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 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 La_0.7Sr_0.3CoO₃ 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 La_0.7Sr_0.3CoO₃ 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.