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Segeun Jang,Yun Sik Kang,Jiwoo Choi,Je Hyeon Yeon,Changwook Seol,Le Vu Nam,Mansoo Choi,Sang Moon Kim,Sung Jong Yoo 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.90 No.-
A simple and facile way of modifying commercial membranes for effective fuel cell operation underelevated temperature/low relative humidity conditions has been developed. Instead of using theconventional casting and evaporation method involving the mixed Nafion1 ionomer and inorganicfillers,a TiO2/Nafion1 composite membrane was fabricated by transferring uniformly constructed porous TiO2layers from a Si wafer to the Nafion1 membrane via spin-coating, followed by a thermal imprintingprocess. From the process,filler agglomeration was prevented during the solvent evaporation, whichsecured water retention effect of the hygroscopic TiO2 layers. Furthermore, the prepared TiO2/Nafion1composite membrane was subjected to an additional prism patterning process to provide more protonpathways by enlarging the interfacial surface area between the composite membrane and the catalystlayer, and offset the reduced proton conductivity due to insertion of the inorganicfillers. The modifiedmembrane exhibited highly improved performance compared to the pristine Nafion1 211 membraneunder elevated temperature/low humidity conditions.
Jang, Segeun,Kim, Sungjun,Kim, Sang Moon,Choi, Jiwoo,Yeon, Jehyeon,Bang, Kijoon,Ahn, Chi-Yeong,Hwang, Wonchan,Her, Min,Cho, Yong-Hun,Sung, Yung-Eun,Choi, Mansoo unknown 2018 Nano energy Vol.43 No.-
<P><B>Abstract</B></P> <P>Capability to fabricate high-performance membrane electrode assemblies (MEAs) is a key to the commercialization of direct methanol fuel cells (DMFCs). This work reports an interface engineering method to introduce a multiscale patterned membrane and a guided metal cracked layer between the catalyst layer and the membrane by the creep-assisted sequential imprinting and simple stretching technique. The MEA with a multiscale patterned membrane, where the nanopatterns covered the whole surface even on the side surface of microstructures, showed improved performance owing to enhanced mass transport by the thinned electrode, effective utilization of the active sites, and increased Pt utilization. To obtain further performance enhancement, we incorporated a guided gold cracked layer into the MEA with the multiscale patterned membrane. The electrochemically inactive thin gold layer acted as a physical barrier for methanol crossover and the guided cracks provided multiple proton pathways. Our interface engineering utility resulted in an enhancement of the device performance by 42.3% compared with that of the reference.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Interface engineering was employed to develop a high-performance DMFC. </LI> <LI> A creep-assisted sequential imprinting and simple stretching method was used. </LI> <LI> Enlarged membrane–electrode interface improved anode kinetics and mass transport. </LI> <LI> Au layer blocked methanol crossover while cracks maintained proton conductivity. </LI> <LI> Multiscale patterned membrane/guided Au cracked layer improved device performance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Membrane/Electrode Interface Design for Effective Water Management in Alkaline Membrane Fuel Cells
Jang, Segeun,Her, Min,Kim, Sungjun,Jang, Jue-Hyuk,Chae, Ji Eon,Choi, Jiwoo,Choi, Mansoo,Kim, Sang Moon,Kim, Hyoung-Juhn,Cho, Yong-Hun,Sung, Yung-Eun,Yoo, Sung Jong American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.38
<P>The recent development of ultrathin anion exchange membranes and optimization of their operating conditions have significantly enhanced the performance of alkaline-membrane fuel cells (AMFCs); however, the effects of the membrane/electrode interface structure on the AMFC performance have not been seriously investigated thus far. Herein, we report on a high-performance AMFC system with a membrane/electrode interface of novel design. Commercially available membranes are modified in the form of well-aligned line arrays of both the anode and cathode sides by means of a solvent-assisted molding technique and sandwich-like assembly of the membrane and polydimethylsiloxane molds. Upon incorporating the patterned membranes into a single-cell system, we observe a significantly enhanced performance of up to ∼35% compared with that of the reference membrane. The enlarged interface area and reduced membrane thickness from the line-patterned membrane/electrode interface result in improved water management, reduced ohmic resistance, and effective utilization of the catalyst. We believe that our findings can significantly contribute further advancements in AMFCs.</P> [FIG OMISSION]</BR>
Multifunctional Moth-Eye TiO<sub>2</sub>/PDMS Pads with High Transmittance and UV Filtering
Jang, Segeun,Kang, Seong Min,Choi, Mansoo American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.50
<P>This work reports a facile fabrication method for constructing multifunctional moth-eye TiO2/polydimethylsiloxane (PDMS) pads using soft nano-imprinting lithography and a gas-phase-deposited thin sacrificial layer. Mesoporous TiO2 nanoparticles act as an effective UV filter, completely blocking high-energy UVB light and partially blocking UVA light and forming a robust TiO2/PDMS composite pad by allowing the PDMS solution to easily fill the porous TiO2 network. The paraboloid-shaped moth-eye nanostructures provided high transparency in the visible spectrum and also have self-cleaning effects because of nanoroughness on the surface. Furthermore, we successfully achieved a desired multiscale-patterned surface by partially curing select regions using TiO2/PDMS pads with partial UVA ray blockers. The ability to fabricate multifunctional polymeric pads is advantageous for satisfying increasing demands for flexible and wearable electronics, displays, and solar cells.</P>
Facile Multiscale Patterning by Creep-Assisted Sequential Imprinting and Fuel Cell Application
Jang, Segeun,Kim, Minhyoung,Kang, Yun Sik,Choi, Yong Whan,Kim, Sang Moon,Sung, Yung-Eun,Choi, Mansoo American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.18
<P>The capability of fabricating multiscale structures with desired morphology and incorporating them into engineering applications is key to realizing technological breakthroughs by employing the benefits from both microscale and nanoscale morphology simultaneously. Here, we developed a facile patterning method to fabricate multiscale hierarchical structures by a novel approach called creep assisted sequential imprinting. In this work, nanopatterning was first carried out by thermal imprint lithography above the glass transition temperature (T-g) of a polymer film, and then followed by creep-assisted imprinting with micropattems based on the mechanical deformation of the polymer film under the relatively long-term exposure to mechanical stress at temperatures below the T-g of the polymer. The fabricated multiscale arrays exhibited excellent pattern uniformity over large areas. To demonstrate the usage of multiscale architectures, we incorporated the multiscale Nafion films into polymer electrolyte membrane fuel cell, and this device showed more than 10% higher performance than the conventional one. The enhancement was attributed to the decrease in mass transport resistance because of unique cone shape morphology by creep-recovery effects and the increase in interfacial surface area between Nafion film and electrocatalyst layer.</P>
Ha, Kyungyeon,Jang, Eunseok,Jang, Segeun,Lee, Jong-Kwon,Jang, Min Seok,Choi, Hoseop,Cho, Jun-Sik,Choi, Mansoo IOP 2016 Nanotechnology Vol.27 No.5
<P>We report three-dimensionally assembled nanoparticle structures inducing multiple plasmon resonances for broadband light harvesting in nanocrystalline silicon (nc-Si:H) thin-film solar cells. A three-dimensional multiscale (3DM) assembly of nanoparticles generated using a multi-pin spark discharge method has been accomplished over a large area under atmospheric conditions via ion-assisted aerosol lithography. The multiscale features of the sophisticated 3DM structures exhibit surface plasmon resonances at multiple frequencies, which increase light scattering and absorption efficiency over a wide spectral range from 350–1100 nm. The multiple plasmon resonances, together with the antireflection functionality arising from the conformally deposited top surface of the 3D solar cell, lead to a 22% and an 11% improvement in power conversion efficiency of the nc-Si:H thin-film solar cells compared to flat cells and cells employing nanoparticle clusters, respectively. Finite-difference time-domain simulations were also carried out to confirm that the improved device performance mainly originates from the multiple plasmon resonances generated from three-dimensionally assembled nanoparticle structures.</P>
Seol, Changwook,Jang, Segeun,Kim, Junsoo,Jun, Tea-Sung,Kim, Sang Moon The Royal Society of Chemistry 2018 SOFT MATTER Vol.14 No.47
<P>Herein, we report the fabrication process and the investigation of mechanically stable, flexible and free-standing polymeric membranes with two-level apertures. By using overlapped oxygen inhibition layers (OILs) with variation in diameters of the micro-sized supporting layer, we successfully fabricated the mechanically stable and free-standing polymeric membrane with micro/nano two-level apertures. The nano aperture membrane was stably sustained on the micro aperture membrane with a diameter of 50 μm and 100 μm, but was torn off in the case of 300 μm and 500 μm sized supporting layers. To analyze the results, we propose a simple model to set the criteria of the geometrical features which are mechanically stable during the demolding process. It is worth noting that an appropriate material modulus, length, and thickness of the membrane are required for designing and achieving the robust free-standing hierarchical polymeric membrane.</P>