INVESTIGATION OF SOLID SODIUM REFERENCE ELECTRODES FOR SOLID-STATE ELECTROCHEMICAL GAS SENSORS

Several types of solid reference electrodes for potentiometric gas sensors based on solid sodium ion conductors (e.g., Na+-beta/beta''-Alumina or NASICON) are described and the observed experimental results are discussed in view of theoretical predictions. Defined sodium activities are established by appropriate equilibria of binary and ternary phases. The binary systems Na-Sb and Na-Bi, and the ternary systems Na-M-O (M is a transition-metal, Co or Ni) were found to show excellent kinetic performance and are capable to fix the chemical potential of sodium well defined over extended periods of time. Some of the sodium reference electrodes are even stable in air. The results are compared with the application of elemental sodium as reference electrode.