Development Of Planar Solid Oxide Fuel Cell Using Cermet Anode Prepared By Electroless Technique

Solid Oxide fuel cell (SOFC) is a very promising electrical conversion device owing to its high efficiency and low gas emissions. In light of the present world scenario relating to the energy sector, research and development works on alternate energy sources viz. fuel cells, solar, hydro etc. holds special drive and attention. Among various classifications of ceramic fuel cells (SOFCs), the present research work is based on the flat planar design owing to its ease of fabrication and potential for providing high power densities compared to other cell configurations. Till date, nickel (Ni) -8 mol % yttria stabilized zirconia (YSZ) [Ni-YSZ] cermet has been evolved out as the most widely accepted anode for SOFC application. However, such Ni-ceramic composite posseses certain shortcomings owing to which the commercialization of SOFC is limited. The endeavour of the present research is based on the development of Ni-YSZ functional anode materials by novel ‘electroless technique’ and its application for SOFC fabrication. Generation of unique core (YSZ)-shell (discreet Ni nanoparticulates around the YSZ core) microstructure in a patterned manner through process optimization is one of the major accomplishment of such electroless technique. Sensitization of YSZ particulates by high energy ultrasonification forms the catalytic Pd0 particulates in-situ in the redox reaction bath. The adsorption of such Pd0 onto YSZ core governs the deposition of Ni around YSZ during electroless technique and hence the microstructure. Optimization of process parameters initially involve mathematical modeling which is followed by experimental validation. The developed electroless anode is found to exhibit the required electrical conduction (~ 500 Scm-1) at much lower Ni content (28 vol %) compared to other conventional cermets. The major drawbacks of thermal incompatibility and poor redox tolerance associated with such Ni-YSZ anode is rectified using the functional electroless anode. Efforts have been exerted to determine the length of triple phase boundary (active sites for electrochemical reactions) and reaction sequences through mathematical modeling approach. The second phase of the present research work is focussed on the fabrication of SOFCs using such functional anodes in assorted configurations. Electroless cermet is configured as anode-support structure, multilayered anode or anode active layer (AAL). The various factors affecting electrochemical activity of single cell such as: a) thickness and sintering temperature of the half cell b) rate of NiO reduction to metallic Ni, c) effect of moisture in fuel and c) type of oxidant used at the cathode side are studied thoroughly during the course of this research work. The load bearing competence of the fabricated SOFCs with the developed anodes are also examined for a considerable period of time to determine the corresponding degradation rates. The experimental results support the superiority of electroless anodes, which showed the highest cell performance of 3.7 Acm-2 at 800oC without any significant degradation and lowest polarization from the associated factors. The experimental outcome of electrochemical reactions are correlated with: a) optical microstructures, b) elemental mapping, c) NiO reduction equilibrium, d) pore-size distribution in anodes, e) effect of moisture in the fuel, f) variation in oxidant type etc. The influence of polarization/resistive factors is also studied in terms of both mathematical approach and electrochemical impedance measurements. Therefore, the entire effort of the present research work is exerted towards the development of functional Ni-YSZ anode by novel ‘electroless’ technique encompassing its potential to act as new-generation anode for ITSOFC application

Influence of sorption kinetics for zirconia sensitization in solid oxide fuel cell functional anode prepared by electroless technique

For preparation of solid oxide fuel cell functional anode (Ni-YSZ) by electroless deposition technique, surface adsorption of metallic palladium (Pd-0) on zirconia is the most important step during the sensitization process. For the sensitization process, the initial reaction kinetics are based on external mass transfer followed by intra-particle mass transfer phenomena. A kinetic model for the reversible sorption of Pd-0 on zirconia is developed that incorporates an effectiveness factor (eta) which estimates the extent of intra-particle mass transfer. Based on the proposed model, an expression for Pd-0 uptake at equilibrium (p), an important property of YSZ, is developed. The theoretical kinetic model proposed is verified with experimental parameters like electrical properties of these functional anodes prepared under various sensitization conditions, e.g., agitation frequencies, equilibration time etc. Due to intra-particle mass transfer, the concentration gradient of Pd-0 from the surface of YSZ to bulk is minimized which favours uniform deposition of Ni on YSZ. Consequently, during subsequent electroless deposition of metallic Ni, the concentration gradient of the same is reduced from the bulk to the YSZ surface and results in enhanced functionality in the cermet anode. The validation is correlated with the electrical properties and surface morphologies of these functional cermets. (C) 2007 Elsevier B.V. All rights reserved

Gene-Gene Interaction and Functional Impact of Polymorphisms on Innate Immune Genes in Controlling <em>Plasmodium falciparum</em> Blood Infection Level

<div><p>Genetic variations in toll-like receptors and cytokine genes of the innate immune pathways have been implicated in controlling parasite growth and the pathogenesis of <em>Plasmodium falciparum</em> mediated malaria. We previously published genetic association of <em>TLR4</em> non-synonymous and <em>TNF-α</em> promoter polymorphisms with <em>P.falciparum</em> blood infection level and here we extend the study considerably by (i) investigating genetic dependence of parasite-load on interleukin-12B polymorphisms, (ii) reconstructing gene-gene interactions among candidate <em>TLR</em>s and cytokine loci, (iii) exploring genetic and functional impact of epistatic models and (iv) providing mechanistic insights into functionality of disease-associated regulatory polymorphisms. Our data revealed that carriage of AA (P = 0.0001) and AC (P = 0.01) genotypes of <em>IL12B</em> 3′UTR polymorphism was associated with a significant increase of mean log-parasitemia relative to rare homozygous genotype CC. Presence of <em>IL12B+1188</em> polymorphism in five of six multifactor models reinforced its strong genetic impact on malaria phenotype. Elevation of genetic risk in two-component models compared to the corresponding single locus and reduction of <em>IL12B</em> (2.2 fold) and lymphotoxin-α (1.7 fold) expressions in patients'peripheral-blood-mononuclear-cells under <em>TLR4Thr399Ile</em> risk genotype background substantiated the role of Multifactor Dimensionality Reduction derived models. Marked reduction of promoter activity of <em>TNF-α</em> risk haplotype (C-C-G-G) compared to wild-type haplotype (T-C-G-G) with (84%) and without (78%) LPS stimulation and the loss of binding of transcription factors detected <em>in-silico</em> supported a causal role of <em>TNF-1031</em>. Significantly lower expression of <em>IL12B+1188</em> AA (5 fold) and AC (9 fold) genotypes compared to CC and under-representation (P = 0.0048) of allele A in transcripts of patients' PBMCs suggested an Allele-Expression-Imbalance. Allele (<em>A+1188C</em>) dependent differential stability (2 fold) of <em>IL12B</em>-transcripts upon actinomycin-D treatment and observed structural modulation (P = 0.013) of RNA-ensemble were the plausible explanations for AEI. In conclusion, our data provides functional support to the hypothesis that de-regulated receptor-cytokine axis of innate immune pathway influences blood infection level in <em>P. falciparum</em> malaria.</p> </div

Genetic and functional association of multifactor models obtained by Multifactorial Dimensionality Reduction analysis.

<p>(A) Forest plots presented the comparison of risk estimates in terms of odds ratio (OR) and 95% confidence interval (CI) for significant gene-gene interaction models and component single loci. The risk corresponding to each single and two factor models was denoted by a dot and the horizontal lines represented odds ratio and 95% CI respectively. The model IDs (A–J) and respective ORs (95% CI) were given at the left and right side of each dot in the forest plot. (B) <i>IL12B</i> and (C) <i>LTA</i> gene expression in patients' PBMCs classified according to <i>TLR4Thr399Ile</i> genotype status by real time quantitative PCR. Distribution of ΔC_t was plotted and compared between the genotypic groups. Statistical significance was determined by Mann Whitney U test. P values and corresponding fold changes obtained for each pairwise comparison were shown in the box plots. (*) indicates these differences to be statistically significant.</p

Association between <i>IL12B+1188</i> genotypes with blood infection level and <i>IL12B</i> gene-expression represented in Box plots.

<p>(A) Diagram represented the distribution of log-parasitemia across three genotypes: 11 (AA), 12 (AC) & 22 (CC) and (B) Diagram represented the comparison of log-parasitemia of minor homozygous genotype (CC) with AA and AC genotypic groups pooled. Statistical significance between pairwise comparisons was mentioned. (C) The ΔC_t distribution of <i>IL12B</i> gene expression across AA (N = 24), AC (N = 28) and CC (N = 12) genotypes and (D) comparison of gene expression between <i>IL12B+1188CC</i> genotype and with that of AA and AC individuals pooled together determined by quantitative real time PCR. Statistical significance was determined by the Mann Whitney U test. P values and fold changes obtained for each pairwise combination were appended in each plot. (*) indicates these differences to be statistically significant. The bottom, middle line, and top of each box correspond to the 25^th percentile, median, and the 75^th percentile, respectively. Bars extend to the lowest value and to the highest value of each group.</p

<i>IL12B</i> 3′UTR polymorphism based RNA ensemble structures.

<p>(A–D) display the SNPfold derived partition function heat maps generated for 101 nucleotide sequences harboring A (risk), G, U and C (non-risk) alleles respectively at the 51^st position. The partition function matrix illustrates the base-pairing probabilities represented by dots. We estimated the pairwise Pearson correlation coefficient with respect to wild-type A allele and P values to quantify the overall modulation in the RNA structural ensemble caused by a mutation. (*) indicates the P value to be statistically significant. (E & F) show the mountain plot diagrams for <i>IL12+1188</i>A and C allele for 101 bases using RNAfold. The upper panel demonstrates the height vs position graph in which the red, green and blue lines depict the minimum free energy structure, the partition function of all possible RNA secondary structures and ensemble centroid structure respectively. The lower panel represents the entropy vs position profile and arrowhead denotes the 51^st position, the location of <i>A+1188C</i>. (G & H) shows allele specific minimum free energy (MFE) conformations generated from RNA MFOLD. Numbers indicate the base position while the arrow directs the position of the polymorphic site.</p

<i>IL12B</i> mRNA-microRNA interaction assay.

<p>(A) Schematic representation of reporter gene constructs for <i>IL12B</i> 3′UTR A and C alleles used for transfection assays. (B) Entire 3′UTR region was mapped for putative microRNA binding sites. The highlighted, boldfaced and underlined segments within <i>IL12B</i> sequence were the seed sequences for the miRNAs. (C) Schematic representation of the score and seed position of four miRNAs on target IL12B. (D & E) Normalized luciferase relative light units (RLU) in HepG2 cells were measured for <i>IL12B+1188</i> A and C allele containing pSiCHECK2 constructs with (+) and without (−) the effect of miRNAs. Co-transfection of the empty pRNAU6.1 (+) vector with pSiCHECK2-IL12B+1188 construct was set as 100% and reductions in luciferase expression in presence of four miRNAs were measured in relation to this. hsa-miR-23a and hsa-miR-23b resulted in significant reduction in luciferase activities for both pSiCHECK2-IL12B+1188A and pSiCHECK2-IL12B+1188C constructs. Statistical significance was measured with t-test. (*) indicates the P values and percentage reduction to be statistically significant.</p