PHOTOACOUSTIC MEASUREMENTS FOR CATALYTIC EFFECTS OF PEROVSKITE ELECTRODES IN A SEALED-OFF CO2 DISCHARGE-TUBE

To investigate catalytic activities of perovskite-type electrodes in a sealed-off CO2 laser cavity, we studied the dissociation and reformat ion reactions of CO2 during electric discharge by monitoring the conce ntration change of CO2 as a function of time. A photoacoustic spectros copy detection was introduced to measure the amount of CO2 in a closed discharge system. The catalytic activities in the dissociation of CO2 were demonstrated and compared for both Cu and La0.7Sr0.3CoO3 cathode s. The discharge with the gas mixture of CO2: N-2: He = 1 : 1 : 8 was performed under nine combinations of different conditions at pressures of 10, 20, and 30 Torr and discharge currents of 3, 4, and 5 mA. With in 1 min after the discharge, the concentration of CO2 reduced drastic ally by as much as 60% for both cathodes. In the case of the Cu cathod e; the amounts of CO2 in the tube had not recovered even after 30 min, while with the perovskite cathode the CO2 contents recovered slowly u p to 90%-95% within 5 min and then remained almost unchanged. The diss ociation of CO2 with the Cu cathode increased as the total pressure de creased and the discharge current increased. The La0.7Sr0.3CoO3 cathod e, however, demonstrated strong suppression in the dissociation of CO2 according to the reformation reaction of CO+ (1/2)O-2-->CO2 by its ca talytic activity. American Institute of Physics. [S0034-6748(98)04009- X]