Modeling Nucleation and Growth of Zinc Oxide During Discharge of Primary Zinc-Air Batteries

Metal-air batteries are among the most promising next-generation energy storage devices. Relying on abundant materials and offering high energy densities, potential applications lie in the fields of electro-mobility, portable electronics, and stationary grid applications. Now, research on secondary zinc-air batteries is revived, which are commercialized as primary hearing aid batteries. One of the main obstacles for making zinc-air batteries rechargeable is their poor lifetime due to the degradation of alkaline electrolyte in contact with atmospheric carbon dioxide. In this article, we present a continuum theory of a commercial Varta PowerOne button cell. Our model contains dissolution of zinc and nucleation and growth of zinc oxide in the anode, thermodynamically consistent electrolyte transport in porous media, and multi-phase coexistance in the gas diffusion electrode. We perform electrochemical measurements and validate our model. Excellent agreement between theory and experiment is found and novel insights into the role of zinc oxide nucleation and growth and carbon dioxide dissolution for discharge and lifetime is presented. We demonstrate the implications of our work for the development of rechargeable zinc-air batteries.Comment: 16 pages, 8 figures, Supplementary Information uploaded as ancillary fil

Modellierung und Simulation Primärer Zink-Luft-Knopfzellen

Primäre Zink-Luft-Knopfzellen werden bereits erfolgreich in Hörgeräten eingesetzt. Für Anwendungen in portablen Geräten, sowie im Rahmen der Elektromobilität und der Energiewende, werden allerdings elektrisch wiederaufladbare Energiespeicher benötigt, weshalb an sekundären Zink-Luft-Zellen geforscht wird. Diese haben allerdings zum aktuellen Stand der Forschung noch eine sehr geringe Lebensdauer. In dieser Arbeit stellen wir ein thermodynamisch konsistentes, eindimensionales Modell für die Transportvorgänge in Zink-Luft-Knopfzellen, unter Berücksichtigung der Reaktionen und porösen Elektroden, auf. Die Modellgleichungen diskretisieren wir mit der Finite-Volumen-Methode und implementieren diese in Matlab und erhalten so eine Simulation der Zelle. Wir rechtfertigen unsere Ortsdiskretisierung durch eine Fehlerabschätzung, die auf Dreiecksgittern auch in zwei Dimensionen gilt. Die Zeitschritte berechnen wir mit dem Solver ode15i. Um dieses Verfahren numerisch zu validieren, berechnen wir die experimentelle Konvergenzordnung an Hand der Wärmeleitungsgleichung als Testproblem. Wir untersuchen das Entladeverhalten von Zink-Luft-Knopfzellen bei konstanter Stromstärke experimentell und vergleichen die Resultate mit denen unserer Simulation. Durch die Analyse der Ergebnisse erhalten wir einen guten Einblick in die Prozesse beim Entladevorgang in der Batterie. Außerdem untersuchen wir die Selbstentladung der Zelle durch die Wechselwirkung mit Kohlendioxid aus der Luft experimentell und führen eine entsprechende Simulation durch. Die Ergebnisse stimmen qualitativ gut überein und liefern eine Aussage über die Lebensdauer der Zelle

Modeling Zinc-Air Batteries with Aqueous Electrolytes

Emerging markets such as electric mobility and renewable power generation are driving a demand for high-performance electrochemical energy storage. Zinc-air batteries are a promising technology due to their high theoretical specific energy, use of cheap materials, and superior operational safety. But they suffer from effects such as poor cycling stability and self-discharge due to carbonate formation in the alkaline electrolyte. The EU Horizon 2020 project Zinc Air Secondary (ZAS!) aims to overcome these limitations and develop a high-performance rechargeable zinc-air battery. Modelling and simulation of novel electrolytes provide crucial support towards achieving this goal. We have developed a 1D finite volume continuum model implemented in MATLAB. Our model includes a thermodynamically consistent description of mass transport in concentrated electrolytes, multi-phase coexistence in porous media, and reaction kinetics with considerations for anode passivation due to types I and II ZnO, among other effects. Within this framework, we simulate performance on mesoscopic and macroscopic scales. Zinc-air batteries have long been commercialized as primary batteries for hearing-aids. The contamination of potassium hydroxide electrolyte due to carbon dioxide from ambient air is known to limit the lifetime of alkaline zinc-air batteries to just a few months. This reaction is irreversibly forms carbonate species and degrades cell performance by consuming hydroxide. Our simulations show that as carbonate species form, the hydroxide concentration decreases linearly with time. The depletion of hydroxide decreases the ionic conductivity and in combination with the logarithmic dependence of anode overpotential on hydroxide concentration, this effect leads to a marked decrease in cell potential over time. Carbon dioxide reactions do not occur in non-alkaline electrolytes. Near-neutral chloride aqueous electrolytes have been proposed to improve zinc-air battery lifetime. These electrolytes do exhibit superior lifetime performance, but also have lower nominal conductivity values. This inhibits ionic transport in the electrolyte, and can be rate-limiting for large geometries. We present the first model-based analysis of zinc-air batteries with near-neutral electrolytes proposed to solve carbon dioxide poisoning

Modeling Secondary Zinc-Air Batteries with Advanced Aqueous Electrolytes

Advances in electric mobility and renewable power generation are driving a demand for high-performance electrochemical energy storage. Zinc-air batteries are a promising technology due to their high theoretical specific energy, use of cheap materials, and superior operational safety. But they suffer from effects such as poor cycling stability and self-discharge due to carbonate formation in the alkaline electrolyte. Modelling and simulation of zinc air batteries with novel electrolytes provide crucial support towards achieving this goal. We have developed a 1D finite volume continuum model implemented in MATLAB. Our model includes a thermodynamically consistent description of mass transport in concentrated electrolytes, multi-phase coexistence in porous media, and reaction kinetics with considerations for anode passivation due to types I and II ZnO, among other effects. Within this framework, we simulate performance on mesoscopic and macroscopic scales. The contamination of potassium hydroxide electrolyte due to carbon dioxide from ambient air is known to limit the lifetime of alkaline zinc-air batteries to just a few months. This reaction irreversibly forms carbonate species and degrades cell performance by consuming hydroxide. Our simulations and experimental results show that as carbonate species form, the hydroxide concentration decreases linearly with time. The depletion of hydroxide decreases the ionic conductivity and slows down zinc dissolution leading to a marked decrease in cell potential over time. Carbon dioxide reactions do not occur in non-alkaline electrolytes. Near-neutral chloride aqueous electrolytes have been proposed to improve zinc-air battery lifetime. These electrolytes utilize an ammonium chloride buffer solution to stabilize the pH during discharge. However, even small changes in pH may significantly alter the dominant aqueous zinc species. Due to this effect, the final discharge product may shift from ZnO to Zn(NH3)2Cl2 or Zn(OH)1.6Cl0.4∙(H2O)0.2, causing serious losses in the conductivity of the electrolyte and theoretical specific energy of the cell. We present the first model-based analysis of zinc-air batteries with near-neutral electrolytes. This work was supported by the EU Horizon 2020 project Zinc Air Secondary (ZAS!

Value of self-performed joint counts in rheumatoid arthritis patients near remission

INTRODUCTION: To determine the validity and reliability of patients' self-performed joint counts compared to joint counts by professional assessors in rheumatoid arthritis (RA) patients in different disease activity states. METHODS: In patients with established RA we determined the inter-rater reliability of joint counts performed by an independent evaluator and the patient using intraclass correlation (ICC), and agreement on activity in individual joints by kappa statistics. We also performed longitudinal analyses to assess consistency of assessments over time. Finally, we investigated the concordance of joint counts of different assessors in patients with different levels of disease activity. RESULTS: The reliability of patient self-performed joint counts was high when compared to independent objective assessment (ICC; 95%confidence interval (CI)) for the assessment of swelling (0.32; 0.15 to 0.46) and tenderness (0.75; 0.66 to 0.81), with higher agreement for larger joints (kappa: 0.57 and 0.45, respectively) compared to smaller joints (metacarpo-phalangeal joint (MCPs): 0.31 and 0.45; and proximal interphalangeal joint (PIPs): 0.22 and 0.47, for swelling and tenderness, respectively). Patients in remission according to the Simplified Disease Activity Index (SDAI ≤ 3.3) showed better concordance of the joint counts (swollen joint count (SJC) ties 25/37, tender joint count (TJC) ties 26/37) compared to moderate/high disease activity states (SDAI > 11; MDA/HDA: SJC ties 9/72, TJC ties 21/72). Positive and negative predictive values regarding the presence of SDAI remission were reasonably good (0.86 and 0.95, respectively). A separate training session for patients did not improve the reliability of joint assessment. The results were consistent in the longitudinal analyses. CONCLUSIONS: Self-performed joint counts are particularly useful for monitoring in patients having attained remission, as these patients seem able to detect state of remission

К вопросу об изменяемости холерных вибрионов в воде : экспериментальное исследование : диссертация на степень магистра фармации

http://tartu.ester.ee/record=b1975902~S1*es

Work stress and reduced health in young physicians: prospective evidence from Swiss residents

Objectives: Job stress, investigated by the effort-reward model in various working environments in different countries, has been widely reported, yet studies addressing physicians are lacking. The present study investigated the perceived job stress, its association with the amount of working hours, and its impact on young physicians' self-reported health and their satisfaction with life during residency. Methods: In a prospective study design, a cohort of Swiss medical school graduates was followed up, beginning in 2001. In their second and fourth years of residency, 433 physicians assessed their effort-reward imbalance, overcommitment, physical and mental well-being and satisfaction in life. Taking the longitudinal design into account, four categories of stressed residents were defined: (1) subjects not reporting high work stress at either measurement, (2) subjects reporting high work stress in the second but not in the fourth year of residency, (3) subjects with onset of high work stress in fourth year and (4) residents reporting high work stress at both measurements. Results: All components of the perceived stress at work were significantly correlated with the amount of working hours, effort showing the highest correlation. While two-thirds of the participants do not report high work stress, assessed by the extrinsic part of the effort-reward imbalance model (the ratio between effort and reward) and 12% show a decrease of stress over time, there are 15% with an increase of stress over time, and 10% with persistently high stress experience. In terms of the intrinsic stress component (overcommitment), 71% show low values, 12% show a decrease, 9% an increase and 8% constantly high values. The groups with constant and increasing extrinsic and intrinsic stress experience exhibit significantly worse health and life satisfaction compared to the remaining groups, after controlling for gender and baseline health. Conclusions: Stress at work in young physicians, especially when being experienced over a longer period in postgraduate training, has to be a matter of concern because of its negative impact on health and life satisfaction and the risk of developing symptoms of burnout in the long ru

A retrospective analysis of submissions, acceptance rate, open peer review operations, and prepublication bias of the multidisciplinary open access journal Head & Face Medicine

<p>Abstract</p> <p>Background</p> <p><it>Head & Face Medicine </it>(HFM) was launched in August 2005 to provide multidisciplinary science in the field of head and face disorders with an open access and open peer review publication platform. The objective of this study is to evaluate the characteristics of submissions, the effectiveness of open peer reviewing, and factors biasing the acceptance or rejection of submitted manuscripts.</p> <p>Methods</p> <p>A 1-year period of submissions and all concomitant journal operations were retrospectively analyzed. The analysis included submission rate, reviewer rate, acceptance rate, article type, and differences in duration for peer reviewing, final decision, publishing, and PubMed inclusion. Statistical analysis included Mann-Whitney U test, Chi-square test, regression analysis, and binary logistic regression.</p> <p>Results</p> <p><it>HFM </it>received 126 articles (10.5 articles/month) for consideration in the first year. Submissions have been increasing, but not significantly over time. Peer reviewing was completed for 82 articles and resulted in an acceptance rate of 48.8%. In total, 431 peer reviewers were invited (5.3/manuscript), of which 40.4% agreed to review. The mean peer review time was 37.8 days. The mean time between submission and acceptance (including time for revision) was 95.9 days. Accepted papers were published on average 99.3 days after submission. The mean time between manuscript submission and PubMed inclusion was 101.3 days. The main article types submitted to HFM were original research, reviews, and case reports. The article type had no influence on rejection or acceptance. The variable 'number of invited reviewers' was the only significant (p < 0.05) predictor for rejection of manuscripts.</p> <p>Conclusion</p> <p>The positive trend in submissions confirms the need for publication platforms for multidisciplinary science. <it>HFM's </it>peer review time comes in shorter than the 6-weeks turnaround time the Editors set themselves as the maximum. Rejection of manuscripts was associated with the number of invited reviewers. None of the other parameters tested had any effect on the final decision. Thus, <it>HFM's </it>ethical policy, which is based on Open Access, Open Peer, and transparency of journal operations, is free of 'editorial bias' in accepting manuscripts.</p> <p>Original data</p> <p>Provided as a downloadable tab-delimited text file (URL and variable code available under section 'additional files').</p