Potentiostated, three-electrode, solid polymer electrolyte (SPE) gas sensor having highly invariant background current characteristics with temperature during zero-air operation

摘要

A compact electrochemical gas sensing cell is described for detecting gases such as carbon monoxide, NO.sub.2, alcohol vapors, etc. The cell is characterized by temperature stability during zero-air operation so that background current with no gas flow is eliminated or minimized. This cell utilizes a hydrated, solid polymer electrolyte having reference, sensing and counter electrodes mounted on the surface thereof with one side of the membrane being flooded with distilled water to provide self- humidification of the cell by water vapor transport across the membrane. A potentiostatic circuit is utilized to control the potential on the sensing circuit and also to maintain a fixed potential difference between the reference and the sensing electrodes. In addition, the chemical, electrochemical, and thermal characteristics of the sensing and reference electrodes are matched so that the sensor is highly temperature invariant during zero-air operation. The sensing and reference electrodes are so positioned that the resistance of the current path between these electrodes is greater than 60 ohms. Furthermore, the sensing to reference electrode resistance is high compared to the sensing and counter electrode resistance with the ratio being greater than 50 to 1. This essentially places the sensing electrodes outside of the current flux lines between the sensing and counter electrodes. By thus eliminating or substantially reducing any current flow between the sensing and reference electrodes, the changes in background current with temperature during "Zero-Air" operations is sufficiently low (1-3&mgr; amps) to eliminate the need for temperature compensation during "Zero- Air" operations.