Towards more active and stable PdAgCr electrocatalysts for formic acid electrooxidation: The role of optimization via response surface methodology

In this study, multiwall carbon nanotube (MCNT)‐supported Pd (Pd/MWCNT) catalysts are prepared by using NaBH₄ reduction method. In order to maximize the oxidation and reduction of H₂SO₄, synthesis conditions (Pd ratio, molar ratio of NaBH₄/K₂PdCl₄, volume of deionized water, and duration of agitation) are optimized by using response surface methodology (RSM). The optimum synthesis conditions are determined as 58.2% of Pd by weight, 154.6 molar ratio of NaBH₄ to K₂PdCl₄, 19.48 mL of deionized water, and 186.16 min of agitation duration. The effect of electrochemical measurement conditions on the oxidation kinetics of Pd/MWCNT is also investigated by RSM. The optimum electrochemical measurement conditions are found as 10 μL of catalyst mixture, 90°C of H₂SO₄ solution, and 5.5 M H₂SO₄. The Pd/MWCNT, Pd₅₀Ag₅₀/MWCNT, and Pd_65.6Ag_33.6Cr_0.80/MWCNT catalysts prepared under optimized conditions are characterized by using X‐ray diffraction, transmission electron microscopy, N₂ adsorption‐desorption, and inductively coupled plasma mass spectrometry. The crystallite sizes of these catalysts are found as 4.85, 5.66, and 5.26 nm for Pd/MWCNT, Pd₅₀Ag₅₀/MWCNT, and Pd_65.6Ag_33.6Cr_0.80/MWCNT catalysts, respectively. Isotherms of all these catalysts are found to be similar to Type V isotherms with H3 hysteresis loop. The average particle size of Pd₅₀Ag₅₀/MWCNT and Pd_65.6Ag_33.6Cr_0.80/MWCNT catalysts are determined as 5.2 and 9.2 nm, respectively. Electrochemical performance of as‐prepared catalysts is evaluated by using cyclic voltammetry and chronoamperometry. The formic acid electrooxidation (FAEO) activities are found as 18.9, 27.8, and 51.6 mA/cm² for Pd/MWCNT, Pd₅₀Ag₅₀/MWCNT, and Pd_65.6Ag_33.6Cr_0.80/MWCNT, respectively. Pd_65.6Ag_33.6Cr_0.80/MWCNT shows the highest activity and stability. Optimization of synthesis conditions and electrochemical measurement parameters allow us to obtain very good electrochemical activity and stability for FAEO reaction compared with anode catalysts in the literature.     

Improvement of the critical current density in Bi-2223 ceramics by sodium–silver co-doping

Bi_1.46Pb_0.36Ag_0.18Sr₂Ca₃Cu_4?xNa_xO_y (x = 0, 0.05, 0.1 and 0.25) samples were prepared by a conventional solid state reaction method. The prepared samples are characterized using X-ray powder diffraction, scanning electron microscope, dc electrical resistivity and magnetic-hysteresis loop measurements. It has been shown that the Na doping in low contents significantly improves the physical properties of Bi-2223 phase. Magnetic hysteresis measurements have shown that the largest hysteresis curve belongs to Bi_1.46Pb_0.36Ag_0.18Sr₂Ca₃Cu_3.95Na_0.05O_y sample including x = 0.05 Na content, indicating that it has best flux pinning capability in samples produced in this work. In addition, J_c values of the samples were calculated from the hysteresis loop measurement by using the Bean’s model showing that J_c increases with small amounts of sodium–silver co-doping.     

Effect of metallic Ag on the properties of Bi-2212 ceramic superconductors

Samples of Bi₂Sr₂CaCu₂Ag_xO_y with small Ag additions (x = 0.05, 0.1 and 0.2) have been prepared by the classical solid state reaction method. The effect of Ag has been investigated using electrical resistivity, scanning electron microscopy, XRD, mechanical and dc-magnetization techniques. It has been found that very small amounts of Ag are enough to improve the physical and magnetic properties of the samples. The best J_c values obtained from dc magnetization measurement (M-H), employing the well known Bean’s critical model, have been obtained for the Bi₂Sr₂CaCu₂O_y samples with 0.05 Ag addition, reaching about 3000 A/cm² at 15 K, which is a very high value for bulk materials with randomly oriented grains.     

Colour and gloss properties of pigment‐printed synthetic leather using an ultraviolet‐curable water‐borne polyurethane acrylate binder and two photoinitiators at different ratios

This study reports on the colour and gloss properties of pigment‐printed polyurethane‐based synthetic leather using an ultraviolet (UV)‐curable water‐borne polyurethane acrylate binder and two types of photoinitiators (Omnirad 819 DW and Omnirad 500) at different ratios. The UV curing of printed synthetic leather samples was conducted with gallium and mercury lamps, either singly or in combination, at three different power levels. Chemical changes in the cured films because of the polymerisation of the UV‐curing process were analysed by Fourier Transform‐infrared spectroscopy, which showed that the polymerisation reaction occurred after UV curing in both the clear and in the pigmented films. The Omnirad 500 photoinitiator is more effective in surface curing and the Omnirad 819 DW photoinitiator is more effective in deep curing. The Omnirad 500 photoinitiator caused the gloss values to drop significantly, especially in the formulation including both photoinitiators, Omnirad 819 DW and Omnirad 500, at a 1:2 ratio, respectively. In the formulation including a higher ratio of the Omnirad 819 DW photoinitiator, higher gloss values were obtained compared with the formulation including a higher ratio of the Omnirad 500 photoinitiator. Considering all the results, the highest gloss value of 20.96 was obtained with samples printed with the formulation of the two photoinitiators at an equal ratio (1:1) cured under a gallium/mercury lamp combination at a power level of 90 W/cm. Moreover, the highest K/S value of 10.86 was obtained with samples printed with the formulation of the two photoinitiators at an equal ratio cured under the gallium lamp at 90 W/cm.     

Effects of different dwell-times under low pelletization pressure on the physical properties of the Bi-2212 ceramics

Journal of Materials Science: Materials in Electronics - We reported the evaluation of superconducting properties of Bi-2212 ceramics prepared under different dwell times between 12 and...     

In vitro cultured human term cytotrophoblast: a model for normal primary epithelial cells demonstrating a spontaneous differentiation programme that requires EGF for extensive development of syncytium

Normal human term cytotrophoblast cells prepared by trypsin-DNAse I digestion with and without secondary immunological purification with CD9 antibodies were investigated for the expression of morphological and genetic markers of proliferation and differentiation. After 24 h of culture, the cell preparations demonstrated spontaneous formation of microvilli and formation of small syncytial units as assessed by desmoplakin staining and FITC-dextran microinjection. EGF was required for mature syncytial formation. Compared to log-phase proliferating HeLa cells, uptake of [3H]thymidine incorporation was low and quickly decreased to negligible levels. Expression of the proto-oncogenes c-myc, c-fos, and c-jun and histone 2A decreased rapidly in the first 24 h of culture in both cell preparations, followed by an increase in expression of c-fos and junB over the next 3 days of culture. Proto-oncogene changes were similar in attached and suspension cells. Spontaneous increases in alpha hCG, pregnancy-specific beta(1)-glycoprotein and 3 beta-hydroxysteroid dehydrogenase (3 beta OHSD) occurred within 1 day in both cell preparations. EGF receptor blocking antibodies did not inhibit minor degrees of spontaneous syncytial formation nor inhibit spontaneous expression of alpha hCG or 3 beta OHSD mRNA, but did prevent extensive synctialization induced by EGF. The results demonstrate that term cytotrophoblast cells even in serum-free conditions or suspension culture rapidly commit to a non-proliferative differentiation program in culture which includes limited syncytialization and marked hormone mRNA expression. However, EGF is required for extensive syncytial development.     

Effect of Nd-Substitution on Thermally Activated Flux Creep in the Bi1.7Pb0.3−x Nd x Sr2Ca3Cu4O12+y Superconductors

The magnetoresistance of Bi_1.7Pb_0.3?x Nd _x Sr₂Ca₃Cu₄O_12+y superconductors with x=0.025, 0.050, 0.075 and 0.10 have been measured for different values of the applied magnetic field. Thermally activated flux creep model has been studied in order to calculate the flux pinning energies. The calculated flux pinning energies decrease with the increasing Nd-content and applied magnetic field.     

Enhancement in superconducting transition temperature and Jc values in Na-doped Bi2Sr2Ca1Cu2−xNaxOy superconductors

The effects of Na substitution on the properties of Bi₂Sr₂Ca₁Cu_2?xNa_xO_y were investigated. The prepared samples are characterized using X-ray powder diffraction, scanning electron microscope, DC electrical resistivity and magnetic-hysteresis loop measurements. It has been found that with increasing Na doping for Cu, the transition temperature gradually increase while crystal lattice parameters slightly change. Magnetic hysteresis measurements have shown that the hysteresis loops of doped samples are greater than the undoped sample. In addition, significant enhancement has been observed in the J_c values of Na-doped samples, which were calculated from the M–H curves by using Bean’s critical state model.     

Structural, superconducting and mechanical properties of molybdenum substituted Bi1.8Sr2Ca1.1Cu2.1Oy

The effect of MoO₃ addition on the properties of Bi-2212 superconducting ceramic samples prepared by solid state reaction method has been investigated. Mo content was varied from 0 to 0.25 on a general stoichiometric formula Bi_1.8Sr₂Mo_xCa_1.1Cu_2.1O_y. Electrical resistivity showed that transition temperature width increased directly with the Mo amount. XRD data have shown that MoO₃ addition in the Bi_1.8Sr₂Mo_xCa_1.1Cu_2.1O_y precursor reduces the amount of Bi-2212 phase. In addition, J_c values of the samples, calculated from the hysteresis loops using the Bean’s model, decreased with increasing Mo substitution. Vickers microhardness measurements show that samples are very sensitive to Mo content and applied load. In addition, various models like Meyer’s Law and Young’s Modulus equations have been used to better explain the mechanical properties of samples.