Oxygen Diffusion and Surface Exchange Coefficients of Porous La0.6Sr0.4Co0.2Fe0.8O3-δ Decorated with Co3O4 Nanoparticles

This work presents a comparative study of the diffusion (Dchem) and surface exchange coefficients (kchem) of porous La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) and Co3O4 nanoparticles decorated LSCF electrodes. The study was carried out using the 3DT-EIS method, which combines Electrochemical Impedance Spectroscopy experiments with FIB-SEM tomography data through an adapted Transmission Line - Adler Lane Steele electrochemical model. A reduction of the polarization resistance of about 60% was measured for the Co3O4 decorated LSCF respect to the reference LSCF cathode, in air at 700 °C. The Co3O4 decoration was found to modify the ORR surface reaction limiting mechanism from O2 dissociation to O-ion incorporation, whereas the diffusion coefficient was not modified by the decoration, which represents a surface diffusion process for both electrodes. After the EIS measurements, the Co3O4 particles were almost no longer visible by Field-Emission SEM on the surface of the decorated sample, but signs that these particles play an active role in Sr Segregation were observed by STEM-EDS, in particular by concentrating the segregated SrO in the surroundings of the decorated particles.

Ship-based estimates of momentum transfer coefficient over sea ice and recommendations for its parameterization

A major source of uncertainty in both climate projections and seasonal forecasting of sea ice is inadequate representation of surface–atmosphere exchange processes. The observations needed to improve understanding and reduce uncertainty in surface exchange parameterizations are challenging to make and rare. Here we present a large dataset of ship-based measurements of surface momentum exchange (surface drag) in the vicinity of sea ice from the Arctic Clouds in Summer Experiment (ACSE) in July–October 2014, and the Arctic Ocean 2016 experiment (AO2016) in August–September 2016. The combined dataset provides an extensive record of momentum flux over a wide range of surface conditions spanning the late summer melt and early autumn freeze-up periods, and a wide range of atmospheric stabilities. Surface exchange coefficients are estimated from in situ eddy covariance measurements. The local sea-ice fraction is determined via automated processing of imagery from ship-mounted cameras. The surface drag coefficient, CD10n, peaks at local ice fractions of 0.6–0.8, consistent with both recent aircraft-based observations and theory. Two state-of-the-art parameterizations have been tuned to our observations with both providing excellent fits to the measurements.

Objective Calibration of Numerical Weather Prediction Model: Application on Fine Resolution COSMO Model over Switzerland

The objective calibration method originally performed on regional climate models is applied to a fine horizontal resolution Numerical Weather Prediction (NWP) model over a mainly continental domain covering the Alpine Arc. The method was implemented on the MeteoSwiss COSMO (consortium for a small-scale modeling) model with a resolution of 0.01° (approximately 1 km). For the model calibration, five tuning parameters of the parameterization schemes affecting turbulence, soil-surface exchange and radiation were chosen. A full year was simulated, with the history of the soil included (hindcast) to find the optimal parameter value. A different year has been used to give an independent assessment of the impact of the optimization process. Although the operational MeteoSwiss model is already a well-tuned configuration, the results showed that a slight model performance gain is obtained by using the Calibration of COSMO (CALMO) methodology.

Surface and Bulk Oxygen Kinetics of BaCo0.4Fe0.4Zr0.2−XYXO3−δ Triple Conducting Electrode Materials

Triple ionic-electronic conductors have received much attention as electrode materials. In this work, the bulk characteristics of oxygen diffusion and surface exchange were determined for the triple-conducting BaCo0.4Fe0.4Zr0.2−XYXO3−δ suite of samples. Y substitution increased the overall size of the lattice due to dopant ionic radius and the concomitant formation of oxygen vacancies. Oxygen permeation measurements exhibited a three-fold decrease in oxygen permeation flux with increasing Y substitution. The DC total conductivity exhibited a similar decrease with increasing Y substitution. These relatively small changes are coupled with an order of magnitude increase in surface exchange rates from Zr-doped to Y-doped samples as observed by conductivity relaxation experiments. The results indicate that Y-doping inhibits bulk O2− conduction while improving the oxygen reduction surface reaction, suggesting better electrode performance for proton-conducting systems with greater Y substitution.

Pure oxygen separation from air using dual-phase SDC-SCFZ disc membrane: A modelling approach

Novel Ce0.8Sm0.2O1.9-SrCo0.4Fe0.55Zr0.05O3-δ (SDC-SCFZ) disc membranes consist of 25 wt.% SDC fluorite ionic conducting phase and 75 wt.% SCFZ perovskite mixed conducting phase, which is more promising than perovskite oxide SCFZ single-phase membrane in terms of the oxygen permeation flux. This work features a modelling approach to simulate the oxygen permeation fluxes of the SDC-SCFZ membrane. Simplified model equations from the Zhu model and Xu-Thomson model based on the limiting cases of surface exchange reactions and bulk diffusion are compared. The Zhu model is found to be more applicable for the membranes with overall good correlation and low sum of squared error. Furthermore, modelling studies revealed that the oxygen transport is limited by surface exchange reactions from 700 to 850 °C and a mixture of both limiting cases above 850 up to 950 °C. It is concluded that the membranes exhibit high oxygen permeation flux of up to 2×10−6 mol s−1 cm−2 at 950 °C with Pair of 5 atm and Po 2 of 0.005 atm. The optimum range of operating conditions of the membrane are found to be at 950 °C with minimum Pair of 1 atm and P11 2 lower than 0.025 atm.

Investigating Neutral and Stable Atmospheric Surface Layers Using Computational Fluid Dynamics

Computational fluid dynamics (CFD) is an effective technique to investigate atmospheric processes at a local scale. For example, in near-source atmospheric dispersion applications, the effects of meteorology, air pollutant sources, and buildings can be included. A prerequisite is to establish horizontally homogeneous atmospheric conditions, prior to the inclusion of pollutant sources and buildings. This work investigates the modelling of the atmospheric surface layer under neutral and stable boundary layer conditions, respectively. Steady-state numerical solutions of the Reynolds averaged Navier–Stokes (RANS) equations were used, including the k-ε turbulence model. Atmospheric profiles derived from the Cooperative Atmosphere-Surface Exchange Study-99 (CASES-99) were used as reference data. The results indicate that the observed profiles of velocity and potential temperature can be adequately reproduced using CFD, while turbulent kinetic energy showed less agreement with the observations under the stable conditions. The results are discussed in relation to the boundary conditions and sources, and the observational data.