Potentiometric Cl[sub 2] Gas Sensor Using a Na[sup +] Conducting Composite NASICON-40 wt % (Na[sub 2]O-Al[sub 2]O[sub 3]-4SiO[sub 2]) Solid Electrolyte

Abstract

A composite Na ϩ conductor of polycrystalline NASICON mixed with glassy Na 2 O-Al 2 O 3 -4SiO 2 (40 wt %) was investigated and used for a Cl 2 gas sensor. The densification of the solid electrolyte was improved by the addition of the glassy material. The sensor probe using the composite electrolyte and RuO 2 ϩ NaCl (1:1) measuring electrode produced a rapid electromotive force (EMF) change for the Cl 2 gas concentration below 10 ppm at above 450ЊC. For the low temperature of 400ЊC, a slow EMF response was obtained due to the side reaction between the Cl 2 gas and Na 2 O on the solid electrolyte and/or slow Cl 2 reduction to Cl Ϫ ion on the electrode. This sensor EMF value in air was only slightly influenced by the changing of the O 2 or CO 2 gas concentration.

Influence of Moisture on Potentiometric Cl[sub 2] Gas Sensor Using a Na[sup +] Conducting Solid Electrolyte

“…16,17 However, the electron number for the electrode reaction was about n ϭ 1.5 which did not agree with the theoretical number of n ϭ 2.0. We assumed that Cl 2 gas directly reacted with Na 2 O on the solid electrolyte.…”

“…The sensor operated at 450°C which has been a suitable temperature for this sensor. 17 The emf of the sensor was measured with a digital electrometer having a high internal resistance (Ͼ10 13 ⍀). …”

“…In our previous study, it was reported that the Cl 2 gas sensor using a Na ϩ conductor with the composite material of polycrystalline sodium superionic conductor ͑NASICON͒ and glassy Na 2 O-Al 2 O 3 -4SiO 2 ͑40 wt %͒ with a NaCl-RuO 2 electrode can even detect in the low Cl 2 concentration region below 10 parts per million ͑ppm͒. 16,17 However, the electron number for the electrode reaction was about n ϭ 1.5 which did not agree with the theoretical number of n ϭ 2.0. We assumed that Cl 2 gas directly reacted with Na 2 O on the solid electrolyte.…”

“…We assumed that Cl 2 gas directly reacted with Na 2 O on the solid electrolyte. 17 Based on this assumption, we did not examine the existence of moisture in the test gas. One of the possibilities for a lower n value is that the Cl 2 reacts with moisture at the operating temperature of the sensor.…”

Sensors, Chemical Sensors, Electrochemical Sensors, and ECS

“…Sensitivity and selectivity to the analyte are provided by the auxiliary phase, e.g., the Na 2 CO 3 /NASICON system can be used for CO 2 sensing because the carbonate can introduce the electrochemical reaction: CO 3 2Ϫ ϭ CO 2 ϩ 1/2O 2 ϩ 2e Ϫ . This approach allows the use of several conventional ceramic solid electrolytes, including YSZ, ␤-alumina, or NASICON to construct sensors for many gases [27][28][29] especially the environmental gaseous pollutants such as CO 2 , CO, NO x , SO x , H 2 , Cl 2 , and NH 3, etc. An important advantage of this approach is the development of detection methods that survive harsh conditions where typical liquid electrochemical sensors would be inappropriate.…”