Perovskite-type Proton Conductors Research Articles

Effect of Cation Nonstoichiometry on Hydration and Charge Transport Processes in Yb-Doped SrZrO3 Perovskite-Type Proton Conductor for Ceramic Electrochemical Cells

The effect of Sr deficiency on the hydration process and ionic and electronic conductivity of Yb-doped SrZrO3 proton conductors with a perovskite-type structure was investigated. Dense SrxZr0.95Yb0.05O3-δ (x = 0.94–1.00) ceramics were prepared using solution combustion synthesis. Thermogravimetry and Raman spectroscopy methods were used to determine the concentration of bulk protonic species. Sr deficiency was found to enhance the hydration ability of the zirconate; however, lowering of Sr content to x = 0.94 deteriorated the proton uptake. The conductivity of the SrxZr0.95Yb0.05O3-δ series depending on the oxygen partial pressure at different humidities was studied by the four-probe direct current technique. Sr-deficient ceramics with x = 0.96 and 0.98 were shown to become purely protonic conductors in humid atmospheres at a temperature close to 500 °C. The ionic conductivity reaches its highest value at a Sr content of x = 0.98 (2 × 10−4 S cm−1 at 500 °C and pH2O = 3.17 kPa). The hydration behavior and transport properties of SrxZr0.95Yb0.05O3-δ are discussed in terms of the defect chemistry model that assumes the distribution of Yb ions over Sr and Zr sites at a large Sr deficiency.

Electrical properties of BaZr0.5Ce0.3Y0.1Yb0.1O3-δ proton conductor for reversible proton-conducting solid oxide electrochemical cells

Proton-conducting oxide-based reversible solid oxide electrochemical cells (protonic-SOEC, P-SOEC) have a great potential to be the most efficient transition technology operating at intermediate temperatures. Here, we have introduced a perovskite-type proton conductor BaZr0.5Ce0.3Y0.1Yb0.1O3-δ (BZCYYb5311) and evaluated its electrochemical and transport properties. The chemical stability of BZCYYb5311 was confirmed by thermo-gravimetric analysis (TGA) under pure CO2 conditions and X-ray diffraction analysis. The total and partial conductivities were obtained using DC four-probe conductivity measurements under various pO2 and pH2O conditions. The ratio of proton conductivity to ionic conductivity including the oxygen-ion conductivity of this material was 98% at 600 °C, indicating that it is a relatively pure proton conductor with most of the ionic conduction almost exclusively carried out by protons. Chemical diffusivities were calculated from Fick's 2nd law by non-linear least squares fitting during oxidation/reduction and hydration/dehydration processes and were faster than other proton conductor BZCY (Y-doped BaCeO3-BaZrO3) series, which have a similar zirconium contents. In addition, the theoretical performance and efficiency of the reversible P-SOEC were determined from the spatial distribution of oxygen and hydrogen partial pressure in BZCYYb5311, calculating the maximum power density (4.5 Wcm−2 at 600 °C, 3% of water vapor pressure) for the fuel cell mode and current density (12.3 Acm−2 at 1.5 V, 600 °C, and 20% of water vapor pressure) for the electrolysis mode. The fuel consumption efficiency is high (99.1% at 0.6 V at 600 °C), while the electrolysis efficiency is low (72.3% at 1.6 V) due to the dominant p-type regime in the electrolyte during electrolysis. This low electrolysis efficiency can be enhanced by recovering the electrolyte regime by increasing pH2O or decreasing pO2 in the air electrode; however, it will still have low efficiency. Consequently, BZCYYb5311 is not an efficient electrolyte material for electrolyzers, but is promising for fuel cells because of its superior chemical stability, exceptional pure proton conductivity, and better bulk diffusion than those of the BZCY system.

Insights on perovskite-type proton conductive membranes for hydrogen permeation

Hydrogen has received widespread attention because as its diverse delivery methods and no GHG emissions. The use of membrane separation can effectively replace the costly low-temperature distillation and pressure swing adsorption technology to achieve the purpose of low-cost hydrogen enrichment. As a promising hydrogen separation material, perovskite-type proton conductor hydrogen permeable membrane has been practically applied in hydrogen separation and purification process. In this paper, the principle of hydrogen permeability of perovskite-type proton conductor hydrogen permeable membrane is expounded, and its preparation method and application are summarized, and the development trend of the material is discussed.

Proton incorporation behavior into grain boundaries of YSZ and GDC

The deuteron incorporation behavior of 8YSZ and 10GDC polycrystals was investigated using secondary ion mass spectrometry (SIMS). As a result of the deuteron solubility measurements of 10GDC polycrystals, the solubilities were found to increase with increasing grain boundary densities. This indicated that deuterons are incorporated mainly into the grain boundaries, which agrees with the finding of our recent study on 8YSZ. It was also observed that the deuteron solubilities in both materials increased with decreasing temperature and showed the opposite relationship with D2O vapor pressure (pD2O). This suggested that deuterons are incorporated into the grain boundaries by the reaction of D2O vapor with the oxygen vacancies, as is the case in perovskite-type proton conductors. However, the expected linear relationship between the solubilities and pD2O1/2, which was theoretically derived from the suggested incorporation reaction, was not observed. Based on the trapping model, this discrepancy is attributed to the existence of two types of deuterons with different incorporation energies. The determined hydration enthalpies for trap-free and trapping sites at the grain boundaries were − 33 and − 184 kJ mol−1 for 8YSZ, and − 47 and − 160 kJ mol−1 for 10GDC, which were in good agreement with the reported hydration enthalpies for the perovskites.

Protonation-Induced B-Site Deficiency in Perovskite-Type Oxides: Fully Hydrated BaSc0.67O(OH)2 as a Proton Conductor

One of the concepts for the design of a highly proton-conductive perovskite-type oxide is to increase the proton concentration. In this study, we focused on Ba–Sc oxide known for its brownmillerite-type structure and great potential for a high proton concentration. To achieve the highly hydrated phase, high-pressure synthesis was conducted using hydroxide as the H2O source. Although the expectation was that perovskite-type BaScO2(OH) would simply be a hydrated phase, the formation of Sc vacancies increased resulting in the greater hydration of the Ba–Sc oxide. It was likely that the fully hydrated phase was perovskite-type BaSc0.67O(OH)2. One third of the Sc sites were vacant, and the effective charge of Sc vacancies were compensated by the excess protons. First principles calculation revealed that the protons residing in the Sc vacancies were orientated toward a Sc vacancy and compensated the B-site charge in a manner similar to that of hydrogarnet substitution. This B-site deficiency caused by the extensive hydration condition is a novel mechanism to increase the proton concentration of perovskite-type proton conductors. The electrical conductivity, 10–2 S·cm–1 at 450–500 °C, was comparable to that of acceptor-doped BaZrO3, although the conductivity discontinuously changed at dehydration temperature.

Effect of Ce/Zr Ratio on Thermal and Chemical Expansions and CO2 Resistance of Rare Earth-Doped Ba(Ce,Zr)O3 Perovskite-Type Proton Conductors

To make clear the effect of Ce/Zr ratio on the thermal and chemical expansions of rare earth-doped Ba(Ce,Zr)O3 perovskite-type proton conductors, we investigated the crystal structures (crystal phase, lattice constants, lattice volume, etc.) of Ba(Ce0.7Zr0.1Y0.1Yb0.1)O3- δ, Ba(Ce0.4Zr0.4Y0.1Yb0.1)O3-δ, etc. on the basis of Rietveld refinement results of high-temperature X-ray diffraction data measured between 298 and 1173 K under dry and wet N2 atmospheres. We will also report on the CO2 resistance of these proton conductors.

Improvement of Energy Efficiency in Anode-Supported Proton Ceramic Fuel Cells By Lanthanum Tungstate Hole Blocking Layer

For efficient operation of proton ceramic fuel cell (PCFC), transport properties of hole and electron are important factors to be controlled as well as that of protons. Ba-based perovskite-type proton conductors have been used as typical electrolytes for the PCFCs because of their high proton conductivity. However, they also exhibit apparent hole conduction under oxidative atmospheres which causes leakage current through the electrolyte. The leakage current leads to not only a decrease in cell voltages but also a reduction of the energy efficiency since the leakage current cannot be utilized as electric power while hydrogen is consumed to generate protons and electrons. Therefore, a novel approach to suppress the leakage current has been required.Lanthanum tungstate (La28−x W4+x O54+3/2x ; LWO) with a high La/W ratio of 6.7 is one of the attractive proton conductors with a quite low hole conductivity. Though its proton conductivity is lower than the typical perovskite-type electrolytes, a high protonic transport number is attractive as a hole blocking layer for the PCFCs. An introduction of a thin LWO hole blocking layer on the Ba-based proton conductors with the high proton conductivity will suppress the leakage current by changing a profile of oxygen chemical potential in the electrolytes as we have proposed previously (Y. Matsuzaki et al., ECS Trans. 91, 1009-1018 (2019)).In this study, we explored the influence of the LWO hole blocking layer on the cell performances of PCFCs by theoretical calculations and experiments. In the theoretical calculations, a BZY|LWO bilayer cell model in which the LWO layer was located at the cathode side was employed. The calculations suggested that the bilayer structure not only improves efficiency but also gives flexibility to control the cell performance as required. Moreover, we experimentally investigated the performance of anode-supported cells with a BZY monolayer electrolyte and with a BZY|LWO bilayer electrolyte to elucidate the effect of the LWO layer.An LWO layer thickness (L LWO) dependence of the OCV in the BZY|LWO bilayer model was calculated based on the transport properties of BZY and LWO. Dependences of the energy efficiency and the power density with respect to a ratio of to a total electrolyte thickness (L total) of 10 μm were calculated for the model at a fixed external current density (I ext) of 250 mA/cm2 and at a fixed terminal voltage (V T) of 1.05 V, respectively. ε was defined by ε = V T I ext/V th I ion, where V th and I ion are a Nernst voltage and an ionic current density. We assumed the following operation conditions; operation temperature of 600 °C, 3% H2O + 97% H2 for anode gas, and 3% H2O + 19.4% O2 + 77.6 % Ar for cathode gas. In the experiments, a BZY monolayer electrolyte and a BZY|LWO bilayer electrolyte were prepared on NiO-BZY cermet substrates by the pulsed-laser deposition (PLD). La0.6Sr0.4Co0.2Fe0.8O3− d (LSCF) cathode was applied for both the cells. To suppress chemical reactions of LWO with BZY and LSCF, thin La-doped ceria (LDC) layers were introduced. The resulted structure of the monolayer cell and the bilayer cell were Ni-BZY|BZY(3.5 μm)|LSCF and Ni-BZY|BZY(3.5 μm)|LDC(40 nm)|LWO(1 μm)|LDC(40 nm)|LSCF, respectively. Cell performance tests were performed at 600 °C supplying 3% humidified H2 + Ar gas for the anode and 3% humidified 20% O2 + Ar gas for the cathode.The calculated OCV of the BZY monolayer model was 1.08 V and steeply increased up to 1.13 V by employing the thin LWO layer with L LWO/L total of 0.017 owing to suppression of the leakage current. Calculated dependences of ε and the power density for the model are shown in Fig.1. The efficiency and the power density showed a steep increase with increasing L LWO/L total. They showed the maximum values at certain L LWO/L total values, and then gradually decreased as L LWO/L total approached 1. This calculation result indicates that the cells exhibiting both the high ε and the high power density can be developed by employing the bilayer structure with the thin LWO hole blocking layer. Moreover, It is notable that, as the performance of the bilayer cell can be tuned by changing as presented in Fig. 1, the bilayer structure increases a degree of freedom for the design of the cells to satisfy various performance requirements. In the experiments, an enhancement of the OCV from 0.95 V for the BZY monolayer cell to 1.01 V for the bilayer cell was actually observed as suggested by the calculation. We consider that these theoretical calculations and experimental results present the effectiveness of the LWO hole blocking layer for the development of the high-performance PCFCs with high-design flexibility. Figure 1

Proton conductivity and transport number of complex perovskite barium strontium tantalate

Previously, complex perovskites barium strontium tantalate, i.e., Ba3Sr1.4T1.6O8.4 (BST40), has exhibited excellent proton conductivity due to its high basicity and oxygen vacancy concentration. Herein, we report proton conduction mechanism of BST40 using brick-layer model and defect equilibria model. Briefly, BST40 is prepared by solid-state synthesis method, resulting in hexagonal perovskite structure with space group of P63/m. Interestingly, grain interior and grain boundary thickness of BST40 are almost equal and the grain boundary conduction mainly dominates the conductivity at T > 500 °C. Total standard molar hydration enthalpy of BST40 and grain interior is found to be −79.6 kJ/mol and −101.3 kJ/mol, respectively. Activation energy for BST40, protons, oxygen-ions, and holes in oxygen-containing humid atmosphere is found to be 0.63 eV, 0.51 eV, 0.92 eV, and 1.08 eV, respectively. These values are higher than corresponding values for the grain interior. At 700 °C, proton transport number of BST40 and grain interior is found to be 0.7 and 0.72, respectively, which is significantly higher than other congeneric complex perovskite-type proton conductors. Overall, these results confirm that BST40 possesses excellent proton conductivity.

Conduction properties and transport number of double perovskite barium tantalate ceramic

Ba3Ca1·18Nb1·82O9-δ(BCN18), which has a high conductivity and protonic conductive dominant above 600 °C, is regarded as a promising double perovskite-type proton conductor for solid oxide fuel cells, catalysis, and electrochemical sensors. To further increase the conduction properties of the double perovskite-type proton conductor, it can be considered to decrease the electronegativities of A and B site elements. In this study, Ba and Ta, which have lower electronegativities than those of Ca and Nb, were introduced to totally substitute Ca and Nb. The double perovskite-type proton conductor Ba4·3Ta1·7O8.55 (BBT30) was prepared by solid-state sintering. We found that the total conductivities increased linearly with the increase of the temperature, with the total conductivities being in the range of 1.2 × 10−5−8.7 × 10−4 S cm−1 in humid air at 400 °C−800 °C; the estimated activation energy of proton was obviously lower than those of oxide ion and hole. The standard molar hydration enthalpy of BBT30 was calculated to be −79.9 kJ/mol. Additionally, the transport numbers were determined systematically by defect equilibria model. Our results indicated that both the transport numbers of oxide ion and hole remarkably increased with increasing oxygen partial pressure, while the protonic conduction was always predominant in those atmospheric conditions, with the protonic transport number being 0.64 at 700 °C, and it was significantly higher than those of other double perovskite-type proton conductors. This indicates that BBT30 is an excellent candidate for an electrochemical sensor, and our work has demonstrated a new direction in developing a high conductivity and protonic transport number perovskite-type proton conductor.

Hydrogen permeation and chemical stability of Ni–BaCe0.7In0.2Ta0.1O3−δ cermet membrane

With its good mechanical strength, high hydrogen permeability, and low price, the dense metal ceramic hydrogen separation membrane has attracted increasing attention. The conductivity of perovskite–type proton conductors can be greatly improved by rare–earth doping. In this study, a new nickel/barium cerate cermet Ni–BaCe0.7In0.2Ta0.1O3–δ electron–proton mixed conducting membrane was prepared and its hydrogen permeability, proton conductivity, and chemical stability were tested. Hydrogen permeability was controlled by the bulk diffusion when the thickness was >0.8 mm, but controlled by both the surface exchange and the bulk diffusion when the thickness was <0.8 mm. Ni paste and Pt paste were coated on the surface of the membrane to a thickness of 0.6 mm. After surface modification with the Pt and Ni, the hydrogen permeability of the membrane surface was greatly improved compared with that of the unmodified membrane, owing to better hydrogen catalytic performance of Pt than Ni. Under different CO2 concentrations, the hydrogen penetration flux quickly decreased and then remained nearly stable. The degree of reduction increases with the carbon dioxide concentration increasing. When the CO2 was turned off, the hydrogen permeation rate was restored, and recyclability decreased with increasing CO2 concentration. The changes in phase composition and microtopography implied the reaction between the sample and the CO2. Therefore, these results showed that hydrogen permeability was further improved, not only by reducing the membrane thickness, but also by catalyzing the membrane surface.

Development of Protonic Ceramic Conductors for SOFC and Sensor

In recent years, commercialization of residential fuel cell "Ene-Farm" has begun in Japan, and SOFC using zirconia as electrolyte is also being introduced into the market. However, in order to disseminate residential and commercial cogeneration systems or mono-generation systems, a more reliable and lower cost system is required, which is considered the key to widespread use. We have been researching and developing fuel cell systems that can realize high reliability and low cost with SOFC since 1989. As an SOFC concept that realizes high reliability and low cost, we consider an SOFC that operates at 600 ° C, which can use inexpensive and highly durable metal materials, and while maintaining high efficiency of SOFC, We aimed to develop SOFC that realizes reliability and low cost. In order to construct an SOFC operating at low temperature, an electrolyte which is sufficiently functional at low temperature and which is chemically and physically stable is required. Proton conductors found by Iwahara et al in the 1980s had low ionic conductivity and no chemical stability was also investigated. However, it was expected that ionic conduction activation energy is low, ionic conduction occurs even at a relatively low temperature, and fuel utilization rate as SOFC can be improved. Therefore, we focused on development of perovskite type proton conductors with high ion conductivity and high durability, and developed them. The target ionic conductivity was 1.0 × 10 -2 S / cm or more, and the chemical stability was aimed not to cause composition and phase change in a fuel gas atmosphere containing water vapor, hydrogen, carbon dioxide gas1-3). Results of examining the moisture resistance, carbon dioxide resistance and conductivity of samples of 348 kinds of BaCe1-xMxO3-α, SrCe1-xMxO3-α, BaZr1-x MxO3-α, CaZr1-x MxO3-α, BaZr1-x-y CexMyO3-α , Finally, it was found that BaZr 0.8 M 0.2 O 3 - α is the best proton conductor from the viewpoint of durability and conductivity, but BaZr 0.4 Ce 0 .4 In 0 .2 O 3 - α can be used as an electrolyte of a hydrogen sensor in air and in a reducing atmosphere. By using BaZr 0.4 Ce 0 .4 In 0 .2 O 3 - α as an electrolyte, platinum for the anode, gold aluminum electrode for the cathode and holes for rate limiting hydrogen diffusion on the anode side, a sensor capable of linearly detecting the hydrogen concentration in the atmosphere was constructed. The sensor was able to detect hydrogen concentration linearly from 0% to 5%4,5). On the other hand, when used as an electrolyte of a fuel cell, it is necessary to confirm that the material of the anode and the cathode do not react with the proton conductor. Because it is made by firing cells at high temperature. We fabricated proton conductors using In, Y, Yb, etc. as substitutional elements of M and investigated the conductivity and reactivity with Ni of anode materials. At the present time, it was found that BaZr0.8 Yb0.2O3 - α, which replaced M with Yb at 20%, was the most stable and had high protonic conductivity. Also, in the cell using BaZr 0.8 M 0.2 O 3 – α proton conductor as the electrolyte, Ni cermet as the anode and LaSrMnO 3 as the cathode, the maximum output of 0.42 W / cm 2 at 600 ° C. could be obtained. References 1) N. Taniguchi, et al., Solid State Ionics, 53-56, 998-1003, (1992) 2) N. Taniguchi, et al., J. Electrochem. Soc., 143(6), 1886-1890, (1996) 3) N. Taniguchi, et al., J. Electrochem. Soc., 145(5), 1744-1748, (1998) 4) N. Taniguchi, et al., Solid State Ionics, 145, 349-355, (2001) 5) N. Taniguchi, et al., Solid State Ionics, 176, 2979-2983, (2005)

Structural and transport properties of lanthanum tungstate with high La/W ratio: Suitability for proton-conducting solid oxide fuel cells operating at intermediate temperature

Systematic characterization of lanthanum tungstate (LWO) with a high La/W ratio was conducted to evaluate its suitability as a proton-conducting solid electrolyte for fuel cells operating at intermediate temperature. In this study, the crystal structure, ionic and electronic transport properties of LWO with a high La/W ratio (La/W=6.7: LWO67), which had high proton conductivity, were investigated. Rietveld analysis using synchrotron powder X-ray diffraction confirmed the single-phase formation of LWO67 having a cubic crystal structure with the Fm3¯m space group. The coefficient of thermal expansion of LWO67 was also evaluated from Rietveld analysis at high temperatures. Thermogravimetric analysis indicated a good chemical stability of LWO67 under wet CO2 conditions. The observed electrical properties indicated that the proton conductivity was dominant under wet conditions below 873K. The dependence of the electrical conductivity on oxygen partial pressure suggested that the electron and hole conductivities were suppressed sufficiently below 973K. Based on the observed transport properties, the superiority of LWO67 applied to a proton-conducting solid electrolyte fuel cells (p-ITFCs) was also discussed. The optimized electrolyte thickness of LWO67 was several tens of micrometers, which is more suitable than perovskite-type proton conductors such as BaZrO3 and BaCeO3 for electrode-supported fuel cells, when they are compared in terms of power generation efficiency.

Synthesis and Characterization of High Density and Low Temperature Sintered Proton Conductor BaCe&lt;sub&gt;0.5&lt;/sub&gt;Zr&lt;sub&gt;0.35&lt;/sub&gt;In&lt;sub&gt;0.1&lt;/sub&gt;Zn&lt;sub&gt;0.05&lt;/sub&gt;O&lt;sub&gt;3-δ&lt;/sub&gt;

Rare-earth-doped BaCeO3 and BaZrO3 electrolytes with perovskite structure have been studied extensively in developing proton conducting intermediate temperature SOFC. Acceptor doped alkaline earth cerates and zirconates have been thoroughly studied because of the great interest in their possible applications as solid proton conductors. The perovskite type proton conductor BaCe0.5Zr0.35In0.1Zn0.05O3-δwas prepared in the traditional solid state reaction method. The density of the sample obtained about 96% of the theoretical density after sintering at 1350 °C and X-ray diffraction study confirms the pure phase. Rietveld refinement of the neutron and X-ray powder diffraction data shows that this material crystallizes in the orthorhombic symmetry in the space group Pm3m. Particle size measurement shows that the average particle size is about 2.4 μm. The average thermal expansion at 894 °C was 9.49 x 10-6/°C. Thermogravimetric analysis (TGA) traces obtained for the sample on heating in wet air shows that the maximum proton uptake occurs from 595 °C.

Atmosphere dependence of anode reaction of intermediate temperature steam electrolysis using perovskite type proton conductor

The effect of oxygen partial pressure on anode reaction of steam electrolysis using SrZr0.5Ce0.4Y0.1O3-α (SZCY-541) proton conducting electrolyte was investigated by AC impedance measurement in this work. The anode reaction was enhanced by increasing oxygen partial pressure, and this result was opposite to the expectation from the conventional anode reaction (water splitting reaction). The increase in the electrode reaction conductivity with oxygen chemical potential was proportional to $$ {P_{{\mathrm{O}}_2}}^{1/4} $$ at 600 °C and at higher oxygen partial pressure region of 700 and 800 °C, suggesting the possibility that the enhancement is caused by the increase in hole concentration on the electrolyte surface near the anode.

Hydrogen extraction characteristics of high-temperature proton conductor ceramics for hydrogen isotopes purification and recovery

To develop high-efficiency and economical hydrogen isotope purification and recovery processes for a tritium extraction system in a fusion reactor, hydrogen extraction characteristics of an electrochemical hydrogen pump using high-temperature proton conductors were studied. The driving forces of hydrogen transportation in the proton conductors are electric potential difference, which can extract hydrogen isotopes selectively from a solid breeder blanket purge gas with low-pressure hydrogen isotope gas. In the experiments, a one-end closed tube made of proton-conducting ceramic CaZr0.9In0.1O3−α (effective electrode area: 160cm2) was developed because of its high chemical stability, mechanical strength, and durability in a series of perovskite-type proton conductors. The hydrogen pumping characteristics were evaluated over the temperature range from 923K to 1073K by extraction of 664–1200ppm H2 balanced with He, H2 was selectively extracted from and the mixture of He and H2 at the rate of Faraday's Law under an applied voltage of 3.5V DC. In the case of He with 0.12% H2 at 1023K and at 1.15V DC, the maximum hydrogen evolution rate was 0.12ml/min, the hydrogen recovery efficiency was more than 99%, suggesting the extraction of hydrogen could be operated with a current efficiency close to unity. The possible application of hydrogen pumps for the TES of CIPITISE at CIAE has been estimated.

Perovskite-type proton conductor for novel direct ionic thermoelectric hydrogen sensor

It was investigated whether a perovskite-type proton conductor, here BaCe 0.95Y 0.05O 3 − δ (BCY), is suitable as sensing material for a novel type of thermoelectric hydrogen sensor. Therefore, the hydrogen and oxygen concentration dependence of the thermopower of BaCe 0.95Y 0.05O 3 − δ was determined and was found to be in the same range as the value derived from theory. The hydrogen dependence was also measured at different temperatures, and only a comparatively small temperature dependence of the thermopower was observed.

ChemInform Abstract: Electrical Conductivity of the High-Temperature Proton Conductor BaZr0.9Y0.1O2.95.

The impedance of the cubic perovskite BaZr0.9Y0.1O3-δ has been systematically investigated in dry and wet atmospheres at high and low oxygen partial pressures. In the grain interior, conductivity contributions from oxygen ions, electron holes, and protons can be identified. Below 300°C, proton conduction dominates and increases linearly with the frozen-in proton concentration. The proton mobility, with an activation energy of 0.44 ± 0.01 eV is among the highest ever reported for a perovskite-type oxide proton conductor. For dry oxygen atmos-pheres, electron hole conduction dominates with an activation energy of ∼0.9 eV. At temperatures <500°C, the grain-boundary conductivity can be separated and increases upon incorporation of protons. The high electrical conductivity and chemical stability make acceptor-doped barium zirconate a good choice for application as a high-temperature proton conductor.

Electrical conductivity and chemical diffusion in Perovskite-type proton conductors in H 2–H 2O gas mixtures

The electrical conductivities of SrZr 0.9Y 0.1O 3-δ (SZY10) and BaCe 0.95Y 0.05O 3-δ(BCY5) were measured as a function of hydrogen partial pressure P(H 2), oxygen partial pressure P(O 2), steam partial pressure P(H 2O) and temperature. Their relaxation processes were analyzed using the solution of Fick's diffusion equation to determine the chemical diffusion coefficients and surface reaction rate constants. There were the differences in chemical relaxation kinetics and the conductivity dependence on P(H 2O) between the both oxides. The chemical diffusion coefficients depend on temperature but are essentially independent of P(H 2), P(O 2) and P(H 2O). The ambipolar diffusion treatment can explain the temperature dependence of chemical diffusion coefficients quantitatively. The chemical diffusion coefficients of SZY10 is one or two order of magnitude smaller than those of BCY5 at low temperature. The sluggish conductivity relaxation in SZY10 was due to considerably small oxygen vacancy diffusion coefficients at low temperatures. The total conductivity depends on P(H 2O) in the case of SZY10, but not for BCY5. This different dependence on P(H 2O) is caused by the difference in the ratio between proton mobility and oxide-ion mobility.

Solid-State Materials for Clean Energy: Insights from Atomic-Scale Modeling

AbstractFundamental advances in solid-state ionics for energy conversion and storage are crucial in addressing the global challenge of cleaner energy sources. This review aims to demonstrate the valuable role that modern computational techniques now play in providing deeper fundamental insight into materials for solid oxide fuel cells and rechargeable lithium batteries. The scope of contemporary work is illustrated by studies on topical materials encompassing perovskite-type proton conductors, gallium oxides with tetrahedral moieties, apatite-type silicates, and lithium iron phosphates. Key fundamental properties are examined, including mechanisms of ion migration, dopant-defect association, and surface structures and crystal morphologies.

BITX: New Electrolyte for Oxide Ion and Proton SOFC

Ba2In2(1-x)Ti2xO5+x•1-x compounds (BITx) have been prepared by solid state reaction. Whereas Ba2In2O5 corresponds to an ordered Brownmillerite structure, for 0.15 < x < 1 all members adopt a disordered cubic perovskite structure at RT. This phase transformation induces a drastic increase of the anionic conductivity level. At 700{degree sign}C, 10-2 S.cm-1 is obtained for BIT07. Stable under hydrogen, the x = 0.7 was selected and a SOFC built on BIT07 and Ni/BIT07 cermet was tested. The peak power is about 500mW at 800{degree sign}C. Due to the basicity of these compounds, water uptake of BITx was investigated. The change of the lattice volume upon hydration, inferred from X-ray diffraction data, appears as an important parameter for the characterization of perovskite-type proton conductors. Proton conductivity higher than 1 mS.cm-1 was measured at 400{degree sign}C for BIT02. A ceramic fuel cell based on this material as electrolyte was evaluated.