Overcurrent Abuse of Primary Prismatic Zinc–Air Battery Cells Studying Air Supply Effects on Performance and Safety Shut-Down

Overcurrent abuse has been performed on commercial 48 Ah primary prismatic zinc (Zn)–Air battery cells with full air supply as well as with shut-off air supply. Compared to other battery technologies, e.g., lithium-ion batteries, metal–air batteries offer the possibility to physically stop the battery operation by stopping its air supply, thus offering an additional protection against severe battery damage in the case of, e.g., an accidental short circuit. This method may also reduce the electrical hazard in a larger battery system since, by stopping the air supply, the voltage can be brought to zero while maintaining the energy capacity of the battery. Measurements of overdischarge currents and current cut-off by suffocation have been performed to assess the safety of this type of Zn–air battery. The time to get to zero battery voltage is shown to mainly be determined by the volume of air trapped in the cell

Crystal structure and proton conductivity of BaZr0.9Sc0

Solid-state sintering has been used to prepare the perovskite BaZr0.9Sc0.1O3-delta. Analysis of X-ray powder diffraction data shows that an increase of the unit cell parameter, a, was observed after deuteration. Rietveld analysis of room-temperature neutron powder diffraction data confirmed cubic symmetry (space group Pm-3m). Dynamic thermogravimetric analysis indicates that the hydration process occurs below 335 degrees C and approximately 58% of the theoretical number of protonic defects can be filled. The presence of protons/deutrons is seen from the strong O-H/O-D stretch band in the infrared spectrum of the hydrated/deuterated samples. The proton conductivity of a prehydrated sample was investigated under dry and wet Ar atmosphere

Crystal structure and proton conductivity of BaSn0.6Sc0.4O3-delta: insights from neutron powder diffraction and solid-state NMR spectroscopy

The solid-state synthesis and structural characterisation of perovskite BaSn(1–x)Sc(x)O(3–δ) (x = 0.0, 0.1, 0.2, 0.3, 0.4) and its corresponding hydrated ceramics are reported. Powder and neutron X-ray diffractions reveal the presence of cubic perovskites (space group Pm3m) with an increasing cell parameter as a function of scandium concentration along with some indication of phase segregation. (119)Sn and (45)Sc solid-state NMR spectroscopy data highlight the existence of oxygen vacancies in the dry materials, and their filling upon hydrothermal treatment with D(2)O. It also indicates that the Sn(4+) and Sc(3+) local distribution at the B-site of the perovskite is inhomogeneous and suggests that the oxygen vacancies are located in the scandium dopant coordination shell at low concentrations (x ≤ 0.2) and in the tin coordination shell at high concentrations (x ≥ 0.3). (17)O NMR spectra on (17)O enriched BaSn(1–x)Sc(x)O(3–δ) materials show the existence of Sn–O–Sn, Sn–O–Sc and Sc–O–Sc bridging oxygen environments. A further room temperature neutron powder diffraction study on deuterated BaSn(0.6)Sc(0.4)O(3–δ) refines the deuteron position at the 24k crystallographic site (x, y, 0) with x = 0.579(3) and y = 0.217(3) which leads to an O–D bond distance of 0.96(1) Å and suggests tilting of the proton towards the next nearest oxygen. Proton conduction was found to dominate in wet argon below 700 °C with total conductivity values in the range 1.8 × 10(–4) to 1.1 × 10(–3) S cm(–1) between 300 and 600 °C. Electron holes govern the conduction process in dry oxidizing conditions, whilst in wet oxygen they compete with protonic defects leading to a wide mixed conduction region in the 200 to 600 °C temperature region, and a suppression of the conductivity at higher temperature

Acceptor-Doped BaZrO3 Perovskite: Synthesis, Structure and Proton Conductivity.

Acceptor-doped perovskite oxides exhibit significant proton conductivity in hydrogen containing atmospheres. Therefore, they have potential for use as separator materials for various electrochemical devices including gas sensors, electrolysers and fuel cells. For example, yttrium doped BaZrO3 perovskites have shown high bulk proton conductivity and high chemical stability. However, significant grain boundary resistance has subdued the technological applications.The work constituting this thesis has mainly been focused on synthesis, structural characterisation and electrochemical investigations of acceptor-doped BaZr1-xMxO3-d (M = Ga3+, Sc3+, In3+, Yb3+ and Y3+: x = 0-0.75) perovskite oxides in bulk form. The polycrystalline samples were prepared via a traditional solid-state sintering route and by wet chemical routes. A combination of techniques such as x-ray and neutron powder diffraction, thermogravimetry, scanning electron microscopy (SEM) and impedance spectroscopy (IS) have been used to characterize the samples. Rietveld analysis of high resolution low temperature neutron powder diffraction data revealed that the deuteron site was localised at, or close to, the 12h crystallographic position of BaZr0.5In0.5O2.5(OD)0.5. It was also confirmed that the hydration/deuteration reaction caused an expansion of the cell parameter, while keeping the lattice symmetry, and thus the basic structure intact. Moreover, from Rietveld analysis of the neutron data the oxygen vacancy concentration was determined and they were found to be statistically distributed in the structure. Heavily doped samples showed higher proton conductivity compared to lightly doped samples, indeed this is an option to improve the conductivity in the material for certain dopants, e.g., In, Sc and Yb. Interestingly, at the same level of doping the proton conductivity differs significantly for different acceptors dopants. The effects of co-doping at the B-site, e.g. BaZr0.9In0.05M0.05O3-d (M = Ga and Yb) were investigated. Surprisingly, lower proton conductivity was obtained for these co-doped samples compared to the sample containing a single dopant ion e.g. BaZr0.9M0.1O3-d (M = Ga, In and Yb).It was also confirmed that samples with smaller grain size show lower total proton conductivity due to high grain-boundary resistance.Through the present work an increased understanding of the factors influencing the proton conductivity in acceptor doped BaZrO3 has been obtained. In particular, the highly doped materials were found to be of considerable interest in the effort of producing materials with high proton conductivity

Acceptor-Doped BaZrO3 Perovskite: Synthesis, Structure and Proton Conductivity.

Acceptor-doped perovskite oxides exhibit significant proton conductivity in hydrogen containing atmospheres. Therefore, they have potential for use as separator materials for various electrochemical devices including gas sensors, electrolysers and fuel cells. For example, yttrium doped BaZrO3 perovskites have shown high bulk proton conductivity and high chemical stability. However, significant grain boundary resistance has subdued the technological applications.The work constituting this thesis has mainly been focused on synthesis, structural characterisation and electrochemical investigations of acceptor-doped BaZr1-xMxO3-d (M = Ga3+, Sc3+, In3+, Yb3+ and Y3+: x = 0-0.75) perovskite oxides in bulk form. The polycrystalline samples were prepared via a traditional solid-state sintering route and by wet chemical routes. A combination of techniques such as x-ray and neutron powder diffraction, thermogravimetry, scanning electron microscopy (SEM) and impedance spectroscopy (IS) have been used to characterize the samples. Rietveld analysis of high resolution low temperature neutron powder diffraction data revealed that the deuteron site was localised at, or close to, the 12h crystallographic position of BaZr0.5In0.5O2.5(OD)0.5. It was also confirmed that the hydration/deuteration reaction caused an expansion of the cell parameter, while keeping the lattice symmetry, and thus the basic structure intact. Moreover, from Rietveld analysis of the neutron data the oxygen vacancy concentration was determined and they were found to be statistically distributed in the structure. Heavily doped samples showed higher proton conductivity compared to lightly doped samples, indeed this is an option to improve the conductivity in the material for certain dopants, e.g., In, Sc and Yb. Interestingly, at the same level of doping the proton conductivity differs significantly for different acceptors dopants. The effects of co-doping at the B-site, e.g. BaZr0.9In0.05M0.05O3-d (M = Ga and Yb) were investigated. Surprisingly, lower proton conductivity was obtained for these co-doped samples compared to the sample containing a single dopant ion e.g. BaZr0.9M0.1O3-d (M = Ga, In and Yb).It was also confirmed that samples with smaller grain size show lower total proton conductivity due to high grain-boundary resistance.Through the present work an increased understanding of the factors influencing the proton conductivity in acceptor doped BaZrO3 has been obtained. In particular, the highly doped materials were found to be of considerable interest in the effort of producing materials with high proton conductivity

Proton conductivity in acceptor-doped lanthanide based pyrochlore oxides

A high interest in developing new materials for SOFC applications in the temperature range of approximately 200–500 degrees C has been growing lately. The lower activation energies for proton (H+) mobility can give higher conductivity in this temperature range. A demand on finding new H+ conducting materials as electrolytes in fuel cells is thereby the result. The materials should preferably have high H+ concentration and mobility, be chemically stable at the required operating temperatures and be electronically insulating. Although structure-types other than the well known perovskites, such as pyrochlores, have been of interest as novel materials for protonic devices, significantly less research has been carried out on these systems. This makes further detailed investigation of proton conduction in pyrochlores an important step on the way to finding the next family of materials for proton conducting applications. This thesis presents the synthesis and characterization of the structure and conductivity of several pyrochlore oxide compounds. The synthesis for all the studies was concentrated on traditional solid state sintering, while characterization have been conducted with X-ray diffraction (XRD), thermogravimetric analysis (TGA), infrared spectroscopy (IR), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Determination of particle size distribution (PSD), calculations of transport numbers via the electromotive force method (EMF) and EIS in a controllable gas cell for the Sm2-xCaxTi2O7-x/2 material were carried out (Paper IV). The proton conductivity in pyrochlore materials has been examined for several acceptor doped compounds, such as A2-xCaxB2O7-x/2 (A = La, Sm, Yb; B = Ti, Sn, Zr, Ce) and A2B2-xYxO7-x/2 (A = Sm; B = Ti, Sn). The materials exhibit high purity and chemical stability. The effects of A- and B-site doping, the significance of the B-site ion, and the importance of the lanthanide size at the A-site were all studied in relation to their impact on proton conductivity. Expansions or reductions of the cell depending on doping site or choice of A- and B-site ions were confirmed by 2θ-shifts in the XRD patterns. TGA gave affirmative results regarding the loss of protons from the hydrated samples at expected temperatures. The results were linked with IR spectra confirming peaks at characteristic positions for O-H stretch vibrations as well as a isotopic shifts for samples treated under heavy water. The EIS measurements showed overall elevated conductivities under wet gas conditions and isotope effects with deuterated water. The A-site doped samples showed close to one order of magnitude higher conductivities compared to the B-site doped samples. Varying the B-site ion with increasing ionic radius (Ti, Sn, Zr, Ce) showed higher proton conductivity levels for the B-site ions with smaller ionic radii and higher electronegativity. Further, the effect of the lanthanide contraction on proton conduction could be seen through varying the A-site constituent along the lanthanide group. The EMF and the EIS measurements carried out under controlled gas atmospheres gave transport numbers supporting dominant proton conductivity in Sm1.92Ca0.08Ti2O7-x/2. Large electrode polarization resistances were noted for all temperatures and gas concentrations. The Gorelov method was used for correction. This work provides a wider understanding of the influence of the doping site, choice of A and B-site ions and microstructure on proton conduction in pyrochlore systems