A Stable Solid-Reference Electrode of BiCuVO_x/Perovskite-Oxide for Potentiometric Solid Electrolyte CO₂ Sensor

Abstract

A laminated solid-reference electrode of BiCuVO_x (Bi₂Cu_0.1V_0.9O_5.35)/perovskite-oxide (La_0.6Sr_0.4Co_0.78Ni_0.02Fe_0.2O₃) was developed for a NASICON (Na₃Zr₂Si₂PO₁₂; Na⁺ conductor)-based potentiometric CO₂ sensor. The fabricated electrochemical cell expressed as, CO₂, O₂/Au (sensing electrode)/Li₂CO₃-BaCO₃ (auxiliary phase)/NASICON/BiCuVO_x/BiCuVO_x-perovskite-oxide (reference electrode)/O₂, responded well to changes in CO₂ concentration (100-400 ppm) at 450°C under high humid conditions (88%RH). The potential of the developed reference electrode was stable and exhibited little interference by water vapor. Furthermore, the reference electrode potential did not response to CO₂ even after the BiCuVO_x layer was contaminated with carbonate, indicating a good stability of BiCuVO_x against CO₂. The sensor device attached with the laminated solid-reference electrode showed a good warming-up characteristic, i.e., the electromotive force (EMF) of the device reached a steady and constant value when the sensor operation is re-started even after the sensor was exposed to humid air containing CO₂ at room temperature.