Combinatorial investigation of Pt–Ru–Sn alloys as an anode electrocatalysts for direct alcohol fuel cells

Low-temperature direct alcohol fuel cells fed with different kinds of alcohol (methanol, ethanol and 2-propanol) have been investigated by employing ternary electrocatalysts (Pt–Ru–Sn) as anode catalysts. Combinatorial chemistry has been applied to screen the 66-PtRuSn-anode arrays at the same time to reduce cost, time, and effort when we select the optimum composition of electrocatalysts for DAFCs (Direct Alcohol Fuel Cells). PtRuSn (80:20:0) showed the lowest onset potential for methanol electro-oxidation, PtRuSn (50:0:50) for ethanol, and PtRuSn (20:70:10) for 2-propanol in CV results respectively, and single cell performance test indicated that Ru is more suitable for direct methanol fuel cell system, Sn for direct ethanol fuel cell system, and 2-propanol could be applied as fuel with low platinum composition anode electrocatalyst. The single cell performance results and electrochemical results (CV) were well matched with the combinatorial electrochemical results. As a result, we could verify the availability of combinatorial chemistry by comparing the results of each extreme electrocatalysts compositions as follows: PtRuSn (80:20:0) for methanol, PtRuSn (50:0:50) for ethanol and PtRuSn (20:70:10) for 2-propanol.     

Dry etching of GaN and related materials: comparison of techniques

The etch rates and feature anisotropy for GaN, AlN, and InN etched in Cl₂-Ar plasmas with four different techniques were examined. Conventional reactive ion etching produces the slowest etch rates, even when high dc self-biases (>-900 V) are employed, and this leads to mask erosion and sloped feature sidewalls during ridge waveguide fabrication. Two high-ion-density techniques, inductively coupled plasma and electron cyclotron resonance, provide the highest etch rates and most anisotropic features through their combination of high-ion flux and moderate-ion energy. Etch selectivities of GaN to AlN and InN are typically ⩽4 in these tools. Reactive ion beam etching utilizing a high density (ICP) source is also an attractive option for pattern transfer in the nitrides, although its etch rates are slower than for ICP or ECR due to its lower operating pressure     

Catalytic activity and characterization of V2O5/γ-Al2O3 for ammoxidation of m-xylene system

An ammoxidation of m-xylene was evaluated in a fixed-bed reactor using V₂O₅ on various oxides. Catalysts were prepared by wet impregnation method. At first, the loading of V₂O₅ was varied from 5 wt% to 20 wt% on γ-Al₂O₃ support to estimate the most effective amount of V₂O₅. Second, the effect of catalyst supports was examined at 10 wt% loading of V₂O₅. V₂O₅/TiO₂ and V₂O₅/SiO₂ catalysts were employed to compare the ammoxidation reaction with V₂O₅/γ-Al₂O₃. Most catalytic activity was observed when γ-Al₂O₃ was used as a support. Careful characterization was followed by physicochemical techniques, such as BET measurement, X-ray diffraction (XRD), Raman spectroscopy and temperature-programmed reduction (TPR). The results provided the clue that monolayer V₂O₅ was favorably dispersed on the surface of γ-Al₂O₃ up to 10 wt%, which led to the highest yield of isophthalonitrile (IPN).     

Crystallization of polycarbonate in solvent/nonsolvent system and its application to high‐density polyethylene composite as a filler

Crystallization of polycarbonate (PC) was attempted by a precipitated method in a ternary system of PC/solvent/nonsolvent. Chloroform was used as a solvent, and isopropanol was used as a nonsolvent. Crystallization of PC was clearly observed as a powdery state when chloroform/isopropanol mixtures were prepared by 68/32 and 61/39 vol%. Crystallinity of PC was evaluated by differential scanning calorimeter and X‐ray diffractometer. As the difference of solubility parameters between PC and binary solvent/nonsolvent mixtures became smaller, the relative crystallinity of PC was increased. The highest degree of PC crystallization was obtained when chloroform/isopropanol was mixed by 61/39 vol%. Subsequently, crystallized PC was used as a filler to high‐density polyethylene (HDPE) composite. HDPE composite incorporated by crystallized PC filler improved its mechanical and thermal properties. Flexural modulus was increased from 620 to 990 N/mm², and flexural strength was increased from 720 to 1080 N/mm². And heat deflection temperature measurement and flammability test supported the enhancement of thermal property when crystallized PC was added to HDPE composite up to 40 wt%. POLYM. ENG. SCI., 54:1893–1899, 2014. © 2013 Society of Plastics Engineers     

Electrochemical characteristics of electrospun La0.6Sr0.4Co0.2Fe0.8O3−δ-Gd0.1Ce0.9O1.95 cathode

The poor activity of cathode materials for electrochemical reduction of oxygen in intermediate and low temperature regime (<700 °C) is a key obstacle to reduced-temperature operation of solid oxide fuel cells (SOFCs). In our previous work, the direct methane fuel cell exhibits approximately 1 W cm⁻² at 650 °C in hydrogen atmosphere without any functional layers when the electrospun LSCF–GDC cathode was applied into the La₂Sn₂O₇–Ni–GDC anode-supported cell, which is approximately two times higher performance than 0.45 W cm⁻² of the cell with the conventional LSCF–GDC cathode. For detailed analysis of the fibrous cathode, the symmetrical cells with the electrospun and conventional LSCF–GDC cathode are fabricated, and then their electrochemical characteristics are measured by using electrochemical impedance spectroscopy (EIS). Each resistance contribution is determined by equivalent circuit consisting of a series resistance (R_s) and three arcs to describe the polarization resistance of the cathode. Total polarization resistance of the electrospun LSCF–GDC cathode is approximately two times lower than that of the conventional LSCF–GDC cathode at 650 °C, which is attributed to fibrous microstructures and large amount of pores in 100–200 nm. The results correspond to the difference in the cell performances obtained from our previous work.     

Peak-switching currents of power transformers

The switching conditions of nonloaded transformers have been investigated to understand the effect of current inrushes and limitations by considering the connecting circuit of the windings, magnetization performances, contact parameters, type of switcher drive, and the value and sign of residual magnetization. The peak-switching currents have been calculated, simulated, and measured and the results have been compared. The obtained results make it possible to increase the power efficiency of the facility by decreasing the losses and maintainign the quality factor of electric power in transient modes.     

Preparation of silica-based proton conductors for intermediate temperature fuel cells

The ternary system SiO₂-P₂O₅-ZrO₂ electrolyte and phosphotungstic acid (PWA) doped SiO₂-P₂O₅-ZrO₂ electrolyte were prepared for intermediate temperature fuel cell by using sol-gel technique. These silica-based proton conductors were confirmed to be non-crystalline structure without phase separation and good thermal stability by XRD and TG/DTA analysis. The doped PWA was found to be stabilized within the silica matrix and to enhance the proton conductivity. The proton conductivities of SiO₂-P₂O₅-ZrO₂ and SiO₂-P₂O₅-ZrO₂-PWA electrolytes showed 3.3×10⁻⁵ and 1.8×10⁻³ S/cm at 90 °C, respectively, and the cell performance of SiO₂-P₂O₅-ZrO₂-PWA electrolyte was obtained as 0.02–0.25 mA/cm² at 300 °C under humid condition.     

Stability and durability of PtRu catalysts supported on carbon nanofibers for direct methanol fuel cells

The chemical stability and durability of PtRu catalysts supported on carbon nanofibers (CNFs) for the anode electrode of a direct methanol fuel cell (DMFC) are investigated by Pt and Ru dissolution tests in sulfuric acid and long-term performance tests of a single cell discharging at a constant current density of 150 mA cm⁻² for approximately 2000 h. A CNF with a herringbone-type structure, which is characterized by the alignment of graphene symmetrically angled to the fiber axis, was selected as the catalyst support because it has an edge-rich surface and a high surface area. In the metal dissolution test, the PtRu/CNF catalysts showed 1.5–2 times lower Ru leaching than a tested commercial catalyst (supported on activated carbon). The results of long-term performance tests also prove the higher durability of the anode catalyst compared with the commercial catalyst, when the anode polarization is compared before and after operation for 2000 h. Some analytical measurements, including X-ray diffraction, energy dispersive spectroscopy, and transmission electron microscopy were conducted to study the degradation of the catalyst activity.     

Pt nanoparticle-reduced graphene oxide nanohybrid for proton exchange membrane fuel cells

A platinum nanoparticle-reduced graphene oxide (Pt-RGO) nanohybrid for proton exchange membrane fuel cell (PEMFC) application was successfully prepared. The Pt nanoparticles (Pt NPs) were deposited onto chemically converted graphene nanosheets via ethylene glycol (EG) reduction. According to the powder X-ray diffraction (XRD) pattern and transmission electron microscopy (TEM) analysis, the face-centered cubic Pt NPs (3-5 nm in diameter) were homogeneously dispersed on the RGO nanosheets. The electrochemically active surface area and PEMFC power density of the Pt-RGO nanohybrid were determined to be 33.26 m2/g and 480 mW/cm2 (maximum values), respectively, at 75 degrees C and at a relative humidity (RH) of 100% in a single-cell test experiment.     

Sr0.92Y0.08TiO3−δ/Sm0.2Ce0.8O2−δ anode for solid oxide fuel cells running on methane

Yttria-doped strontium titanium oxide (Sr_0.92Y_0.08TiO_3−δ; SYT) was investigated as an alternative anode material for solid oxide fuel cells (SOFCs). The SYT synthesized by the Pechini method exhibits excellent phase stability during the cell fabrication processes and SOFC operation and good electrical conductivity (about 0.85 S/cm, porosity 30%) in reducing atmosphere. The performance of SYT anode is characterized by slow electrochemical reactions except for the gas-phase diffusion reactions. The cell performance with the SYT anode running on methane fuel was improved about 5 times by SDC film coating, which increased the number of reaction sites and also accelerated electrochemical reaction kinetics of the anode. In addition, the SDC-coated SYT anode cell was stably operated for 900 h with methane. These results show that the SDC-coated SYT anode can be a promising anode material for high temperature SOFCs running directly on hydrocarbon fuels.