POTENTIOMETRIC AND AMPEROMETRIC GAS SENSORS BASED ON THE PROTONIC CONDUCTION OF LAYERED ZIRCONIUM-PHOSPHATES AND PHOSPHONATES

Solid-state protonic conductors can be usefully employed in the field of electrochemical sensors. In particular, we describe here potentiometric and amperometric gas sensors based on the protonic conduction of layered zirconium phosphates or phosphonates. The main components of these sensors are: (1) a suitable catalytic sensing electrode, possibly exhibiting high selectivity for the species to be analysed; (2) a thin him of the layered zirconium phosphate or phosphonate as a solid-state proton conductor; (3) a non-catalytic reference electrode capable of exchanging protons with the solid-state protonic conductors. Some interstitial metal hydrides such as TiHx and ZrHx have been shown to be very suitable reference electrodes possessing such a characteristic. After a brief account of potentiometric and amperometric gas sensors previously developed in this laboratory for H-2, O-2 (room temperature) and CO, some recent results obtained with these sensors in the detection of NO2 and NO are reported and discussed.