Triethylamine Sensing with a Mixed Potential Sensor Based on Ce0.8Gd0.2O1.95 Solid Electrolyte and La1-XSrxMnO3 (x = 0.1, 0.2, 0.3) Sensing Electrodes

Abstract

Introduction The threshold limit of triethylamine concentration is 10 ppm in air by Occupational Safety and Health Administration (OSHA). In addition, it is reported that the concentration of triethylamine at 7 days is less than 4 ppm from rotten crucian (about 200 g) at room temperature, which indicates a great challenge in meeting the requirements of the food freshness test. Recently, gas sensor with low cost and the ability of in-situ measurement has been used to triethylamine detection. The mixed potential sensor based on Ce0.8Gd0.2O1.95 (GDC) has the advantages of high sensing performance, reliable stability and good moisture resistance, which is expected to realize the real-time detection of triethylamine in the atmospheric environment and microenvironment, and to determine the freshness of fish [1, 2]. Method Fabrication and measurement of the gas sensor The sensor was fabricated utilizing Ce0.8Gd0.2O1.95 (GDC) plates (made by Ningbo Sofman Energy Technology Co., Ltd.). A point-shaped and a narrow stripe-shaped Pt electrode were formed on two ends of the GDC plate using a commercial Pt paste (Sino-platinum Metals Co. Ltd.), and sintered at 900°C. The paste which was mixed by a minimum quantity of deionized water and the sensing materials La1-xSrxMnO3 (x = 0.1, 0.2, 0.3). Next, the resultant paste was applied on the point-shade Pt to form stripe-shaped La1-xSrxMnO3 (x = 0.1, 0.2, 0.3) electrode . Afterward, the device was annealed at 800°C to make a good contact between the sensing electrode and electrolyte. A Pt heater and a linear DC Power Supply (Gwinstek GPD-3303S) were used to provide required heat to regulate the operating temperature of the sensor. Results and Conclusions In this paper, CeO2-based mixed potential sensor with La1-xSrxMnO3 (x = 0.1, 0.2, 0.3) and Pt electrodes was developed for the triethylamine detection. It can be seen from Fig. 1(a) that the response value of S2 is the highest, which is -113 mV, so the optimum substitution amount of Sr element in La1-xSrxMnO3 is 20%. Therefore, the sensing performances of the sensor S2, such as the continuous response, sensitivity, selectivity, repeatability and long-term stability were focused in the following content of this study. The dynamic response/recovery transients of the sensor S2 exposed to triethylamine in a concentration gradient 1-200 ppm is shown in Fig. 1(b). It can be seen from the figure that the response value is gradually increasing in the range of 1-100 ppm. When the concentration is higher than 100 ppm, the response value is basically saturated. The response value of sensor S2 to 100 ppm triethylamine is -113 mV, and the sensor S2 is able to detect 1 ppm triethylamine with a response of -8 mV. As shown in Fig.1(c), the typical 90% response time to 100 ppm triethylamine of the sensor S2 is less than 1 s, and the typical 90% recovery time is 9 s. They are quite short time among time cost of the sensors reported. According to the recovery and response curve for sensor S2 to 1-100 ppm triethylamine, the dependence of ΔV on the logarithm of triethylamine concentration for the sensor is shown in Fig. 1(d). A linear relationship between ΔV and the logarithm of concentration towards 1-100 ppm triethylamine at 580°C is shown in the figure, and the sensor S2 displays a sensitivity of -59.2 mV/decade. Next, the cross-sensitivity response of the sensor S2 to 10 ppm various gases (such as ethanol, methanol, methanol, n-butanol and acetone) is shown in Fig. 1(e). It is obvious that the response value of the sensor S2 to triethylamine is much higher than that to other gases, indicating that the sensor S2 has a good selectivity. The continuous response and recovery transient curve of the sensor S2 to 10 ppm triethylamine in five cycles was studied. As shown in Fig. 1(f), the response values remain basically unchanged in the examined five-time cycles, which indicates that sensor S2 displays good repeatability to 10 ppm triethylamine. As shown in Fig. 1(g), the response value of the sensor S2 to 100 ppm triethylamine is basically unchanged under continuous heating to 580°C during 30 days measurement and the sensor S2 exhibited good stability. Taken together, the presented sensor S2 could be considered as a potential sensor for monitoring triethylamine in atmosphere environment and microenvironment, and determining the freshness of fish.