Hydrogen oxidation in H2/O2/N2 gas mixture by pulsed DBD at atmospheric pressure

The removal of hydrogen in the off-gas from fuel cells in a safe manner is desirable. In the present research, a model gas mixture, 2.0 vol% H2 and 19.5 vol% O2 balanced with nitrogen, was directly treated with a pulsed dielectric barrier discharge (DBD). The DBD plasma reactor had coaxial electrode geometry with quartz glass tubes. The gas mixture was allowed to flow into one end of the coaxial quartz glass tubes, and the DBD plasma was generated in a gap at atmospheric pressure. The applied voltage (peak-to-peak value) was varied from 17.5 to 37.5 kV, with repetition rates from 2.1 to 49.6 kHz. The discharge power in the DBD plasma ranged from 50 to 1230 W. Effects of the applied voltage, its repetition rate, and the exhaust gas temperature on the hydrogen conversion rate were investigated. The hydrogen conversion rate generally increased with an increase in the exhaust gas temperature and discharge power. The most important characteristic of this procedure is that hydrogen was oxidized easily below the ignition temperature in normal combustion. A conversion rate as high as 99% was attained at a discharge power of 1200 W and an exhaust gas temperature of 80 °C. To understand the reaction mechanism of hydrogen oxidation in the DBD plasma, a reaction kinetic study was carried out. The chemistry was resolved into separate contributions from radiolysis processes and gas phase reactions. H and O radicals generated by electron-impact reactions in the DBD plasma play an important role in promoting hydrogen oxidation in the gas phase reactions. Three important characteristics of hydrogen oxidation in DBD plasma, the advantage of the DBD plasma, effect of gas temperature, and effect of discharge power, are discussed based on simulation results.