Y-doped BaZrO3 Research Articles

Investigation of BaZrO3 Nanoparticles for Photocatalytic Activity and the Effects of Y-doping

A straightforward co-precipitation technique with yttrium doping (X = 0, 0.02, 0.04, 0.06) was used to fabricate perovskite Ba1−xYxZrO3 nanoparticles. Employing Powder X-ray diffraction (PXRD) technique, the compound was characterized and found to have a perovskite structure crystallized in a cubic lattice. Images from scanning electron microscopy (SEM) show plenty of pores between the grains and a structure resembling a rod. The purity and formation of B-site in the nanostructure was confirmed by a Fourier Transform Infrared (FT-IR) spectrophotometer. The UV-Vis profile and photoluminescence (PL) spectra of the powder were also ascertained. Using methylene blue as a model organic pollutant, the powder as a photocatalyst was tested for two hours under UV light irradiation. The Y-doped nanoparticles broke down the dye by ∼98.5% at pH = 8 when exposed to UV light. The enhanced photocatalytic performance exhibited by Y-doped BaZrO3 nanoparticles can be attributed to their efficient charge separation and increased adsorption capabilities by the presence of BaZrO3.

High-Temperature Mechanical–Conductive Behaviors of Proton-Conducting Ceramic Electrolytes in Solid Oxide Fuel Cells

Proton-conducting solid oxide fuel cells (P-SOFCs) are widely studied for their lower working temperatures than oxygen-ion-conducting SOFCs (O-SOFCs). Due to the elevated preparation and operation temperatures varying from 500 °C to 1500 °C, high mechanical stresses can be developed in the electrolytes of SOFCs. The stresses will in turn impact the electrical conductivities, which is often omitted in current studies. In this work, the mechanical–conductive behaviors of Y-doped BaZrO3 (BZY) electrolytes for P-SOFCs under high temperatures are studied through molecular dynamics modeling. The Young’s moduli of BZY in fully hydrated and non-hydrated states are calculated with different Y-doping concentrations and at different temperatures. It is shown that Y doping, oxygen vacancies, and protonic point defects all lead to a decrease in the Young’s moduli of BZY at 773 K. The variations in the conductivities of BZY are then investigated by calculating the diffusion rates of protons in BZY at different triaxial, biaxial, and uniaxial strains from 673 K to 873 K. In all cases, the diffusion rate present a trend of first increasing and then decreasing from compression state to tension state. The variations in elementary affecting factors of proton diffusion, including hydroxide rotation, proton transfer, proton trapping, and proton distribution, are then analyzed in detail under different strains. It is concluded that the influences of strains on these factors collectively determine the changes in proton conductivity.

Lattice distortion and strain induced crack formation in Y-doped BaZrO3

Proton conducting ceramics are promising solid electrolytes for protonic ceramic fuel cells. However, the presence of cracks remains a challenge before successful commercialization of the proton ceramic devices. This study investigates the impact of internal strain and lattice distortion on the crack formation in BaZr0.8Y0.2O3-δ. During sintering, pellets are covered with controlled amount of sacrificial powder 2 or 3 times of the pellet mass, and the effects of adding BaCO3 in the sacrificial powder is studied. The pellets sintered with 2 times sacrificial powder remain intact when dried, yet 53 % show cracks after hydration in 0.03 atm water vapor pressure. All pellets fracture into pieces when sintered with additional BaCO3 in sacrificial powder, in which 0.07 mol% excessive Ba is observed in the actual composition. These Ba excess pellets show larger lattice constant compared to those prepared under other conditions. Strain analysis indicates that 0.14 % to 0.15 % micro strain is observed in the batches with cracks. Raman spectra reveal higher degree of lattice distortion in the BO6 octahedra in the cracked batches. The findings highlight the role of lattice distortion in internal strain, and crack formation. This work may contribute to the processing of solid electrolytes in protonic ceramic fuel cells.

Influence of Ba non-stoichiometry on the processing properties of Y- and Sc-doped BaZrO3

Y-doped BaZrO3 is a well-researched material for proton-conducting fuel cells. One of the main limitations is the very high sintering temperature (∼ 1600 °C) necessary to densify the material. As Ba is lost at this temperature due to BaO evaporation, the stoichiometry is changed uncontrollably. This study is focused on evaluating the influence of slight changes in stoichiometry on microstructure, chemical stability, and conductivity of 20% Y-doped BaZrO3 (BZY20) as well as 10% Y- and 10% Sc-co-doped BaZrO3 (BZY10Sc10). Overall, Ba excess resulted denser microstructures with larger grains. Still, these samples were prone to decomposition by forming BaCO3. Therefore, a slight Ba deficiency is favorable as the conductivity did not suffer in the examined stoichiometry region.

Mn Additive Improves Zr Grain Boundary Diffusion for Sintering of a Y-Doped BaZrO3 Proton Conductor.

Yttrium-doped barium zirconate (BZY) has garnered attention as a protonic conductor in intermediate-temperature electrolysis and fuel cells due to its high bulk proton conductivity and excellent chemical stability. However, the performance of BZY can be further enhanced by reducing the concentration and resistance of grain boundaries. In this study, we investigate the impact of manganese (Mn) additives on the sinterability and proton conductivity of Y-doped BaZrO3 (BZY). By employing a combinatorial pulsed laser deposition (PLD) technique, we synthesized BZY thin films with varying Mn concentrations and sintering temperatures. Our results revealed a significant enhancement in sinterability as Mn concentrations increased, leading to larger grain sizes and lower grain boundary concentrations. These improvements can be attributed to the elevated grain boundary diffusion of zirconium (Zr) cations, which enhances material densification. We also observed a reduction in Goldschmidt's tolerance factor with increased Mn substitution, which can improve proton transport. The high proton conduction of BZY with Mn additives in low-temperature and wet hydrogen environments makes it a promising candidate for protonic ceramic electrolysis cells and fuel cells. Our findings not only advance the understanding of Mn additives in BZY materials but also demonstrate a high-throughput combinatorial thin film approach to select additives for other perovskite materials with importance in mass and charge transport applications.

Hydrated doped-BaZrO3 proton conductors studied by positron annihilation lifetime spectroscopy

The study of defect chemistry for doped BaZrO3 proton conductors is of particular interest because of defect interactions that can affect the proton conductivity of the material. Protons incorporated due to the material's hydration can be trapped by negatively charged immobile dopants, reducing proton mobility. The reduction of the proton conduction impedes the use of BaZrO3 materials in energy conversion applications at intermediate temperatures (300 °C – 600 °C). The probing of proton trapping in doped BaZrO3 is hindered by the limited availability of techniques sensitive to defect chemistries. In this work, we used positron annihilation lifetime spectroscopy (PALS) to study the defect chemistry of Y-doped and Sc-doped BaZrO3. Using a two-state positron trapping model we showed that PALS can be applied to study the defect chemistry of hydrated dense proton conductors. Positron trapping rates and lifetimes were correlated with doping levels of the materials. Probability significance t-tests were carried out for PALS parameters to verify whether there are differences/similarities for various populations: non-doped/doped, level and type of doping, high temperature, and surface effects. The results revealed that the initial doping generates a significant number of traps available for positrons. Doping with yttrium increased the positron trapping rate, while this effect was not observed with scandium. Low-temperature hydration affects specimens significantly inhibiting positron trapping at undoped BaZrO3 material and highly doped specimens. Positronium formation in rough surface layers, and highly doped specimens was detected but does not exceed 1%.

Thermochemical Expansion and Protonic and Electronic Hole Conductivity of Grain Interior and Grain Boundaries in 10 Mole% Y-Substituted SrZrO3.

Proton conducting acceptor-doped SrZrO3 has a history as long as that of BaZrO3 , but has attracted less interest. Inspired by its higher transport number of ionic conduction in wet oxygen revealed by our recent work, we here explore further aspects of doped SrZrO3 as electrolyte in proton ceramic electrochemical cells. In-situ high temperature XRD (HT-XRD) analysis of SrZr0.9 Y0.1 O3-δ (SZY10) indicated an anisotropic chemical expansion of hydration, stronger along the b than the a direction, and negative in the c direction. A systematic electromotive force (EMF) and impedance spectroscopy study as a function of and allowed determination of partial conductivities of electron holes and ions (mainly protons) in bulk (grain interior) and grain boundaries. Enthalpies and preexponentials were determined and interpreted for bulk and grain boundary partial conductivities based on defect chemistry and a brick layer model. The hole conductivity in bulk is modest and ensures high ionic transport numbers in oxidizing atmospheres, while grain boundaries exhibit lower ionic transport numbers from a relatively higher hole conductivity attributed primarily to tunnelling past the deepest part of the space charge region. Y-doped SrZrO3 (SZY) materials exhibit lower proton conductivities but excel over Y-doped BaZrO3 (BZY) in terms of thermal expansion compatibility with electrode materials and higher ionic transport numbers in oxidizing atmospheres and may hence be candidates for functional layers between BZY-based electrolytes and positrodes in proton ceramic electrochemical cells.

Local Structure and Mixed Proton-Hole Conduction in Y and Al-Doped BaZrO3

Enhancing proton-hole mixed conduction is one of the promising methods to improve the cathode performance of proton-conducting fuel cells. In this study, Al-doping is conducted to enhance the hole conduction in Y-doped BaZrO3. The relationship between the defect structure around Al and the electrical conductivity is investigated. 27Al NMR results indicated the formation of more than one oxygen vacancy around Al and the clustering of the acceptors. The electrical conductivity shows dominant proton conduction below 600ºC while other charge carriers, such as oxygen vacancies and electron holes, dominate at 800ºC. The Al-doping affects the formation of the defects but shows negligible influence on the dominant charge carriers at lower temperatures.

Synthesis of Y-doped BaZrO3 proton conducting electrolyte material by a continuous hydrothermal process in supercritical conditions: Investigation of the formation mechanism and electrochemical performance

In this work, BaZr0.85Y0.15O3-δ was elaborated by a continuous hydrothermal process in supercritical conditions (410 °C/30.0 MPa). X-Ray diffraction, Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy analysis allowed to propose a description of the formation mechanism for this oxide in supercritical water. This mechanism consists in the precipitation of core-shell nanoparticles in which, the core is a Ba-deficient perovskite and the shell an oxyhydroxide species of Y and Zr. Then, Ba2+, Zr4+ and Y3+ are incorporated in the perovskite from the solution and from the shell. After an annealing treatment at 1000 °C for 1 h to homogenize the composition, the powder was pressed into a pellet and sintered at 1550 °C for 5 h to analyze its electrochemical properties. The total conductivity of this oxide is 2.5 × 10-3 S cm-1 at 600 °C in wet H2 (3% H2O). Furthermore, electrochemical impedance spectroscopy measurements showed that its conduction is mainly protonic at a temperature lower than 575 °C.

Engineering oxygen vacancy to accelerate proton conduction in Y-doped BaZrO3

Proton conducting oxides have drawn great interest as electrolytes for proton-conducting reversible solid oxide cells (P-RSOCs), but suffered from the inferior ionic conductivity. To accelerate proton conduction, oxygen vacancy engineering via calcium-doping is proposed and validated, which generates more oxygen vacancies to increase proton concentration and importantly tailors the position of oxygen vacancy to accelerate proton diffusion. TG and EIS results show that calcium-doped BaZr0.8Y0.2O3-δ (BZY2), BaZr0.8Ca0.1Y0.2O3-δ (BZCa1Y2), owns higher proton concentration, and demonstrates ionic conductivity of 0.008 S cm−2 at 700 °C, 2.7 times higher than BZY2. The lower activation energy of conductivity in BZCa1Y2 confirms the faster proton conduction behavior. DFT calculation concludes that oxygen vacancies prefer to cluster with Ca site and proton diffusion barrier is decreased most when vacancy is tailored to generate nearing Ca. When considering the concentration of proton and oxygen vacancy, proton diffusion coefficient obtained from Ab-initio Molecular Dynamics simulation is 1.1×10−5 cm2s−1 for BZCa1Y2 in 200 °C, larger than BZY2 (9.0×10−6 cm2s−1) and verifying the accelerated proton diffusion due to the tailored oxygen vacancy. The oxygen vacancy engineering provides a further understanding of proton diffusion in proton conducting oxides and a new promising opportunity to improve conductivity.

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.

Production and Characterization of Sputtered Y-doped BaZrO3 for Proton Conducting Oxides

Production and Characterization of Sputtered Y-doped BaZrO3 for Proton Conducting Oxides

Proton conduction-assisted direct CO2 methanation using Ni/CaO/Y-doped BaZrO3 proton conductor

This study investigates the conversion of captured CO2 to CH4 with Ni and CaO supported on 10 mol% Y-doped BaZrO3 (BZY10) proton-conducting oxides. The on-site treatment of CO2 to cut back CO2 emission has been demonstrated, further transforming it into an energy carrier. This report describes direct CO2 methanation using Ni materials in O2– and H2O-containing gases at the carbonation step. Ni and CaO supported on BZY10 were used to capture CO2 in simulated flue gas containing O2 or H2O and convert it into CH4 at the same temperature (380–450 °C). High reducibility of Ni and high methanation reactivity were observed. Through the FTIR spectra observation, it was found out that transformation of bicarbonate to formate was facile due to proton-conducting property of the BZY10 support, i.e., hydrogen spillover, compared to BaZrO3-supported materials., It is hypothesized that the hydroxyl ions at the interface of CaO and BZY10 intervene in the carbonation and methanation steps. Also, carbonation accelerates the kinetic and diffusion-controlled regions with a high affinity for CO2. In the methanation step, the adsorbed CO2 enables the hydrogen species to produce CH4.

Highly durable Sr-doped LaMnO3-based cathode modified with Pr6O11 nano-catalyst for protonic ceramic fuel cells based on Y-doped BaZrO3 electrolyte

Sr-doped LaMnO3 (LSM) is one of the state-of-the-art cathodes with outstanding chemical stability but suffers from poor electrochemical activity. It is promising that LSM can be used as good cathode for protonic ceramic fuel cells (PCFCs), provided that its catalytic activity can be improved. Herein, we have developed a high-performance and durable LSM-based cathode used for PCFCs with stable Y-doped BaZrO3 electrolyte. In this work, commercial LSM cathode is mixed with high-performance BaZr0.85Y0.15O3-δ particles. Pr6O11 nano-catalysts are homogeneously dispersed into the composite cathode, resulting in a significant decrease in the cathode polarization resistance from 0.51 to 0.12 Ω·cm2 at 600 °C. The power output improves by ~96% at 600 °C. Distribution of relaxation time analysis indicates that the processes of oxygen adsorption/dissociation and oxygen species diffuse to triple phase boundary sites are significantly promoted by Pr6O11. Furthermore, the 100 h stability tests show that the modified cathode is extremely stable.

On the anomalous diffusion of proton in Y-doped BaZrO3 perovskite oxide

Proton transport in perovskite oxides (ABO3) is a complex dynamical process involving hydroxide ion rotation and proton transfer. Combining ab initio molecular dynamics (AIMD) and machine-learning molecular dynamics (MLMD) simulations of proton dynamics in Y-doped BaZrO3 perovskite oxide, we systematically illustrate the anomalous characteristics of proton motion. At short times, proton performs superdiffusion through the OH wag and proton transfer. At intermediate times, the larger rotation angle results in the larger plateau value. At longer times, proton diffusion first becomes subdiffusive due to the hydroxide ion rotations then gradually turns to normal diffusion. A theoretical model is also offered to quantitatively describe this abnormal proton diffusion. In all, this work provides a more complete understanding of proton dynamics in perovskite oxides.

Isotopic effect of proton conductivity in barium zirconates for various hydrogen-containing atmospheres

Among various perovskite proton conducting oxides, Y-doped BaZrO3 perovskite is a promising material for electrochemical hydrogen devices due to its good chemical stability and higher proton conductivity at higher operating temperatures like 500–800 °C. For the practical application of the functional BaZrO3 proton conductors in electrochemical hydrogen devices like tritium purification and recovery systems in a nuclear fusion reactor (where deuterium and tritium isotopes are utilized as fuel), it’s necessary to understand the isotopic effect of proton conductivity. To understand the isotopic effect of proton conductivity in the barium zirconates, in this study, the proton conductivities in the Ar, (Ar + 4% H2), (Ar + 4% D2), (Ar + H2O), (Ar + D2O), and O2 atmospheres were measured for two different compositions: BaZr0.9Y0.1O2.95 (BZY), and BaZr0.955Y0.03Co0.015O2.97 (BZYC) in the temperature range from 500 °C to 1000 °C. By comparing the obtained results, a significant difference in sinterability, conductivity, and the isotopic effect was observed due to the co-doping of the Co element in the BaZr1−xYxO3-α proton conductor.

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.

Toward Durable Protonic Ceramic Cells: Hydration-Induced Chemical Expansion Correlates with Symmetry in the Y-Doped BaZrO3–BaCeO3 Solid Solution

Toward Durable Protonic Ceramic Cells: Hydration-Induced Chemical Expansion Correlates with Symmetry in the Y-Doped BaZrO₃–BaCeO₃ Solid Solution

Influence of sintering activators on electrical property of BaZr0.85Y0.15O3-δ proton-conducting electrolyte

In this study, the influence of CuO and ZnO sintering activators on the densification behavior, distribution of sintering activators, and electrical properties of Y-doped BaZrO 3−δ proton conducting oxide were examined over a wide range of oxygen and water vapor partial pressures. With the use of 1 mol% CuO and 4 mol% ZnO, a relative density above 97% was achieved at sintering temperatures of 1500 °C and 1300 °C, respectively. The bulk and grain boundary conductivities of fully sintered BaZr 0.85 Y 0.15 O 3−δ , Ba(Zr 0.84 Y 0.15 Cu 0.01 )O 3−δ , and Ba(Zr 0.81 Y 0.15 Zn 0.04 )O 3−δ were assessed using electrochemical impedance spectroscopy. The amount of sintering activators incorporated into the bulk was investigated using an energy dispersive spectrometer equipped with a high-resolution transmission electron microscope, whereas the equilibrium concentrations of proton and oxygen vacancies as a function of water vapor pressure were estimated by thermogravimetric analysis. Using these results, the total electrical conductivities of the three compositions at 800 °C over a wide range of oxygen and water vapor partial pressures were analyzed via a non-linear fitting based on the defect structure of Y-doped BaZrO 3−δ . As a result, the proton, oxygen ion, and hole partial conductivities were calculated, and the proton transference numbers of the three compositions were compared. • Additions of CuO and ZnO in BZY effectively lower a sintering temperature • Cu was evenly distributed, whereas most of Zn was presented at grain boundaries • Concentration and mobility of proton in BZY-Cu and BZY-Zn were lower than BZY • Transference number of proton is in the order of BZY-Zn > BZY-Cu ≈ BZY

Novel Perovskite Semiconductor Based on Co/Fe-Codoped LBZY (La0.5Ba0.5 Co0.2Fe0.2Zr0.3Y0.3O3−δ) as an Electrolyte in Ceramic Fuel Cells

Introducing triple-charge (H+/O2–/e–) conducting materials is a promising alternative to modify a cathode as an electrolyte in advanced ceramic fuel cells (CFC). Herein, we designed a novel triple-charge conducting perovskite-structured semiconductor Co0.2/Fe0.2-codoped La0.5Ba0.5Zr0.3Y0.3O3−δ (CF-LBZY) and used as an electrolyte and an electrode. CF-LBZY perovskite as an electrolyte exhibited high ionic (O2–/H+) conductivity of 0.23 S/cm and achieved a remarkable power density of 656 mW/cm2 550 °C. X-ray photoelectron spectroscopy (XPS) analysis revealed that the Co/Fe codoping supports the formation of oxygen vacancies at the B-site of a perovskite structure. Besides, using CF-LBZY as a cathode, the fuel cell delivered 150 and 177 mW/cm2 at 550 °C, respectively, where Y-doped BaZrO3 and Sm-doped ceria (SDC) were used as electrolytes. During the fuel-cell operation, H+ injection into the CF-LBZY electrolyte may suppress electronic conduction. Furthermore, the metal–semiconductor junction (Schottky junction) has been proposed by considering the work function and electron affinity to interpret short-circuiting avoidance in our device. The current systematic study indicates that triple-charge conduction in CF-LBZYO3−δ has potential to boost the electrochemical performance in advanced low-temperature fuel-cell technology.