Photoacoustic measurements for catalytic effects of perovskite electrodes in a sealed-off CO2 discharge tube

Abstract

To investigate catalytic activities of perovskite-type electrodes in a sealed-off CO2 laser cavity, we studied the dissociation and reformation reactions of CO2 during electric discharge by monitoring the concentration change of CO2 as a function of time. A photoacoustic spectroscopy 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 cathodes. The discharge with the gas mixture of CO2:N2: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. Within 1 min after the discharge, the concentration of CO2 reduced drastically by as much as 60% for both cathodes. In the case of the Cu cathode, the amounts of CO2 in the tube had not recovered even after 30 min, while with the perovskite cathode the CO2 contents recovered slowly up to 90%–95% within 5 min and then remained almost unchanged. The dissociation of CO2 with the Cu cathode increased as the total pressure decreased and the discharge current increased. The La0.7Sr0.3CoO3 cathode, however, demonstrated strong suppression in the dissociation of CO2 according to the reformation reaction of CO+(1/2)O2→CO2 by its catalytic activity.