Woo-Jae Lee

Bio: Woo-Jae Lee is an academic researcher from Pusan National University. The author has contributed to research in topics: Atomic layer deposition & Thin film. The author has an hindex of 8, co-authored 22 publications receiving 198 citations.

Synthesis of highly dispersed Pt nanoparticles into carbon supports by fluidized bed reactor atomic layer deposition to boost PEMFC performance

Abstract: The performance of proton exchange membrane fuel cells (PEMFCs) depends on the controlled size, dispersion and density of Pt nanoparticles (NPs) on carbon supports, which are strongly affected by the carbon characteristics and fabrication methods. Here, we demonstrated a high-performance Pt/carbon catalyst for PEMFCs using fluidized bed reactor atomic layer deposition (FBR-ALD) that was realized by an effective matching of the carbon supports for the FBR-ALD process and an optimization of the ionomer content during the preparation of the membrane electrode assembly (MEA). For this, the synthesis of Pt NPs was conducted on two porous supports (Vulcan XC-72R and functionalized carbon) by FBR-ALD. The functionalized carbon possessed a higher surface area with a large pore volume, abundant defects in a disordered structure and a large number of oxygen functional groups compared to those of the well-known Vulcan carbon. The favorable surface characteristics of the functionalized carbon for nucleation produced Pt particles with an increased uniformity and density and a narrow size range, which led to a higher electrochemical surface area (ECSA) than that of Pt/Vulcan carbon and commercial Pt/carbon. The PEMFC test of the respective Pt/carbon samples was investigated, and highly dense and uniform Pt/functionalized-carbon showed the highest performance through optimization of the higher ionomer content compared to that for the ALD Pt growth on Vulcan carbon and commercial Pt/carbon. In addition, the Pt catalyst using ALD demonstrated a significant long-term stability for the PEMFC. This finding demonstrates the remarkable advantages of FBR-ALD for the fabrication of Pt/carbon and the ability of functionalized carbon supports to achieve a high PEMFC efficiency and an enhanced durability. Small tweaks to techniques used to manufacture platinum catalysts can have a big impact on the long-term stability of fuel cells. Platinum nanoparticle catalysts help fuel cells turn hydrogen and oxygen into water and electricity, but their small size makes them tricky to manipulate. Se-Hun Kwon from Pusan National University in Busan, South Korea, and colleagues have now optimized a high-tech procedure for attaching these tiny nanocatalysts to large, porous materials known as carbon supports. Their process coats various supports with platinum nanoparticles, less than one monolayer at a time, until the desired thicknesses are reached. Various factors including the physical textures of the supports and leftover chemical impurities were shown to significantly affect coating uniformity. Adjusting these factors enabled the team to generate supports with greater durability than commercial platinum–carbon composites. Very efficient, fast and scalable Fluidized Bed Reactor Atomic Layer Deposition (FBR-ALD) of highly dense and uniform Pt nanoparticles (NPs) on the functionalized carbon were successfully demonstrated for the proton exchange membrane fuel cell (PEMFC) application. The textural properties, functional groups and structural defects of the carbon supports significantly influenced Pt NPs deposition. A proper carbon supporter matching for FBR-ALD of Pt resulted in excellent electrochemical properties, long-term durability and fuel cell performance.

Atomic Layer Deposition Assisted Pattern Multiplication of Block Copolymer Lithography for 5 nm Scale Nanopatterning

Abstract: 5-nm-scale line and hole patterning is demonstrated by synergistic integration of block copolymer (BCP) lithography with atomic layer deposition (ALD). While directed self-assembly of BCPs generates highly ordered line array or hexagonal dot array with the pattern periodicity of 28 nm and the minimum feature size of 14 nm, pattern density multiplication employing ALD successfully reduces the pattern periodicity down to 14 nm and minimum feature size down to 5 nm. Self-limiting ALD process enable the low temperature, conformal deposition of 5 nm thick spacer layer directly at the surface of organic BCP patterns. This ALD assisted pattern multiplication addresses the intrinsic thermodynamic limitations of low χ BCPs for sub-10-nm scale downscaling. Moreover, this approach offers a general strategy for scalable ultrafi ne nanopatterning without burden for multiple overlay control and high cost lithographic tools.

Electrocatalysis on Platinum Nanoparticles: Particle Size Effect on Oxygen Reduction Reaction Activity

Abstract: We determined the size-dependent specific and mass activities of the oxygen reduction in HClO(4) solutions on the Pt particles in the range of 1-5 nm. The maximal mass activity at 2.2 nm is well explained based on density functional theory calculations performed on fully relaxed nanoparticles. The presence of the edge sites is the main reason for the low specific activity in nanoparticles due to very strong oxygen binding energies at these sites. Our results clearly demonstrate that the catalytic activity highly depends on the shape and size of the nanoparticles.

Topographically-designed triboelectric nanogenerator via block copolymer self-assembly.

Abstract: Herein, we report a facile and robust route to nanoscale tunable triboelectric energy harvesters realized by the formation of highly functional and controllable nanostructures via block copolymer (BCP) self-assembly. Our strategy is based on the incorporation of various silica nanostructures derived from the self-assembly of BCPs to enhance the characteristics of triboelectric nanogenerators (TENGs) by modulating the contact-surface area and the frictional force. Our simulation data also confirm that the nanoarchitectured morphologies are effective for triboelectric generation.

Guanidinium-FunctionalizedAnionExchangePolymerElectrolytesvia Activated Fluorophenyl-Amine Reaction

Abstract: Guanidinium-functionalized poly(arylene ether sulfone) anion exchange polymer electrolytes were synthesized via activated fluorophnyl-amine reaction, followed by the methylation with dimethyl sulfate. The activated fluorine-amine reaction gives precise control of cation functionality without the deleterious side reactions and allows the direct connection of guanidinium into stable phenyl rings.

Synthesis of doped, ternary, and quaternary materials by atomic layer deposition: a review

Abstract: In the past decade, atomic layer deposition (ALD) has become an important thin film deposition technique for applications in nanoelectronics, catalysis, and other areas due to its high conformality...