CO Oxidation on LaCoO3 Perovskite

Rhee, Choong Kyun,Lee, Ho In 한국화학공학회 1994 NICE Vol.12 No.2

A study of CO oxidation on LaCoO₃ perovskite was performed in an ultrahigh vacuum system by means of adsorption and daorption. All gases were adsorbed at ambient temperature. Two adsorption states(α- and β-) of CO exist. The a-peak at 440 K is attributed to carbonyl species adsorbed on Co^(3+) ions while the peak at 663 K likely comes from bidentate carbonate formed by adsorption on lattice oxygens. CO₂ shows a single desorption peak(R-state, 483 K) whose chemical state may be monodentate carbonate. A new CO₂ desorption peak at 590 K can be created by oxidation of CO. Ov also shows two adsorption states. One desorbs at 600 K, which may reflect adsorption on Co^(3+) ions. The other apparently incorporates with bulk LaCoO₃ and desorbs above 1000 K. The two adsorption tates of CO are oxidized via different mechanisms. The rate determining step in oxidation of a α-CO is the surface reaction whereas for that of β-CO, it is desorption of product CO₂.

Electrochemical Atomic Layer Processing of Compound Semiconductors

( Choong Kyun Rhee ),( John L. Stickney ) 한국공업화학회 1993 한국공업화학회 연구논문 초록집 Vol.1993 No.0

We present two electrochemical methods of atomic layer processing of compound semiconductors. One is electrochemical formation of compound semiconductors, based on the principles of atomic layer epitaxy (ALE). This method is referred to ”Electrochemical Atomic Layer Epitaxy (ECALE)”. The other is electrochemical removal of atomic layers in a compound semiconductor in a sequential way. This method is called ’’Electrochemical Digital Etching (ECDE)”. The principle of the electrochemical atomic layer processing methods is associated with a famous phenomena in electrochemistry, which is “Underpotential Deposition (UPD)”. When one element deposits on a second metal surface, the deposition occurs at a potential prior to (under) the potential of bulk deposition (i.e. deposition of the element on itself). The UPD process occurs when compound formation is favored thermodynamically. In fact, the amount of underpotentially deposited element is limited to submonolayer or full monolayer. In the ECALE method, individual solutions of depositing elements are sequentially exposed to a substrate as in gas-phase ALE. One element is deposited on the substrate surface at an appropriate underpotential to obtain one monolayer. Then, a second element is deposited on the substrate whose surface is already covered with one monolayer of the first element. In this way, a compound semiconductor can be formed. The selection of deposition potentials is critical because one of the elements should be deposited without stripping the already-deposited atomic layers. In the ECDE method, the top layer element of a compound semiconductor is stripped underpotentially since it has dangling bonds (i.e. the corresponding element in the bulk is more stable). Upon removing one element in the top layer, a second element, which is exposed to electrolyte, is stripped in the same way. Accordingly, layer-by-layer etching results from a sequential application of underpotentials for each elements with removing the dissolved ion. In this seminar, experimental evidences for the electrochemical atomic layer processing will be presented. The ECALE method will be exemplified with deposition of ZnTe and CdTe on polycrystalline Au electrodes. Likewise, the ECDE method will be explained with etching of CdTe(100) surfaces. In addition, the problems associated with the methods will be discussed.

CO OXIDATION ON LaCoO3 PEROVSKITE

Rhee, Choong Kyun,Lee, Ho In 한국화학공학회 1994 Korean Journal of Chemical Engineering Vol.11 No.1

A study of CO oxidation on LaCoO₃ perovskite was performed in an ultrahigh vacuum system by means of adsorption and desorption. All gases were adsorbed at ambient temperature. Two adsorption states (α- and β-) of CO exist. The α-peak at 440 K is attributed to carbonyl species adsorbed on Co^(3+) ions while the β-peak at 663 K likely comes from bidentate carbonate formed by adsorption on lattice oxygens. CO₂ shows a single desorption peak (β-state, 483 K) whose chemical state may be monodentate carbonate. A new CO₂ desorption peak at 590 K can be created by oxidation of CO. O₂ also shows two adsorption states. One desorbs at 600 K, which may reflect adsorption on Co^(3+) ions. The other apparently incorporates with bulk LaCoO₃ and desorbs above 1000 K. The two adsorption states of CO are oxidized via different mechanisms. The rate determining step in oxidation of α-CO is the surface reaction whereas for that of β-CO, it is desorption of product CO₂.

Electrochemical Atomic Layer Processing of Compound Semiconductors

( Choong Kyun Rhee,John L . Stickney ) 한국공업화학회 1993 한국공업화학회 연구논문 초록집 Vol.1990 No.3

Pt(100) 단결정 전극 상에서 urea의 흡착

이충균 충남대학교 기초과학연구소 1995 忠南科學硏究誌 Vol.22 No.1

In this paper, I present the results of voltammetric studies of the adsorption behavor of urea on Pt(100) single crystal electrode. The voltammetric characteristics of urea are interpreted in terms of slow adsorption kinetics and charge transfer adsorption. The saturate surface coverage of urea on Pt(100) electrode is calculated based on the charge transfer process and discussed in comparison with in-situ and ex-situ data.

Experimental Simulation of Iron Oxide Formation on Low Alloy Steel Evaporator Tubes for Power Plant in the Presence of Iron Ions

Mihwa Choi,Choong Kyun Rhee 대한화학회 2009 Bulletin of the Korean Chemical Society Vol.30 No.11

Presented are the formation of iron oxide layers on evaporator tubes in an actual fossil power plant operated under all volatile treatment (AVT) condition and an experimental simulation of iron oxide formation in the presence of ferrous and ferric ions. After actual operations for 12781 and 36326 hr in the power plant, two iron oxide layers of magnetite on the evaporator tubes were found: a continuous inner layer and a porous outer layer. The experimental simulation (i.e., artificial corrosion in the presence of ferrous and ferric ions at 100 ppm level for 100 hr) reveals that ferrous ions turn the continuous inner oxide layer on tube metal to cracks and pores, while ferric ions facilitate the production of porous outer oxide layer consisting of large crystallites. Based on a comparison of the oxide layers produced in the experimental simulation with those observed on the actually used tubes, we propose possible routes for oxide layer formation schematically. In addition, the limits of the proposed corrosion routes are discussed in detail

Structural evolution of irreversibly adsorbed Bi on Pt(111) under potential excursion

Kim, Jandee,Rhee, Choong Kyun Springer-Verlag 2013 Journal of solid state electrochemistry Vol.17 No.12

Atomic and Molecular Adsorption on the Bi(111) Surface: Insights into Catalytic CO₂ Reduction

Oh, Wooseok,Rhee, Choong Kyun,Han, Jeong Woo,Shong, Bonggeun American Chemical Society 2018 The Journal of Physical Chemistry Part C Vol.122 No.40

<P>Bismuth is known to exhibit high selectivity toward production of HCOOH when used as an electrocatalyst for reduction of CO<SUB>2</SUB>. However, the current deficiency of knowledge on the surface chemical properties of Bi hinders mechanistic understanding and efficient development of Bi catalysts. In this study, molecular adsorption phenomena on the Bi(111) surface related to the electrocatalytic reduction of CO<SUB>2</SUB> (ERC) are studied using dispersion-corrected density functional theory calculations. It is shown that the Bi(111) surface is inert toward adsorption of molecular species other than O<SUB>2</SUB>, such as CO, CO<SUB>2</SUB>, and HCOOH, confirming the low chemical reactivity of the surface. The adsorbates with O-Bi bonds are systematically more stable than those with C-Bi bonds. As a result, *OCHO (formate) is significantly preferred over *COOH (carboxyl), leading to selective formation of HCOOH over CO as ERC product. Direct formation of *OCHO by proton-coupled electron transfer to CO<SUB>2</SUB> is suggested as the reaction mechanism for ERC. Structural, vibrational, and electronic details of these two adsorbates are provided to guide future experimental mechanistic studies.</P> [FIG OMISSION]</BR>

Adsorptive Behavior of Dimethylglyoxime on Au(111)

Kim, Jandee,Kim, Sechul,Rhee, Choong Kyun American Chemical Society 2011 Langmuir Vol.27 No.23

<P>Dimethylglyoxime (DMG) adsorbed on Au(111) was investigated using electrochemical scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). STM experiments revealed three different structures of adsorbed DMG at open circuit potential (∼0.07 V versus Ag/AgCl): (2√3×2√3)R30°-α, (2√3×4√3)R30°-β, and (2√3×4√3)R30°-γ. The coverage of adsorbed DMG obtained using XPS was 0.33. A combination of structural and quantitative information identified the adsorbed DMG as an anionic tetramer, held together by intermolecular hydrogen bonding and arrayed in three ordered patterns. Domains of adsorbed DMG underwent phase transitions between the observed structures, most likely due to the influence of the STM tip. However, a significant correlation between the observed structures and the imaging conditions was not found. The ordered layers existed only at open circuit potential as evidenced by their disappearance when the potential was shifted to 0.2 or −0.15 V. The ordered layers were also removed by immersion in a solution of Ni<SUP>2+</SUP>, implying that the adsorbed DMG was converted to a soluble dimer complex with the Ni<SUP>2+</SUP> ion. This particular observation is discussed in terms of the rigidity of the organic network.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2011/langd5.2011.27.issue-23/la202594s/production/images/medium/la-2011-02594s_0002.gif'></P>

Formation of Single-Layered Pt Islands on Au(111) Using Irreversible Adsorption of Pt and Selective Adsorption of CO to Pt

Kim, Jandee,Shin, Dongwan,Rhee, Choong Kyun,Yoon, Seong-Ho American Chemical Society 2014 Langmuir Vol.30 No.15

<P>This communication compares two different multiple deposition routes of Pt on Au(111), using irreversible adsorption of Pt precursor ions and selective adsorption of CO. A scanning tunneling microscopy study revealed that the conventional route, not utilizing CO, produced multiple-layered Pt cluster islands, while the CO route, employing CO, formed single-layered Pt islands exclusively. The role of CO selectively adsorbed on pre-existing Pt islands was to prevent additional irreversible adsorption of Pt precursor ions onto Pt islands. Cyclic voltammetric works disclosed that the CO and hydrogen coverages on single-layered Pt islands were higher than those on multiple-layered ones, and that the Pt islands on Au were more effective in adsorbing CO than hydrogen.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2014/langd5.2014.30.issue-15/la500005p/production/images/medium/la-2014-00005p_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/la500005p'>ACS Electronic Supporting Info</A></P>