Generalized Poisson--Nernst--Planck-based physical model of O2_2 I LSM I YSZ electrode

The paper presents a generalized Poisson-Nernst-Planck model of an yttria-stabilized zirconia electrolyte developed from first principles of nonequilibrium thermodynamics which allows for spatial resolution of the space charge layer. It takes into account limitations in oxide ion concentrations due to the limited availability of oxygen vacancies. The electrolyte model is coupled with a reaction kinetic model describing the triple phase boundary with electron conducting lanthanum strontium manganite and gaseous phase oxygen. By comparing the outcome of numerical simulations based on different formulations of the kinetic equations with results of EIS and CV measurements we attempt to discern the existence of separate surface lattice sites for oxygen adatoms and O2- from the assumption of shared ones. Furthermore, we discern mass-action kinetics models from exponential kinetics models

Characterization of Commercial Polymer–Carbon Composite Bipolar Plates Used in PEM Fuel Cells

Bipolar plates represent a crucial component of the PEM fuel cell stack. Polymer–carbon composites are recognized as state-of-the-art materials for bipolar plate manufacturing, but their use involves a compromise between electrical and heat conductivity, mechanical strength and costs. Thus, all key parameters must be considered when selecting a suitable plate satisfying the demands of the desired application. However, data relevant to commercial materials for such selection are scarce in the open literature. To address this issue, 13 commercially available polymer–carbon composites are characterised in terms of the following parameters: through-plane conductivity, hydrogen permeability, mechanical strength, water uptake, density, water contact angle and chemical stability. None of the materials tested reached the DOE target for electrical conductivity, while five of the materials met the target for flexural strength. The overall best-performing material showed a conductivity value of 50.4 S·cm−1 and flexural strength of 40.1 MPa. The data collected provide important supporting information in selecting the materials most suitable for the desired application. In addition, the key parameters determined for each bipolar plate supply important input parameters for the mathematical modelling of fuel cells

Elektrochemicka redukce dusicnanovych iontu.

The present work deals with a method of NO_3 removal from drinking water based on a combination of ion exchange and electrochemical treatment of the regenerant solution. The main part focuses on the electrochemical reduction of NO_3 ions in a concentrated NaHCO_3 solution.Summary in EnglishAvailable from STL, Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi

Kinetika degradace Pt během provozu vysokoteplotního PEM palivového článku Část III: Napěťově závislá degradace Pt v experimentech s individuálními palivovými články

Degradace Pt katalyzátoru je jedním z největších problémů ve vysokoteplotních palivových článcích s PEM membránami (HT PEM FC). Přestože na toto téma bylo napsáno mnoho publikací, nebyl doposud jasně objasněn vztah mezi růstem velikosti nanočástic Pt a provozními podmínkami HT PEM FC. Cílem předkládané práce je určit závislost růstu nanočástic Pt na provozním napětí HT PEM FC pomocí experimenálních pokusů s individuálními palovovými články (single cell) s následnou post-mortem analýzou katalytických vrstev na obou elektrodách. Dlouhodobé experimenty za dobře definovaných podmínek prováděné za konstatního napětí v kombinaci s několika post-mortem instrumentálními metodami umožnily předpověď vývoje distribuce nanočástic Pt v čase. Při vyšších napětích byl růst velikosti nanočástic Pt méně výrazný než při napětích nižších. To je pravděpodobně způsobeno změnou rychlost určujícího kroku při růstu velikosti nanočástic Pt.Degradation of the Pt catalyst is one of the most serious problems related to the high-temperature fuel cell with a proton-exchange membrane (HT PEM FC). Despite many publications on this topic, no clear relationship between Pt nanoparticle growth and HT PEM FC operating conditions has been formulated yet. The goal of the presented study is to determine the dependence of Pt nanoparticle growth on the operational voltage of the HT PEM FC by means of experimental single-cell testing with subsequent post mortem analysis of the catalyst layers on the two electrodes. Well-defined, long-term tests performed at constant voltage in combination with several post mortem instrumental methods enabled the prediction of the development of Pt nanoparticle distribution. At higher voltages, Pt nanoparticle growth was less pronounced than at low voltages. This was likely caused by the change in the rate-limiting step in Pt nanoparticle growth

Impact of Preparation Method and Y2O3 Content on the Properties of the YSZ Electrolyte

This study is an effort to cover and interconnect multiple aspects of the fabrication of the yttria-stabilized zirconia (YSZ) from powder preparation to a solid electrolyte suitable for utilization in solid oxide cells. Thus, a series of YSZ electrolytes was prepared, differing in the content of the Y2O3 dopant and in the method of preparation. Combustion synthesis along with the thermal decomposition of precursors was used for YSZ powder synthesis with a dopant content of 8 to 18 mol.%. Post-synthesis treatment of the powder was necessary for achieving satisfactory quality of the subsequent sintering step. The morphology analyses of the YSZ powders and sintered electrolytes produced proved that small particles with a uniform size distribution are essential for obtaining a dense electrolyte. Furthermore, the conductivity of YSZ electrolytes with different Y2O3 contents was examined in the temperature range of 400 to 800 °C. The lowest conductivity was found for the sample with the highest Y2O3 content. The obtained results enable the preparation methods, YSZ powder morphology, and composition to be connected to the mechanical and electrochemical properties of the YSZ electrolyte. Thus, this study links every step of YSZ electrolyte fabrication, which has not been sufficiently clearly described until now

Generalized Poisson--Nernst--Planck-based physical model of O2_2 I LSM I YSZ electrode

The paper presents a generalized Poisson-Nernst-Planck model of an yttria-stabilized zirconia electrolyte developed from first principles of nonequilibrium thermodynamics which allows for spatial resolution of the space charge layer. It takes into account limitations in oxide ion concentrations due to the limited availability of oxygen vacancies. The electrolyte model is coupled with a reaction kinetic model describing the triple phase boundary with electron conducting lanthanum strontium manganite and gaseous phase oxygen. By comparing the outcome of numerical simulations based on different formulations of the kinetic equations with results of EIS and CV measurements we attempt to discern the existence of separate surface lattice sites for oxygen adatoms and O2- from the assumption of shared ones. Furthermore, we discern mass-action kinetics models from exponential kinetics models

The role of ion exchange membrane in vanadium oxygen fuel cell

The effect of membrane properties on the vanadium-oxygen fuel cell performance was studied on a series of commercially available ion exchange membranes of different thickness and ion exchange capacity by selected characterization techniques including electrochemical impedance spectroscopy (ohmic and charge transfer resistance), steady load curves (performance stability) and galvanostatic charge-discharge cycles (efficiencies and capacity decay). Performance stability of the fuel cell was studied under defined conditions (state of charge, temperature, air flow rate) using continuous charging of vanadium electrolyte. In contrast to the previous studies, our results revealed that the membrane affects the fuel cell performance mainly via water management in the catalytic layer of gas diffusion cathode, while vanadium permeation across the membrane has only a minor impact. Generally, the fuel cell shows improved performance stability for more conductive membranes (thinner and with higher ion-exchange capacity), partially due to reduced ohmic losses, but more significantly due to the better ability of the membrane to drain water from the cathode via osmosis, which prevents the flooding of the cathodic catalytic layer. With the optimized membrane, we achieved stable fuel cell performanc at the highest current and power density values reported (75 mA cm−2 and 57 mW cm−2 in 50% state of charge)

Generalized Poisson--Nernst--Planck-based physical model of O2_2 I LSM I YSZ electrode

The paper presents a generalized Poisson-Nernst-Planck model of an yttria-stabilized zirconia electrolyte developed from first principles of nonequilibrium thermodynamics which allows for spatial resolution of the space charge layer. It takes into account limitations in oxide ion concentrations due to the limited availability of oxygen vacancies. The electrolyte model is coupled with a reaction kinetic model describing the triple phase boundary with electron conducting lanthanum strontium manganite and gaseous phase oxygen. By comparing the outcome of numerical simulations based on different formulations of the kinetic equations with results of EIS and CV measurements we attempt to discern the existence of separate surface lattice sites for oxygen adatoms and O2- from the assumption of shared ones. Furthermore, we discern mass-action kinetics models from exponential kinetics models

Alkali doped poly (2,5-benzimidazole) membrane for alkaline water electrolysis: Characterization and performance

The properties and performance of linear and cross-linked KOH doped ABPBI membranes as electrolyte/separator for zero gap alkaline water electrolysis cells are evaluated and compared with a commercial Zirfon® diaphragm. Stability in alkaline environment, swelling, thermal properties, water sorption, KOH uptake and conductivity of linear (L-ABPBI) and cross-linked (C-ABPBI) membranes doped with different concentrations of KOH are analyzed. Linear membranes show stability up to 3.0 mol·dm−3 KOH doping, while cross-linked membranes are stable up to 4.2 mol·dm−3 KOH doping. Both kinds of membranes exhibit good thermal stability and reasonable specific ionic conductivity at 22 °C in the range between 7 and 25 mS·cm−1, being slightly higher the conductivity of C-ABPBI membranes than that of L-ABPBI ones. In short-term electrolysis tests both L-ABPBI and C-ABPBI membranes show better performance than Zirfon diaphragm in the range from 50 to 70 °C. A current density of 335 mA·cm−2 at a cell voltage of 2.0 V is attained with C-ABPBI membranes doped in 3 mol·dm−3 KOH at 70 °C, a performance comparable with that of commercial units operating at temperatures ca. 80 °C and 30 wt% KOH (6.7 mol·dm−3) as electrolyte.Fil: Díaz, Liliana Alicia. Instituto Nacional de Tecnología Industrial; ArgentinaFil: Hnát, Jaromír. University of Chemistry and Technology Prague; República ChecaFil: Heredia, Nayra. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; ArgentinaFil: Bruno, Mariano Martín. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; ArgentinaFil: Viva, Federico Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; ArgentinaFil: Paidar, Martin. University of Chemistry and Technology Prague; República ChecaFil: Corti, Horacio Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; ArgentinaFil: Bouzek, Karel. University of Chemistry and Technology Prague; República ChecaFil: Abuin, Graciela Carmen. Instituto Nacional de Tecnología Industrial; Argentin