Y-doped BaCeO3 Research Articles

Ionic conductivity increase by one order of magnitude in BCY composite electrolyte added with Li2O

The low ionic conductivity of proton conductor electrolytes at low temperatures was one of the key issues that restrict the reduction of operating temperature in ceramic fuel cells. The traditional Y-doped BaCeO3 proton conductor (BCY) has an ionic conductivity of only a few tens of mS·cm−1 at 500 °C, which cannot meet the needs of high-performance low-temperature ceramic fuel cells. In this paper, we found that the ionic conductivity of the composite electrolyte made by adding 20 % Li2O to BCY at 550 °C was 0.526 S cm−1, which was 40 times that of the dense BCY electrolyte sintered at 1550 °C. The maximum power density of a ceramic fuel cell using a BCY- Li2O composite material with a thickness of 1 mm as the electrolyte and porous Ag as the symmetrical electrode was 129 mW cm−2 in H2 at 550 °C. The characterization results of XRD, EPR, and FTIR showed that there may be a region with a large number of oxygen vacancies and lithium vacancies created at the interface of the BCY and Li2O–LiOH composite electrolyte formed in the BCY-Li2O composite electrolyte during the testing conditions for fuel cell performance due to the migration of Li+. The formation of this region should be the main reason for the extremely high conductivity of the BCY-Li2O–LiOH composite electrolytes formed in the cell at low temperatures.

Y-Doped BaCeO3 Perovskite-Supported Ru Catalysts for COx-Free Hydrogen Production from Ammonia: Effect of Strong Metal–Support Interactions

The development of highly efficient Ru-based catalysts for NH3 decomposition is necessary to enable the utilization of NH3 as a COx-free H2 carrier. Modulation of the interactions between the basic support materials and Ru particles significantly enhances the performance of Ru-based catalysts for NH3 decomposition. In this study, the strong metal–support interaction (SMSI) interface between the BaCeO3 perovskite support and Ru particles was controlled by yttrium (Y) doping in the range of 0–20 mol %. The substitution of Y3+ into Ce4+ sites improved the reducibility of the support for the removal of lattice oxygen atoms, which promoted the formation of the SMSI interface between the mobile oxygen-deficient suboxide supports and Ru particles. The Ru catalysts supported on Y-doped BaCeO3 exhibited superior activity compared to undoped and other representative Ru catalysts. Moreover, the SMSI shell encapsulating the Ru particles improved the stability of the Y-doped Ru catalyst. This comprehensive study demonstrates that the enhancement in catalytic performance is attributable to facilitated N2 desorption, which is the rate-limiting step for NH3 decomposition over Ru-based catalysts, via the formation of the SMSI interface. These research findings show that the control of the SMSI interface is a promising strategy for designing highly active catalysts to be used in NH3 decomposition.

Interface-reinforcing sintering step for highly stable operation of proton-conducting fuel cell stack

Proton conducting fuel cells (PCFCs) are promising power generation systems due to their low operating temperature by conducting proton activated with low kinetic energy. However, well-known proton conducting materials such as Y-doped BaCeO3−δ (BCY), Y-doped BaZrO3−δ (BZY), and BaCe0.8-xZrxY0.1Yb0.1O3−δ (BCZYYb) have a limitation in that the planar cell is fragile during operation attributed to the low mechanical strength. This study proposes a two-step sintering method to fabricate mechanically superior PCFC large cells based on the BCZYYb electrolyte. The two-step sintering process consists of a heat treatment step at a temperature in which the anode and electrolyte have similar shrinkage values during the sintering process and another step that can improve the bonding strength of each layer by grain growth. The vulnerable anode/electrolyte interface, which acts as a significant mechanical failure factor, is optimized through the two-step sintering process. Two-step sintered cells show high mechanical stability in lab-scale and 6 cm × 6 cm planar cells for stack systems. A two-step sintered large cell exhibits outstanding stability during 350 h at 600 °C with the stack system. Our strategy provides a method to build practical proton-conducting fuel cells.

Strain‐induced tunable energy barrier of proton diffusion in Y‐doped BaCeO 3 and Y‐doped BaZrO 3

In this paper, the strain effects on the energy barrier of proton diffusion in Y-doped BaCeO3 (BCY) and Y-doped BaZrO3 (BZY) are investigated by detailed density functional theory calculations. The energy barrier of proton rotation decreases when the tensile strain is applied. For intra-octahedral proton transfer, the energy barrier decreases when the tensile strain is applied while for inter-octahedral proton transfer the energy barrier increases when the tensile strain is applied. However, we found that for intra-octahedral proton transfer the energy barrier of BZY shows the opposite strain effect. To understand the underlying mechanism behind this opposite trend we decomposed proton diffusion into three elementary steps and the opposite trend of the energy barrier of BCY and BZY during intra-octahedral proton transfer is pinpointed to the opposite bond order change of the hydrogen bond. In all, we explored the strain effects on the energy barrier of proton diffusion in BCY and BZY from a microscopic perspective, showing the potential to tune the energy barrier of proton transport in perovskite oxide with strain engineering and thus design novel proton conductors.

Proton Conductive BaZr0.8-x Cex Y0.2 O3-δ : Influence of NiO Sintering Additive on Crystal Structure, Hydration Behavior, and Conduction Properties.

Y-doped BaZrO3 , BaCeO3 and BaZr1-x Cex O3 show high proton conductivity at intermediate temperature and are promising electrolyte candidates in electrochemical devices. However, in most cases, the present cell fabrication process seems to be unavailable to avoid the addition of NiO, which is either added to improve the sinterability of these electrolyte or diffuses from the electrode substrate during co-sintering. In this work, a systematic investigation was performed to study the effect of NiO on BaZr0.8-x Cex Y0.2 O3-δ (BZCY20) covering the full Ce range from 0 to 0.8. The results revealed that regardless of the composition of BZCY20, both the dehydration temperature and proton concentration decreased by adding NiO, which further greatly decreased the ionic conductivity and the transport number. And it is found that the redox cycles in Ce-rich samples containing Ni makes the grain boundary conductivity worse and the electrolyte brittle. The conclusion is that NiO is detrimental to the performance of the electrochemical cells using these materials as the electrolyte, although compromise might be achieved in certain degree by tuning the Ce content. However, it should be noted that to further improve the cell performance, a new sintering additive or new processing for cell fabrication is essential.

Molecular dynamics simulation of proton conductivity enhancement in polymer membranes by Y-doped BaCeO3 nanoparticles

Molecular dynamics simulation method was used to study the effect of BaCeO3 nanoparticles on proton conductivity enhancement in nanocomposite membranes of PVA (Polyvinyl alcohol), PBI (Polybenzimidazole) and SPEEK (Sulfonated polyether ether ketone). The simulation results indicated that the addition of BaCeO3 nanoparticles to polymeric membranes cause to increase diffusion coefficient of hydronium ions 1.5, 1.5 and 3.5 times more than their diffusivity in pure polymer membranes of PBI, SPEEK and PVA, respectively. The results of the radial distribution function analyses show that the addition of nanoparticles to polymeric membranes decreases the interaction between polymer chains and hydronium ions. In addition, the effect of Y atomic percentage doped in BaCeO3 nanoparticles with 14%, 29% and 43% was investigated for more improvement of the proton conductivity of the nanocomposite membranes. It was found that the increase of Y atomic percentage doped in BaCeO3 nanoparticles reduces the diffusion coefficient of hydronium ions in PVA membrane. It is also considerable that the addition of 43% of Y doped in BaCeO3 nanoparticles improves the conductivity of hydronium ions in PBI nanocomposite membranes with 40%.

Effects of Al2O3 doping in BaCeO3 on chemical stability and electrical conductivity of proton conducting oxides

BaCeO3 doped with trivalent ions have high proton conductivity but poor chemical stability against CO2. Al-doped BaCeO3 (Ba(Ce1−xAlx)O3−δ) was fabricated via conventional solid oxide reactions, and their chemical stabilities against CO2 and electrical conductivities were compared with those of Y-doped BaCeO3, which is a promising proton conducting oxide. The chemical stabilities against CO2 were enhanced by doping with Al; however, the electrical conductivities decreased. However, an abnormal increase in the electrical conductivity at temperatures ranging from 400 to 470 °C occurred when the Al content was above 15 mol%. In order to explain such an abnormal increase in electrical conductivity, thermogravimetric and X-ray diffraction analyses were performed at high temperatures, and the abnormal increase in electrical conductivity was correlated with water incorporation reactions and a transformation of the crystal structures with changes in temperature.

Reactivity of solid BaCe0.9Y0.1O3-δ towards melted WO3

High-temperature impregnation of solid single-phase Y-doped BaCeO3 with melted WO3 was performed towards the evaluation of the possibility of formation of chemically stable material with relatively high electrical conductivity in this system. Impregnation was performed at 1470 °C as a function of time. Due to the relatively high reactivity in solid BaCe0.9Y0.1O3-δ - liquid WO3 system the reactive and the inner layers were distinguished and analysed. The obtained results clearly indicate the decomposition of Y-doped BaCeO3 in contact with melted WO3. X-ray diffraction method together with SEM observation, EDS analysis and EIS measurements results were applied to discuss the mechanism of this multi-stage process and the influence of the reaction time on materials structure and microstructure. As it was observed, partial incorporation of tungsten into the barium cerate structure can process not only on the surface of the materials but also in the inner layer of the synthesised materials. This donor-type doping of the perovskite structure finds reflection in both, materials electrical properties and chemical stability towards CO2/H2O. The decrease of proton defects concentration was observed together with the significant increase of the materials chemical stability in comparison to un-modified single-phase BaCe0.9Y0.1O3-δ. The calculated values of activation energy of conductivity confirm the change in the conduction mechanism. Also, the presence of an additional phase in the intergranular voids of doped BaCeO3 was postulated.

Synthesis and Characterizations of Y-Doped BaCeO<sub>3</sub> Ceramic for Use as Electrolyte in Solid Oxide Fuel Cell

Fuel cell is an electrochemical cell which converts chemical energy into electricity via electrochemical reaction of hydrogen and oxygen gases. It is also an alternative energy with environmental friendly. Generally, the fuel cell consists of many parts. Electrolyte is an important part for fuel cell because it has high ion conductivity which leads to increase electrical conductivity of the fuel cell. In case solid oxide fuel cell, barium cerate-based ceramics have been much attention due to their good properties for the fuel cell. In this work, the BaCe1-xYxO3-δ(x= 0.20) ceramic was synthesized by a solid state reaction in order to study their mechanical and electrical properties. The ceramic was sintered at high temperature of 1500°C with various soaking times. The crystalline phase structure was investigated by X-ray diffraction (XRD). The surface morphologies was observed by a scanning electron microscope (SEM). The impedance properties was measured by LCR meter. The obtained results suggestes that the ceramic sinter at 1500°C with 15 h dewell time shows the best properties as compared to other ceramics.

Structure, chemical stability and electrical properties of BaCe0.9Y0.1O3\u2212\u03b4 modified with V2O5

Wet vacuum impregnation method was applied in order to evaluate the possibility of the formation of the material in BaCe0.9Y0.1O3−δ–V2O5 system. Single-phase BaCe0.9Y0.1O3−δ samples, synthesised by solid-state reaction method, were impregnated with the solution of vanadium(V) oxide precursor. Multi-step, multi-cycle impregnation procedure was applied to enhance the impregnation efficiency. Partial decomposition of Y-doped BaCeO3 in contact with the solution of the precursor, resulting in the formation of vanadium containing phases (CeVO4 and BaV2O6) on the materials surface, was observed. However, the presence of vanadium was also confirmed for the inner parts of the materials. The synthesised materials were submitted for exposition test to evaluate their chemical stability towards CO2/H2O. All BaCe0.9Y0.1O3-based materials modified by impregnation revealed higher chemical stability in comparison with single-phase un-modified BaCe0.9Y0.1O3−δ, since the amount of barium carbonate formed during the exposition was significantly lower. The total electrical conductivity of the received multi-phase materials was generally slightly lower than for the reference BaCe0.9Y0.1O3−δ sample, since the presence of the additional phases had a blocking effect on materials conductivity. The values of BaCeO3 lattice parameters and the Seebeck coefficient did not show the modification of the defects structure of Y-doped BaCeO3 during applied synthesis procedure.

Reactivity of solid BaCe0.9Y0.1O3 towards liquid V2O5

In this work the reactivity in solid BaCe0.9Y0.1O3-δ - liquid V2O5 system was investigated in order to evaluate the possibility of composite formation in this system. Impregnation of melted vanadium(V) oxide into solid Y-doped BaCeO3 was performed in various temperature and time conditions. Due to the relatively high reactivity of components in this system an analysis of the synthesized materials was divided into discussion of the properties of the reactive layer and the inner part. As was shown, decomposition of Y-doped BaCeO3 in contact with melted vanadium(V) oxide occurs already at temperature 700 °C and results in formation of CeVO4 as one of the main phases. Moreover, the presence of Ba8V7O22 as the intermediate phase was observed. The extension of reaction time and increase of temperature resulted in significant changes in the microstructure and chemical composition of the reactive layer. The incorporation of vanadium into yttrium doped BaCeO3 structure for inner parts of the synthesized materials was postulated based on the modification of the materials electrical properties and chemical stability towards CO2 and H2O. Also, the presence of additional phase in the intergranular voids of doped-BaCeO3 was suggested.

High performance In, Ta and Y-doped BaCeO3 electrolyte membrane for proton-conducting solid oxide fuel cells

A novel BaCe0.7In0.15Ta0.05Y0.1O3-δ (BCITY) electrolyte membrane was fabricated on a NiO-BCITY (mass ratio: 6:4) composite anode by combing solid state reaction and Pechini method. The BCITY membrane exhibits high sintering activity, conductivity and apparently improved chemical stability in boiled water or 100% CO2 at 600 °C. Using the mixture of La0.7Sr0.3FeO3-δ (LSF) and BaZr0.1Ce0.7Y0.2O3-δ (BZCY) with mass ratio of 7:3 as the composite cathode, a single cell with BCITY electrolyte generated the maximum power densities of 315, 303, 274, 200, and 116 mW/cm2 at 750, 700, 650, 600, and 550 °C, respectively. No detectable variations of open circuit voltage and power density were observed for the cell worked at 600 °C for 100 h. The interface resistance of the cell was also studied under open circuit condition.

Further optimization of barium cerate properties via co-doping strategy for potential application as proton-conducting solid oxide fuel cell electrolyte

Yttrium-doped BaCeO3 is one of the most promising electrolyte candidates for solid oxide fuel cells because of its high ionic conductivity. Nd and Y co-doped BaCeO3 strategy is adopted for the further optimization of Y-doped BaCeO3 electrolyte properties. X-ray diffraction results indicate that the structure of BaCe0.8Y0.2-xNdxO3-δ (x = 0, 0.05, 0.1, 0.15) with orthorhombic perovskite phase becomes more symmetric with increasing Nd concentration. The scanning electron microscope observation demonstrates that the densification and grain size of the sintered pellets significantly enhance with the increase of Nd doping level. Whether in dry and humid hydrogen or air, the increase of Nd dopant firstly increases the conductivities of BaCe0.8Y0.2-xNdxO3-δ (x = 0, 0.05, 0.1, 0.15) and then decrease them after reaching the peak value at x = 0.05. Electrochemical impedance spectra at 350 °C can distinguish clearly the contribution of grain and grain boundary to total conductivity and the highest conductivity of BaCe0.8Y0.15Nd0.05O3-δ ascribes to the decrease in bulk and grain boundary resistances due to the synergistic effect of Nd and Y doping. The anode-supported single cell with BaCe0.8Y0.15Nd0.05O3-δ electrolyte shows an encouraging peak power density of 660 mW cm−2 at 700 °C, suggesting that BaCe0.8Y0.15Nd0.05O3-δ is a potential electrolyte material for the highly-efficient proton-conducting solid oxide fuel cell.

Insights into B-Site Ordering in Double Perovskite-Type Ba3Ca1+ xNb2- xO9-δ (0 ≤ x ≤ 0.45): Combined Synchrotron and Neutron Diffraction and Electrical Transport Analyses.

Perovskite-type metal oxides are being used in a wide range of technologies, including fuel cells, batteries, electrolyzers, dielectric capacitors, and sensors. One of their remarkable structural properties is cationic ordering in A or B sites, which affects electrical transport properties under different gaseous atmospheres, and chemical stability under CO2 and humid conditions. For example, a simple-perovskite-type Y-doped BaCeO3 forms BaCO3 and ((Ce,Y)O2-δ) under CO2 at elevated temperature, while B-site-ordered double-perovskite-type Ba3Ca1.18Nb1.82O9-δ remains chemically stable under the same conditions. Early structural studies on Ba3Ca1+ xNb2- xO9-δ (BCN) showed that the B-site ordering (1:1) is sensitive to the Ca content. However, ambiguity rises, as 1:2 B-site ordering was not observed in the parent and doped analogues when x was varied, which motivated us to revisit the complex oxides BCN ( x = 0-0.45) to determine the atomic structure by a mean of combined synchrotron X-ray and neutron diffraction methods. Surprisingly, the B-site ordering increases with increasing Ca/Nb mixing in the B-sites in BCN. In addition, the electrical conductivity of BCN was found to be the highest at x = ∼0.18, and it decreased as the Ca/Nb ratio further increased in BCN. Such a result was very similar to that for the Y-doped BaZrO3, where the mobility of proton carriers was found to decrease as the dopant (Y) increased. A higher Ca/Nb ratio also promotes the growth of grain size, as Ca ions could serve as a sintering aid, improving the structural integrity.

Reaction mechanism in solid BaCe0.9Y0.1O3 – liquid BaWO4 system

BaCeO3–based protonic conductors may be considered as perspective materials for construction of various electrochemical devices as fuel cells, gas sensors, electrochemical pumps, separators or membrane chemical reactors. The desired properties, as high electrical conductivity or chemical stability of these materials may be further improved by formation of composite, by introduction of modifying phase as BaWO4 into the host Y-doped BaCeO3 material. The high temperature process of composite formation requires the recognition of chemical reactivity between the used component. In this work the mutual reactivity and reaction mechanism in the solid BaCe0.9Y0.1O3 – liquid BaWO4 system were investigated. The synthesis of BaCe0.9Y0.1O3 and BaWO4 compounds was done by solid-state reaction method. The formation of BaCe0.9Y0.1O3 – BaWO4 materials was obtained by high temperature impregnation of melted BaWO4 into solid BaCe0.9Y0.1O3 with different impregnation time applied (2, 4 and 8 h). The evolution of crystal structure, phase composition, microstructure, chemical composition and electrical properties with impregnation time, for surface and interior of the samples allowed to analyse the mutual reactivity of composite components and to propose the multi-step reaction mechanism in the solid BaCe0.9Y0.1O3 – liquid BaWO4 system.

Operando Investigation of the Chemical Interaction of Water Vapor with Ceramic Proton Conductors

The protons are the key players in ceramic proton conductors. But they are very elusive and had to detect. I will shows a suite of experiments, ex situ, in situ and operando, where the protons are shown as structural elements at low temperatures where they do not yet constitute charge carriers. They actually constitute OH groups in the crystal lattice. With increasing temperature, the protons participate with the lattice vibrations while and OH-bond breaking takes place at some transition temeprature where the protons become charge carriers. We have observed this on the Y-doped BaZrO3 and BaCeO3 model proton conductors with quasi elastic neutron scattering under ambient and under high temperature high pressure conditions. The phonon modes as determined from high presssure Raman spectroscopy propel the protons and cause a net protonic charge transfer via phonons. The changes in the chemical bond environment were observed with ambient pressre x-ray spectroscopy, particular changes in the oxygen core lecvel spectra and the Ce, Y and Zr resonant valence band spectra under humidified high temperature conditions. We are able to sketch the changes in bond breaking at exactly the temperature where the ptoton conductivty sets on. [1] Q. Chen, F. El Gabaly, F. Aksoy Akgul, Z. Liu, B.S. Mun, S. Yamaguchi, A. Braun, Observation of 8.238 oxygen vacancy filling under water vapor in ceramic proton conductors in-situ with ambient pressure XPS; Chem. Mater., 2013, 25 (23), pp 4690–4696. [2] Q. Chen, J. Banyte, X. Zhang, J. P. Embs, A. Braun; Proton Diffusivity in Spark Plasma Sintered BaCe0.8Y0.2O3-δ: in-situ combination of quasi-elastic neutron scattering and impedance spectroscopy; Solid State Ionics 252 (2013) 2–6. [3] Q. Chen, T.-W. Huang, M. Baldini, A. Hushur, A. Pomjakushin, S. Clark, W. Mao, M. Manghnani, A. Braun, T. Graule, The Effect of Compressive Strain on the Raman Modes of the Dry and Hydrated BaCe0.8Y0.2O3 Proton Conductor, J. Phys. Chem. C, 2011, 115 (48), pp 24021–24027.

Effect of CuO on microstructure and conductivity of Y-doped BaCeO3

Effect of CuO additions on sinterability and conductivity of BaCe0·85Y0.15O2.925 was studied. Two different amounts, 0.75 and 1.5wt% with respect to the pure powder, were considered. Microstructural characterization showed that for smaller additions Cu was completely incorporated on B-site of the perovskite, while formation of the secondary phase Y2BaCuO5 was detected when higher amount of CuO was added. Enhanced cations diffusivity at grain boundary is responsible for a pronounced reduction of sintering temperature and grain growth. Density as high as 96–97% of theoretical value was obtained when sintering at 1000°C for 2h.As long as Cu is incorporated in the perovskite, higher conductivity and lower activation energy of grain core were found. In addition, total conductivity of 0.75wt% doped material was limited by fine grain size that resulted in apparent poor conductivity of the grain boundary.On the contrary when Cu segregates in the Y2BaCuO5 phase, overall conductivity increased mostly because of the contribution from the electronic conductivity of that phase.

Synthesis of Yttrium-Doped Barium Zirconate/Barium Cerate (BZY20/BCY20) Core-Shell Structured Proton-Conducting Solid Electrolyte via Modified Pechini Method

Intermediate temperature solid oxide fuel cells (IT-SOFCs) operating at 400-700°C utilizes proton conducting electrolytes and are now being one of the focus of many research studies with regards to efficient, clean power sources and energy conversion. Potential electrolyte materials include acceptor-doped barium zirconates and barium cerates. In this study, preparation of a core-shell structured proton-conducting solid electrolytes of 20 vol% BaZr0.8Y0.2O3-δ (20BZY20) for the core and 80 vol% BaCe0.8Y0.2O3-δ (80BCY20) for the shell is done by wet chemistry route. The synthesized core-shell structured material (20BZY20/80BCY20) is developed to possibly address the problem of high grain boundary impedance of Y-doped BaZrO3 and low chemical stability of Y-doped BaCeO3. The obtained samples were characterized for its structure, thermal stability, morphology and elemental distribution of the material. At a lower sintering temperature of 1150°C, a densified pellet was obtained as observed by SEM analysis. The diffraction pattern of 20BZY20/80BCY20 powder shows two distinct phases corresponding to BZY20 and BCY20 suggesting a successful synthesis of the core-shell solid electrolyte.

Hydrogen solubility and diffusivity in a barium cerate protonic conductor using tritium imaging plate technique

A tritium imaging plate technique has been applied to visualize hydrogen distribution and examine hydrogen solubility and diffusivity in a proton-conducting oxide, Y-doped BaCeO3 (BaCe0.9Y0.1O3−α). Tritium charging of the BaCe0.9Y0.1O3−α specimens was carried out by a gas absorption method using partially tritiated water vapor (HTO, 3 kPa, T/H~10−6) at temperatures ranging from 673K to 873K for a given time. After charging, tritium distributions of the surface and cross section of the halved specimens were visualized using an imaging plate technique. From the tritium concentration and distributions of the surface and cross section, hydrogen solubility and hydrogen (tritium) diffusivity of the BaCe0.9Y0.1O3−α specimens were determined.

Investigation of Transport Properties of Bzcy (BaZrxCe1-xY0.15O3- δ, x=0, 0.2, 0.4, 0.6)

Some perovskite-type oxides have shown high proton conductivity in wet hydrogen atmosphere. In these perovskite oxides the partial substitution of an acceptor dopant for B-site results in formation of oxygen vacancies, which lead to the formation of protonic defects by the absorption of water in wet atmosphere. Among various proton conducting perovskite-type oxides, Y-doped Barium cerate and barium zirconate are nearly isomorphic. Therefore, the basic phases of a binary solid solution where B-sites are randomly occupied by either Zr4+ or Ce4+. This is because the chemical instability of Y-doped BaCeO3- δ in the presence of CO2-, H2O- or SO2-containing atmosphere below 973K was substantially improved by replacing Ce with Zr to form a solid solution, and the mechanical strength was also enhanced when the proton conductivity and thermal stability remained adequate over a wide range of operation conditions for the fuel cell.To elucidate the transport properties and defect structure of a Ce/Zr-coexisting preovskite structure, BZCY(BaZrxCe1-xY0.15O3- δ, x=0, 0.2, 0.4, 0.6) was chosen as the model system. First, we study the electrical properties of BZCY in various oxygen and water vapor atmospheres by four-probe DC measurements as a function of temperature. And then, these properties are analyzed analytically, based on the defect structure of the material. Furthermore, we use the conductivity relaxation measurement technique to monitor the monotonic/non-monotonic(two-fold) relaxation for the BZCY under various themodynamic conditions and extract the chemical diffusivities by solving Fick’s second law for each case on the basis of hydrogen- and oxygen- decoupled diffusion as proposed by Professor Yoo1-3.Fig. 1 shows the typical relaxation profiles of the mean total conductivity upon oxidation and reduction across an identical oxygen activity window. During the redox reaction driven by the oxygen chemical potential gradient at a fixed water vapor activity, oxygen may be incorporated into the BZCY by ambipolar diffusion of V•• o and 2h• in the p-type oxidizing regime. In Fig. 2, conductivity relaxation profiles upon hydration and dehydration at a fixed pO2(≈0.21 atm) are shown as a function of water vapor activities at 1023K. The figures clearly reveal the violation of monotonic relaxation governed by the chemical diffusion of water, according to the ambipolar diffusion of oxygen vacancies and proton. As shown in the fig. 2, non-monotonic twofold relaxation behavior was clearly observed for the BCZY system.1. H.I. Yoo et al., Phys Chem Chem Phys, 10, 974 (2008)2. H.I. Yoo et al., Solid State Ionics, 180, 1443 (2009)3. J.I. Yeon et al., Solid State Ionics, 181, 1323 (2010)4. S. Hamakawa et al., Solid State Ionics, 148, 71 (2002)5. S.-J. Song et al., Solid State Ionics, 167, 99 (2004)6. S.M. Haile et al., Nature, 125, 271 (1999)7. D. Pergolesi et al., Nature Materials, 9, 846 (2010)8. H. Iwahara et al., Solid State Ionics, 125, 271 (1999)9. Y.C. Yang et al., Sensors and Actuators B, 140, 273 (2009)10. C. Zuo et al., Advanced Materials, 18, 3318 (2006).