An amperometric CO sensor using a solid oxide electrolyte was studied and it was found that the oxygen pumping current increased with increasing CO concentration when Au(10 wt%)/In1.9Sn0.1O3 and RuO2(10 wt%)/La0.6Sr0.4CoO3(LSC) were used for cathode and anode, respectively and La0.9Sr0.1Ga0.8Mg0.2O3 as the electrolyte. Changes in oxygen pumping current was caused by difference in electrode activity to CO oxidation upon exposure to CO and so sensitivity is strongly dependent on difference in electrode activity. Effects of additives to RuO2/LSC electrode on CO sensitivity were studied and it was found that addition of Pt is highly effective for increasing CO sensitivity. This could be explained by increased oxidation activity to CO. Further addition of Pd as the second additive to Pt-RuO2/LSC was effective for achieving high sensitivity and the highest CO sensitivity in our previous study was achieved on this type sensor. Amperometric sensor using RuO2-PtPd/LSC and Au/ITO anode and cathode, respectively, shows the high sensitivity to CO and so this sensor is promising as a CO sensor directly inserted into exhaust gas.
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