Vanadium Redox Flow Batteries Using <i>meta</i>-Polybenzimidazole-Based Membranes of Different Thicknesses

15, 25, and 35 μm thick <i>meta</i>-polybenzimidazole (PBI) membranes are doped with H₂SO₄ and tested in a vanadium redox flow battery (VRFB). Their performances are compared with those of Nafion membranes. Immersed in 2 M H₂SO₄, PBI absorbs about 2 mol of H₂SO₄ per mole of repeat unit. This results in low conductivity and low voltage efficiency (VE). In ex-situ tests, <i>meta</i>-PBI shows a negligible crossover of V³⁺ and V⁴⁺ ions, much lower than that of Nafion. This is due to electrostatic repulsive forces between vanadium cations and positively charged protonated PBI backbones, and the molecular sieving effect of PBI’s nanosized pores. It turns out that charge efficiency (CE) of VRFBs using <i>meta</i>-PBI-based membranes is unaffected by or slightly increases with decreasing membrane thickness. Thick <i>meta</i>-PBI membranes require about 100 mV larger potentials to achieve the same charging current as thin <i>meta</i>-PBI membranes. This additional potential may increase side reactions or enable more vanadium ions to overcome the electrostatic energy barrier and to enter the membrane. On this basis, H₂SO₄-doped <i>meta</i>-PBI membranes should be thin to achieve high VE and CE. The energy efficiency of 15 μm thick PBI reaches 92%, exceeding that of Nafion 212 and 117 (N212 and N117) at 40 mA cm^–2

In Situ Analyses of Carbon Dissolution into Ni-YSZ Anode Materials

A combination of in situ analyses, including measurement of both electrical resistance and volumetric expansion, and thermogravimetric analysis (TGA) was employed to elucidate the deactivation process of a nickel-yttria-stabilized zirconia (Ni-YSZ) cermet (60 wt % NiO-YSZ) upon exposure to methane at 750 °C. In conjunction with the aforementioned in situ techniques, a number of ex situ analyses, including scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD), and Raman spectroscopy, revealed that carbon deposition initially occurred at the Ni centers, followed by carbon dissolution into the Ni-YSZ cermet after an induction period of 200 min, which then led to three-dimensional expansion. The structural change of the Ni-based cermet induced increases in electrical resistance of the material. The increased electrical resistance likely originated from the breakage of the Ni–Ni conducting network as well as from the formation of microscopic cracks within the Ni-YSZ material, resulting from the observed process of carbon dissolution. Moreover, a combination of TGA involving measurements of electrical resistance was demonstrated to be useful for determining amounts of carbon deposits critical for carbon dissolution. These results strongly suggest that changes in electrical resistance can be utilized to monitor the extent of carbon dissolution into the Ni-YSZ catalysts in situ, which would be helpful for the development of an efficient curing system for solid oxide fuel cells (SOFCs)

Role of Small Pd Ensembles in Boosting CO Oxidation in AuPd Alloys

We present a theoretical explanation on how PdAu alloy catalysts can enhance the oxidation of CO molecules based on density functional theory calculations of CO adsorption and oxidation on AuPd/Pd(111) surfaces. Our study suggests that the enhanced activity is largely attributed to the possible existence of “partially-poisoned” Pd ensembles that accommodate fewer CO molecules than Pd atoms. Whereas the oxidation of preadsorbed CO is likely governed by O₂ trapping, our study shows that small Pd ensembles such as dimers and compact trimers tend to provide more active sites than larger ensembles; CO adsorbed on a Pd monomer is found to react hardly with O₂ to form CO₂. In addition, we find the tendency of CO-induced Pd agglomeration, which may in turn facilitate CO oxidation by creating more dimers and compact trimers as compared with the adsorbate-free surface where monomers are likely prevailing

Role of Heteronuclear Interactions in Selective H₂ Formation from HCOOH Decomposition on Bimetallic Pd/M (M = Late Transition FCC Metal) Catalysts

In this study, by using spin-polarized density functional theory calculations, we have elucidated the role of heteronuclear interactions in determining the selective H₂ formation from HCOOH decomposition on bimetallic Pd_shell/M_core (M = late transition FCC metal (Rh, Pt, Ir, Cu, Au, Ag)) catalysts. We found that the catalysis of HCOOH decomposition strongly depends on the variation of surface charge polarization (ligand effect) and lattice distance (strain effect), which are caused by the heteronuclear interactions between surface Pd and core M atoms. In particular, the contraction of surface Pd–Pd bond distance and the increase in electron density in surface Pd atoms in comparison to the pure Pd case are responsible for the enhancement of the selectivity to H₂ formation via HCOOH decomposition. Our calculations also unraveled that the d band center location and the density of states for the d band (particularly d_<i>z</i>², d_<i>yz</i>, and d_<i>xz</i>) near the Fermi level are the important indicators that explain the impact of strain and ligand effects in catalysis, respectively. That is, the surface lattice contraction (expansion) leads to the downshift (upshift) of d band centers in comparison to the pure Pd case, while the electronic charge increase (decrease) in surface Pd atoms results in the depletion (augmentation) of the density of states for d_<i>z</i>², d_<i>yz</i>, and d_<i>xz</i> orbitals. Our study highlights the importance of properly tailoring the surface lattice distance (d band center) and surface charge polarization (the density of states for d_<i>z</i>², d_<i>yz</i>, and d_<i>xz</i> orbitals near the Fermi level) by tuning the heteronuclear interactions in bimetallic Pd_shell/M_core catalysts for enhancing the catalysis of HCOOH decomposition toward H₂ production, as well as other chemical reactions

The miRNA expression profiles were compared between 2D and 3D cultures.

<p>A heatmap of differentially expressed miRNAs generated by unsupervised hierarchical cluster analysis (A). Differential expression levels of miRNAs between 2D and 3D cultures were confirmed using qRT-PCR for several genes selected from microarray data. Among the differentially expressed miRNAs, up-regulated miRNAs including miR-34b-5p, miR-578, miR-1304, and miR-324-5p and down-regulated miRNAs including miR-7-5p, and miR-34b-3p were analyzed using primers for mature mRNAs (B). Data are expressed as the mean ± SE of triplicates. * p<0.05, n = 3.</p

Analysis of pancreatic cancer stem cell markers.

<p>Expression patterns of stem cell markers such as CD44, CD24, and ESA were compared between 2D (A) and 3D cultures (B). Percentages of the cell population expressing CD44, CD24, and ESA in Panc-1 cells cultured under 2D and 3D conditions are summarized in the table.</p

Differentially expressed miRNAs in Panc-1 cell cultured under 2D and 3D conditions. Fold change indicates 3D intensity/2D intensity.

<p>Differentially expressed miRNAs in Panc-1 cell cultured under 2D and 3D conditions. Fold change indicates 3D intensity/2D intensity.</p

Penetration of DOX into Panc-1 spheroids.

<p>Penetration was evaluated by imaging DOX autofluorescence in sections of spheroids. Spheroids were cultured in a concave microwell 600 plate for 5 μM for 12 h. Fluorescence intensity across sections was measured and expressed as the mean ± SE of 5 replicates. (Scale bar  = 100 μm) * and **, p<0.01 and p<0.001, respectively.</p

Concave PDMS microwell plate for culture and growth of pancreatic tumor spheroids (TS).

<p>Shape and dimension of concave microwell plate 600 (A). Changes in size of three different pancreatic spheroids cultured in microwell 600 (B). Size distribution of Panc-1 spheroids cultured in three different sized-microwell plate during 13 days of culture (C). Data are expressed as mean ± SE of a minimum of 10 spheroids cultured in one microwell plate.</p

Morphology and histological examination of tumor spheroids (TS) cultured in concave microwell 600 or in 96 well plates.

<p>Representative images of H&E stained paraffin sections or toluidine blue stained semi-thin sections, SEM and TEM images of HT-29 (A), Panc-1 (B), Aspc-1 (C), and Capan-2 (D) spheroids cultured in concave microwell 600 plates for 5 and 13 days. Aggregates of Panc-1, Aspc-1, and Capan-2 cells formed in agarose-coated 96 well plates shown as an H&E stained paraffin section or bright field images (E). Arrow: desmosome; dotted lines: gap junctions; arrow head: tight junction; cross: lipid droplet; I: invagination structure; N: necrotic regions. The scale bars indicate 100 μm, 50 μm, 2 μm and 500 μm, in H&E or toluidine blue stained, SEM, TEM and bright-field images, respectively.</p