Inﬂuence of electrode conﬁguration on ozone synthesis and microdischarge property in dielectric barrier discharge reactor Koichi Takaki * , Yuki Hatanaka, Kaname Arima, Seiji Mukaigawa, Tamiya Fujiwara Department of Electrical and Electronic Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551, Japan Keywords: Ozone Dielectric barrier discharge Multipoint Dielectric Non-thermal plasma abstract Characteristics of a dielectric barrier discharge were investigated experimentally to clarify an inﬂuence of an electrode conﬁguration on ozone synthesis and a microdischarge behavior. Three difference conﬁg- urations: plane, trench and multipoint were employed as ground electrode. The alumina dielectric barrier coated plane electrode was used as a high-voltage electrode, to which a sinusoidal high-voltage was applied with 10 kHz frequency. Pure oxygen gas was fed into the reactor with gas ﬂow rate of 5 L/ min. The maximum yielding rate increased from 80 to 120 g/kWh by changing an electrode conﬁguration from plane to multipoint, which has 528 number of a right-pyramid shape projection on a 6 cm  22 cm plane electrode. The yielding rate was strongly dependent on a produced ozone concentration in the plane electrode case, whereas slightly depended on the concentration in the multipoint electrode case. The electrode conﬁguration also affected a number of the microdischarges per one applied voltage cycle. The multipoint electrode showed the largest number of microdischarges at same input energy. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction High-pressure dielectric barrier discharges (DBD, so-called silent discharge) have become one of the powerful methods for ozone synthesis since the pioneering work by Siemens [1]. DBD plasmas are usually produced using AC high voltage and plane or cylindrical electrodes covered with dielectric barrier layer. The dielectric barrier layer prohibits thermalization of the DBD plasma, i.e. quenches the discharge in short time duration (several tens of nanoseconds). This non-thermal plasma can produce atomic oxygen radicals with low energy cost. However, some reactor conﬁgurations’ experimental conditions curse inhomogeneous heat-up of the dielectric barrier and/or neutral gas, which courses a decrease of ozone production efﬁciency. There have been many attempts to improve ozone production efﬁciency for industrial uses of such a discharge [2]. The efﬁciency depends on the gas pressure, the temperature, and the gas used as well as the discharge condi- tions such as gap-width, applied voltage, its waveforms, electrode surface, and electrode material including a dielectric barrier [3–10]. An employment of multipoint-to-plane conﬁguration electrode, which strongly distorts the electric ﬁeld around tip of projection, in DBD plasma reactor has some advantages as follows: (1) low- pressure drop with high ﬂow rate ﬂue gas, (2) small loss in the dielectric barrier, and (3) low-voltage operation compared with a plane-to-plane conﬁguration [11]. The multipoint DBD plasma reactor was applied to remove nitrogen oxide (NO x ) from a diesel engine exhaust gas stream and the multipoint DBD plasma reactor showed the higher nitric oxide (NO) removal efﬁciency than the parallel-plane electrode DBD plasma reactor [12–15]. The multi- point DBD plasma reactor was also applied to synthesize ozone and showed higher ozone yield than the parallel-plane electrode DBD plasma reactor [16]. However, the mechanism of the improvement ozone yield by changing the electrode conﬁguration from plane to multipoint is not clear. Characteristics of the microdischarges generated in the DBD plasma reactor strongly affect the performance of ozone synthesis and/or pollutant gas removals [2]. Sun reported that a large number of microdischarges with small amount of energy deposition per one microdischarge resulted in a higher efﬁciency [17]. It is important to clarify the inﬂuence of electrode conﬁguration on characteristics of the microdischarges to understand the inﬂuence on ozone syn- thesis. Here, the inﬂuence of the electrode conﬁguration on ozone yield was experimentally investigated using three different electrode conﬁgurations: plane, trench and multipoint. Moreover, the characteristics of the microdischarges generated in the DBD reactor were also investigated to discuss the mechanism of the ozone yield change with the electrode conﬁguration. 2. Experimental setup Three conﬁgurations were employed as the ground electrode as shown in Fig. 1 . The multipoint electrode has 5 mm height 528 pyramid shape projections with tip angle of 45  in an area of 132 cm 2 * Corresponding author. Tel./fax: þ81 19 621 6941. E-mail address: takaki@iwate-u.ac.jp (K. Takaki). Contents lists available at ScienceDirect Vacuum journal homepage: www.elsevier.com/locate/vacuum Vacuum 83 (2009) 128–132 Contents lists available at ScienceDirect Vacuum journal homepage: www.elsevier.com/locate/vacuum 0042-207X/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2008.03.047