We present a mechanistic modeling methodology to predict both the percolation threshold and effective conductivity of infiltrated Solid Oxide Fuel Cell (SOFC) electrodes. The model has been developed to mirror each step of the experimental fabrication process. The primary model output is the infiltrated electrode effective conductivity which provides results over a range of infiltrate loadings that are independent of the chosen electronically conducting material. The percolation threshold is utilized as a valuable output data point directly related to the effective conductivity to compare a wide range of input value choices. The predictive capability of the model is demonstrated by favorable comparison to two separate published experimental studies, one using strontium molybdate and one using La0.8Sr0.2FeO3-δ as infiltrate materials. Effective conductivities and percolation thresholds are shown for varied infiltrate particle size, pore size, and porosity with the infiltrate particle size having the largest impact on the results.

A mechanistic model for the prediction of total and active three phase boundary density (TPB), in combination with effective conductivity, of infiltrated solid oxide fuel cell (SOFC) electrodes is presented. Varied porosities, scaffold:infiltrate size ratios, and pore:infiltrate size ratios were considered, each as a function of infiltrate loading. The results are presented in dimensionless form to allow for the calculation of any infiltrate particle size. The model output compares favorably to the available experimental result. The results show that the scaffold:infiltrate size ratio has the greatest impact on the TPB density, followed by the porosity and then the pore:infiltrate size ratio. The TPB density is shown to monotonically decrease with increasing scaffold:infiltrate and pore:infiltrate size ratios; however, it shows a maximum with respect to porosity. Each of these results are explained by examining the interfacial areas of each of the three phases as a function of the infiltrate loading. The model provides insight toward the rational design of infiltrated electrodes. Infiltrated solid oxide fuel cell (SOFC) electrodes offer numerous advantages over conventional co-sintered electrodes. First, a broader choice of electrode materials is possible because materials that melt or chemically react with the electrolyte at conventional sintering temperatures can be considered.1-6 Second, a higher three-phase boundary (TPB) density can be achieved, which is attributed to the smaller particle sizes.2,3,7-9 These two advantages result from a lower processing temperature of the infiltrated phase compared to conventional sintering temperatures required of co-sintered electrodes.Three additional advantages of infiltrated electrodes are associated with the unique morphology created by coating the surface of a presintered porous scaffolding with an infiltrated phase. The first morphological advantage is a mitigation of the coefficient of thermal expansion (CTE) mismatch between the electrolyte and the electrode. 10,11The second advantage is a stabilization of the electrode mechanical properties during redox cycling, 5,12 Finally, less material is needed to form an interconnected network of the infiltrated phase throughout the electrode. 6,10,[12][13][14][15] Although the benefits of infiltrated electrodes have been clearly demonstrated experimentally, researchers suggest that the electrode designs are not optimized. 3,5,6,14,16 This is understandable because it is laborious to consider all of the combinations and permutations of the sizes and shapes of infiltrate particles, scaffold particles, and pores as well as the wide range of possible porosities. In order to more effectively and efficiently design electrodes, several computational models have been recently reported. Zhang et al. utilized a particle-layer model to estimate the TPB density, effective thickness of the electrochemically active region, and polarization resistance of cathodes.9 A more recent report by Zhang et al. utilized a numerically generated thr...

Dc-pulsed magnetron sputtering from Ti target in reactive Ar+O2+N2 atmosphere was used to grow stoichiometric TiO2:N and non-stoichiometric TiO2-x:N thin films. X-ray diffraction at glancing incidence, atomic force microscopy AFM, scanning electron microscopy SEM, X-ray photoelectron spectroscopy XPS, and optical spectrophotometry were applied for sample characterization. Measurements of photocurrent versus voltage and wavelength over the ultraviolet uv and visible vis ranges of the light spectrum were performed in order to assess the performance of nitrogen-doped titanium dioxide thin films as photoanodes for hydrogen generation in photoelectrochemical cells, PEC. Undoped TiO2 and TiO2-x films were found to be composed of anatase and rutile mixture with larger anatase crystallites (25-35 nm) while the growth of smaller rutile crystallites (6-10 nm) predominated at higher nitrogen flow rates etaN2 as measured in standard cubic centimeters, sccm. Nitrogen-to-titanium ratio increased from N/Ti = 0.05 at etaN2 = 0.8 sccm for stoichiometric TiO2:N to N/Ti = 0.11 at etaN2 = 0.8 sccm for nonstoichiometric TiO2-x:N thin films. A red-shift in the optical absorbance was observed with an increase in etaN2. Doping with nitrogen improved photoelectrochemical properties over the visible range of the light spectrum in the case of nonstoichiometric samples.