Reaction Pathway for Oxygen Reduction on FeN₄ Embedded Graphene

The detailed reaction pathways for oxygen reduction on FeN₄ embedded graphene have been investigated using density functional theory transition-state calculations. Our first-principles calculation results show that all of the possible ORR elementary reactions could take place within a small region around the embedded FeN₄ complex. It is predicted that the kinetically most favorable reaction pathway for ORR on the FeN₄ embedded graphene would be a four-electron OOH dissociation pathway, in which the rate-determining step is found to be the OOH dissociation reaction with an activation energy of 0.56 eV. Consequently, our theoretical study suggests that nonprecious FeN₄ embedded graphene could possess catalytic activity for ORR comparable to that of precious Pt catalysts

Role of Local Carbon Structure Surrounding FeN₄ Sites in Boosting the Catalytic Activity for Oxygen Reduction

Development of effective nonprecious metal and nitrogen codoped carbon catalysts for the oxygen reduction reaction (ORR) requires a fundamental understanding of the mechanisms underlying their catalytic activity. In this study, we employed the first-principles density functional theory calculations to predict some key parameters (such as activation energy for O–O bond breaking and free-energy evolution as a function of electrode potential) of ORR on three FeN₄-type active sites with different local carbon structures. We find that the FeN₄ site surrounded by eight carbon atoms and at the edge of micropores has the lowest activation energy (about 0.20 eV) for O–O bond breaking among the three FeN₄-type active sites for promoting a direct four-electron ORR. Consequently, our computational results suggest that introduction of micropores in the nonprecious metal catalysts could enhance their catalytic activity for ORR through facilitating the formation of FeN₄–C₈ active sites with high specific activity

Atomic-Scale Imaging of Cation Ordering in Inverse Spinel Zn₂SnO₄ Nanowires

By using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) coupled with density functional theory (DFT) calculations, we demonstrate the atomic-level imaging of cation ordering in inverse spinel Zn₂SnO₄ nanowires. This cation ordering was identified as 1:1 ordering of Zn²⁺ and Sn⁴⁺ at the octahedral sites of the inverse spinel crystal with microscopic symmetry transition from original cubic <i>Fd</i>3̅<i>m</i> to orthorhombic <i>Imma</i> group. This ordering generated a 67.8% increase in the elastic modulus and 1–2 order of magnitude lower in the electric conductivity and electron mobility compared to their bulk counterpart

Associations between Two Polymorphisms (FokI and BsmI) of Vitamin D Receptor Gene and Type 1 Diabetes Mellitus in Asian Population: A Meta-Analysis

<div><p>Background</p><p>Vitamin D receptor (VDR) gene polymorphisms are possibly involved in the development of type 1 diabetes mellitus (T1DM). However, the results to date have been inconclusive. We performed a meta-analysis to examine the association between 2 polymorphisms (FokI and BsmI) of the VDR gene and T1DM in the Asian population.</p><p>Methods</p><p>Literature was retrieved from PubMed, Web of Science, CBM, Embase and Chinese databases. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were calculated using a random or fixed effect model.</p><p>Results</p><p>In total, 20 papers (BsmI: 13 studies; FokI: 13 studies) were included. In contrast to the FokI polymorphism, the BsmI polymorphism was associated with an increased risk of T1DM in the Asian population (OR = 1.47, 95% CI = 1.13–1.91, P = 0.004 for B vs. b). Upon stratification by regional geography, an increased risk of T1DM in association with the BsmI polymorphism was observed in the East Asian population (OR = 1.97, 95% CI = 1.38–2.83, P<0.001 for B vs. b), whereas the FokI polymorphism was associated with an increased risk of T1DM in the West Asian population (OR = 1.45, 95% CI = 1.12–1.88, P = 0.004 for F vs. f).</p><p>Conclusions</p><p>Our meta-analysis suggests that the BsmI polymorphism may be a risk factor for susceptibility to T1DM in the East Asian population, and the FokI polymorphism is associated with an increased risk of T1DM in the West Asian population. However, because the study size was limited, further studies are essential to confirm our results.</p></div

Selection of articles for inclusion in the meta-analysis.

<p>Selection of articles for inclusion in the meta-analysis.</p

Molecular and Electronic Structures of Transition-Metal Macrocyclic Complexes as Related to Catalyzing Oxygen Reduction Reactions: A Density Functional Theory Study

Transition-metal (TM) macrocyclic complexes have potential applications as nonprecious electrocatalysts in polymer electrolyte membrane fuel cells. In this study, we employed density functional theory calculation methods to predict the molecular and electronic structures of O₂, OH, and H₂O₂ molecules adsorbed on TM porphyrins, TM tetraphenylporphyrins, TM phthalocyanines, TM fluorinated phthalocyanines, and TM chlorinated phthalocyanines (here TM = Fe or Co). Relevant to their performance on catalyzing oxygen reduction reaction (ORR), we found for the studied TM macrocyclic complexes: (1) The type of the central TM is the most determinant factor in influencing the adsorption energies of O₂, OH, and H₂O₂ (chemical species involved in ORR) molecules on these macrocyclic complexes. Specifically, the calculated adsorption energies of O₂, OH, and H₂O₂ on the Fe macrocyclic complexes are always distinguishably lower than those on the Co macrocyclic complexes. (2) The peripheral ligands are capable of modulating the binding strength among the adsorbed O₂, OH, and H₂O₂, and the TM macrocyclic complexes. (3) A N–TM–N cluster structure (like N–Fe–N) with a proper distance between the two ending N atoms and a strong electronic interaction among the three atoms is required to break the O–O bond and thus promote the efficient four-electron pathway of the ORR on the TM macrocyclic complexes

Distribution of VDR genotype and the allele among T1DM patients and controls.

<p>Distribution of VDR genotype and the allele among T1DM patients and controls.</p

Meta-analysis for the association between T1DM risk and the VDR FokI polymorphism(F vs f).

<p>Each study was shown by a point estimate of the effect size (OR) (size inversely proportional to its variance) and its 95% confidence interval (95%CI) (horizontal lines). The white diamond denotes the pooled OR.</p

Meta-analysis for the association between T1DM risk and the VDR BsmI polymorphism (B vs b).

<p>Each study was shown by a point estimate of the effect size (OR) (size inversely proportional to its variance) and its 95% confidence interval (95%CI) (horizontal lines). The white diamond denotes the pooled OR.</p

Tabel 2. Summary ORs and 95% CIs of the association between VDR gene polymorphism and type 1 diabetes mellitus risk.

<p>SNPs: single nucleotide polymorphisms.</p><p>A represent B allele and a represent b allele for BsmI, A present F allele and a represent f allele for FokI, respectively.</p