Lifetime prediction of a polymer electrolyte membrane fuel cell via an accelerated startup–shutdown cycle test

To expand commercial applications of polymer electrolyte membrane fuel cells (PEMFCs), the evaluation time for their durability must be shortened. This article provides a straightforward accelerated degradation testing (ADT) procedure for PEMFC for easy and quick implementation of the procedure. The ADT procedure includes statistical modeling of degradation patterns of membrane electrode assemblies (MEAs) in PEMFCs under startup–shutdown cycling conditions. For this purpose, we propose a nonparametric degradation model to describe the nonlinear performance degradation paths of PEMFC MEAs. The analysis results indicate that the nonparametric approach provides more accurate estimates of the observed degradation data than other parametric approaches. Based on the nonparametric degradation model, we suggest a method to predict failure-times under normal operating conditions by estimating the time-scale factor under accelerated operating conditions.     

Stable operation of air-blowing direct methanol fuel cell stacks through uniform oxidant supply by varying fluid flow fixtures and developing the flow sensor

Air-blowing type direct methanol fuel cells (DMFCs) are becoming more attractive for portable electronic devices as alternatives to the currently used Li-ion batteries because they are quieter with less parasitic power loss than the active-type DMFCs used a compressor. However, the blower has difficulty in providing a uniform air supply with a high flow rate to the cathode manifolds of the stack. In this study, a design that allows accurate measurements of the flow distribution on the air-blowing DMFC stack is developed using a novel scientific approach and careful construction of the experimental apparatus. Using this novel experimental technique, a novel stack design is produced to improve the performance and stability of the DMFC system under air-blowing conditions. Furthermore, auxiliary devices, such as ducts, guide vanes, foams, membrane and wedges are integrated and evaluated to the stack to assist in uniform flow by the blower. In particular, the inlet foam, membrane and upper angle duct help improve the uniformity of the lateral and longitudinal flow distribution in the air-blowing stack. Finally, the air-blowing stack with these auxiliary devices shows high performance with operational stability.     

A fractional filter-based beamformer architecture using postfiltering approach to minimize hardware complexity

A novel beamformer architecture using fractional delay filters is proposed and verified through experiments. By performing interchannel summation prior to filtering operation in the manner producing no error, the proposed architecture requires only three four-tap filters for the whole beamformer and four simple demultiplexers per each channel.     

Various synthesis methods of aliovalent-doped ceria and their electrical properties for intermediate temperature solid oxide electrolytes

This article investigates the relationship between ionic conductivity and various processing methods for aliovalent-doped, ceria solid solution particles, as an intermediate temperature-solid oxide electrolyte to explain the wide range of conductivity values that have been reported. The effects of doping material and content on the ionic conductivity are investigated comprehensively in the intermediate temperature range. The chemical routes such as coprecipitation, combustion, and hydrothermal methods are chosen for the synthesis of ceria-based nanopowders, including the conventional solid-state method. The ionic conductivity for the ceria-based electrolytes depends strongly on the lattice parameter (by dopant type and content), processing parameters (particle size, sintering temperature and microstructure), and operating temperature (defect formation and transport). Among other doped-ceria systems, the Nd_0.2Ce_0.8O_2−d electrolyte synthesized by the combustion method exhibits the highest ionic conductivity at 600 °C. Further, a novel composite Nd_0.2Ce_0.8O_2−d electrolyte consisting of a combination of powders (50:50) synthesized by coprecipitation and combustion is designed. This electrolyte demonstrates an ionic conductivity two to four times higher than that of any singly processed electrolytes.     

Computational simulation of cold work effect on PWSCC growth in Alloy 600TT steam generator

The paper presents verification results for the validity of a numerical method considering the effect of cold work on Primary water stress corrosion cracking (PWSCC) growth rate in the Alloy 600TT steam generator tubes with a part-through single axial PWSCC. PWSCC growth simulations using Finite element (FE) analysis were performed with considering various cold work levels of the material. From the FE analysis results, the cold work effect was investigated from the variations of the PWSCC growth rate vs. Stress intensity factor (SIF) for the various cold work degrees and initial SIF values. Investigated results were compared with experimental test data available. It was identified that the numerical method could adequately assess the cold work effect on PWSCC growth in the Alloy 600TT tubes. In the simulation, it was found that the cold work could strongly influence the PWSCC growth rate even in a low degree of cold work, less than 2%.

     

Inhibitory Effect of Avenanthramides (Avn) on Tyrosinase Activity and Melanogenesis in α-MSH-Activated SK-MEL-2 Cells: In Vitro and In Silico Analysis

Melanin causes melasma, freckles, age spots, and chloasma. Anti-melanogenic agents can prevent disease-related hyperpigmentation. In the present study, the dose-dependent tyrosinase inhibitory activity of Avenanthramide (Avn)-A-B-C was demonstrated, and 100 µM Avn-A-B-C produced the strongest competitive inhibition against inter-cellular tyrosinase and melanin synthesis. Avn-A-B-C inhibits the expression of melanogenesis-related proteins, such as TRP1 and 2. Molecular docking simulation revealed that AvnC (−7.6 kcal/mol) had a higher binding affinity for tyrosinase than AvnA (−7.3 kcal/mol) and AvnB (−6.8 kcal/mol). AvnC was predicted to interact with tyrosinase through two hydrogen bonds at Ser360 (distance: 2.7 Å) and Asn364 (distance: 2.6 Å). In addition, AvnB and AvnC were predicted to be skin non-sensitizers in mammals by the Derek Nexus Quantitative Structure–Activity Relationship system.     

Low and high temperature storage characteristics of membrane electrode assemblies for direct methanol fuel cells

This paper investigates changes in the performance of membrane electrode assemblies (MEAs) of Direct Methanol Fuel Cells (DMFC) that are caused by undergoing storage at −10 °C and 60 °C under different experimental conditions. Storage at 60 °C exhibited negative effects on an MEA’s performance only when storing the MEA at a 4 M CH₃OH solution. Here, application of a reverse current for 10 s was found to reinstall the original performance. The effect of storage at −10 °C on an MEA’s performance strongly depends upon the MEA’s properties. MEAs are grouped into three different categories with regard to their suitability for low temperature storage: not affected, temporarily affected, irreversibly affected. The temporarily affected MEAs could be instantly and completely reactivated by a reverse current. Changes in the MEA properties that had been caused by being stored at −10 °C were investigated for two MEAs using electrochemical methods, scanning electron microscopy and porosity measurements. The following MEA materials and manufacturing methods had been found to be principally suitable to build MEAs tolerant to storage at −10 °C: the manufacturing methods CCM (catalyst coated on the membrane) and CCS (catalyst coated on the substrate), several hydrocarbon membranes, high Pt and Pt-Ru catalyst loadings. By carefully selecting the proper MEA material, MEAs with tolerance towards low and high storage temperatures can be designed.     

Design of flat broadband sound insulation metamaterials by combining Helmholtz resonator and fractal structure

Journal of Mechanical Science and Technology - A new sound insulation metamaterial (SIM) is designed by combining a Helmholtz resonator and a fractal structure for sound insulation in the frequency...     

Ceria-based electrolyte reinforced by sol–gel technique for intermediate-temperature solid oxide fuel cells

High performance solid oxide fuel cells (SOFCs) based on gadolinia-doped ceria (GDC) electrolyte are demonstrated for intermediate temperature operation. The inherent technical limitations of the GDC electrolyte in sinterability and mechanical properties are overcome by applying sol–gel coating technique to the screen-printed film. When the quality of the electrolyte film is enhanced by the additional sol–gel coating, the OCV and maximum power density increase from 0.73 to 0.90 V and from 0.55 to 0.95 W cm⁻², respectively, at 650 °C with humidified hydrogen (3% H₂O) as fuel and air as oxidant. The impedance analysis reveals that the reinforcement of the thin electrolyte with sol–gel coating significantly reduces the polarization resistance. Elementary reaction steps for the anode and cathode are analyzed based on the systematic impedance study, and the relation between the structural integrity of the electrolyte and the electrode polarization is discussed in detail.     

High-current field emission of point-type carbon nanotube emitters on Ni-coated metal wires

The fabrication and field emission characteristics are reported for point-type carbon nanotube (CNT) emitters formed by transferring a CNT film onto a Ni-coated Cu wire with a diameter of 1.24 mm. A Ni layer plays a role in enhancing the adhesion of CNTs to the substrate and improving their field emission characteristics. On firing at 400 °C, CNTs appear to directly bonded to a Ni layer. With a Ni layer introduced, a turn-on electric field of CNT emitters decreases from 1.73 to 0.81 V/μm by firing. The CNT film on the Ni-coated wire produces a high emission current density of 667 mA/cm² at quite a low electric field of 2.87 V/μm. This CNT film shows no degradation of emission current over 40 h for a current density of 60 mA/cm² at electric field of 6.7 V/μm. X-ray imaging of a printed circuit board with fine features is demonstrated by using our point-type CNT emitters.