Yukwon Jeon

A facile preparation method of surface patterned polymer electrolyte membranes for fuel cell applications

We report a facile patterning method that facilitates production of large-area platforms with well-arrayed micro/nanopatterns of a polymer electrolyte membrane (PEM) at low cost using an elastomeric mold at room temperature without hot-pressing. Membrane–electrode interfacial properties on the cathode side are controlled by the patterned structure of the membrane, which in turn directly affects the electrochemically active surface area (ECSA) and Pt utilization of the catalyst. This confirmed that electrochemical properties improve the performance of the membrane electrode assembly (MEA). A MEA fabricated with a 3 × 5 μm (width × gap) micropatterned Nafion membrane exhibits a current density of 1.79 A cm−2 at 0.6 V and a power density of 1.26 W cm−2 at 75 °C; these values are 53% and 59% greater than those of the corresponding MEA without a patterned membrane, respectively, and are among the highest performances reported for polymer electrolyte membrane fuel cells (PEMFCs). However, use of a nanopatterned membrane decreases the performance due to insufficient infiltration of the ionomer into the grooved surface, leading to a poor mechanical/electrical contact between the membrane and the electrode. Membrane morphology and the structure of the membrane–electrode interface are characterized by field emission scanning electron microscopy (FE-SEM), cyclic voltammetry (CV), and impedance spectroscopy.

Hollow Fibers Networked with Perovskite Nanoparticles for H2 Production from Heavy Oil

Design of catalytic materials has been highlighted to build ultraclean use of heavy oil including liquid-to-gas technology to directly convert heavy hydrocarbons into H2–rich gas fuels. If the H2 is produced from such heavy oil through high-active and durable catalysts in reforming process that is being constructed in hydrogen infrastructure, it will be addressed into renewable energy systems. Herein, the three different hollow fiber catalysts networked with perovskite nanoparticles, LaCr0.8Ru0.2O3, LaCr0.8Ru0.1Ni0.1O3, and LaCr0.8Ni0.2O3 were prepared by using activated carbon fiber as a sacrificial template for H2 production from heavy gas oil reforming. The most important findings were arrived at: (i) catalysts had hollow fibrous architectures with well-crystallized structures, (ii) hollow fibers had a high specific surface area with a particle size of ≈50 nm, and (iii) the Ru substituted ones showed high efficiency for H2 production with substantial durability under high concentrations of S, N, and aromatic compounds.

Interface-designed Membranes with Shape-controlled Patterns for High-performance Polymer Electrolyte Membrane Fuel Cells

Polymer electrolyte membrane fuel cell is a promising zero-emission power generator for stationary/automotive applications. However, key issues, such as performance and costs, are still remained for an economical commercialization. Here, we fabricated a high-performance membrane electrode assembly (MEA) using an interfacial design based on well-arrayed micro-patterned membranes including circles, squares and hexagons with different sizes, which are produced by a facile elastomeric mold method. The best MEA performance is achieved using patterned Nafion membrane with a circle 2 μm in size, which exhibited a very high power density of 1906 mW/cm2 at 75 °C and Pt loading of 0.4 mg/cm2 with 73% improvement compared to the commercial membrane. The improved performance are attributed to the decreased MEA resistances and increased surface area for higher Pt utilization of over 80%. From these enhanced properties, it is possible to operate at lower Pt loading of 0.2 mg/cm2 with an outstanding performance of 1555 mW/cm2 and even at air/low humidity operations.

Direct spun aligned carbon nanotube web-reinforced proton exchange membranes for fuel cells

A new method combining electrospinning of SPEEK and direct spinning of CNT forests has been used to prepare sulfonated poly(ether ether ketone) (SPEEK)/directly spinnable carbon nanotube (dsCNT) composite proton exchange membranes. The SPEEK/dsCNT membrane is more robust than SPEEK alone, and in a fuel cell significantly outperforms both SPEEK and the commercial Nafion 212 membranes.

Solvent screening for the separation of ethylbenzene and p-xylene by extractive distillation

Extractive distillation is one of the most effective processes for the separation of ethylbenzene and p-xylene. The goal was to find single solvents or combinations of multi-solvents with good properties while minimizing the ratio of solvent to feed. The distillations were performed at equilibrium to determine the relative volatility of ethylbenzene to p-xylene with the extractive solvents under isothermal condition. For a single extraction solvent, 1,2,4-trichlorobenzene had the highest relative volatility at 1.123. In some cases, combinations of two or three solvents were used as well as different ratios of solvent to feed to investigate the synergy effect of the mixture solvents. The binary solvent mixture of 1,2,4-trichlorobenzene and maleic anhydride (2: 1) had the best performance with a relative volatility of 1.228 at the solvent/feed ratio of 1: 1. Some of the solvents were further studied at different solvent/feed (S/F) ratios. Selected solvents generally tended to have higher relative volatilities at high S/F ratios, but the operation cost will increase. Therefore, it is important to find the proper conditions to optimize the S/F ratio for extractive distillation from the industrial point of view.

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).

Corn-cob like nanofibres as cathode catalysts for an effective microstructure design in solid oxide fuel cells

An efficient cathode for solid oxide fuel cells (SOFC) is mainly determined by the oxygen reduction reaction (ORR) activity of mixed materials. We demonstrate a new microstructure design through a nanofibrous electrode based on a unique corn-cob structure. A one-step process to produce corn-cob ceramic nanofibers of La0.8Sr0.2MnO3 (LSM) and Y2O3-stabilized ZrO2 (YSZ) is introduced using an electrospinning system equipped with a coaxial nozzle. From the microscope analysis, perfect corn-cob nanofibers are finely produced with a diameter of 350 nm for the core and nanoparticles (30–40 nm) stacked on the surface similar to a core–shell structure. The cathode fabricated using nanofibers with LSM outside and YSZ inside (YSZ@LSM) shows the best maximum power density of 1.15 W cm−2 at 800 °C with low polarization resistance, which is higher than that of the reverse core and shell positions (LSM@YSZ) and even the commercial LSM–YSZ. This better outcome is more prominent at elevated temperatures due to its accelerated catalytic activity. Therefore, insight into the key factors that enhance ORR activity and single cell performance is obtained in terms of not only the nanofibrous core@shell structure but also more reaction active sites from the optimum catalyst position at the designed corn-cob nanofiber based cathodes.

The particle size effect of N-doped mesoporous carbons as oxygen reduction reaction catalysts for PEMFC

The particle size effect of N-doped mesoporous carbon was investigated for ORR activity in acid condition and for issue of a mass transfer and gas diffusion in PEMFCs. As for a non-Pt ORR catalyst, nitrogen (N)-doped ordered mesoporous carbons (OMCs) with a various particle sizes with the range of the average 20, 45 and 75 μm were synthesized by the precursor of polyaniline for the N/C species, and a mesoporous silica template was used for the physical structure for preparation of nitrogen doped OMCs. The N-doped mesoporous carbons are promoted by a transition metal (Fe) to improve catalytic activity for ORR in PEMFCs. All the prepared carbons were characterized by via scanning electron microscopy (SEM), and to evaluate the activities of synthesized doped carbons, linear sweep was recorded in an acidic solution to compare the ORR catalytic activities values for the use in the PEMFC system. The surface area and pore volume were increased as the particles decreased, which was effective for the mass transfer of the reactant for higher activity at the limiting current regions.

One-step synthesis of dual-transition metal substitution on ionic liquid based N-doped mesoporous carbon for oxygen reduction reaction

Nitrogen (N)-doped ordered mesoporous carbons (OMCs) with a dual transition metal system were synthesized as non-Pt catalysts for the ORR. The highly nitrogen doped OMCs were prepared by the precursor of ionic liquid (3-methyl-1-butylpyridine dicyanamide) for N/C species and a mesoporous silica template for the physical structure. Mostly, N-doped carbons are promoted by a single transition metal to improve catalytic activity for ORR in PEMFCs. In this study, our N-doped mesoporous carbons were promoted by the dual transition metals of iron and cobalt (Fe, Co), which were incorporated into the N-doped carbons lattice by subsequently heat treatments. All the prepared carbons were characterized by via transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). To evaluate the activities of synthesized doped carbons, linear sweep was recorded in an acidic solution to compare the ORR catalytic activities values for the use in the PEMFC system. The dual transition metal promotion improved the ORR activity compared with the single transition metal promotion, due to the increase in the quaternary nitrogen species from the structural change by the dual metals. The effect of different ratio of the dual metals into the N doped carbon were examined to evaluate the activities of the oxygen reduction reaction.

Oxide–Carbon Nanofibrous Composite Support for a Highly Active and Stable Polymer Electrolyte Membrane Fuel-Cell Catalyst

Well-designed electronic configurations and structural properties of electrocatalyst alter the activity, stability, and mass transport for enhanced catalytic reactions. We introduce a nanofibrous oxide-carbon composite by an in situ method of carbon nanofiber (CNF) growth by highly dispersed Ni nanoparticles that are exsoluted from a NiTiO3 surface. The nanofibrous feature has a 3D web structure with improved mass-transfer properties at the electrode. In addition, the design of the CNF/TiO2 support allows for complex properties for excellent stability and activity from the TiO2 oxide support and high electric conductivity through the connected CNF, respectively. Developed CNF/TiO2-Pt nanofibrous catalyst displays exemplary oxygen-reduction reaction (ORR) activity with significant improvement of the electrochemical surface area. Moreover, exceptional resistance to carbon corrosion and Pt dissolution is proven by durability-test protocols based on the Department of Energy. These results are well-reflected to the single-cell tests with even-better performance at the kinetic zone compared to the commercial Pt/C under different operation conditions. CNF/TiO2-Pt displays an enhanced active state due to the strong synergetic interactions, which decrease the Pt d-band vacancy by electron transfer from the oxide-carbon support. A distinct reaction mechanism is also proposed and eventually demonstrates a promising example of an ORR electrocatalyst design.