Yong Gun Shul

Influence of pore-size distribution of diffusion layer on mass-transport problems of proton exchange membrane fuel cells

The influence of pore-size distribution of the diffusion layer on mass-transport problems of proton exchange membrane fuel cells (PEMFCs) is investigated using electrodes with hydrophobic diffusion layers for which the pore-size distribution is designed by pore-former and heat treatment. It is confirmed that the pore-size distribution of the diffusion layer is a more critical parameter for mass-transport processes within the electrode and for cell performance characteristics than the total porosity itself. Data obtained from mercury intrusion porosimetry, single-cell performance tests and ac impedance analyses indicate that the performance loss due to mass-transport limitations can be reduced by enlarging the macropore volume in the diffusion layer. The water flooding problem is discussed in terms of condensation phenomena which are dependent on pore-size.

Scratch Resistant and Transparent UV-Protective Coating on Polycarbonate

UV-protective coating material has been developed to improve the scratch resistance and transparency of polycarbonate substrates. Acetyl acetone (AcAc) chelated silanes and 3-glycidoxypropyl-trimethoxysilane (GPTMS) modified nano-titania sols were used for the UV-protective hard coating materials by the sol-gel technique. The hybrid network is formed as a result of the controlled hydrolysis and condensation of the MTMS (Methyl Tri Methoxy Silane) and DMDMS (Di Methyl Di Methoxy Silane). Surface modified TiO2 nano particles were dispersed in sterically stabilized in the hybrid network by the chelating agent. The coatings dried at 130°C after spray coating were shown to have excellent scratch resistance and adhesion and in addition, it roles as efficient UV-protector under UV irradiation. The long time UV test resulted in no crack formation, without loss of adhesion within the test period of 20 weeks.

Tailoring gadolinium-doped ceria-based solid oxide fuel cells to achieve 2 W cm(-2) at 550 °C.

Low-temperature operation is necessary for next-generation solid oxide fuel cells due to the wide variety of their applications. However, significant increases in the fuel cell losses appear in the low-temperature solid oxide fuel cells, which reduce the cell performance. To overcome this problem, here we report Gd0.1Ce0.9O1.95-based low-temperature solid oxide fuel cells with nanocomposite anode functional layers, thin electrolytes and core/shell fibre-structured Ba0.5Sr0.5Co0.8Fe0.2O3-δ-Gd0.1Ce0.9O1.95 cathodes. In particular, the report describes the use of the advanced electrospinning and Pechini process in the preparation of the core/shell-fibre-structured cathodes. The fuel cells show a very high performance of 2 W cm(-2) at 550 °C in hydrogen, and are stable for 300 h even under the high current density of 1 A cm(-2). Hence, the results suggest that stable and high-performance solid oxide fuel cells at low temperatures can be achieved by modifying the microstructures of solid oxide fuel cell components.

Characterization of photoreduced PtTiO2 and decomposition of dichloroacetic acid over photoreduced PtTiO2 catalysts

Abstract The effect of photoreduction on the properties of Pt TiO 2 catalysts was investigated. A decrease of the white-line area in the XANES spectra of Pt TiO 2 catalysts at the Pt LIII edge was observed with increasing photoreduction time, which denoted the photoreduction of Pt TiO 2 with UV illumination. From the EXAFS fitting results, the growth of Pt particles with the photoreduction time could be monitored. The XPS spectra of Pt TiO 2 catalysts at the Pt4f 5 2 and Pt4f 7 2 bands showed the presence of Pt0 and Pt2+ states after photoreduction and the fraction of metallic Pt0 was increased with increasing photoreduction time. The optimum photoreduction time for DCA (dichloroacetic acid) decomposition was 6 h. The partially reduced state of Pt seems to be effective to obtain a high quantum yield in DCA decomposition with minimizing the agglomeration of Pt clusters on the TiO2 surface.

A New Family of Perovskite Catalysts for Oxygen-Evolution Reaction in Alkaline Media: BaNiO3 and BaNi0.83O2.5

Establishment of a sustainable energy society has been strong driving force to develop cost-effective and highly active catalysts for energy conversion and storage devices such as metal-air batteries and electrochemical water splitting systems. This is because the oxygen evolution reaction (OER), a vital reaction for the operation, is substantially sluggish even with precious metals-based catalysts. Here, we show for the first time that a hexagonal perovskite, BaNiO3, can be a highly functional catalyst for OER in alkaline media. We demonstrate that the BaNiO3 performs OER activity at least an order of magnitude higher than an IrO2 catalyst. Using integrated density functional theory calculations and experimental validations, we unveil that the underlying mechanism originates from structural transformation from BaNiO3 to BaNi(0.83)O(2.5) (Ba6Ni5O15) over the OER cycling process.

DNA Core@Inorganic Shell

A chemically well-defined Bio Core@Inorganic Shell nanohybrid, which consists of rationally designed DNA molecule core with a size of ∼100 nm and spherical inorganic nanoshell with an overall thickness of ∼10 nm reassembled with exfoliated layered metal hydroxide (MH nanosheets), is prepared. The DNA encapsulation and its release, due to the pH-dependent solubility of the MH nanoshell, plays a crucial role in maximizing the stability of base sequence-manipulated and probe-functionalized DNA molecules with designed information. The present DNA Core@MH Shell nanohybrid can provide wide bioinspired applications converged with nanotechnology, such as an advanced gene delivery system and a biomedical diagnostics, tracing/collection/sensing system for DNA-based information.

Preparation of Organic-Inorganic Composite Adsorbent Beads for Removal of Radionuclides and Heavy Metal Ions

Composite ion exchanger beads were prepared to remove the strontium and silver ions in acidic solution. Potassium titanate and nickelferrocyanate powder, which are acid resistant inorganic ion exchangers were synthesized and then mixed with polyacrylonitrile (PAN) binder to form a PAN-potassium titanate and a PAN-nickelferrocyanate composite ion exchanger beads. Spherical composite beads could be obtained by adjusting the viscosities of the composite dope in the range of 700–1000 cP. The composite beads porosities such as macropore volume and pore size were increased in proportion to the contents of PVP (polyvinylpyrrolidone) which was used as the porosity modifying chemical. The synthesized composite ion exchangers were evaluated on their adsorption characteristics for the Ag1 and Sr21 ion solutions of pH 2.

Morphology of particles prepared by spray pyrolysis from organic precursor solution

To control the morphology of the particles prepared from high-concentration solution under severe preparation conditions, an organic polymeric precursor solution was introduced in spray pyrolysis. In the aqueous solution, hollow particles were formed by the surface precipitation because of rapid drying rate of droplet in the severe preparation condition. On the other hand, in the polymeric precursor solution, the polymeric chain formed from the esterification reaction between carboxyl and hydroxy groups of citric acid (CA) and ethylene glycol (EG) changed the drying characteristics of droplet. When a droplet was passing through the quartz reactor, a droplet turned into viscous gel precursors, which retarded the precipitation of salts inside droplet. Therefore, the particles prepared from polymeric precursor solution had a spherical shape and a filled morphology by the volume precipitation of salt.

Effect of metal and glycol on mechanochemical dechlorination of polychlorinated biphenyls (PCBs)

This paper assesses the potential of mechanochemical method with fine metal powder, glycol and alkali for polychlorinated biphenyls (PCBs) removal from waste insulating oil. The effects of relevant parameters, such as kinds of chemicals, rate and time of milling were examined. After each run, the total PCBs content in waste insulating oil was measured. Polyethylene glycol 200, long chain-glycol was more effective than triethylene glycol and ethylene glycol, short chain-glycol as hydrogen donor in mechanochemical dechlorination of PCBs. A maximum of 99.9% PCBs removal (below 2 ppm) and 94% total chlorine removal were achieved with the mechanochemical process for 2 h.

Comparison Study of Mixing Effect on Batch Cooling Crystallization of 3-Nitro-1,2,4-triazol-5-one (NTO) Using Mechanical Stirrer and Ultrasound Irradiation

The insensitive explosive 3-nitro-1,2,4-triazol-5-one (NTO) has been recrystallized from water in an effort to prepare crystals with smaller size and narrower distribution in a batch cooling crystallizer. Two mixing devices, i.e., a mechanically stirred system with and without ultrasound in aqueous media were employed to compare the mixing effect on the crystallization. Under ultrasound irradiation, the metastable zone width was significantly reduced by more than 2 fold and the crystal size was shifted from 140∼160 μm to 50∼70 μm with a narrower CSD compared to the mechanically stirred system. However in the mechanical stirrer, the mixing effect on NTO crystallization was negligible if the impeller speed was sufficient to suspend all crystals in the crystallizer. It was found that the crystal growth was not influenced by mixing. We suggest that the NTO crystals were formed by primary heterogeneous nucleation that is common in batch cooling system. Finally, the population balance model (PBM), with the empirical nucleation and growth kinetic expressions, was solved numerically to predict the crystal size and the CSD with batch time, and the results were in good agreement with the experimental data.