In-situ redox cycling behaviour of Ni-BaZr_0.85Y_0.15O_3−δ cermet anodes for Protonic Ceramic Fuel Cells

The current work investigates the redox behaviour of peak performing Ni-BaZr0.85Y0.15O3−δ (Ni-BZY) cermet anodes for protonic ceramic fuel cells (PCFCs) by electrochemical impedance measurements, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Peak performing PCFC cermet anodes are documented to require much lower porosity levels than those needed in oxide-ion conducting counterparts. The polarisation behaviour of these optimised PCFC anodes is shown to be drastically impaired by redox cycling, with depletions in performance that correspond to around 80% of the original resistance values noted after the first redox cycle. The ohmic resistance (Rohmic) is also shown to be increased due to delamination at the electrode/electrolyte interface, as confirmed by postmortem microstructural analysis. In-situ measurements by environmental scanning electron microscopy (ESEM) reveal that degradation proceeds due to volume expansion of the nickel phase during the re-oxidation stage of redox cycling. The present study reveals degradation to be very fast for peak performing Ni-BZY cermets of low porosity. Hence, methods to improve redox stability can be considered to be essential before such anodes can be implemented in practical devices

Chemically transformed additive phases in Mg2TiO4 and MgTiO3 loaded hydrogen storage system MgH2

The present work deals with a comparative study of Mg2TiO4, MgTiO3 and titania additives incorporated MgH2. Hydrogen storage measurements suggest that all these additives improve the hydrogen desorption/absorption performance of MgH2. X-ray diffraction (XRD) and X ray photoelectron spectroscopy (XPS) studies highlight that rock salt phases consisting of highly reduced Ti exist in the samples. These results reiterate that in-situ formation of chemically reduced Ti containing active species is a critical step in the catalysis of TiO2/Mg2TiO4/MgTiO3 additives loaded MgH2

Modeling of electrical conductivity in the proton conductor Ba0.85K0.15ZrO3-delta

The electrical conductivity of Ba0.85K0.15ZrO3-delta (BKZ) has been studied as a function of both oxygen and water vapor partial pressure in the temperature range of 550-700 degrees C, to determine the partial conductivities of protons, holes, and oxygen vacancies from the defect model. It is shown that p-type conduction is dominant in dry oxidative atmospheres, while in wet oxidative atmospheres, a conduction transition from proton to hole conduction is found with increasing temperature. On the contrary, in wet nitrogen atmosphere, proton conduction is dominant over the whole temperature range. The calculated activation energies for oxide-ion, electron-hole and proton conduction are 0.86, 1.36 and 0.59 eV, respectively. The standard solution enthalpy for water dissolution is -90 kJ/mol, which is lower in absolute terms than that typically reported for doped barium cerates but very close to that reported for BaZr0.85Y0.15O3-delta. (C) 2015 Elsevier Ltd. All rights reserved

A review on sintering technology of proton conducting BaCeO3-BaZrO3 perovskite oxide materials for Protonic Ceramic Fuel Cells

Ceramic proton conductors can reduce the operating temperature of solid oxide fuel cells (SOFCs) to the intermediate temperature range, 400-600 degrees C, due to their higher ionic conductivity in comparison to oxide-ion conductors under these conditions. Nonetheless, the most promising proton conducting materials, typically yttrium-doped barium cerates and zirconates with nominal compositions: BaCe1-xYxO3-delta (BCY ), BaZr1-xYxO3-delta (BZY) and Ba(Ce,Zr)(1-y)YyO3-delta (BCZY) exhibit major challenges with respect to the production of dense electrolyte membranes. To improve the processing of these materials, liquid phase sintering (LPS) induced by the addition of transition and alkali metal oxides as sintering additives, is proposed as an effective way to promote densification, where the benefits of LPS may be further extended when this method is used in combination with solid-state reactive sintering (SSRS) to reduce the fabrication time and cost. Nonetheless, recent literature highlights that the addition of these sintering additives can have highly negative secondary impacts on bulk transport properties and overall fuel cell performance. This review summarises the recent developments and the innovative methods employed to overcome the processing difficulties in these materials, including diverse potential sintering methods, the effect of different sintering additives and their impact on densification, ionic transport and electrochemical properties

Exploring the Thermoelectric Performance of BaGd2NiO5 Haldane Gap Materials

One-dimensional Haldane gap materials, such as the rare earth barium chain nickelates, have received great interest due to their vibrant one-dimensional spin antiferromagnetic character and unique structure. Herein we report how these 1D structural features can also be highly beneficial for thermoelectric applications by analysis of the system CaxBaGd2‑xNiO5 0 ≤ x ≤ 0.25. Attractive Seebeck coefficients of 140−280 μV K−1 at 350−1300 K are retained even at high acceptor-substitution levels, provided by the interplay of low dimensionality and electronic correlations. Furthermore, the highly anisotropic crystal structure of Haldane gap materials allows very low thermal conductivities, reaching only 1.5 W m−1 K−1 at temperatures above 1000 K, one of the lowest values currently documented for prospective oxide thermoelectrics. Although calcium substitution in BaGd2NiO5 increases the electrical conductivity up to 5−6 S cm−1 at 1150 K < T < 1300 K, this level remains insufficientfor thermoelectric applications. Hence, the combination of highly promising Seebeck coefficients and low thermal conductivities offered by this 1D material type underscores a potential new structure type for thermoelectric materials, where the main challenge will be to engineer the electronic band structure and, probably, microstructural features to further enhance the mobility of the charge carriers

Ionic Conductivity of Na3Al2P3O12 Glass Electrolytes Role of Charge Compensators

In glasses, a sodium ion (Na+) is a significant mobile cation that takes up a dual role, that is, as a charge compensator and also as a network modifier. As a network modifier, Na+ cations modify the structural distributions and create nonbridging oxygens. As a charge compensator, Na+ cations provide imbalanced charge for oxygen that is linked between two network-forming tetrahedra. However, the factors controlling the mobility of Na+ ions in glasses, which in turn affects the ionic conductivity, remain unclear. In the current work, using high-fidelity experiments and atomistic simulations, we demonstrate that the ionic conductivity of the Na3Al2P3O12 (Si0) glass material is dependent not only on the concentration of Na+ charge carriers but also on the number of charge-compensated oxygens within its first coordination sphere. To investigate, we chose a series of glasses formulated by the substitution of Si for P in Si0 glass based on the hypothesis that Si substitution in the presence of Na+ cations increases the number of SiOAl bonds, which enhances the role of Na as a charge compensator. The structural and conductivity properties of bulk glass materials are evaluated by molecular dynamics (MD) simulations, magic angle spinning-nuclear magnetic resonance, Raman spectroscopy, and impedance spectroscopy. We observe that the increasing number of charge-imbalanced bridging oxygens (BOs) with the substitution of Si for P in Si0 glass enhances the ionic conductivity by an order of magnitudefrom 3.7 x 10(-8) S.cm(-1) to 3.3 x 10(7) S.cm(-1) at 100 degrees C. By rigorously quantifying the channel regions in the glass structure, using MD simulations, we demonstrate that the enhanced ionic conductivity can be attributed to the increased connectivity of Na-rich channels because of the increased charge-compensated BOs around the Na atoms. Overall, this study provides new insights for designing next-generation glass-based electrolytes with superior ionic conductivity for Na-ion batterie