Electrochemical Sensors for Sulfur- and Lead-Containing Gases: Effect of Nonstoichiometry of Measuring Electrodes

In accordance with the fact that the region of homogeneity of lead sulfide is two-sided, i.e. it includes compositions with both sulfur excess and lead excess relative to the stoichiometric composition, it is shown that a sensor with a Pb_{1 ±} S measuring electrode (ME) may be used for analyzing both sulfur- and lead-containing media. The general principle of operation of electrochemical sensor Me, Pb/PbCl₂–CaCl₂/Pb_{1 ±} S, is based on measuring EMF of an electrochemical circuit with a lead-conducting electrolyte at a specified sulfur vapor pressure above the reference electrode. At a fixed temperature, the cell's EMF is uniquely defined by the sulfur content on ME. The studies are done in the temperature interval 285 to 300°C where characteristics of the solid electrolyte used are optimum; its upper boundary is limited by mp of the lead reference electrode (327°). The interval of determinable concentrations of sulfur- and lead-containing gases is 10^–1 to 10^–9 vol %. If analysis is performed in a dynamic mode (in a carrier gas flow), the limiting stage is the adsorption of gas molecules on the ME surface and the sensor sensitivity increases after modifying the surface by various techniques and also due to the ME composition altering only in a surface layer. The sensor's working characteristics are affected mostly by the degree of deviation of the ME material from stoichiometry.