Solid oxide fuel cells that enable the detection of CO in reformed gases

Solid oxide fuel cells (SOFCs) using Pd metal as the anode were fabricated for detection of CO in a flowing mixture of 0–4000 ppm CO, 50% H2, 10% CO2 and 6% H2O vapor between 300 and 400 °C. When 20 mol% Sm3+-doped CeO2 (SDC) was used as the electrolyte, the Pd anode was subjected to a large and reversible change in the anodic-reaction resistance with the CO concentration. This behavior brought about an almost linear relationship between the electromotive force (EMF) generated from the cell or the short-circuit current through the cell and the logarithm of the CO concentration. In both signals, the minimum detectable CO concentration was 50 ppm, and the 90% response and 90% recovery times were about 60 s. However, the EMF of the cell at a CO concentration of 0 ppm significantly deviated from the theoretical value, which made it difficult to obtain reproducible data. In addition, the current signal of a few μA at a CO concentration of 4000 ppm was not large enough to monitor the CO concentration exactly. The improvement of these problems could be achieved by using 25 mol% Y3+-doped BaCeO3 (BCY25) with higher ionic conduction as the electrolyte: the EMF of the cell at a CO concentration of 0 ppm was near the theoretical value; the current signal reached 66 μA at a CO concentration of 4000 ppm.