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The sulfur gas potentials in the H2S+H2 buffer gases were measured by a galvanic cellPs2)(normalg,normalAu)(normalPt|)(MoS2+normalCaS|CaF2|)(normalCu+Cu2S+normalCaS|normalAu)(normalPtin the temperature range from 650° to 950°C and Ps2 region from 10−2 to 10−10 atm. A quick response time (within 5 to 10 min) in emf with the change of Ps2 at a given temperature was observed by placing a MoS2 and normalCaS mixed pellet auxiliary electrode at the bottom of the cylindrical single‐crystal CaF2 electrolyte. The observed emf's agreed well with those calculated from the Nernst equation. Using this sensor, Ps2 values in the SO2+H2+H2S gas system were also evaluated from the measured emf at 827°C and were found to be in close agreement with those calculated from the thermochemical tables.

In this study, we investigated the suppression of potential oscillations that occur while feeding H2 gas including a large amount of CO to polymer electrolyte fuel cells. A carbon‐supported Pt–Ru alloy (Pt–Ru/C) sample was prepared by the polygonal barrel‐sputtering method. Electrochemical measurement was conducted in 1 N H2SO4 electrolyte solution saturated with H2 gas including CO of 1,000 ppm. From the measurement, it was found that the prepared Pt–Ru/C sample showed higher CO tolerance than a commercially available sample, and therefore, potential oscillations in the case of the prepared sample occurred for slightly longer intervals. Additional samples were prepared by sputtering different amounts of Ru on the prepared Pt–Ru/C sample, and it was observed that the average interval of potential oscillations increased with the amount of Ru. This result suggests that in the case of the polygonal barrel‐sputtering method, Ru plays an important role in suppressing potential oscillations and influences the CO tolerance of Pt–Ru/C.