Water splitting in low-temperature ac plasmas at atmospheric pressure |
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Authors: | Jian Luo Steven L Suib Yuji Hayashi Hiroshige Matsumoto |
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Institution: | (1) U-60, Department of Chemistry, University of Connecticut, Storrs, CT 06269-4060, USA;(2) Department of Chemical Engineering and Institute of Materials Science, University of Connecticut, Storrs, CT 06269-4069, USA;(3) Fujitsu Laboratories, Ltd., 1015 Kamikodanaka, Nakahara 211, Japan;(4) Department of Chemistry, Nagasaki University, Bunkyomachi 1-14, Nagasaki 852, Japan |
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Abstract: | Plasma-induced water splitting at atmospheric pressure has been studied with a novel fan-type Pt reactor and several tubular-type
reactors: an all-quartz reactor, a glass reactor, and three metal reactors with Pt. Ni, and Fe as electrodes. Reaction products
have been analyzed by using GC (gas chromatography) and Q-MS (quadrupole mass spectrometry). Optical emission spectroscopic
studies of the process have been carried out by employing a CCD (charge-coupled device) detector. Water splitting with tubular
quartz and glass reactors is probably non-catalytic. However, a heterogeneous catalytic function of surface of metal electrodes
has been observed. The variation of hydrogen yield (YH) and energy efficiency (Ee) with operational parameters such as input voltages (Uin), flow rates of carrier gas (FHe), and concentrations of water (CW) has been examined. Plasma-induced water splitting can be described with a kinetic equation of-dCw/dt = kCW
0.2. The rate constants at 3.25 kV are 2.8 × 10−4, 3.5 × 10−3, and 3.4 × 10−2 mol0.8L−0.8 min−1 for tubular glass reactor, a tubular Pt reactor, and a fan-type Pt reactor, respectively. A CSTR (continuous-stirred tank
reactor) and PFR (piston-flow reactor) model have been applied to a fan-type reactor and tubular reactor, respectively. A
mechanism on the basis of optical emission spectroscopic data has been obtained comprising the energy transfer from excited
carrier gas species to water molecules, which split via radicals of HO·, O·, and H· to form H2 and O2. The fan-type Pt reactors exhibit highest activity and energy efficiency among the reactors tested. Higher yields of hydrogen
are achieved at higher input voltages, low flow rates, and low concentrations of water (YH = 78 % at Uin of 3.75 kV, FHe of 20 mL/min, and CW of 0.86 %). The energy efficiency exhibits an opposite trend (Ee = 6.1 % at Uin of 1.25 kV, FHe of 60 mL/min and CW of 3.1 %). |
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