The effectiveness of platinum/carbon electrocatalysts: Dependence on catalyst layer thickness and Pt alloy catalytic effects

In our previous work, we have proposed a new method to estimate the effective Pt utilization or “effectiveness” (Ef_Pt) using the ratio of the mass activity (MA) for the oxygen reduction reaction in the membrane-electrode assembly (MEA) in the polymer electrolyte fuel cell to that in the channel flow double electrode measurement, MA_max, under similar conditions. In the present research, applying this method, we have focused on elucidating the effect of the thickness of the catalyst layer (CL), the effect of Pt-based alloy catalysts, and effect of the state of dispersion of the Pt/C catalysts in the CL in measurements carried out at 80 °C and various relative humidities (RH), in either O₂ or air. The effect of a thin CL (0.04 mg cm⁻², Pt/C) has improved Ef_Pt by a factor of four, going from 3% to 12%, and the integrated effect of a thin CL and alloying (0.05 mg cm⁻² Pt₃Co) has improved Ef_Pt by a factor of six, going from 3% to 17% for air at 0.85 V, T_cell = 80 °C, and 30% RH. Furthermore, we found that the Ef_Pt values were dependent upon the state of Pt dispersion in the CL. The highest Ef_Pt value obtained thus far for air at 0.85 V, T_cell = 80 °C, and 100% RH was ca. 22%, shown by a low Pt loading CL diluted with added uncatalyzed carbon black (0.04 mg cm⁻², overall average 30 wt%-Pt).     

Experiment and computation multi-fidelity multi-objective airfoil design optimization of fixed-wing UAV

Journal of Mechanical Science and Technology - Optimization with a surrogate model is a popular method used in design to avoid a high computational cost problem and is often encountered in...     

Phase Separation Phenomenon and Mechanism of Ce0.6Zr0.4O2 Powders Prepared Using Chemical Coprecipitation Method

Ce_0.6Zr_0.4O₂ (C60Z) powders were synthesized using the chemical coprecipitation method to investigate the phase separation mechanism. The phase separation of C60Z powders occurred during the heating step (>1100°C), suggesting that it might be a thermally activated process. The activation energy for the phase separation of C60Z was 398 (±20) kJ/mol and the Avrami parameter was ~1.0, indicating that the phase separation may be interface controlled. We suggested that Zr⁺⁴ diffusion played an important role in C60Z phase separation due to the ionic radius of Zr⁺⁴ being smaller than that of Ce⁺⁴. The C60Z powders tended to aggregate, which induced the driving force for the phase separation resulting from the surface energy difference between the particle surface and the interface. The phase separation behavior of C60Z powders was very similar to the initial stage of sintering. After high‐temperature treatment, more Zr⁺⁴ ions diffused to the interface between C60Z particles to lower the surface energy of the system than did Ce⁺⁴ ions, which resulted in the composition gradually being changed and phase separation. Therefore, the phase separation of C60Z powders can be effectively decreased by the addition of Al⁺³, which suppresses aggregation.     

Synthesis of single-walled carbon nanotubes using laser-vaporized metal nanoparticle catalyst

SWNTs were synthesized by laser-vaporized CCVD (catalytic chemical vapor deposition). The diameter distributions and the abundance of SWNTs synthesized at different temperatures and using different catalysts were investigated by Raman spectroscopy. Further, this technique was compared with other synthesis techniques (laser-oven and conventional-alcohol CCVD), and C₆₀ was synthesized simultaneously as a byproduct only using the laser-oven technique. With increasing synthesis temperature, the diameter distribution shifted towards larger diameters, and the G/D ratio became larger as the synthesis temperature increased to 1000°C. Ni, Co, and Fe played a catalytic role, though Fe was less effective under our experimental conditions. The diameter distribution of SWNTs synthesized with the Fe catalyst was shifted to smaller values compared to those synthesized with Ni or Co catalysts.     

Near-Infrared Bioluminescence Imaging with a through-Bond Energy Transfer Cassette

A coelenterazine (CTZ) analogue emitting near-infrared (NIR) bioluminescence was synthesized for through-bond energy transfer (TBET)-based imaging modalities. The analogue, named Cy5-CTZ, was prepared by conjugating cyanine-5 (Cy5) dye to CTZ through an acetylene linker. This novel derivative is intrinsically fluorescent and emits NIR-shifted luminescence upon reacting with an appropriate luciferase, the Renilla luciferase. This Cy5-CTZ substrate is optically stable in physiological samples and rapidly permeabilize through the plasma membrane into the cytosolic compartment of live cells.     

Total Syntheses and Chemical Biology Studies of Hymeglusin and Fusarilactone A,Novel Circumventors of β-Lactam Drug Resistance in Methicillin-Resistant Staphylococcus aureus

Hymeglusin, a previously known eukaryotic hydroxymethylglutaryl-CoA (HMG−CoA) synthase inhibitor, was identified as circumventing the β-lactam drug resistance in methicillin-resistant Staphylococcus aureus (MRSA). We describe the concise total syntheses of a series of natural products, which enabled determination of the absolute configuration of fusarilactone A and provided structure-activity relationship information. Based on previous reports, we speculated that the target protein of this circumventing effect may be MRSA bacterial HMG−CoA synthase (mvaS). We found that this enzyme was dose-dependently inhibited by hymeglusin. Furthermore, overexpression of the MRSA mvaS gene and site-directed mutagenesis studies suggested its binding site and the mechanism of action.