MATHEMATICAL MODELING OF MASS TRANSFER AND REACTION IN AN INNOVATIVE SOLID OXIDE FUEL CELL

IDEAL-Cell is an innovative concept of a solid oxide fuel cell (SOFC), which is supposed to possess some advantages over conventional SOFCs by building an independent compartment to evacuate water that normally is present either at the anode in ACFCs or at the cathode in PCFCs. The namely advantages have been demonstrated by thermodynamic analysis in chapter 1 that IDEAL cell can potentially provide 15% higher Nernst potential than PCFCs and 30% higher Nernst potential than ACFCs at high fuel utilizations. Modelling activities in this innovative fuel cell are mainly concentrated on its peculiar feature: dual membrane which consists of two dense electrolytes and central membrane in the middle. This particular design brings many challenges for describing complex phenomenon of mass transfer and mechanism of ionic recombination reaction, whose understanding requires dedicated experimental and theoretical work. In this thesis, a series of mathematic models for characterizing mass transfer in dense electrolyte (chapter 2), mass transfer in porous composite central membrane (chapter 3), and kinetic reaction in central membrane (chapter 4) have been built and preliminarily validated by experimental results. These models enable one to theoretically explain electrochemical processes, to indicate technique difficulties confronted in processing and to predict steady-state response of the IDEAL-Cell under varying operating conditions (temperatures and gas atmospheres). In the presence of more effective data to validate and modify, these models are useful to support the design of materials, components and IDEAL-Cell prototype as well

Thermochemical recycling of hydrolyzed NaBH4. Part II: Systematical study of parameters dependencies

This paper focuses on the yields of both main product NaBH4and byproduct MgH2of the thermochemical process. The influence of parameters such as i) the isothermal reaction temperature in the range 480 Ce660 C, ii) the stoichiometric ratio of solid reactants NaBO2:Mg prepared from 1:2 to 1:8, iii) H2pressure supplied from 2 to 31 bars and iv) the reaction time kept at isotherm from 0 to 16 h have been systematically investigated. The yields are estimated by in-situ and ex-situ evaluations. Two temperature regimes for MgH2 and NaBH4formation are recognized from 370 C to 450 C and above 500 C respectively. With regard to NaBH4regeneration, temperature is the most important factor that positively accelerates the apparent reaction rate between 500 C and 650 C providing a sufficient H2 pressure. To efficiently obtain high NaBH4 yield mixtures with molar stoichiometric ratio between solid reactants not less than 1:4 is suggested. Experimental results also reveal that at 12 bars of H2pressure high NaBH4yield is obtained. Hence, more efficient way to improve mass transfer of solid reactants (e.g. advance reactor enhances mobility of reactants) rather than increasing H2 pressures is advised. Under optimized condition, 100% conversion of NaBO2can be achieved within 1.5 h

Thermodynamic and kinetic studies of NaBH4 regeneration by NaBO2\u2013Mg\u2013H2 ternary system at isothermal condition

NaBH4is a candidate for H2storage in solid phase. NaBH4hydrolysis readily produces H2 gas and NaBO2which can regenerate NaBH4with pressurized hydrogen and the aid of a reducing agent like Magnesium above 500 C. This paper deals with the NaBH4thermochemical regeneration from the NaBO2eMgeH2ternary system at isothermal temperatures between 558 and 634 C and H2 pressure in the range 2e31 bar. A simplified Langmuir adsorption model has been applied for the interpretation of the in-situ H2pressure variations. The applied model is zero-dimensional but provides a reasonable approach to identify the rate determining step and acquire relevant thermodynamic and kinetic parameters such as equilibrium constant (Keq), Gibbs free energy (DrG 0 ) and reaction rate coefficients (k). The study provides an apparent activation energy and Gibbs free energy of this process of 29.2 kJ/mol and76.9 kJ/mol, respectively

Thermochemical recycling of hydrolyzed NaBH4. Part I: In-situ and ex-situ evaluations

This paper presents a combined application of in-situ and ex-situ evaluations of products obtained by thermochemical recycling process of NaBH4 from NaBO2eMgeH2 ternary system. In-situ yield evaluation according to on-line pressure measurements of hydrogen gas, although already applied by some authors, is presented here with an innovative analysis which offers a thorough comprehension of the NaBH4 regeneration process making feasible the qualitative and quantitative estimations of product and by-product. On the basis of in-situ observations, NaBH4formation in presence of NaBO2eMgeH2ternary system initiates slowly from 400 C and accelerates above 550 C to the melting point of Mg at 650 C. MgH2is significantly produced between 370 C and 450 C in both heating and cooling. The amounts of these products produced at the different temperatures are clearly detectable by hydrogen pressure drops. Additionally, ex-situ evaluations by titration of NaBH4 have also been performed in order to confirm the correct interpretation of the experimental data

A Facile Approach for Syntheses of Nearly Monodisperse Nanocrystals: Sol-Solvothermal Process

A novel facile approach, sol-solvothermal process, is reported here for syntheses of nearly monodisperse inorganic nanocrystals (NCs), such as elementary metals, simple metal oxides, composite oxides, and selenides by using inexpensive metal salts and environmental friendly solvents as reactants without a further size-selection treatment. The results revealed that mean diameter of the synthetic NCs measured by Dynamic Light Scattering (DLS) was consistent with the observed size by Field-emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM) images, demonstrating the agglomeration-free feature of the nanosized crystals. Moreover, the particle size and morphology of the synthetic NCs could be effectively controlled under various appropriate sets of experimental conditions