Development and working principle of an ammonia gas sensor based on a refined model for solvate supported proton transport in zeolites
Some of the work relating to the development of a selective ammonia exhaust gas sensor are reported in this contribution. The sensor itself meets all the technological and economic demands of the automotive industry. As the gas-sensitive material the proton conducting zeolite H-ZSM-5 is used. The selective and concentration dependent interaction of the mobile protons with ammonia, i.e., the resulting change in proton conductivity, is detected directly by means of impedance spectroscopy. The sensor development was supported by a detailed picture of ammonia supported proton transport, deduced from impedance measurements on H-ZSM-5 with different SiO2/Al2O3 ratios in a wide temperature and frequency range. It provides understanding of the transport control parameters, e.g. temperature, composition of the zeolite structure and concentration of the guest molecules, respectively.