Methanol dehydrogenation reaction at Au@Pt catalysts: Insight into the methanol electrooxidation

Jeong, Hwakyeung,Kim, Jongwon Elsevier 2018 ELECTROCHIMICA ACTA Vol.283 No.-

<P><B>Abstract</B></P> <P>The electrochemical methanol oxidation reaction (MOR) has received considerable attention because of its importance in the development of fuel cells. Recently, bimetallic Au-Pt catalyst systems were developed as efficient MOR electrocatalysts. In this work, we investigated the methanol dehydrogenation reaction (MDHR, CH<SUB>3</SUB>OH → CO + 2H<SUB>2</SUB>) on the Au@Pt core-shell surfaces using an in situ surface-enhanced Raman spectroscopy (SERS) technique. The CO intermediates produced by the MDHR and adsorbed on the Pt surfaces play an important role in the electrochemical MOR. The formation of CO on Au@Pt surfaces during the MDHR was examined as a function of the coverage and thickness of the Pt layers on Au. The effect of the electrode potential applied to the Au@Pt surface on the MDHR behavior was also investigated. The SERS results regarding the MDHR behaviors on the different Pt layers on Au surfaces could provide rational comparisons of the electrochemical MOR activities of the Au@Pt and Pt/C catalysts that can be evaluated differently depending on the contact time between the electrode and methanol and the scan rate. The present work provides insight into the electrocatalytic activity of bimetallic core-shell catalysts from the mechanistic perspective.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Synthesis of Actinide Chloride Complexes from Actinide Oxide in High Temperature Molten Salt

Hwakyeung Jeong,Sang-Eun Bae 한국방사성폐기물학회 2020 한국방사성폐기물학회 학술논문요약집 Vol.2020 No.12

Electrodeposition of Nanoflake Pd Structures: Structure-Dependent Wettability and SERS Activity

Jeong, Hwakyeung,Kim, Jongwon American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.13

<P>The characteristic properties of metal surfaces, i.e., wettability and surface-enhanced Raman scattering (SERS) activity, have been the subject of intensive research because of their useful applications. In the present work, we report a simple electrodeposition of nanoflake Pd structures onto clean Au surfaces without the use of additives. The fine structure of the nanoflake Pd surfaces was regulated by controlling the deposition charge, and the effect of the structural variations on the wettability and SERS activity was examined. The wettability of nanoflake Pd structures in terms of water contact angle was closely related to the fine structures of Pd deposits and their surface roughness. The SERS activity of the nanoflake Pd surfaces was highly dependent on the presence of sharp edge sites on the Pd structures. Well-defined nanoflake Pd structures prepared using a deposition charge of 0.04 C exhibited superhydrophobic natures and reproducible SERS activity. The effect of the metal surface structures on the wettability and the SERS activity demonstrated in this work provides insight into the fabrication of functional metal nanostructures.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2015/aamick.2015.7.issue-13/acsami.5b02113/production/images/medium/am-2015-02113d_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5b02113'>ACS Electronic Supporting Info</A></P>

Insights into the Electrooxidation Mechanism of Formic Acid on Pt Layers on Au Examined by Electrochemical SERS

Jeong, Hwakyeung,Kim, Jongwon American Chemical Society 2016 The Journal of Physical Chemistry Part C Vol.120 No.42

<P>The electrooxidation of formic acid (FA) on Pt has received great attention because of its fundamental significance as a model reaction and its technical importance in fuel cells. Pt layers modified on Au surfaces were recently reported to exhibit enhanced electrocatalytic activity for FA oxidation; however, the mechanistic details have not been clearly elucidated. In this work, the mechanism of FA electrooxidation on Pt layers on Au surfaces was investigated via in situ electrochemical surface-enhanced Raman scattering (SERS). SERS-active DAR@Pt(n) substrates were prepared using the self-terminating electrodeposition of Pt on dendritic Au rod (DAR) surfaces, wherein the amount and coverage of Pt were precisely controlled by applying a different number of potential steps (n) during the electrodeposition process. The electrocatalytic activity of FA was highly dependent on the Pt coverage and thickness on DAR@Pt(n), which was investigated by electrochemical SERS. The amount of CO produced by the dehydration of FA, the potential-dependent SERS intensity variation, and the Stark slopes were examined on different DAR@Pt(n) surfaces. DAR@Pt(1) surfaces with island-type Pt layers on Au exhibited typical electrooxidation behavior that has been proposed to proceed through direct reaction pathways; however, adsorbed CO produced by dehydration was observed, indicating that the indirect electrooxidation of FA operates even on this surface. As the Pt coverage on DAR@Pt(n) increased, a greater amount of CO was produced by FA dehydration, and the adsorbed CO persisted longer in the early stage of FA electrooxidation. The direct electrooxidation of FA was mostly prohibited by the adsorbed CO initially produced by the dehydration of FA on DAR@Pt(15) with monolayer-level Pt layers. The present work provides insight into the mechanistic interpretation of FA electrooxidation on Pt-Au systems.</P>

A Study on the pH Speciation and Stability Constants for Chelating Agents With Metals

Hwakyeung Jeong,Byungman Kang,Hyejin Cho,Jihye Kim 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.2

Chelating agents, such as ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), and nitrilotriacetic acid (NTA) are widely used in industry and agriculture as water softeners, detergents, and metal chelating agents. In wastewater treatment plants, a significant amount of chelating agents can be discharged into natural waters because they are difficult to degrade. Since those compounds affect the mobility of radionuclides or heavy metals in decontamination operations at nuclear facilities and radioactive waste disposal, quantification of the amount of ligand is very important for safe nuclear waste management. To predict the behavior of the main complexation in sample matrices of radioactive wastes, it is essential to evaluate the distribution of the metal-chelating species and their stabilities in order to develop analytical techniques for quantifying chelating agents. We have investigated to collect information on the pH speciation of metal chelation and the stability constants of metal complexes depending on three chelating agents (EDTA, DTPA, and NTA). For example, Zhang’s group recently reported that the initial coordination pH of Cu(II) and EDTA4? is delayed with the addition of Fe(III), and the pH range for the stable existence of [Cu(EDTA)]2? is narrowed compared to when it is alone in the sample matrix. The addition of Fe(III) clearly impacts the chemical states of the Cu(II)-EDTA solution. Additionally, Eivazihollagh’s group demonstrated differences in the speciation and stability of Cu(II) species between Cu(II) and three chelating ligands (EDTA, DTPA, and NTA). This study will be greatly helpful in identifying the sample matrix for binding major chelating agents and metals as well as developing chemically sample pretreatment and separation methods based on the sample matrix. Finally, these advancements will enable reliable quantitative analysis of chelating agents in decommissioning radioactive wastes.

A rapid separation of Cs, Sr and Ba using gas pressurized extraction chromatography with inductively coupled plasma-mass spectrometry

Sojin Jeong,Jihye Kim,Hanul Cho,Hwakyeung Jeong,Byungman Kang,Sang Ho Lim 한국분석과학회 2024 분석과학 Vol.37 No.2

We present a rapid method for the determination of Cs, Sr, and Ba, heat generators found in highly active liquid wastes, by gas-pressurized extraction chromatography (GPEC) using a column containing a cationexchange resin. GPEC is a microscale column chromatographic technique that uses a constant flow rate of solvent (0.07 mL/min) with pressurized nitrogen gas supplied through a valve. In particular, because this method uses a small sample volume (a few hundred microliters), it produces less chemical waste and allows for faster separation compared to traditional column chromatography. In this study, we evaluated the separation of Cs, Sr, and Ba using GPEC. The eluate from the column (GPEC or conventional column chromatography) was quantitatively analyzed using inductively coupled plasma-mass spectrometry to measure the column recovery and precision. The column reproducibility of the proposed GPEC system (RSDs of recoveries) ranged from 2.7 to 4.1 %, and the column recoveries for the three elements ranged from 72 to 98% when aqueous HCl was used as the eluent. The GPEC results are slightly different in efficiency and separation resolution compared to those of conventional column chromatography because of the differences in the eluent flow rate as well as the internal diameter and length of the column. However, the two methods had similar recoveries for Cs and Sr, and the precision of GPEC was improved by two-fold. Remarkably, the solvent volume required for GPEC analysis was five times lower than that of the conventional method, and the total analysis time was 11 times shorter.

Carbon thin-layer-coated manganese oxide nanocrystals as an effective support for high-performance Pt electrocatalysts stabilized at a metal–metal oxide–carbon triple junction

Lee, Dong-Gyu,Jeong, Hwakyeung,Jeon, Ki-Wan,Zhang, Luojiang,Park, Kwanghee,Ryu, Sunmin,Kim, Jongwon,Lee, In Su The Royal Society of Chemistry 2017 Journal of Materials Chemistry A Vol.5 No.42

<▼1><P>Carbon thin-layer-coated manganese-oxide nanocrystals as an effective support for high-performance Pt electrocatalysts stabilized at a metal–metal oxide–carbon triple junction.</P></▼1><▼2><P>The use of the metal-oxide support has been proved to be an effective approach in the development of fuel-cell catalysts especially for improving the stability of Pt-based electrocatalysts, which is not attainable with conventional carbonaceous materials. Nonetheless, because of the intrinsic low electrical conductivity of pure metal-oxides, metal-oxide-supported systems have not been productive in terms of mass activity that is a primary criterion for the cost-effective electrocatalysts. This paper reports the fabrication of a unique Pt/Mn3O4–carbon triple-junction (TJ) structure, bearing a high density of Pt catalysts entirely sandwiched in between the nano-sized Mn3O4 core and surrounding carbon shell, which integrates the complementary advantages of metal-oxide and carbon supports and thus endows Pt catalysts with optimized electrocatalytic performance. In this study, the unexplored capacity of the Mn3O4 surface was found to accelerate the polymerization process of the surface attached dopamine molecule even under an ordinarily unreactive condition, which enabled the formation of a very thin and contiguous polydopamine layer. The resultant polydopamine film could be converted into a 1.8 nm-thin N-doped carbon layer with sufficiently high electrical conductivity, which allowed the Pt deposition during the galvanic replacement reaction to occur exclusively onto the manganese oxide surface covered underneath the carbon layer and therefore produced the TJ of Pt/Mn3O4–carbon. The resultant TJ structure exhibited the 10-fold enhanced mass activity in the oxygen reduction reaction compared with that of the Mn3O4-supported Pt, which is the highest mass activity for the ORR achieved with oxide-supported catalysts that has been reported so far, while preserving the sufficient durability.</P></▼2>

카복실산 용액에서 양극산화에 의해 형성된 나노다공성 금 표면상의 전기화학적 글루코오스 산화

노성진,정화경,이금섭,김민주,김종원,Roh, Seongjin,Jeong, Hwakyeung,Lee, Geumseop,Kim, Minju,Kim, Jongwon 한국전기화학회 2013 한국전기화학회지 Vol.16 No.2

세 가지 종류의 카복실산(포름산, 아세트산, 프로피온산) 용액 하에서 양극산화 반응을 통한 나노 다공성 금(nanoporous gold, NPG) 구조의 형성과 NPG 전극 표면 상의 전기화학적 글루코오스 산화반응을 관찰하였다. 세 가지 카복실산 용액 조건 중에서 포름산 용액 조건하의 양극산화를 통해 형성된 NPG 전극에서 글루코오스의 산화 활성이 가장 우수하였다. 포름산 용액 조건하의 양극산화 과정에서 가장 우수한 글루코오스 산화 활성을 얻기 위한 최적 조건은 인가전위 5.0 V와 반응시간 4시간이었다. 카복실산 용액 하에서 형성된 NPG 상의 전기화학적 글루코오스 산화 활성을 염소이온의 부재 및 존재 하 조건에서 관찰하고, 이를 옥살산 용액 하에서 형성된 NPG 상의 거동과 비교 분석하였다. 포름산 용액 하에서 최적 조건으로 형성된 NPG 전극상에서 글루코오스의 전류법 검출 응용을 제시하였다. We investigate the formation of nanoporous gold (NPG) surfaces by anodization in three carboxylic acid (formic acid, acetic acid, and propionic acid) solutions and the electrochemical oxidation of glucose at NPG surfaces. Among three carboxylic acids, formic acid provided the most efficient conditions for NPG formation towards glucose oxidation. The optimized conditions during anodization in formic acid for glucose oxidation were 5.0 V of applied potential and 4 hour of reaction time. Electrocatalytic activities for glucose oxidation at NPG surfaces prepared by anodization in carboxylic acids were examined under the absence and presence of chloride ions, which were compared to those observed at NPG prepared in oxalic acid solutions. The application NPG prepared by optimized anodization conditions in formic acid to the amperometric detection of glucose was demonstrated.

Effect of Nanostructures of Au Electrodes on the Electrochemical Detection of As

Kastro, Kanido Camerun,Seo, Min Ji,Jeong, Hwakyeung,Kim, Jongwon The Korean Electrochemical Society 2019 Journal of electrochemical science and technology Vol.10 No.2

The development of simple methods for As detection has received great attention because As is a toxic chemical element causing environmental and health-related issues. In this work, the effect of nanostructures of Au electrodes on their electroanalytical performance during As detection was investigated. Different Au nanostructures with various surface morphologies such as nanoplate Au, nanospike Au, and dendritic Au structures were prepared, and their electrochemical behaviors toward square-wave anodic stripping voltammetric As detection were examined. The difference in intrinsic efficiency for As detection between nanostructured and flat Au electrodes was explained based on the crystallographic orientations of Au surfaces, as examined by the underpotential deposition of Pb. The most efficient As detection performance was obtained with nanoplate Au electrodes, and the effects of the pre-deposition time and interference on As detection of the nanoplate Au electrodes were also investigated.

Surface-Specific Deposition of Catalytic Metal Nanocrystals on Hollow Carbon Nanospheres <i>via</i> Galvanic Replacement Reactions of Carbon-Encapsulated MnO Nanoparticles

Lee, Dong-Gyu,Kim, Soo Min,Jeong, Hwakyeung,Kim, Jongwon,Lee, In Su American Chemical Society 2014 ACS NANO Vol.8 No.5

<P>This paper reports the findings of our efforts toward gaining a more complete understanding and utilization of galvanic replacement reactions involving manganese oxide with noble metals. It was revealed that the site of metal deposition is significantly affected by the variable oxidation state of manganese oxide. The use of carbon-encapsulated MnO nanoparticles as a reaction template led to metal growth specifically on the outermost surfaces of the carbon shells rather than on the MnO cores, which allowed for the selective decoration of the external surfaces of hollow carbon nanospheres with catalytic nanocrystals of various noble metals, including Pt, Pd, Rh, and Ir. By rearranging the sequence between carbon-shell coating and galvanic replacement processes, the deposited metal nanocrystals could be placed on the interior surfaces of hollow carbon nanospheres and, moreover, separately on the internal and the external surfaces, which may enable the respective control of the catalytic functionalities of each specific surface.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2014/ancac3.2014.8.issue-5/nn5020598/production/images/medium/nn-2014-020598_0011.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn5020598'>ACS Electronic Supporting Info</A></P>