Synergistic enhancement in the sensing performance of a mixed-potential NH3 sensor using SnO2@CuFe2O4 sensing electrode

https://doi.org/10.1016/j.snb.2020.127748Get rights and content

Highlights

  • Highly sensitive and NH3 selective mixed-potential type sensor using CuFe2O4 spinel-oxide electrode was firstly developed.

  • CuFe2O4 and SnO2@CuFe2O4 was successfully synthesized by modified Pechini route.

  • Sensitivity was critically dependent over the extent of Triple-phase boundary (TPB) lengths and operating conditions.

  • SnO2@CuFe2O4 electrode displayed a synergistic enhancement in response compared to bare-CuFe2O4 and SnO2 for NH3 detection.

  • The sensor displayed high sensitivity, NH3 selectivity and excellent long-term stability.

Abstract

A mixed-potential type NH3 sensor equipped with CuFe2O4 and SnO2@CuFe2O4 sensing electrode is presented. The CuFe2O4 spinel-oxide and SnO2@CuFe2O4 composites were synthesized by a modified-Pechini route. The electrode materials were characterized for the physical properties by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM) and Energy dispersive spectroscopy (EDS) analysis. It was found that the sensing characteristics were critically dependent on the extent of Triple-phase boundary (TPB) lengths and operating conditions of the sensor. Furthermore, the sensing performance of CuFe2O4 spinel-oxide was enhanced by compositing with SnO2 nanocrystals resulting in a synergistically enhanced response (ΔV) of −40 mV towards 80 ppm NH3, almost double and quadruple of the response of bare CuFe2O4 and SnO2 electrodes at 650 ℃, respectively. The sensor also displayed excellent stability towards oxygen and humidity variations, along with low cross-sensitivities towards interfering gases; e.g. NO, CO, CH4, and NO2. The complex impedance spectra (EIS) and dc polarization (I–V) measurements were performed for an insightful analysis of the sensing mechanism conforming to the mixed-potential model.

Introduction

The selective catalytic reduction (SCR) closed-loop control system has emerged as a prominent technique for controlling the nitrogen oxides (NOX) emissions from the all-purpose diesel engines. [1,2] In SCR, the nitrogen oxides (NOX) are in-situ reduced to produce nitrogen (N2) and water (H2O) by the application of a dedicated catalyst under the co-existence of oxygen (O2) and ammonia (NH3) according to the following equations–NH2CONH2 (Urea) + H2O (steam) → 2NH3 + CO24NO + 4NH3 + O2 (Air) → 4N2 + 6H2O2NO2 + 4NH3 + O2 (Air) → 3N2 + 6H2ONO + NO2 + 2NH3 → 2N2 + 3H2O

Typically, NH3 as a product of urea-water solution decomposition (Eq. 1) is fed directly into the exhaust chamber, while the closed-loop feedback control system benefits a precise control over the amount of dosing to avoid the leakage resulting in environmental and human-health issues. [3,4] Therefore, a high-performance NH3 sensor is needed to facilitate the on-board diagnosis (OBD) of NH3, downstream the SCR system. [5,6] Among various sensing technologies, solid-electrolyte based electrochemical gas sensors appeared to be the most promising candidates due to their excellent thermochemical stabilities under harsh conditions [7].

Over the past decade, various solid-electrolyte based NH3 sensors were developed, demonstrating potentiometric, amperometric, and impedance metric measurement operations. [[8], [9], [10]] While yttria-stabilized zirconia (YSZ) has become a distinctive choice of electrolyte, researchers have focused upon identifying novel electrode materials for high sensitivity and selectivity. The majority of the investigations utilized noble-metals such as Au, Ag, etc. or their composite with metal oxides as the sensing electrode (SE) [[11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22]]. Miura and co-workers introduced an NH3 selective mixed-potential type sensor for the very first time utilizing NiO/Au electrode. [21] Moos and co-workers presented another approach by covering one of the identical Au electrodes with commercially available SCR catalyst (V2O5-WO3-TiO2) and found an excellent sensitivity towards NH3 [[14], [15], [16],19]. Tests downstream of an SCR catalyst showed that the sensor could detect a tiny ammonia slip. However, the high cost and issues related to the long-term stability of noble metal electrodes encouraged researchers to look for alternative all metal-oxide SEs, which could selectively detect NH3 at high temperatures. In this approach, the multi-cation metal oxide systems gained special attention in comparison to the single-cation metal oxide materials. [10,[23], [24], [25], [26], [27], [28], [29], [30], [31]] Lu et al. synthesized several metal tungstates, MWO4 (M = Co, Zn, and Ni), and studied the NH3 sensing properties at 700 ℃. [29] The CoWO4 sintered at 800 ℃ displayed a response of −8 mV towards 100 ppm NH3 with reasonable cross-sensitivities towards hydrocarbons. Wang et al. synthesized a TiO2@WO3 core-shell composite and obtained excellent NH3 sensing characteristics. [30] Regretfully, the sensor also displayed a noticeable cross-sensitivity toward NO2.

Considering the tremendous effort in exploration for the suitable electrode materials, spinel-oxide materials remained as an unexplored area for mixed-potential type NH3 sensor despite their advantages such as ease of synthesis, high stability, and modulable functional properties. [[32], [33], [34], [35]] Among various spinel oxides, CuFe2O4, being considerably cheap to synthesize, has proved a great benefit in various electrochemical and adsorption applications; e.g. batteries, [36,37] catalysis [38,39], wastewater treatment [40,41] and sensors [[42], [43], [44]]. It was also investigated as a catalyst for ammonia oxidation or DeNOX purposes. [[45], [46], [47]] Dash and co-workers [42] investigated the potential application of CuFe2O4 and rGO-CuFe2O4 composites for chemiresistive gas sensors and found a substantially high sensitivity towards ammonia. Although the sensing mechanism of mixed-potential sensors is entirely distinctive from the chemiresistive one, the effects of selective adsorption on the electrode potential and sensing characteristics are well-known. [19,48] In this context, the materials with selective adsorbtivity towards a particular gas species; e.g. CuFe2O4 for ammonia could be promising SEs for the mixed-potential ammonia sensors. Therefore, for the first time to the authors’ knowledge, CuFe2O4 spinel-oxide is being examined as the NH3 selective electrode for a mixed-potential sensor. Since the microstructure of the electrode-electrolyte interface or Triple-phase boundaries (TPB) govern the electrocatalytic activity and sensing properties of the mixed-potential sensor [27,31,49], we also study the effect of electrode morphology over the sensing properties of CuFe2O4-SE. For a mixed-potential type sensor, it is well reported that composites of chemically distinct components could synergistically improve the sensing performance. [30,50] Tin oxide (SnO2), a state of art material for the chemiresistive sensors, has also demonstrated impressive electrochemical properties in several applications. [36,51] For mixed-potential sensors, the pure SnO2 displays very poor selectivity, resulting in no practical advantage. [20] However, its composite with metal or metal oxides has proved its great potential to be utilized for the sensing electrodes of mixed-potential sensor [50,[52], [53], [54]]. Therefore, we composited the CuFe2O4 with SnO2 nanocrystals by a solution-phase route and the resulting SnO2@CuFe2O4 was evaluated for the sensing characteristics in details. The prosperity of the presented composite system is that the individual components; CuFe2O4 and SnO2 do not react with each other under the sensor operating conditions. The SnO2@CuFe2O4 SE produced a response (ΔV) of −40 mV towards 80 ppm NH3, about double and quadruple of the response of bare CuFe2O4 and SnO2 electrodes, respectively. Also, it presented high cyclability, long term-durability, stability towards pO2 and pH2O variations and high selectivity to NH3. Finally, to perform an insightful analysis of the sensing mechanism, dc polarization curves and electrochemical impedance spectroscopy was employed over a variety of thermodynamic conditions.

Section snippets

Powder synthesis and sensor fabrication

The CuFe2O4 and SnO2@CuFe2O4 were synthesized by a solution-phase route. First, a stoichiometric amount of metal-ion precursors (Cu(NO3)2radical dot3H2O and Fe(NO3)2radical dot3H2O, Thermo Fisher Scientific Inc., United States) were dissolved in deionized water (D.I.W.). Subsequently, the chelating agent: citric acid and polymerizing agent: ethylene glycol was added (Molar ratio; M: C.A.: E.G. = 1:1:4), and the solution was heated at 80 ℃. While most of the water slowly evaporates during this heating, the resulting

Physical properties

Fig. 1a shows the profile matching of the XRD pattern of CuFe2O4 spinel-oxide powder calcined at 900 ℃. It was observed that the synthesized CuFe2O4 has a high level of crystallinity with a tetragonal lattice structure (s. g.: I-41/amd, #141). All the diffraction peaks corresponded well to the crystal planes of the standard crystallographic database (JCPDS #34-0425). The lattice parameter calculated from the profile matching was found to be a = b = 5.807 Å and c = 8.712 Å. The theoretical

Conclusion

Stabilized zirconia-based mixed-potential sensor was fabricated using CuFe2O4 spinel-oxide sensing electrodes and realized for the selective NH3 detection. It was determined that the sensing properties were significantly affected by the electrode morphology and extent of TPB lengths regulated through the sintering parameters. The NH3 sensing characteristics of the CuFe2O4-SE was further enhanced by compositing with SnO2 nanocrystals for which the SnO2@CuFe2O4 SE produced a response (ΔV) of

Declaration of Competing Interest

None.

Acknowledgments

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2018R1A5A1025224 and 2019R1F1A1064078).

Aman Bhardwaj received Master of Technology in Ceramic Engineering from Indian Institute of Technology (I.I.T-B.H.U.), Varanasi, India in 2017. He is currently pursuing his doctoral studies at the School of Materials Science and Engineering, Chonnam National University, Republic of Korea. His research interests include gas sensors, electrocatalysts, fuel cells and batteries.

References (74)

  • D. Schönauer-Kamin et al.

    Influence of the V2O5 content of the catalyst layer of a non-Nernstian NH3 sensor

    Solid State Ion.

    (2014)
  • C. Wang et al.

    Effect of V2O5-content on electrode catalytic layer morphology and mixed potential ammonia sensor performance

    Sens. Actuators, B Chem.

    (2016)
  • X. Li et al.

    The effects of Cu-content on Mg2CuxFe1O3.5+x electrodes for YSZ-based mixed-potential type NH3 sensors

    Ceram. Int.

    (2016)
  • J. Zhang et al.

    Mixed-potential NH 3 sensor based on Ce 0.8 Gd 0.2 O 1.9 solid electrolyte

    Sens. Actuators, B Chem.

    (2017)
  • I. Lee et al.

    Mixed potential NH3 sensor with lacoo3 reference electrode

    Sens. Actuators, B Chem.

    (2013)
  • F. Liu et al.

    Highly selective and stable mixed-potential type gas sensor based on stabilized zirconia and Cd 2 V 2 O 7 sensing electrode for NH 3 detection

    Sens. Actuators, B Chem.

    (2019)
  • Y. Yuan et al.

    Effects of CoFe2O4 electrode microstructure on the sensing properties for mixed potential NH3 sensor

    Sens. Actuators, B Chem.

    (2017)
  • W. Meng et al.

    Mixed-potential type NH3 sensor based on TiO2 sensing electrode with a phase transformation effect

    Sens. Actuators, B Chem.

    (2017)
  • Q. Diao et al.

    Ammonia sensors based on stabilized zirconia and CoWO 4 sensing electrode

    Solid State Ion.

    (2012)
  • W. Meng et al.

    A novel mixed potential NH3 sensor based on TiO2@WO3 core-shell composite sensing electrode

    Electrochim. Acta

    (2016)
  • F. Liu et al.

    Mixed-potential type NH3 sensor based on stabilized zirconia and Ni3V2O8 sensing electrode

    Sens. Actuators, B Chem.

    (2015)
  • C. Wu et al.

    Electrochemically activated spinel manganese oxide for rechargeable aqueous aluminum battery

    Nat. Commun.

    (2019)
  • R. Kalai Selvan et al.

    CuFe2O4/SnO2 nanocomposites as anodes for Li-ion batteries

    J. Power Sources

    (2006)
  • Z. Xing et al.

    One-step solid state reaction to selectively fabricate cubic and tetragonal CuFe2O4 anode material for high power lithium ion batteries

    Electrochim. Acta

    (2013)
  • W.F. Shangguan et al.

    Promotion effect of potassium on the catalytic property of CuFe2O4 for the simultaneous removal of NO(x) and diesel soot particulate

    Appl. Catal. B Environ.

    (1998)
  • G. Zhang et al.

    CuFe2O4/activated carbon composite: a novel magnetic adsorbent for the removal of acid orange II and catalytic regeneration

    Chemosphere.

    (2007)
  • Y. Ding et al.

    Sulfate radicals induced degradation of tetrabromobisphenol A with nanoscaled magnetic CuFe2O4 as a heterogeneous catalyst of peroxymonosulfate

    Appl. Catal. B Environ.

    (2013)
  • L.S.K. Achary et al.

    Reduced graphene oxide-CuFe2O4 nanocomposite: a highly sensitive room temperature NH3 gas sensor

    Sens. Actuators, B Chem.

    (2018)
  • Z. Sun et al.

    Simple synthesis of CuFe2O4 nanoparticles as gas-sensing materials

    Sens. Actuators, B Chem.

    (2007)
  • R. Bavandpour et al.

    Liquid phase determination of adrenaline uses a voltammetric sensor employing CuFe2O4 nanoparticles and room temperature ionic liquids

    J. Mol. Liq.

    (2016)
  • E.N. Armstrong et al.

    NOx adsorption behavior of LaFeO3 and LaMnO 3+δ and its influence on potentiometric sensor response

    Sens. Actuators, B Chem.

    (2011)
  • A. Bhardwaj et al.

    Influence of sintering temperature on the physical, electrochemical and sensing properties of α-Fe 2 O 3 -SnO 2 nanocomposite sensing electrode for a mixed-potential type NOx sensor

    Ceram. Int.

    (2019)
  • A. Bhardwaj et al.

    Transition metal oxide (Ni, Co, Fe)-tin oxide nanocomposite sensing electrodes for a mixed-potential based NO2 sensor

    Sens. Actuators, B Chem.

    (2019)
  • J. Yoo et al.

    NO2/NO response of Cr2O3- and SnO2-based potentiometric sensors and temperature-programmed reaction evaluation of the sensor elements

    Sens. Actuators, B Chem.

    (2007)
  • M. Yamaguchi et al.

    Stabilized zirconia-based sensor utilizing SnO2-based sensing electrode with an integrated Cr2O3 catalyst layer for sensitive and selective detection of hydrogen

    Int. J. Hydrogen Energy

    (2013)
  • E. Kanazawa et al.

    Mixed-potential type N2O sensor using stabilized zirconia- and SnO2-based sensing electrode

    Sens. Actuators, B Chem.

    (2001)
  • A. Bhardwaj et al.

    Effects of electronic probe’s architecture on the sensing performance of mixed-potential based NOX sensor

    Sens. Actuators, B Chem.

    (2019)
  • Cited by (40)

    • Efficient nitric oxide sensing on nanostructured La<inf>2</inf>MMnO<inf>6</inf> (M: Co, Cu, Zn) electrodes

      2023, Ceramics International
      Citation Excerpt :

      The sensor assembly (shown in Fig. S1) was sintered at 1200 °C for 2 h to acquire good adhesion between electrodes and electrolyte. The gas sensing measurements were conducted by the static mounting method as shown in Fig. S1 [41]. The sensor was operated in the temperature range of 450–600 °C supplied with air, as base gas with the total flow rate kept fixed at 100 sccm.

    View all citing articles on Scopus

    Aman Bhardwaj received Master of Technology in Ceramic Engineering from Indian Institute of Technology (I.I.T-B.H.U.), Varanasi, India in 2017. He is currently pursuing his doctoral studies at the School of Materials Science and Engineering, Chonnam National University, Republic of Korea. His research interests include gas sensors, electrocatalysts, fuel cells and batteries.

    Aniket Kumar received his Ph.D. degree from the Department of Chemistry, National Institute of Technology, Rourkela, India in 2018. He is currently working as a postdoctoral researcher in the Ionics Laboratory, School of Material Science and Engineering, Chonnam National University, Republic of Korea. His research interests include polymer electrolyte membrane (PEM) fuel cells, heterogenous and electrochemical catalysis, adsorption chemistry and gas sensing.

    Uk Sim received his Ph.D. degree from the Department of Materials Science & Engineering, Seoul National University, Republic of Korea in 2016. Presently, he is an Assistant Professor at the School of Materials Science and Engineering, Chonnam National University (CNU), Republic of Korea. At CNU, his research interests include the development of nanomaterials for energy production, conversion, and storage applications.

    Ha-Ni Im received her Ph.D. degree from the School of Materials Science and Engineering, Chonnam National University, Republic of Korea in 2015. Since then she is working as a researcher in the Ionics laboratory and her research interests include oxygen transport and electrochemical properties of ceramic materials.

    Sun-Ju Song received his Ph.D. degree in Materials Science and Engineering, from University of Florida, USA in 2003. He joined Energy Technology/Systems Division, Argonne National Laboratory, Argonne, USA as a postdoctoral research associate in 2004, working mainly on ceramic materials for different electro-chemical applications. He has been a Professor at the School of Materials Science and Engineering, Chonnam National University (CNU), Republic of Korea since 2007. He also served as the visiting professor in Department of Materials Science and Engineering, University of Maryland, USA from 2011 to 2012, and Department of Chemistry and Chemical Biology, RPI, Troy, USA in 2015. He has published more than 150 papers in peer-reviewed journals and filed more than 30 patents. At CNU, his research interests include solid state electrochemistry, defect chemistry and transport properties, ceramic processing and functional ceramics.

    View full text