare metal, such as stainless steel or aluminum or copper (Cu) in single dielectric (SD) of different GGs], are used. A high-frequency (4–30 kHz) ac power supply is employed for plasma as well as H2 generations. Dissipated powers in reactors are measured under similar conditions that differ marginally between DD and SD reactors. The formation of •OH and Ar metastable species is observed in optical emission spectra confirming the free radical-based water-splitting reactions for H2 generation. Interestingly, the use of high frequency leads to various frequency gaps within the 4–30 kHz range where there is neither the generation of filamentary discharge nor the H2 formation. These frequency gaps vary with GGs and the type of central electrode materials used in DBD reactors. In addition, an increase in the applied voltage controls the frequency gaps under study. H2 production of ∼3600 ppmv obtained with the Cu-containing SD reactor translates to over 21% water conversion.