Nasicon-Based Planar-Type CO2 Sensor Attached with Solid Reference Electrode Stable Under High Humid Conditions

In order to improve the stability of a NASICON (Na₃Zr₂Si₂PO₁₂; Na⁺ conductor)-based potentiometric CO₂ sensor under humid conditions, a new solid-reference electrode of the BiCuVOx (Bi₂Cu_0.1V_0.9O_5.35)/perovskite-type oxide (La_0.6Sr_0.4Co_0.78Ni_0.02Fe_0.2O₃) composite was investigated. The fabricated electrochemical cell (CO₂+O₂, Au/Li₂CO₃-BaCO₃/ NASICON/ BiCuVOx-La_0.6Sr_0.4Co_0.78Ni_0.02Fe_0.2O₃, O₂) responded well to changes in CO₂ concentration (100-400 ppm) at 400-450degC under high humid conditions (86% RH) without degradation. The sensor device also exhibited a good warming-up characteristic, i.e., the electromotive force of the device quickly reached a steady and constant value when the sensor operation is re-started even after the sensor was exposed to high humid air at room temperature.