Mixed Ionic and Electronic Conduction in Li3PO4 Electrolyte for a CO2 Gas Sensor

Abstract

An electrochemical gas sensor using and as sensing and reference electrodes, respectively, and as the electrolyte is the subject of this paper. The sensor response to gas showed a systematic deviation from the prediction of the Nernst equation at low . Based on the electromotive force (emf) measurement, the transference numbers of , a lithium-ion conductor, were estimated for different values, and the conduction domain boundary for separating n-type electronic conduction from ionic conduction was constructed. The conduction domain predicts that change in the Li activity in the sensing side of the cell drives the electrolyte to a mixed (n-type electronic and ionic) conduction region at low . Hebb-Wagner dc polarization measurements also indicate n-type electronic conduction in with a mixture of and gold as a reversible electrode. The transference numbers obtained from both the emf measurement and the Hebb-Wagner polarization measurements demonstrate that the origin of the non-Nernstian behavior of the sensor is due to the lithium mass transport from the -sensing electrode to the electrolyte, resulting in nonstoichiometry of at temperatures above .