Search

To address the global climate change issues, polymer electrolyte fuel cells (PEFCs) are receiving attention as electrochemical energy conversion devices employing green hydrogen. Notably, the PEFC fuel cell is because the electrochemical reaction occurs on the Catalyst Layer (CL), the CL is the core of the Membrane Electrode Assembly (MEA). The conventional CL is usually prepared from catalyst ink comprising the various catalyst, ionomer, and solvents and deposited via blade coating to the decal substrate. Therefore, it is necessary to confirm the optimal decal transfer conditions based on analyzing the characteristics of the catalyst ink and the decal substrate. In the study, the characterize the internal microstructure of the catalyst ink was confirmed through rheology, and the coating velocity was tunable based on catalyst property. In addition, the characteristics of the various decal substrate were confirmed through Atomic Force Microscopy (AFM) and Contact Angle, and differences including variations in loading amount were confirmed despite the same slurry. The structure of CL on the decal sheet was confirmed through a scanning electron microscope (SEM) surface image and cross-section image, and the distribution of Pt and ionomer was confirmed through Energy Dispersive X-Ray Spectrometer (EDS) mapping. The definition of electrochemical performance between catalyst ink characterizes and decal substrates property was investigated through polarization curves and electrochemical impedance spectroscopy (EIS). Also, cyclic voltammetry (CV) techniques are used to characterize electrochemical surface areas (ECSA) areas of the CL. As a result, the property between the catalyst ink and the decal substrate, based on the difference that occurs in the rheology characterized in the catalyst ink, leads to a variation in the CL structure. Therefore, it is very important to determine the decal process conditions by understanding the characteristics of various catalyst ink on rheology and decal sheet.

A unique nanostructured NiO-yttria-stabilized zirconia (YSZ) composite is synthesized in-situ via a water-in-oil microemulsion technique for the solid oxide fuel cell (SOFC) anode. Thermogravimetric analysis and X-ray diffraction confirm that as-synthesized powders are crystallized in-situ at ∼500 °C as the distinct NiO and YSZ phases without any impurities. Moreover, transmission electron microscopy analysis reveals that the as-synthesized primary particles via microemulsion are ∼40 nm in size and have a characteristic structure in which NiO and YSZ nanograins are heterogeneously distributed. The electrochemical activity of the nanostructured NiO-YSZ composite is evaluated using an YSZ supported cell with a La0.8Sr0.2MnO3-δ-YSZ (50:50 wt.%) cathode. The maximum power density of the SOFC employing the microemulsion-mediated NiO-YSZ anode is 2.2 times greater than that of the SOFC with the conventionally ball-milled nano-sized NiO-YSZ anode. The higher performance with our nanocomposite NiO-YSZ anode is primarily attributed to its heterogeneous nanograin structure, thus leading to a significant increase in triple phase boundary densities.

Time-saving stack activation and effective long-term storage are one of most important issues that must be resolved for the commercialization of polymer electrolyte membrane fuel cell (PEMFC). Herein, we developed the cost-effective stack activation method to finish the whole activation within 30 min and the long-term storage method by using humidified N 2 without any significant decrease in cell's performance for 30 days. Specifically, the pre-activation step with the direct injection of DI water into the stack and storage at 65 or 80 °C for 2 h increases the distinctive phase separation between the hydrophobic and hydrophilic regions in Nafion membrane, which significantly reduces the total activation time within 30 min. Additionally, the long-term storage with humidified N 2 has no effect on the Pt oxidation and drying of Nafion membrane for 30 days due to its exergonic reaction in the cell. As a result, the high water content in Nafion membrane and the decrease of Pt oxidation are the critical factors that have a strong influence on the activation and long-term storage for high-performance PEMFC.

We studied the degradation and durability of polymer electrolyte membrane fuel cell (PEMFC) at membrane-electrode-assembly (MEA) level by injection of octamethylcyclotetrasiloxane (D4) as a representative siloxane, which has been found in many industrial and personal products. Specifically, i ) GC/MS analysis demonstrated that the ring-opening polymerization of D4 could result in the formation of various linear and cyclic siloxanes in both electrodes of MEA; ii ) post-test analysis revealed that the transformed siloxanes were transported from the anode to the cathode via free-volumes in the polymer membrane; iii ) RDE measurement and DFT calculation revealed that D4 was not directly responsible for the electrocatalytic activity of Pt; iv ) electrochemical analysis demonstrated that the residual methyl groups of siloxane and various siloxanes did not hinder the proton transport in the polymer membrane; and v ) siloxanes accumulated in the primary and secondary pores with the exception of an external surface of carbon, causing an increase in the oxygen reactant's resistance and resulting in a decrease of the cell performance. In addition, we confirmed that injection of D4 did not affect the carbon corrosion adversely because the siloxane had little influence on water sorption in the catalyst layer.

This paper proposes a shortened transmit technique using repetitive transmission in the frequency domain. For a single antenna OFDM system, a hybrid selection combining and maximum ratio receive combining technique was proposed for better performance, but it is effective only for high Eb/N0 region. This paper suggests a new method of removing zeros generated from repetitive transmission and of reconfiguring repetitive transmit time domain signals for maximum ratio receive combining at the receiver, by which we can obtain better performance comparing to SISO case at the expense of a few algebraic calculations and FFT/IFFT executions.

Recently, there have been several interesting researches on the microfactory especially in Japan, U.S., and Korea. Since the microfactory possess the advantage of flexible manufacturing system and/or reconfigurable manufacturing system, we introduced the concept of modular reconfigurable machine structure in our micro machine tool design for microfactory. Modular reconfigurable machine tools can easily perform machining processes of different kinds such as milling, turning, drilling and or grinding by simply adding or exchanging machine tool units or modules. In this study, we have developed a reconfigurable micro machine tool for microfactory, which can be reconfigured from a milling machine to a tuning lathe or vice versa. In structural design of the machine tools, we already studied a new theoretical method of creating machine configurations of modular-reconfigurable machine tools (MRMT) in the preliminary design stage. According to our design methodology, we designed the structural modules and RMTs after reviewing all feasible configurations in the preliminary design stage. By using some modules, we have built RMT based the micro milling machine with enough stiffness. The 3-axis micro milling machine of RMT has a mini-desktop size of 300 mm times200 mm times320 mm and its travel volume is 10 times 10times 10 mm3. Dynamic characteristics including natural frequencies and dynamic stiffness of the developed MRMT were analyzed and examined by using F.E.M. and impact hammer test. And we carried out positioning control test and cutting test using a motion controller. Consequently, we successfully developed reconfigurable micro machine tool with reconfigurable structures of milling machine and turning machine for microfactory by means of configuration simulation, structure and module design, FE analysis, and dynamic characteristic tests such as a modal test and dynamic compliance test.

The new local dimming method and new electrode structure of MFFL were proposed. It was found that long-gap panel was more appropriate to increase the lamp efficiency. A new method of controlling the number of pulses to achieve partial discharge of the panels and this method was demonstrated. The system efficiency was measured as 20 lm/W.