Elsevier

Journal of Power Sources

Volume 249, 1 March 2014, Pages 131-136
Journal of Power Sources

Fabrication and performance of BaCe0.8Y0.2O3−δ–BaZr0.8Y0.2O3−δ bilayer electrolyte for anode-supported solid oxide fuel cells

https://doi.org/10.1016/j.jpowsour.2013.10.120Get rights and content

Highlights

  • Fabricate thin BZY layer on BCY half-cell with pulsed laser deposition.

  • The bilayer electrolyte proves a good chemical stability against CO2 atmosphere.

  • The bilayer cell exhibits a good long-term stability under cell testing condition.

  • The bilayer electrolyte cell shows a comparable electrochemical performance.

Abstract

BaZr0.8Y0.2O3−δ (BZY) layers with various thicknesses (∼0.7, ∼1.7, ∼2.4 and ∼3.6 μm) are fabricated using the pulsed laser deposition (PLD) technique on anode-supported BaCe0.8Y0.2O3−δ (BCY) electrolyte films. Sm0.5Sr0.5CoO3−δ-SDC (SSC-SDC, 70:30 wt.%) cathode is applied onto the BZY/BCY bilayer electrolyte to form a single cell. The chemical stability of the BZY/BCY bilayer electrolytes improves with increasing BZY layer thickness. The BZY (∼3.6 μm)/BCY bilayer electrolyte shows an excellent chemical stability after treated in 100% CO2 atmosphere at 900 °C. The maximum power densities of 447, 370, 276, 218 and 163 mW cm−2 are measured with the BZY layer thicknesses of 0, 0.7, 1.7, 2.4 and 3.6 μm at 700 °C, respectively. In general, the BZY/BCY bilayer electrolyte cell with an optimum BZY layer thickness can improve chemical stability without great influence on the electrochemical performance for intermediate temperature solid oxide fuel cells.

Introduction

High temperature proton conductors (HTPCs) have been extensively investigated since Iwahara et al. have reported some perovskite materials with excellent protonic conductivity at elevated temperatures [1], [2], [3]. HTPCs are considered to be the promising electrolyte candidates for intermediate temperature solid oxide fuel cells (IT-SOFCs) due to their larger ionic conductivities and smaller activation energies than conventional oxygen-ion conducting electrolytes [4], [5]. Besides, HTPCs form water at the cathode side and thus fuel at the anode side remains pure without recirculation [1]. Acceptor-doped BaCeO3 and BaZrO3 compounds have been studied as the promising proton conductors [6], [7], [8], [9]. However, the balance between high proton conductivity and chemical stability seems to be a challenge. Acceptor-doped BaCeO3 has a high proton conductivity but shows a poor chemical stability in H2O and CO2-containing atmospheres. Doped-BaZrO3 materials have a high chemical stability. However, the BaZrO3-based materials show a low proton conductivity due to the high grain boundary resistance [10], [11]. In order to find a compromise between proton conductivity and chemical stability, one effective approach is to incorporate a thin doped-BaZrO3 film as a protecting layer between BaCeO3 electrolyte and cathode. However, the doped-BaZrO3 layer thickness can increase ohmic loss due to the lower proton conductivity compared with that of BaCeO3. Thus the BaZrO3 layer thickness is a key factor in balancing proton conductivity and chemical stability. The pulsed laser deposition (PLD) technique can exactly control film thickness. Besides, it is a promising method to deposit thin films that are of high quality and stoichiometric with multi-component materials [12]. Furthermore, films deposited by PLD do not require high annealing temperatures [13], which is useful for low temperature SOFCs applications and avoids the formation of a solid solution between BaZrO3 and BaCeO3. Fabbri et al. [14] have successfully fabricated a proton conductor bilayer electrolyte cell with a thin BaZr0.8Y0.2O3−δ (BZY) layer deposited on a sintered BaCe0.8Y0.2O3−δ (BCY) pellet using PLD technique. There are two disadvantages in their work. First, the BCY electrolyte-supported fuel cell increased the ohmic loss compared to the anode-supported fuel cell. Besides, the use of Pt electrodes on the BZY/BCY bilayer electrolyte impeded better electrochemical performance. Therefore, it is necessary to fabricate an anode-supported proton conductor bilayer electrolyte cell. In this work, we fabricated thin BZY layers on a NiO–BaZr0.1Ce0.7Y0.2O3−δ (BZCY)/BCY half-cell using the PLD technique. The thickness of the BZY layer is controlled from ∼700 nm to ∼3.6 μm to study the effect of BZY layer thickness on the chemical stability and overall performance of the bilayer electrolyte cells.

Section snippets

Powder synthesis and cell fabrication

BCY and BZCY powders were fabricated using a citric acid-nitrate gel combustion process [15]. First, BaCO3, Ce(NO3)4·4H2O, Zr(NO3)4·5H2O and Y(NO3)3·6H2O was added to a solution of HNO3. After the solution became clear, citric acid was added in a 1:1.5 metal ions:citric acid molar ratio. The pH value was adjusted to approximately 7 with ammonia. The solution was continuously stirred and heated at 70 °C until a gel formed. The gel was then heated on a hot plate and combusted to form powder

Results and discussion

Fig. 1 presents XRD patterns of the BCY single electrolyte layer and the BZY/BCY bilayer samples. BCY has an orthorhombic perovskite structure as shown in Fig. 1a. The diffraction patterns in Fig. 1b–e depict the cubic reflections of the BZY crystalline structure. The reflections of the two crystalline structures can be grouped into pairs, and each of the pairs corresponds to the same set of Miller indices, which indicates an epitaxial grain by grain growth [14]. The relative densities of the

Conclusions

PLD technique has been used in this study to deposit the BZY protecting layer on anode-supported BCY electrolyte SOFCs with the BZY layer thicknesses varied from ∼700 nm to ∼3.6 μm. The BCY-BZY solid solution compounds were avoided due to the low processing temperatures of the PLD technique. BZY (∼3.6 μm)/BCY bilayer electrolyte proves to be stable against 100% CO2 atmosphere treated at 900 °C. The OCV values of the BZY/BCY bilayer electrolyte cells are 0.933, 0.943, 0.94, 0.91 and 0.934 V with

Acknowledgments

This work was supported by Ministry of Science and Technology of China (grant no: 2012CB215403). The project was also supported by research fund of Key Laboratory for Advanced Technology in Environmental Protection of Jiangsu Province and Anhui Nature Science Foundation.

References (29)

  • L. Bi et al.

    Electrochem. Commun.

    (2008)
  • W. Sun et al.

    J. Power Sources

    (2013)
  • H. Iwahara et al.

    Solid State Ionics

    (1981)
  • K.D. Kreuer

    Solid State Ionics

    (1999)
  • K.D. Kreuer et al.

    Solid State Ionics

    (2001)
  • J.H. Joo et al.

    Solid State Ionics

    (2006)
  • D. Pergolesi et al.

    Electrochem. Commun.

    (2010)
  • W. Sun et al.

    J. Power Sources

    (2011)
  • Y. Liu et al.

    J. Membr. Sci.

    (2012)
  • Y. Guo et al.

    J. Power Sources

    (2009)
  • H.-I. Ji et al.

    Solid State Ionics

    (2011)
  • L. Bi et al.

    J. Power Sources

    (2009)
  • Z. Tao et al.

    J. Power Sources

    (2010)
  • L. Bi et al.

    J. Alloys Compd.

    (2009)
  • Cited by (23)

    • Effect of yttrium-stabilized bismuth bilayer electrolyte thickness on the electrochemical performance of anode-supported solid oxide fuel cells

      2021, Ceramics International
      Citation Excerpt :

      Mio et al. [40] studied the effect of ESB bilayer thickness on fuel cell performance and found that power density can increase from 84 to 249 mW/cm2 when the bilayer electrolyte thickness is increased correspondingly from 13 to 20 μm at 500 °C; their study concluded that thin electrolyte layers are highly susceptible to fuel gas erosion. Advanced deposition techniques based on ceramic powder processing have been used to improve the chemical and physical properties of bilayer electrolyte layers on dense electrolyte substrates [32,42,43]. These methods are well established, but the investment costs for their respective apparatus is higher than that for dip coating [9].

    • Processing and characterization of novel Ce<inf>0.8</inf>Sm<inf>0.1</inf>Bi<inf>0.1</inf>O<inf>2-δ</inf>-BaCe<inf>0.8</inf>Sm<inf>0.1</inf>Bi<inf>0.1</inf>O<inf>3-δ</inf> (BiSDC-BCSBi) composite electrolytes for intermediate-temperature solid oxide fuel cells

      2021, International Journal of Hydrogen Energy
      Citation Excerpt :

      However, at low oxygen partial pressure or reducing atmosphere, partial Ce4+ in SDC is easily reduced to be Ce3+, generating undesirable electronic conductions, thus resulting in decreased open circuit voltages (OCVs) and poor output performance of cells [5,16,17]. The commonly approach is to prepare a double-layer electrolyte, in which another layer of electrolyte (such as YSZ, BaZr0.8Y0.2O3-δ, BaCe0.8Y0.2O3-δ, etc.) is introduced between the SDC electrolyte and the anode to avoid or decrease the electronic conduction [18–20]. However, this process is complicated, and the electrolyte layer is susceptible to thermal expansion mismatches during SOFC operating, resulting in a severe delamination.

    • Spatial investigation of electronic properties in composite electrolytes for solid oxide fuel cells using embedded probes

      2019, Journal of Power Sources
      Citation Excerpt :

      Doped BaCeO3 exhibits the highest proton conduction among Ba containing perovskite type oxides while its chemical stability is poor in atmospheres containing water vapor and carbon dioxide [15–21]. Doped BaZrO3 that has good chemical stability can be utilized as a protecting layer; however, its poor sinterability, i.e., high grain boundary resistance, sacrifices electrochemical performances [22–26]. To compensate each other's weakness, a hybrid concept of composite electrolytes that conducts both protons and oxygen ions has been suggested [5,27–34].

    • Durability tests of BCY-BZY electrolyte fuel cells under severe operating conditions

      2018, Journal of Alloys and Compounds
      Citation Excerpt :

      A thin and dense BZY layer with low grain boundary resistance is preferred; however, it cannot be easily achieved with conventional ceramic processing because of BZY's poor sinterability. Advanced techniques (such as pulsed laser deposition, sintering aid and high shrinkage substrate) should be used to achieve a thin and dense BZY layer with a low grain boundary resistance [42,58]. The purpose of the present work is to show that BCY based cells' durability can be significantly improved with a bi-layer structure, which was prepared by a conventional fabrication method (slurry drop-coating and high temperature sintering), thus additional works should be conducted in future to optimize performance by using a different fabrication method.

    • Investigation of Electronic Transport Property and Durability of BCY-BZY Electrolyte Cells Using Embedded Probes

      2017, Electrochimica Acta
      Citation Excerpt :

      Many efforts have been made to take advantage of both the BCY (high ionic conductivity) and BZY (high chemical stability). These have included synthesis of BCY-BZY solid solution [18–21], design of dual and multi-layers consisting of a BZY layer to protect the BCY layer from H2O and CO2 [22–26], and co-doping of BaCeO3 with M (M = Ta, Ti, Nb, Sn, and In) and Y [27–29]. If we want to utilize this kind of electrolyte for the SOFC stack, the following issue should be taken into account.

    View all citing articles on Scopus
    View full text