A numerical model for solid oxide fuel cells with Ni-infiltrated porous anode has been described. The novel contribution of the work is the development of a semi-continuous film model to describe the infiltrated Ni-phase. This model relates experimentally controllable parameters, namely, Ni- loading, porosity and pore size to the effective electronic conductivity of the Ni-phase and the number of active reaction sites or the triple phase boundary (TPB). The semi-continuous film model was incorporated in a two-dimensional (2D) SOFC model. The 2D model considers the coupled gas-phase transport, charge transport and electrochemical kinetics to directly examine the effect of Ni loading and porosity on the electrochemical performance of Ni-infiltrated SOFC anodes. From the semi-continuous film model, an optimal Ni loading that corresponds to a maximum in TPB length was identified. Comparison of effective electronic conductivity and TPB length for a Ni-infiltrated anode with those for a composite Ni-YSZ anode suggests that an infiltrated Ni anode with adequate electrical conductivity and sufficiently high TPB length can be fabricated even at a very low Ni loading. Comparison of various porous anodes with varying Ni loading, it was determined that maximum electrochemical performance does indeed correspond to anode with maximum TPB length. It was also determined that an infiltrated anode will have higher performance capabilities when compared to the conventional composite electrodes. However, degradation of performance may result due to degradation of connectivity in the infiltrated Ni. The methodology to model the latter effect was also proposed. / Thesis (Master, Chemical Engineering) -- Queen's University, 2012-06-13 13:09:49.182

The reaction of nitric oxide with secondary amines to form diazeniumdiolate anions with the structure R2NN2O2 - has been studied in order to investigate the stereochemistry and mechanism of this reaction. The stereochemical preference of the cis (Z) isomer for these compounds was proved using vibrational spectroscopy, namely infrared spectroscopy (IR) and Raman. Theoretical (B3LYP/aug-cc-pVDZ) rotation barriers for the simple diazeniumdiolate anion, Me2NN(O)=NO- are calculated in the gas phase to be 26.2 kcal/mol with the cis isomer predicted to be stabilized by only 0.5 kcal/mol compared to the trans isomer, therefore stereochemical preference for the cis is due to kinetic rather than thermodynamic control. Using vibrational spectroscopy to characterize the anion, it was determined that if the trans (E) isomer is present it represents <0.002% of the total composition. / The mechanism of nitric oxide's reaction with secondary amines was elucidated using both synthetic and kinetic methods. Attempts at preparing diazeniumdiolates (NONOates) by reacting nitric oxide directly to various radical anions proved to be unsuccessful. The result of these reactions is the formation of many reaction products, many of which could not be conclusively identified. / The rate of these NO-amine condensation reactions was found to be dependent upon the solvent in which the reaction was conducted, with modest rate enhancements obtained in heterocyclic organic bases. In addition to differences in rate, the overall yield of diazeniumdiolate recovered was found to be highly dependent on solvent choice as well as amine structure. / Kinetic measurements for the formation of these compounds indicate that the rate law is multi-term and the order of reaction with respect to nitric oxide depends greatly on the concentration of nitric oxide. At low nitric oxide concentrations the dependency on nitric oxide is first order, however as the NO concentration increases the order of the reaction becomes second order in [NO]. / The decomposition profile of amine derived diazeniumdiolates in aqueous media is significantly different than in organic solutions. In alkaline aqueous solutions the rate of decomposition is slow, with no significant decomposition occurring after several hours. This decomposition can be accelerated by lowering the pH. In non-aqueous solutions, the rate decomposition of the anion was determined to be comparable to the rate in neutral aqueous solutions. / Finally the equilibrium constant for the rate determining step for the reaction of nitric oxide with the secondary amine, pyrrolidine in pyridine was elucidated. The equilibrium constant for the rate limiting step was found to be 1.1 M-1.

One of the main interests in the vanadium oxides V2O5 and VO2 is that, when doped with a metal such as Fe, these oxides display semiconductor-to-metal transitions at certain critical temperatures. These transitions are also accompanied with changes in the crystallographic phases of the oxides. This thesis describes the use of hyperfine interactions at dopant sites in the vanadium oxides V2O5 and VO2 to infer information on the phase transitions that take place in these oxides. The hyperfine interaction techniques of Mossbauer Spectroscopy and Time Differential Perturbed Angular Correlation (TDPAC) are used to study the hyperfine parameters in the Fe - V2O5 system and Cd - V2O5 system, respectively. X-ray powder diffraction spectroscopy were also conducted on the samples to establish the phases created. A large part of this project was spent in the design of apparatus. The apparatus constructed were (i) a furnace to perform a solid state reaction in order to introduce Fe into V2O5, the maximum operating temperature of the furnace being 1473 K, (ii) a Mossbauer sample chamber and sample holder which enabled the sample to be heated up to a temperature of 873 K, and (iii) a device constructed to determine the electrical conductivities of powder samples at temperatures ranging from 773 K to room temperature. For the Mossbauer studies, the Fe-V2O5 system was studied as a function of the Fe concentration. Six symmetric doublets, with intensities changing as the Fe concentration changed, were observed. Correlating the Mossbauer components of the individual spectra with the phases identified using powder x-ray diffraction patterns in terms of the reflection intensities, allowed two of the doublets to be assigned to lattice sites in the vanadium oxide bronze system, θ-YOB, a further two doublets to substitutional and interstitial sites in the Fe doped V2O5 system, respectively, and the fifth doublet to the super-paramagnetic Fe2O3 phase. The sixth doublet observed was attributed to an unresolved crystallographic phase observed in the x-ray diffraction spectra at large Fe concentrations. The magnitude of the quadrupole splittings of the doublets assigned to the vanadium oxide bronze and the Fe-V2O5 systems indicate that the electronic environment of the Fe atoms in the bronze phase displays a greater symmetry than those in the V2O5 phase. In order to gain insight on the semiconducting nature of the Fe doped V2O5 and the θ-VOB phases, temperature dependent Mossbauer measurements ranging from 300 K to 573 K, together with electrical conductivity measurements, were performed on a few samples. The temperature dependent Mossbauer spectra displayed the usual second order Doppler shift of the isomer shifts for the various components as a function of temperature, but no significant change in the magnitude of the quadrupole splittings. From this result, on the basis of the Duncan-Golding correlation diagram, the valence state of the Fe ions was inferred to be 3+. No components were observed (with increasing temperature) that could be correlated with the population of Fe2+ states. This therefore suggests that the semiconducting properties of the Fe doped V2O5 phase and the θ-VOB phase are associated with electron hopping between V4+ - V5+ valence sites rather than Fe3+ - Fe2+ valence sites. 111In-TDPAC measurements were made on V2Os and VO2. For V2O5, the measurements yielded one distinct substitutional cation site for the 1llCd ions, with quadrupole coupling constant vQ =88,1(3) MHz, and asymmetry η =0,619(3) In VO2, temperature dependent TDPAC measurements yielded two well defined quadrupole coupling frequencies for the 1llCd probe nuclei, the first, vQ =43,0(7) MHz, observed at room temperature, corresponding to a monoclinic or triclinic phase of VO2, and the second, vQ =89,1(1) MHz, observed at 423 K and above, corresponding to the rutile phase of VO2. / Thesis (Ph.D.)-University of Durban-Westville, 1999.

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