Theory of gas sensors: response of an electrochemical sensor to multi-component gas mixtures

A first-principles model of the operation of an electrochemical metal oxide gas sensor had been previously used to analyze the response when the sensor was exposed to a simple gas mixture (e.g. O 2 /CO/CO 2 ). Here, the model is extended to study the sensor response to a complex gas mixture containing two reducing gases e.g. O 2 /CO/CO 2 /H 2 /H 2 O. In a first version, it is assumed that there is no interaction between the reducing and product gases (e.g. CO and H 2 O or H 2 and CO 2 ). The response to the complex gas mixture is deduced using the values of the model parameters obtained by fitting the experimental results for the simple gas mixtures O 2 /CO/CO 2 and 02/H2/H20 individually. In the second version, the so-called 'water-gas' reaction between adsorbed species is included. A wide variety of response is predicted depending upon the electrode material, the reactivities of the gases and the rate of reactions involving product gases. This analysis is helpful in providing insight and design guidance in optimizing sensor operation for specific applications.