Enhanced CO Response of NASICON-based Gas Sensors Using Oxide-added Pt Sensing Electrode at Low Temperature Operation

摘要

NASICON (Na3Zr2Si2PO12)-based solid electrolyte-type sensors equipped with various metal oxides (MO)-added Pt sensing electrode (SE, Pt(nMO) (n: MO additive amount in wt%) and Pt counter electrode (CE, Pt) on the same side of the NASICON disc were fabricated and their (Pt(nMO)/Pt sensors) CO-sensing properties were examined at 25-300°C. The Pt(15Bi2O3)/Pt sensor showed the largest CO response with a change in electromotive force to a positive direction (positive response) at 25°C, while the Pt(15CeO2)/Pt sensor showed the largest negative CO response at 25°C. The CO response of the Pt(15CeO2)/Pt sensor seems to be determined by mixed potential at the triple phase boundaries (TPBs) containing the electrochemical reactions of CO oxidation and oxygen reduction. X-ray photoelectron spectroscopy of the Pt(15Bi2O3) SE before and after exposure to CO indicated a slight reduction of Bi3+ after the exposure to CO. Therefore, the additional electrochemical reactions containing the reduction of Bi2O3 were anticipated to occur at the TPBs of the Pt(15Bi2O3) SE, which resulted in the large positive CO response of the Pt(15Bi2O3)/Pt sensor. Furthermore, the addition of 15wt% CeO2 to Pt CE of the Pt(15Bi2O3)/Pt sensor largely enhanced the magnitude of CO response and attained relatively excellent CO selectivity against H2.