Characteristics and performance of NASICON-based CO2 sensor using Bi8Nb2O17 plus Pt as solid-reference electrode
Introduction
Development of compact, inexpensive, low energy consumption and reliable solid state sensors for measuring CO2 concentrations has been in high demand for numerous applications ranging from control of combustion processes to environmental monitoring [1]. So far, many types of solid state CO2 sensors based on optical properties [2], capacitance [3], field effect transistor (FET) [4] and electrochemical potential [5] have been investigated. Among them, the electrochemical-type is more suitable than others because CO2 is not a redox gas but an acid–base active gas, which usually reacts with ions of solid rather than electrons [6]. NASICON (Na3Zr2Si2PO12: Na+-ion conductor)-based potentiometric CO2 sensors covered with a binary carbonate Li2CO3–BaCO3 (1:2 in molar ratio) are one of the most popular candidates due to their excellent performance such as good sensitivity, high selectivity and fast response time [7]. However, such sensors suffer from significant interference from humidity [8], [9]. Thus the long-term stability of the sensors cannot be guaranteed. The existing researches confirm that the stability of the sensor is affected not only by the electrode composition [10], [11], but also by the geometry of sensor [12], [13], [14], thermal treatment history [15], and the presence of humidity [16], [17], [18]. And the alkaline metal carbonates often used as auxiliary electrode was attached on one side of NASICON disk by mechanical press [19], leading to poor chemical stability [20] and low mechanical strength due to the thermal expansivity of auxiliary electrode layer was much different from that of NASICON electrolyte. From this point of view, our previous work demonstrated that the use of Li2CO3, NASICON and Pt as auxiliary electrode enhanced the electrode mechanical strength as well as expanded the amount of triple phase boundaries (TPBs), giving a good performance of the sensor [21]. Sadaoka et al. [22] reported that the degradation of the performance of the sensors due to humidity resulted from the formation of NaHCO3 and NaOH at the grain boundary of the NASICON electrolyte, due to the easy diffusion of H2O and CO2 into NASICON. And both Lee et al. [23] and Aono and Sadaoka [24] pointed out that the following reactions might occur when the reference electrode was not sealed.2Na+ + CO2 + 1/2O2 + 2e− = Na2CO3
or2Na+ + H2O + 2CO2 + 1/2O2 + 2e− = 2NaHCO3
Thus, the Na2O activity in NASICON may probably be altered by the formation of these new compounds at the reference electrode, which results in the electromotive force (EMF) drift of the sensors. Especially, once the Na2CO3 formed on the surface of reference electrode, the identical electrode reaction will occur at both auxiliary electrode and reference electrode, resulting in the EMF to deviate from Nernst equation.
In an attempt to overcome such a problem, a promising approach seems to introduce a new reference electrode system that works as an oxygen-conduction membrane and physical barrier of hindering diffusion of CO2 and water vapor [25], [26]. Up to now, some oxygen ion conductors such as yttrium stabilized zirconia (YSZ) [27] and BICUVOX [28], [29], [30] have been investigated.
In the present work, we propose another fast oxygen ionic conductor of Bi8Nb2O17 (i.e. x = 0.2 in (1 − x)Bi2O3·xNb2O5 system) for reference electrode material to upgrade the performance of the sensor. As for oxygen ion conductors, the high-temperature form of bismuth oxide δ-Bi2O3 has a face-centered cublic (fcc) structure with an average oxygen vacancy rate of 25%, is recognized as one of the best solid state oxygen ionic conductors, and Nb2O5 can be added by 7.6–25.0 mol% to stabilize the cubic phase down to room temperature [31]. Meng et al. [32] reported that the conductivity of Bi8Nb2O17 was 1.9 × 10−1 S cm−1 at 700 °C, which was approximately 1–2 orders of magnitude higher than that of YSZ [33]. In addition, the thermal expansion coefficient of δ-Bi2O3 decreases with increasing Nb2O5 content [34]. Thus, Nb2O5 containing could be tailored to match the thermal expansivity of NASICON electrolyte. The applicability of Bi8Nb2O17 plus Pt as solid-reference electrode materials for the NASICON-based potentiometric CO2 sensor was examined in this work.
Section snippets
Preparation of materials
NASICON solid electrolyte was prepared by a sol–gel method using Na3PO4·12H2O, Si(OC2H5)4 and ZrO(NO2)·2H2O as main reagents, as described in our previous work [35]. The as-prepared NASICON precursor was compacted into a disk (8 mm in diameter and 2 mm in thickness) in a stainless steel die at a pressure of 50 kN. The disk was then sintered at different temperature in air for 2 h to obtain crystalline NASICON. And Bi8Nb2O17 was prepared through a conventional solid-state reaction using a mixture of
Characterization of NASICON and Bi8Nb2O17
The XRD patterns of NASICON and Bi8Nb2O17 powders are presented in Fig. 2, Fig. 3, respectively. As shown in Fig. 2, a broad single peak (1 1 6) ascribable to NASICON phase could be clearly observed at diffracting angle of 30–31° for the sample sintered at 600 °C, indicating the initial formation of crystalline NASICON. After being sintered at 900 °C, all the characteristic peaks are in good agreement with the literature data [36] and without any second phase. Whereas ZrO2 exists as impurity when
Conclusions
In this work, a composite of Bi8Nb2O17 and Pt as a solid-reference electrode material has been prepared for NASICON-based CO2 sensors. The EMF of the as-fabricated sensor is linear to the logarithm of CO2 concentration, obeying Nernst's correction. Moreover, no any obvious interference from oxygen partial pressure is observed. In comparison, there is no the deserved detectability above 60% CO2 for the sensor using Pt as reference electrode, suggesting that the solid-reference electrode can
Acknowledgements
This work was supported in part by the National Natural Science Foundation of China (No. 50974012) and Program Changjiang Scholars and Innovative Research Team in University (No. 0708).
Heng-Yao Dang received the B.S. degree in applied physics from the Inner Mongolia University of Science and Technology, Baitou, China, in 2007. He has been pursuing the Ph.D. degree in physical chemistry of metallurgy with the University of Science and Technology Beijing, China, since 2007. His current research interests include solid electrolyte base CO2 sensors.
References (45)
- et al.
A capacitive CO2 sensor system with suppression of the humidity interfercnce
Sensors and Acturators B: Chemistry
(1999) - et al.
Development of FET-type CO2 sensor operative at room temperature
Sensors and Acturators B: Chemistry
(2004) - et al.
NASICON thick film-based CO2 sensor prepared by a sol–gel method
Sensors and Acturators B: Chemistry
(2001) Electrochemical sensor principles for redox-active and acid-based-active gases
Sensors and Acturators B: Chemistry
(2000)- et al.
The performance and long-time stability of potentiometric CO2 gas sensors based on the (Li–Ba)/NASICON/(Na–Ti–O) electrochemical cells
Solid State Ionics
(2003) - et al.
Na3Zr2Si2PO12-based CO2 gas sensor with heat-treated mixture of Li2CO3 and Nd2O3 as an auxiliary electrode
Sensors and Acturators B: Chemistry
(2007) - et al.
Thin film micro carbon dioxide sensor using MEMS process
Sensors and Acturators B: Chemistry
(2004) - et al.
Characterization of a NASICON based potentiometric CO2 sensor
Journal of the European Ceramic Society
(2005) - et al.
Effect of macrostructural control of an auxiliary layer on the CO2 sensing properties of NASICON-based gas sensors
Sensors and Acturators B: Chemistry
(2009) - et al.
Stability of solid electrolyte base thick-film CO2 sensors
Mircoelectronics Reliability
(2009)
Stability of NASICON-based CO2 sensor under humid conditions at low temperature
Sensors and Acturators B: Chemistry
Toward innovations of gas sensor technology
Sensors and Acturators B: Chemistry
Investigation of porous counter electrode for the CO2 sensing properties of NASICON based gas sensor
Solid State Ionics
High-performance solid-electrolyte carbon dioxide sensor with a binary carbonate electrode
Sensors and Acturators B: Chemistry
Strontium cobaltite coated optical sensors for high temperature carbon dioxide detection
Sensors and Acturators B: Chemistry
Solid-state amperometric CO2 sensor using a sodium ion conductor
Journal of the European Ceramic Society
Long-term stability of potentiometric CO2 sensors based on NASICON as a solid electrolyte
Sensors and Acturators B: Chemistry
Sensors and Acturators B: Chemistry
Solid electrolyte for gas sensors and fuel cells applications
Journal of the European Ceramic Society
High temperature potentiometric carbon dioxide sensor with minimal interference to humidity
Sensors and Acturators B: Chemistry
Fast CO2 selective potentiometric sensor with open reference electrode
Solid State Ionics
The order–disorder transition in Bi2O3–Nb2O5 fluorite-like dielectrics
Journal of the European Ceramic Society
Cited by (13)
New promising NASICON material as solid electrolyte for sodium-ion batteries: Correlation between composition, crystal structure and ionic conductivity of Na<inf>3+x</inf>Sc<inf>2</inf>Si<inf>x</inf>P<inf>3-x</inf>O<inf>12</inf>
2016, Solid State IonicsCitation Excerpt :This term is now used for all ceramic materials with the same crystal structure and the general composition A1 + 2x + y + zM(II)xM(III)yM(IV)2 − x − ySizP3 − zO12 where A is usually a mono- or divalent cation (here, A = Na) and M are divalent, trivalent or tetravalent cations; P can also be substituted with Si or As. The materials belonging to the NASICON family are very attractive because of their compositional diversity leading to many possible applications, such as electrode materials or solid electrolytes in batteries as tested in an all-NASICON battery by Lalère et al. [3], Cl2 and CO2 sensors [4,5], or photoluminescent devices [6]. The conductivity of the NASICON materials is strongly related to their Na concentration and their crystallographic structure, which is influenced by the size of the M cations.
Properties of Nasicon-based CO<inf>2</inf> sensors with Bi<inf>8</inf>Nb<inf>2</inf>O<inf>17</inf> reference electrode
2015, Solid State IonicsCitation Excerpt :For example as reference electrode material in sensor based on sodium conductive electrolytes Na2Ti6O12/TiO2 [11], Na2Ti6O13/Na2Ti3O7 [4,5,11], Na2SnO3/SnO2 [6], and Bi2Cu0.1V0.9O5.35 [7] were used. One of the newest approaches is usage of the oxide ion conductor Bi8Nb2O17/Pt reference electrode [8]. According to the authors of this work Bi8Nb2O17/Pt electrode provides no interference from oxygen partial pressure and smaller humidity interference.
CO-sensing properties of a NASICON-based gas sensor attached with Pt mixed with Bi<inf>2</inf>O<inf>3</inf> as a sensing electrode
2015, Electrochimica ActaCitation Excerpt :Various types of gas sensors (e.g., semiconductor type [1,2], diode type [3–5], catalytic-combustion type [6] and solid-electrolyte type [7–23]) have been widely investigated and developed to detect various gases such as volatile organic compounds (VOCs) [7,8], carbon monoxide (CO) [1,2,6,9,10] and hydrogen (H2) [5,11,12] under different atmospheres.
Selectivity and sensitivity of Pd-loaded and Fe-doped SnO<inf>2</inf> sensor for CO detection
2014, Sensors and Actuators, B: ChemicalCitation Excerpt :For convenience, we marked the final composite material as S10−XFXPY, and (10 − X):X:Y represent the atom ratio of Sn, Fe and Pd in Pd-loaded and Fe-doped SnO2 composites. The sensors were fabricated with a conventional sintered-block-type [40]. The as-prepared powder was compacted into a disk (8 mm in diameter and 2 mm in thickness) in a stainless steel die at a pressure of 50 kN.
Heng-Yao Dang received the B.S. degree in applied physics from the Inner Mongolia University of Science and Technology, Baitou, China, in 2007. He has been pursuing the Ph.D. degree in physical chemistry of metallurgy with the University of Science and Technology Beijing, China, since 2007. His current research interests include solid electrolyte base CO2 sensors.
Xing-Min Guo received the Ph.D. degree from Northeastern University, Shenyang, China, in 1992. He is a professor with the University of Science and Technology Beijing, Beijing, China. His current research interests include iron-minerals utilization, electrochemical metallurgy, and electrochemical gas sensors.