Humidity effect on ammonia sensing properties of substituted and unsubstituted cobalt phthalocyanines

In this paper, we studied the effect of humidity on the response of cobalt phthalocyanine—containing resistors to ammonia, in the ppm range. We pointed out the fact that, when alternating exposure periods with recovery periods, the humidity effect had to be carefully studied, in correlation with the flow variation. Thus, for a sulfonated cobalt phthalocyanine, the effect of NH3 was totally screened as soon as the relative humidity (RH) was above 10%. On the contrary, when using unsubstituted cobalt phthalocyanine (CoPc) as sensing material, the sensorsʹ response to NH3 appears to be quite stable in a wide RH range, allowing a discrimination between 12, 25 and 50 ppm of NH3 over the 10–70% RH range. Finally, CoPc offers a promising perspective as sensing material for air quality control applications, even at relatively high humidity levels.