| Summary: | The effect of NH<sub>3</sub> in H<sub>2</sub> and in air was investigated at various concentrations ranging from 1.0 ppm to 100 ppm in air and ranging from 0.25 ppm to 10 ppm in fuel. The effect of NH<sub>3</sub> on cathode caused an instantaneous decrease in cell voltage which dropped from 0.734 V to 0.712 V in 30 h and drop rates was 0.73 mV/h for 1 ppm; however, the cell voltage dropped to 0.415 V in 1 h for 100 ppm of NH<sub>3</sub>. The voltage could not be recovered after the polarization test (V-I test) but could be recovered to 84.4% after operation with neat air for 1.5 h and 98.4% after cycle voltammogram (CV). It was found that the voltage drop was obvious, and the drop rate increased with the NH<sub>3</sub> concentration in H<sub>2</sub>. The voltage drop rates at 500 mA/cm<sup>2</sup> were 0.54 mV/h for 0.5 ppm of NH<sub>3</sub>, 0.8 mV/h for 1 ppm, and 2 mV/h for 10 ppm. The voltage could be recovered from 70.6% to 77.3% after discharged with high purity H<sub>2</sub> for 24 h, to 92.8% after being purged with clean air for 10 h and to 98.4% after CV scan. The tolerance concentration of NH<sub>3</sub> in H<sub>2</sub> for 1000 h was 40 ppb, for 2000 h was 20 ppb, and for 5000 h was 9 ppb.
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