Publications by authors named "Sung Jong Yoo"

42 Publications

Hydrogen-Mediated Thin Pt Layer Formation on NiN Nanoparticles for the Oxygen Reduction Reaction.

ACS Appl Mater Interfaces 2021 Jun 18;13(21):24624-24633. Epub 2021 May 18.

Center for Hydrogen Fuel Cell Research, Korea Institute of Science and Technology (KIST), Seoul 02792, Republic of Korea.

A simple wet-chemical route for the preparation of core-shell-structured catalysts was developed to achieve high oxygen reduction reaction (ORR) activity with a low Pt loading amount. Nickel nitride (NiN) nanoparticles were used as earth-abundant metal-based cores to support thin Pt layers. To realize the site-selective formation of Pt layers on the NiN core, hydrogen molecules (H) were used as a mild reducing agent. As H oxidation is catalyzed by the surface of NiN, the redox reaction between H and Pt(IV) in solution was facilitated on the NiN surface, which resulted in the selective deposition of Pt on NiN. The controlled Pt formation led to a subnanometer (0.5-1 nm)-thick Pt shell on the NiN core. By adopting the core-shell structure, higher ORR activity than the commercial Pt/C was achieved. Electrochemical measurements showed that the thin Pt layer on NiN nanoparticle exhibits 5 times higher mass activity and specific activity than that of commercial Pt/C. Furthermore, it is expected that the proposed simple wet-chemical method can be utilized to prepare various transition-metal-based core-shell nanocatalysts for a wide range of energy conversion reactions.
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http://dx.doi.org/10.1021/acsami.1c01544DOI Listing
June 2021

Poly(fluorenyl aryl piperidinium) membranes and ionomers for anion exchange membrane fuel cells.

Nat Commun 2021 Apr 22;12(1):2367. Epub 2021 Apr 22.

Department of Energy Engineering, College of Engineering, Hanyang University, Seoul, Republic of Korea.

Low-cost anion exchange membrane fuel cells have been investigated as a promising alternative to proton exchange membrane fuel cells for the last decade. The major barriers to the viability of anion exchange membrane fuel cells are their unsatisfactory key components-anion exchange ionomers and membranes. Here, we present a series of durable poly(fluorenyl aryl piperidinium) ionomers and membranes where the membranes possess high OH conductivity of 208 mS cm at 80 °C, low H permeability, excellent mechanical properties (84.5 MPa TS), and 2000 h ex-situ durability in 1 M NaOH at 80 °C, while the ionomers have high water vapor permeability and low phenyl adsorption. Based on our rational design of poly(fluorenyl aryl piperidinium) membranes and ionomers, we demonstrate alkaline fuel cell performances of 2.34 W cm in H-O and 1.25 W cm in H-air (CO-free) at 80 °C. The present cells can be operated stably under a 0.2 A cm current density for ~200 h.
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http://dx.doi.org/10.1038/s41467-021-22612-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8062622PMC
April 2021

Polystyrene-Based Hydroxide-Ion-Conducting Ionomer: Binder Characteristics and Performance in Anion-Exchange Membrane Fuel Cells.

Polymers (Basel) 2021 Feb 25;13(5). Epub 2021 Feb 25.

Center for Hydrogen and Fuel Cell Research, Korea Institute of Science and Technology (KIST), Hwarang-ro 14-gil 5, Seongbuk-gu, Seoul 02792, Korea.

Polystyrene-based polymers with variable molecular weights are prepared by radical polymerization of styrene. Polystyrene is grafted with bromo-alkyl chains of different lengths through Friedel-Crafts acylation and quaternized to afford a series of hydroxide-ion-conducting ionomers for the catalyst binder for the membrane electrode assembly in anion-exchange membrane fuel cells (AEMFCs). Structural analyses reveal that the molecular weight of the polystyrene backbone ranges from 10,000 to 63,000 g mol, while the ion exchange capacity of quaternary-ammonium-group-bearing ionomers ranges from 1.44 to 1.74 mmol g. The performance of AEMFCs constructed using the prepared electrode ionomers is affected by several ionomer properties, and a maximal power density of 407 mW cm and a durability exceeding that of a reference cell with a commercially available ionomer are achieved under optimal conditions. Thus, the developed approach is concluded to be well suited for the fabrication of next-generation electrode ionomers for high-performance AEMFCs.
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http://dx.doi.org/10.3390/polym13050690DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7956690PMC
February 2021

Monolayer Quantum-Dot Based Light-Sensor by a Photo-Electrochemical Mechanism.

Micromachines (Basel) 2020 Aug 28;11(9). Epub 2020 Aug 28.

Department of Chemistry, Myongji University, Yongin-si 17058, Korea.

Monolayer nanocrystal-based light sensors with cadmium-selenium thin film electrodes have been investigated using electrochemical cyclic voltammetry tests. An indium tin oxide electrode system, with a monolayer of homogeneously deposited cadmium-selenium quantum dots was proven to work as a photo-sensor via an electrochemical cell mechanism; it was possible to tune current densities under light illumination. Electrochemical tests on a quantum dot capacitor, using different sized (red, yellow and green) cadmium-selenium quantum dots on indium tin oxide substrates, showed typical capacitive behavior of cyclic voltammetry curves in 2M HSO aqueous solutions. This arrangement provides a beneficial effect in, both, charge separation and light sensory characteristics. Importantly, the photocurrent density depended on quantum yield rendering tunable photo-sensing properties.
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http://dx.doi.org/10.3390/mi11090817DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7570193PMC
August 2020

Direct Synthesis of Intermetallic Platinum-Alloy Nanoparticles Highly Loaded on Carbon Supports for Efficient Electrocatalysis.

J Am Chem Soc 2020 Aug 5;142(33):14190-14200. Epub 2020 Aug 5.

Center for Nanoparticle Research, Institute for Basic Science (IBS), Seoul 08826, Republic of Korea.

Compared to nanostructured platinum (Pt) catalysts, ordered Pt-based intermetallic nanoparticles supported on a carbon substrate exhibit much enhanced catalytic performance, especially in fuel cell electrocatalysis. However, direct synthesis of homogeneous intermetallic alloy nanocatalysts on carbonaceous supports with high loading is still challenging. Herein, we report a novel synthetic strategy to directly produce highly dispersed MPt alloy nanoparticles (M = Fe, Co, or Ni) on various carbon supports with high catalyst loading. Importantly, a unique bimetallic compound, composed of [M(bpy)] cation (bpy = 2,2'-bipyridine) and [PtCl] anion, evenly decomposes on carbon surface and forms uniformly sized intermetallic nanoparticles with a nitrogen-doped carbon protection layer. The excellent oxygen reduction reaction (ORR) activity and stability of the representative reduced graphene oxide (rGO)-supported L1-FePt catalyst (37 wt %-FePt/rGO), exhibiting 18.8 times higher specific activity than commercial Pt/C catalyst without degradation over 20 000 cycles, well demonstrate the effectiveness of our synthetic approach toward uniformly alloyed nanoparticles with high homogeneity.
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http://dx.doi.org/10.1021/jacs.0c05140DOI Listing
August 2020

Formation Mechanism and Gram-Scale Production of PtNi Hollow Nanoparticles for Oxygen Electrocatalysis through In Situ Galvanic Displacement Reaction.

ACS Appl Mater Interfaces 2020 Apr 24;12(14):16286-16297. Epub 2020 Mar 24.

Center for Hydrogen·Fuel Cell Research, Korea Institute of Science and Technology, Seoul 02792, Republic of Korea.

Galvanic displacement reaction has been considered a simple method for fabricating hollow nanoparticles. However, the formation of hollow interiors in nanoparticles is not easily achieved owing to the easy oxidization of transition metals, which results in mixed morphologies, and the presence of surfactants on the nanoparticle surface, which severely deteriorates the catalytic activity. In this study, we developed a facile gram-scale methodology for the one-pot preparation of carbon-supported PtNi hollow nanoparticles as an efficient and durable oxygen reduction electrocatalyst without using stabilizing agents or additional processes. The hollow structures were evolved from sacrificial Ni nanoparticles via an in situ galvanic displacement reaction with a Pt precursor, directly following a preannealing process. By sampling the PtNi/C hollow nanoparticles at various reaction times, the structural formation mechanism was investigated using transmission electron microscopy with energy-dispersive X-ray spectroscopy mapping/line-scan profiling. We found out that the structure and morphology of the PtNi hollow nanoparticles were controlled by the acidity of the metal precursor solution and the nanoparticle core size. The synthesized PtNi hollow nanoparticles acted as an oxygen reduction electrocatalyst, with a catalytic activity superior to that of a commercial Pt catalyst. Even after 10 000 cycles of harsh accelerated durability testing, the PtNi/C hollow electrocatalyst showed high performance and durability. We concluded that the Pt-rich layers on the PtNi hollow nanoparticles improved the catalytic activity and durability considerably.
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http://dx.doi.org/10.1021/acsami.9b22615DOI Listing
April 2020

Membrane/Electrode Interface Design for Effective Water Management in Alkaline Membrane Fuel Cells.

ACS Appl Mater Interfaces 2019 Sep 11;11(38):34805-34811. Epub 2019 Sep 11.

Fuel Cell Research Center , Korea Institute of Science and Technology (KIST) , Seoul 02792 , Republic of Korea.

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.
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http://dx.doi.org/10.1021/acsami.9b08075DOI Listing
September 2019

Bio-Derived Co P Nanoparticles Supported on Nitrogen-Doped Carbon as Promising Oxygen Reduction Reaction Electrocatalyst for Anion Exchange Membrane Fuel Cells.

Small 2019 Sep 22;15(36):e1902090. Epub 2019 Jul 22.

Center for Hydrogen Fuel Cell Research, Korea Institute of Science and Technology (KIST), Seoul, 02792, Republic of Korea.

Recently, nonnoble-metal catalysts such as a metal coordinated to nitrogen doped in a carbon matrix have been reported to exhibit superior oxygen reduction reaction (ORR) activity in alkaline media. In this work, Co P nanoparticles supported on heteroatom-doped carbon catalysts (NBSCP) are developed with an eco-friendly synthesis method using bean sprouts. NBSCP can be easily synthesized through metal precursor absorption and carbonization at a high temperature. It shows a very large specific surface area with various dopants such as nitrogen, phosphorus, and sulfur derived from small organic molecules. The catalyst can exhibit activity in various electrochemical reactions. In particular, excellent performance is noted for the ORR. Compared to the commercial Pt/C, NBSCP exhibits a lower onset potential, higher current density, and superior durability. This excellent ORR activity and durability is attributable to the synergistic effect between Co P nanoparticles and nitrogen-doped carbon. In addition, superior performance is noted on applying NBSCP to a practical anion exchange membrane fuel cell system. Through this work, the possibility of applying an easily obtained bio-derived material to energy conversion and storage systems is demonstrated.
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http://dx.doi.org/10.1002/smll.201902090DOI Listing
September 2019

Boosting Fuel Cell Durability under Shut-Down/Start-Up Conditions Using a Hydrogen Oxidation-Selective Metal-Carbon Hybrid Core-Shell Catalyst.

ACS Appl Mater Interfaces 2019 Aug 26;11(31):27735-27742. Epub 2019 Jul 26.

Center for Fuel Cell Research , Korea Institute of Science and Technology (KIST) , Seoul 136-791 , Republic of Korea.

Performance degradation generated by reverse current flow during fuel cell shut-down/start-up is a big challenge for commercialization of polymer electrolyte membrane fuel cells in automobile applications. Under transient operating conditions, the formation of H/O boundaries on Pt surfaces and the occurrence of undesired oxygen reduction reaction (ORR) in an anode cause severe degradation of carbon supports and Pt catalysts in a cathode because of an increase of the cathode potential up to ∼1.5 V. Herein, to directly prevent the formation of H/O boundaries in the anode, we propose a unique metal-carbon hybrid core-shell anode catalyst having Pt nanoparticles encapsulated in nanoporous carbon shells for selective H permeation. This hybrid catalyst exhibits high hydrogen oxidation reaction (HOR) selectivity along with fully subdued ORR activity during long-term operation because of the excellent stability of the carbon molecular sieves. Furthermore, the HOR-selective catalyst effectively suppresses the reverse current flow in a single cell under shut-down/start-up conditions.
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http://dx.doi.org/10.1021/acsami.9b06309DOI Listing
August 2019

A new etching process for zinc oxide with etching rate and crystal plane control: experiment, calculation, and membrane application.

Nanoscale 2019 Jul 19;11(25):12337-12346. Epub 2019 Jun 19.

Department of Chemical Engineering, College of Engineering, Kyung Hee University, Yongin 17140, Korea.

The etching process can be a useful method for the morphology control of nanostructures. Using precise experiments and theoretical calculations, we report a new ZnO etching process triggered by the reaction of ZnO with transition metal cations and demonstrate that the etching rate and direction could be controlled by varying the kind of transition metal cation. In addition, the developed etching process was introduced to form a thin and uniform ZnO layer, which was utilized for the fabrication of an improved propylene-selective ZIF-8 membrane via conversion seeding and secondary growth.
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http://dx.doi.org/10.1039/c9nr02248aDOI Listing
July 2019

Anomalous in situ Activation of Carbon-Supported NiP Nanoparticles for Oxygen Evolving Electrocatalysis in Alkaline Media.

Sci Rep 2017 08 15;7(1):8236. Epub 2017 Aug 15.

Fuel Cell Research Center, Korea Institute of Science and Technology (KIST), 02792, Seoul, Republic of Korea.

Electrochemical water splitting is one of the most promising systems by which to store energy produced from sustainable sources, such as solar and wind energy. Designing robust and stable electrocatalysts is urgently needed because of the relatively sluggish kinetics of the anodic reaction, i.e. the oxygen evolution reaction (OER). In this study, we investigate the anomalous in situ activation behaviour of carbon-supported NiP nanoparticles (NiP/C) during OER catalysis in alkaline media. The activated NiP/C shows an exceptionally high activity and stability under OER conditions in which the overpotential needed to achieve 10 mA cm was reduced from approximately 350 mV to approximately 300 mV after 8,000 cyclic voltammetric scans. In situ and ex situ characterizations indicate that the activity enhancement of NiP catalysts is due to a favourable phase transformation of the Ni centre to β-NiOOH, including increases in the active area induced by structural deformation under the OER conditions. These findings provide new insights towards designing transition metal/phosphide-based materials for an efficient water splitting catalyst.
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http://dx.doi.org/10.1038/s41598-017-08296-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5557805PMC
August 2017

Transition metal alloying effect on the phosphoric acid adsorption strength of Pt nanoparticles: an experimental and density functional theory study.

Sci Rep 2017 08 3;7(1):7186. Epub 2017 Aug 3.

Fuel Cell Research Center, Korea Institute of Science and Technology, Hwarangno 14-gil 5, Seongbuk-gu, Seoul, 02792, Republic of Korea.

The effect of alloying with transition metals (Ni, Co, Fe) on the adsorption strength of phosphoric acid on Pt alloy surfaces was investigated using electrochemical analysis and first-principles calculations. Cyclic voltammograms of carbon-supported PtM/C (M = Ni, Co, and Fe) electrocatalysts in 0.1 M HClO with and without 0.01 M HPO revealed that the phosphoric acid adsorption charge density near the onset potential on the nanoparticle surfaces was decreased by alloying with transition metals in the order Co, Fe, Ni. First-principles calculations based on density functional theory confirmed that the adsorption strength of phosphoric acid was weakened by alloying with transition metals, in the same order as that observed in the electrochemical analysis. The simulation suggested that the weaker phosphoric acid adsorption can be attributed to a lowered density of states near the Fermi level due to alloying with transition metals.
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http://dx.doi.org/10.1038/s41598-017-06812-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5543171PMC
August 2017

Highly Durable and Active PtFe Nanocatalyst for Electrochemical Oxygen Reduction Reaction.

J Am Chem Soc 2015 Dec 3;137(49):15478-85. Epub 2015 Dec 3.

Center for Nanoparticle Research, Institute for Basic Science (IBS) , Seoul 151-742, South Korea.

Demand on the practical synthetic approach to the high performance electrocatalyst is rapidly increasing for fuel cell commercialization. Here we present a synthesis of highly durable and active intermetallic ordered face-centered tetragonal (fct)-PtFe nanoparticles (NPs) coated with a "dual purpose" N-doped carbon shell. Ordered fct-PtFe NPs with the size of only a few nanometers are obtained by thermal annealing of polydopamine-coated PtFe NPs, and the N-doped carbon shell that is in situ formed from dopamine coating could effectively prevent the coalescence of NPs. This carbon shell also protects the NPs from detachment and agglomeration as well as dissolution throughout the harsh fuel cell operating conditions. By controlling the thickness of the shell below 1 nm, we achieved excellent protection of the NPs as well as high catalytic activity, as the thin carbon shell is highly permeable for the reactant molecules. Our ordered fct-PtFe/C nanocatalyst coated with an N-doped carbon shell shows 11.4 times-higher mass activity and 10.5 times-higher specific activity than commercial Pt/C catalyst. Moreover, we accomplished the long-term stability in membrane electrode assembly (MEA) for 100 h without significant activity loss. From in situ XANES, EDS, and first-principles calculations, we confirmed that an ordered fct-PtFe structure is critical for the long-term stability of our nanocatalyst. This strategy utilizing an N-doped carbon shell for obtaining a small ordered-fct PtFe nanocatalyst as well as protecting the catalyst during fuel cell cycling is expected to open a new simple and effective route for the commercialization of fuel cells.
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http://dx.doi.org/10.1021/jacs.5b09653DOI Listing
December 2015

Design of an Advanced Membrane Electrode Assembly Employing a Double-Layered Cathode for a PEM Fuel Cell.

ACS Appl Mater Interfaces 2015 Dec 9;7(50):27581-5. Epub 2015 Dec 9.

Department of Materials Science & Engineering, Korea Advanced Institute of Science and Technology , 291 Daehak-ro Yuseong-gu, Daejeon 305-701, Republic of Korea.

The membrane electrolyte assembly (MEA) designed in this study utilizes a double-layered cathode: an inner catalyst layer prepared by a conventional decal transfer method and an outer catalyst layer directly coated on a gas diffusion layer. The double-layered structure was used to improve the interfacial contact between the catalyst layer and membrane, to increase catalyst utilization and to modify the removal of product water from the cathode. Based on a series of MEAs with double-layered cathodes with an overall Pt loading fixed at 0.4 mg cm(-2) and different ratios of inner-to-outer Pt loading, the MEA with an inner layer of 0.3 mg Pt cm(-2) and an outer layer of 0.1 mg Pt cm(-2) exhibited the best performance. This performance was better than that of the conventional single-layered electrode by 13.5% at a current density of 1.4 A cm(-2).
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http://dx.doi.org/10.1021/acsami.5b07346DOI Listing
December 2015

A simple synthesis of urchin-like Pt-Ni bimetallic nanostructures as enhanced electrocatalysts for the oxygen reduction reaction.

Chem Commun (Camb) 2016 Jan 10;52(3):597-600. Epub 2015 Nov 10.

Center for Nanoparticle Research, Institute for Basic Science (IBS), Seoul, 151-742, Korea.

The synthesis of urchin-like Pt-Ni bimetallic nanostructures is achieved by a controlled one-pot synthesis. Pt-Ni nanostructures have superior oxygen reduction reaction activities in both with and without specific anion adsorption electrolytes due to the geometric and alloying effects.
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http://dx.doi.org/10.1039/c5cc08088fDOI Listing
January 2016

Highly efficient and durable TiN nanofiber electrocatalyst supports.

Nanoscale 2015 Nov 22;7(44):18429-34. Epub 2015 Oct 22.

Fuel Cell Research Center, Korea Institute of Science and Technology, Seongbuk-Gu, Seoul 136-791, Republic of Korea.

To date, carbon-based materials including various carbon nanostructured materials have been extensively used as an electrocatalyst support for proton exchange membrane fuel cell (PEMFC) applications due to their practical nature. However, carbon dissolution or corrosion caused by high electrode potential in the presence of O2 and/or water has been identified as one of the main failure modes for the device operation. Here, we report the first TiN nanofiber (TNF)-based nonwoven structured materials to be constructed via electrospinning and subsequent two-step thermal treatment processes as a support for the PEMFC catalyst. Pt catalyst nanoparticles (NPs) deposited on the TNFs (Pt/TNFs) were electrochemically characterized with respect to oxygen reduction reaction (ORR) activity and durability in an acidic medium. From the electrochemical tests, the TNF-supported Pt catalyst was better and more stable in terms of its catalytic performance compared to a commercially available carbon-supported Pt catalyst. For example, the initial oxygen reduction performance was comparable for both cases, while the Pt/TNF showed much higher durability from an accelerated degradation test (ADT) configuration. It is understood that the improved catalytic roles of TNFs on the supported Pt NPs for ORR are due to the high electrical conductivity arising from the extended connectivity, high inertness to the electrochemical environment and strong catalyst-support interactions.
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http://dx.doi.org/10.1039/c5nr04082eDOI Listing
November 2015

Green synthesis of carbon-supported nanoparticle catalysts by physical vapor deposition on soluble powder substrates.

Sci Rep 2015 Sep 18;5:14245. Epub 2015 Sep 18.

Fuel Cell Research Center, Korea Institute of Science and Technology (KIST), Seoul 136-791, Republic of Korea.

Metal and metal oxide nanoparticles (NPs) supported on high surface area carbon (NP/Cs) were prepared by the physical vapor deposition of bulk materials on an α-D-glucose (Glu) substrate, followed by the deposition of the NPs on carbon supports. Using Glu as a carrier for the transport of NPs from the bulk materials to the carbon support surfaces, ultrafine NPs were obtained, exhibiting a stabilizing effect through OH moieties on the Glu surfaces. This stabilizing effect was strong enough to stabilize the NPs, but weak enough to not significantly block the metal surfaces. As only the target materials and Glu are required in our procedure, it can be considered environmentally friendly, with the NPs being devoid of hazardous chemicals. Furthermore, the resulting NP/Cs exhibited an improvement in activity for various electrochemical reactions, mainly attributed to their high surface area.
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http://dx.doi.org/10.1038/srep14245DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4585564PMC
September 2015

A highly active and durable Co-N-C electrocatalyst synthesized using exfoliated graphitic carbon nitride nanosheets.

Nanoscale 2015 Jun;7(23):10334-9

Fuel Cell Research Center, Korea Institute of Science and Technology, Hwarangno 14-gil 5, Seongbuk-gu, Seoul 136-791, Republic of Korea.

Exfoliated graphitic carbon nitride nanosheets (g-C3N4-NS) were applied for the first time for the preparation of an electrocatalyst for the oxygen reduction reaction (ORR). A less dense structure with increased surface area was observed for g-C3N4-NS compared to bulk g-C3N4 from detailed analyses including TEM, STEM, AFM with depth profiling, XRD, and UV-Vis spectroscopy. The pyrolysis of the prepared g-C3N4-NS with Co and carbon under an inert environment provided an enhanced accessibility to the N functionalities required for efficient interaction of Co and C with N for the formation of Co-N-C networks and produced a hollow and interconnected Co-N-C-NS structure responsible for high durability. The Co-N-C-NS electrocatalyst exhibited superior catalytic activity and durability and further displayed fast and selective four electron transfer kinetics for the ORR, as evidenced by various electrochemical experiments. The hollow, interconnected structure of Co-N-C-NS with increased pyridinic and graphitic N species has been proposed to play a key role in facilitating the desired ORR reaction.
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http://dx.doi.org/10.1039/c5nr01584gDOI Listing
June 2015

Epitaxial growth of a single-crystal hybridized boron nitride and graphene layer on a wide-band gap semiconductor.

J Am Chem Soc 2015 Jun 22;137(21):6897-905. Epub 2015 May 22.

†Department of Physics, Sungkyunkwan University, Suwon 440-746, Republic of Korea.

Vertical and lateral heterogeneous structures of two-dimensional (2D) materials have paved the way for pioneering studies on the physics and applications of 2D materials. A hybridized hexagonal boron nitride (h-BN) and graphene lateral structure, a heterogeneous 2D structure, has been fabricated on single-crystal metals or metal foils by chemical vapor deposition (CVD). However, once fabricated on metals, the h-BN/graphene lateral structures require an additional transfer process for device applications, as reported for CVD graphene grown on metal foils. Here, we demonstrate that a single-crystal h-BN/graphene lateral structure can be epitaxially grown on a wide-gap semiconductor, SiC(0001). First, a single-crystal h-BN layer with the same orientation as bulk SiC was grown on a Si-terminated SiC substrate at 850 °C using borazine molecules. Second, when heated above 1150 °C in vacuum, the h-BN layer was partially removed and, subsequently, replaced with graphene domains. Interestingly, these graphene domains possess the same orientation as the h-BN layer, resulting in a single-crystal h-BN/graphene lateral structure on a whole sample area. For temperatures above 1600 °C, the single-crystal h-BN layer was completely replaced by the single-crystal graphene layer. The crystalline structure, electronic band structure, and atomic structure of the h-BN/graphene lateral structure were studied by using low energy electron diffraction, angle-resolved photoemission spectroscopy, and scanning tunneling microscopy, respectively. The h-BN/graphene lateral structure fabricated on a wide-gap semiconductor substrate can be directly applied to devices without a further transfer process, as reported for epitaxial graphene on a SiC substrate.
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http://dx.doi.org/10.1021/jacs.5b03151DOI Listing
June 2015

Structure dependent active sites of NixSy as electrocatalysts for hydrogen evolution reaction.

Nanoscale 2015 Mar;7(12):5157-63

Center for Nanoparticle Research, Institute for Basic Science (IBS), Seoul 151-742, Republic of Korea.

Structure effects of NiS and Ni3S2 nanoparticles were investigated for their electrocatalytic activity in the hydrogen evolution reaction in both acid and alkaline media. Owing to the different atomic configurations and crystalline structures, there is a hydrogen adsorption energy difference, which induces a difference in the activity. From density functional theory calculations and experimental observations, the importance of designing an electrocatalyst with an appropriate atomic configuration is evident.
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http://dx.doi.org/10.1039/c4nr07648fDOI Listing
March 2015

Third-body effects of native surfactants on Pt nanoparticle electrocatalysts in proton exchange fuel cells.

Chem Commun (Camb) 2015 Feb;51(14):2968-71

Fuel Cell Research Center, Korea Institute of Science and Technology (KIST), Seoul 136-791, Republic of Korea.

The residual surfactant organic molecules on electrocatalysts are expected to enhance the tolerance to specific anion adsorption, whereas the surfactants have been generally regarded as contaminants that block active surfaces. In this study, the Pt nanoparticles with adsorbed surfactants were prepared, and their electrochemical characteristics at various phosphoric acid concentrations were studied by the half-cell test. The third-body effect was experimentally confirmed by the single-cell test with a phosphoric acid-doped polybenzimidazole membrane.
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http://dx.doi.org/10.1039/c4cc09019eDOI Listing
February 2015

Inhibition of CO poisoning on Pt catalyst coupled with the reduction of toxic hexavalent chromium in a dual-functional fuel cell.

Sci Rep 2014 Dec 12;4:7450. Epub 2014 Dec 12.

1] Center for Nanoparticle Research, Institute for Basic Science (IBS), Seoul 151-742, Republic of Korea [2] School of Chemical and Biological Engineering, Seoul National University, Seoul 151-742, Republic of Korea.

We propose a method to enhance the fuel cell efficiency with the simultaneous removal of toxic heavy metal ions. Carbon monoxide (CO), an intermediate of methanol oxidation that is primarily responsible for Pt catalyst deactivation, can be used as an in-situ reducing agent for hexavalent chromium (Cr (VI)) with reactivating the CO-poisoned Pt catalyst. Using electro-oxidation measurements, the oxidation of adsorbed CO molecules coupled with the concurrent conversion of Cr (VI) to Cr (III) was confirmed. This concept was also successfully applied to a methanol fuel cell to enhance its performance efficiency and to remove toxic Cr (VI) at the same time.
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http://dx.doi.org/10.1038/srep07450DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4264001PMC
December 2014

P-modified and carbon shell coated Co nanoparticles for efficient alkaline oxygen reduction catalysis.

Chem Commun (Camb) 2014 Dec;50(100):15940-3

Fuel Cell Research Center, Korea Institute of Science and Technology (KIST), Seoul 136-791, Korea.

Described herein is the development of a novel Co-based oxygen electrode catalyst coupled with unique carbon structures. The present carbon shell coated Co nanoparticles of which the surface composites are modified by phosphorus incorporation, exhibit efficient oxygen reduction activities as well as oxygen evolving properties.
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http://dx.doi.org/10.1039/c4cc07143cDOI Listing
December 2014

One-step synthesis of carbon-supported [email protected]/C core-shell nanoparticles as oxygen reduction electrocatalysts and their enhanced activity and stability.

Nanoscale 2014 Apr;6(8):4038-42

School of Chemical Engineering, Department of Hydrogen and Fuel Cell Engineering, Chonbuk National University, JeonJu 561-756, Jeonbuk, Republic of Korea.

A close encounter with reality on core-shell catalysts for fuel cells: the outstanding significance of the work is (i) suggestion of a computational methodology to design a specific combination of core and shell materials in terms of both the activity and the durability, (ii) development of a novel facile synthesis of core-shell/C electrocatalysts, and (iii) experimental validation of the design and synthesis of the core-shell/C catalysts and their performance as well as long-term stability.
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http://dx.doi.org/10.1039/c3nr05133aDOI Listing
April 2014

Edge-exposed MoS2 nano-assembled structures as efficient electrocatalysts for hydrogen evolution reaction.

Nanoscale 2014 Feb 6;6(4):2131-6. Epub 2013 Dec 6.

Center for Nanoparticle Research, Institute for Basic Science (IBS), Seoul 151-742, Republic of Korea.

Edge-exposed MoS2 nano-assembled structures are designed for high hydrogen evolution reaction activity and long term stability. The number of sulfur edge sites of nano-assembled spheres and sheets is confirmed by Raman spectroscopy and EXAFS analysis. By controlling the MoS2 morphology with the formation of nano-assembled spheres with the assembly of small-size fragments of MoS2, the resulting assembled spheres have high electrocatalytic HER activity and high thermodynamic stability.
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http://dx.doi.org/10.1039/c3nr05228aDOI Listing
February 2014

Effect of morphology of electrodeposited Ni catalysts on the behavior of bubbles generated during the oxygen evolution reaction in alkaline water electrolysis.

Chem Commun (Camb) 2013 Oct;49(81):9323-5

Fuel Cell Research Center, Korea Institute of Science and Technology, Hwarangno 14-gil 5, Seoungbuk-gu, Seoul 136-791, Republic of Korea.

We have investigated the release of active sites blocked by bubbles attached on the surface of catalysts during the oxygen evolution reaction (OER) in alkaline water electrolysis, via the modulation of the wetting properties of the four different morphologies of a nickel catalyst.
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http://dx.doi.org/10.1039/c3cc44891fDOI Listing
October 2013

Chemical tuning of electrochemical properties of Pt-skin surfaces for highly active oxygen reduction reactions.

Phys Chem Chem Phys 2013 Oct;15(40):17079-83

Fuel Cell Research Center, Korea Institute of Science and Technology (KIST), Seoul 136-791, Korea.

Pt-skin surfaces were successfully fabricated by the chemical deposition of additional Pt on corrugated Pt-Ni nanoparticles with Pt-skeleton surfaces. Compared to the Pt-skin formed by heat annealing, the chemically-tuned Pt-skin had a higher Pt coordination number and surface crystallinity, which resulted in superior ORR activity and durability.
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http://dx.doi.org/10.1039/c3cp52807cDOI Listing
October 2013

Effect of particle size of PtRu nanoparticles embedded in WO3 on electrocatalysis.

J Nanosci Nanotechnol 2013 May;13(5):3591-6

Fuel Cell Research Center, Korea Institute of Science and Technology, Seoul 136-791, Korea.

Size-controlled PtRu nanoparticles embedded in WO3 were prepared by simultaneous multigun sputtering on pure targets of Pt, Ru, and WO3. The mean diameter of the PtRu nanoparticles, as confirmed by high-resolution transmission electron microscopy, can be varied from -2.3 to -3.6 nm by varying the RF power ratio of PtRu and WO3. On the basis of transmission electron diffraction results for the PtRu nanoparticles embedded in WO3, it was confirmed that PtRu exists as an alloy metal phase, whereas the WO3 matrix is present as an amorphous phase. Size-controlled PtRu/WO3 electrodes were found to exhibit unique electronic properties depending on their size, which affected the potential of zero total charge and the methanol oxidation reaction. The mass activity of PtRu/WO3 for methanol oxidation was determined by the interplay of the surface electronic factors at the metal-solution interface; the oxophilicity of the nanoparticles increased with decreasing particle size.
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http://dx.doi.org/10.1166/jnn.2013.7323DOI Listing
May 2013

Supported [email protected] electrocatalysts for fuel cells: close encounter with reality.

Sci Rep 2013 ;3:1309

Fuel Cell Research Center, Korea Institute of Science and Technology, 39-1 Hawolgok-dong, Seoul 136-791, Korea.

[email protected] electrocatalysts for fuel cells have the advantages of a high utilization of Pt and the modification of its electronic structures toward enhancement of the activities. In this study, we suggest both a theoretical background for the design of highly active and stable [email protected]/C and a novel facile synthetic strategy for their preparation. Using density functional theory calculations guided by the oxygen adsorption energy and vacancy formation energy, Pd₃Cu₁@Pt/C was selected as the most suitable candidate for the oxygen reduction reaction in terms of its activity and stability. These predictions were experimentally verified by the surfactant-free synthesis of Pd3Cu1/C cores and the selective Pt shell formation using a Hantzsch ester as a reducing agent. In a similar fashion, [email protected]₄Ir₆/C catalyst was also designed and synthesized for the hydrogen oxidation reaction. The developed catalysts exhibited high activity, high selectivity, and 4,000 h of long-term durability at the single-cell level.
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http://dx.doi.org/10.1038/srep01309DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3575584PMC
August 2013
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