Effect of gas humidity on the potential of pseudoreference Pt/air electrode in amperometric solid-state gas sensors

The effect of air relative humidity (RH) on the potential of two different Pt/air electrodes was examined. One electrode was platinum in contact with a hydrophilic Nafion (Pt-Nafion/air), the other was platinum in contact with a plasticized polyvinyl chloride containing a hydrophobic electrolyte (Pt-PVC/air). Over the RH range, from 11 to 72%, the potential of the Pt-Nafion/air electrode decreases non-linearly with increasing RH from 880 to 710 mV versus Ag/AgCl electrode. The potential decrease at the steepest part of the dependence (for RH from 30 to 70%) amounts to about −4 mV/%RH. The potential of the Pt-PVC/air electrode increases linearly with increasing RH from 324 to 337 mV versus Ag/AgCl electrode, with a slope of 0.21 mV/%RH. The change of the reference electrode potential with changing RH might influence the properties of the sensors where the current is measured on the increasing or descending part of the current–potential curve (e.g. the sensors with an indicator electrode exposed to test gas without a diffusion barrier).