Sang Hyun Ahn

Korea Institute of Science and Technology, Sŏul, Seoul, South Korea

Are you Sang Hyun Ahn?

Claim your profile

Publications (59)175.55 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To reduce the use of noble metals, iridium oxide (IrO2) catalysts are prepared on carbon paper (CP) by electrodeposition for use as the anodes in polymer electrolyte membrane water electrolysis (PEMWE). The activities of the fabricated electrodes toward the oxygen evolution reaction are evaluated. The loading amount and morphology of the IrO2 deposits are varied by controlling the electrodeposition potential (Edep) and time (tdep). When electrodeposited at 0.7 V, the IrO2 loading ranges from 0.007 to 0.464 mg cm−2 (tdep: 1 ∼ 30 min). In the PEMWE test at 90 °C, the IrO2/CP electrode with an IrO2 loading of 0.1 mg cm−2 shows the highest performance (1.92 A cm−2 at 1.8 V) in which high IrO2 utilization is achieved without significant exposure of the substrate carbon surface. The developed IrO2/CP electrodes provide cell performances comparable to those in previous reports with a higher IrO2 loading, indicating markedly enhanced mass activity.
    Applied Catalysis B Environmental 12/2015; 179. DOI:10.1016/j.apcatb.2015.05.027 · 7.44 Impact Factor
  • Ki Myoung Song · Sang Hyun Ahn · Young-Sam Cho ·

    Surface and Coatings Technology 10/2015; DOI:10.1016/j.surfcoat.2015.10.022 · 2.00 Impact Factor

  • Applied Surface Science 10/2015; DOI:10.1016/j.apsusc.2015.10.082 · 2.71 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The particle-type electrodes with ultra-low electrocatalyst loading (<10μgcm-2) were developed as cathodes in the anion exchange membrane water electrolyzer (AEMWE). The Pt-decorated Ni electrocatalysts were prepared on the surface of carbon paper by Ni electrodeposition and subsequent displacement of Ni by Pt; the composition and morphology were controlled by varying HCl concentration. In half cell test, the increase of hydrogen evolution reaction (HER) activity by Pt decoration was confirmed for Pt-Ni/CP-2 that has Pt ratio of 39.4% (1.85μgPtcm-2). A membrane electrode assembly employing Pt-Ni/CP-2 as the HER electrode (total catalyst loading: 13.2μgcm-2) exhibited a current density of 250mAcm-2 at 1.9Vcell (50°C), which is comparable to the previous reports with much larger loading of 3.1~80mgcm-2.
  • [Show abstract] [Hide abstract]
    ABSTRACT: NiW alloy catalysts were prepared on a Cu foil substrate by using a co-electrodeposition method for use in the hydrogen evolution reaction (HER) in alkaline water electrolysis. The compositions of the alloy catalysts were controlled over a wide range by varying the molar ratio [W6+]/[Ni2+] in the electrolyte. At high W contents (∼41 at %) in the deposited catalyst, the morphologies of the NiW alloys showed drastic changes compared with those of electrodeposited Ni, in particular a significant decrease in surface coverage and aggregates’ sizes. All of NiW alloys deposited in a citrate-containing bath demonstrated an amorphous structure, regardless of W content. Electrochemical measurements employing repeated cyclic voltammetry (CV) showed enhanced HER activities for the NiW alloy catalysts compared with the pure Ni catalyst. The maximum HER activity was obtained with a W content of 41 at %; the alloying effects, including morphological changes, and the high affinity for hydrogen absorption shown by this alloy's amorphous structure are dominant factors in the enhanced HER activity. The results presented herein provide advanced information of significant relationship between material properties and HER activity of NiW alloys.
    Applied Surface Science 05/2015; 349. DOI:10.1016/j.apsusc.2015.05.040 · 2.71 Impact Factor
  • Sang Hyun Ahn · Yihua Liu · Thomas P. Moffat ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Self-terminating electrodeposition was used to grow ultrathin Pt overlayers on 111 textured Au thin films. The Pt thickness was digitally controlled by pulsed potential deposition that enabled the influence of overlayer thickness on electrocataytic reactions, such as methanol and formic acid oxidation, to be examined. Bimetallic and ensemble effects associated with sub-monolayer coverage of Pt on Au yield enhanced catalysis. For films grown using one deposition pulse the peak rate of CH3OH oxidation was enhanced by a factor of 4 relative to bulk Pt. The overlayer consisted of 2 nm diameter monolayer Pt islands that covered 75% of the surface. However, voltammetric cycling resulted in a loss of the enhanced activity associated with the as-deposited sub-monolayer films. For thicker Pt films the electrocatalytic activity decreased monotonically with thickness until bulk Pt behavior was obtained beyond three monolayers. For HCOOH oxidation improvements in Pt area normalized activity in excess of a 100-fold were observed for sub-monolayer Pt films. The performance improved with voltammetric cycling due to a combination of Pt dissolution, Au segregation and Pt-Au alloy formation. The maximum activity was associated with fractional surface coverage between 0.28 and 0.21 although the films were subject to a deactivation process at longer times related to a diffusional process. Bulk Pt behavior for formic acid oxidation was observed for Pt films greater than three monolayers in thickness.
    ACS Catalysis 04/2015; 5(4):2124-2136. DOI:10.1021/cs501228j · 9.31 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We have investigated phosphate adsorption on the Au surface by in situ electrochemical surface-enhanced Raman spectroscopy to assess the possible use of Au-based alloys as catalysts for the oxygen reduction reaction (ORR) in high-temperature proton exchange membrane fuel cells. Compared with its strong adsorption in neutral or basic electrolytes, the adsorption of phosphate species on the Au surface were significantly altered in acidic electrolyte. Thus, PtxAu100-x catalysts of various compositions were prepared by electrodeposition and exhibited better ORR activities than pure Pt in phosphoric acid electrolyte, which can be explained in terms of alloying effects and the different phosphate adsorption behavior.
    Applied Catalysis B Environmental 04/2015; 165:495-502. DOI:10.1016/j.apcatb.2014.10.042 · 7.44 Impact Factor
  • Source

    Applied Catalysis B Environmental 03/2015; 174-175. DOI:10.1016/j.apcatb.2015.03.010 · 7.44 Impact Factor

  • Energy & Environmental Science 01/2015; DOI:10.1039/C5EE02541A · 20.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The adsorption mechanism of thiourea (TU) and its effect on Cu electrodeposition were verified using TU derivatization. Contrary to the previously reported behavior of TU as an inhibitor, TU either promoted or inhibited Cu reduction according to the derivatization time. During the short derivatization time, the adsorbed TU with low surface coverage was oxidized to spontaneously reduce Cu2+ to Cu+, thereby, accelerating the Cu deposition. However, TU inhibited the Cu deposition as the coverage of TU-Cu+ increased with the derivatization time. Furthermore, a deterioration in the resistivity of the Cu film, which occurred when TU was added, was largely improved by the derivatization method while maintaining an enhancement in the film hardness. TU derivatization resulted in a 9.2% enhancement in the film hardness and only a 26.0% deterioration in the film resistivity compared to those of Cu films deposited in the absence of TU, which were not simultaneously obtainable upon the direct addition of TU to the deposition bath.
    Journal of The Electrochemical Society 10/2014; 161(14):D749-D755. DOI:10.1149/2.0271414jes · 3.27 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Electrochemical reduction of CO2 to HCOOH was performed on a Sn electrode using a proton exchange membrane-embedded electrolysis cell. The effects of reaction conditions such as catholyte and anolyte types, reduction potential, catholyte pH, and reaction temperature on the amount of HCOOH and its faradaic efficiency were investigated. Four different electrolytes (KOH, KHCO3, KCl, KHSO4) were chosen as the candidate catholyte and anolyte; the most suitable electrolyte was chosen by monitoring the amount of HCOOH and faradaic efficiency. The effect of the pH of the selected catholyte on the conversion of CO2 to HCOOH was also investigated. In addition, the reaction temperature was varied and its effect was studied. From the observations made, we determined the optimal reaction conditions for the production of HCOOH via the electrochemical reduction of CO2 by a systematic approach.
    International Journal of Hydrogen Energy 10/2014; 39(29):16506–16512. DOI:10.1016/j.ijhydene.2014.03.145 · 3.31 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Carbon-supported Pt nanoparticles have been widely used as electrocatalysts for electrochemical hydrogen pumps. However, Pt surfaces are susceptible to poisoning under CO2 atmosphere, and as a result, need greater applied cell voltages. Instead of Pt as an anode catalyst in electrochemical hydrogen pumps, we synthesized Ir-based catalysts and characterized them by XRD, XPS, TEM, and TGA. The electrochemical characteristics of the Ir catalysts were evaluated by a halfcell test, and their catalytic activities toward the hydrogen oxidation and hydrogen evolution reactions were evaluated by micro polarization analysis. The exchange current density of the Ir catalyst that was heat treated at 300 degrees C was larger than that of commercial Pt. CO2 stripping analysis confirmed that the Ir catalyst was not affected by CO2, unlike the Pt catalyst. Focusing on H-2 separation from H-2/CO2 gas, an evaluation using a single-cell test indicated that the Ir catalyst performed better than the Pt catalyst.
    Applied Catalysis B: Environmental 10/2014; s 158–159:348–354. DOI:10.1016/j.apcatb.2014.04.016 · 7.44 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Electroless deposition of a NiWP barrier layer on a SiO2 substrate was investigated for all-wet Cu interconnect fabrication. In this study, the entire fabrication process including substrate activation, barrier layer electroless deposition, and direct Cu electrodeposition wasmodified. The SiO2 substrate was activated via Pd nanoparticles that were immobilized on the substrate by using a preformed self-assembled monolayer composed of 3-aminopropyl-triethoxysilane. Reduction of NiWP layer resistivity was achieved by applying ultrasound during the substrate activation process and by adding poly(ethylene glycol) to the electroless deposition bath. The Cu electrodeposition was performed directly on the NiWP layer after performing coulometric oxide reduction, thus improving the adhesion and nucleation density of Cu on the NiWP layer. The electrodeposition process was conducted in two steps: Cu nucleation and Cu thin film formation at a high overpotential followed by additional Cu film growth at a low overpotential. As a result, a uniform, smooth Cu film covered the NiWP layer. In addition, bottom-up Cu filling was accomplished on a 120 nm wide, patterned substrate with a 2.5 aspect ratio. Barrier layer performance was evaluated by using a Cu / NiWP / Pd / SiO2 stacked specimen formed by applying the proposed procedure.
    Journal of The Electrochemical Society 10/2014; 161(14):D756-D760. DOI:10.1149/2.0291414jes · 3.27 Impact Factor
  • Ji-Eun Lim · Sang Hyun Ahn · Jong Hyun Jang · Hansoo Park · Soo-Kil Kim ·
    [Show abstract] [Hide abstract]
    ABSTRACT: NiCu alloys have been suggested as potential candidates for catalysts in glucose oxidation. In this study, NiCu alloys with different compositions were prepared on a glassy carbon substrate by changing the electro-deposition potential to examine the effect of Ni/Cu ratio S in alloys on catalytic activity toward glucose oxidation. Cyclic voltammetry and chronoamperometry showed that NiCu alloys had higher catalytic activity than pure Ni and Cu catalysts. Especially, Ni59Cu41 had superior catalytic activity, which was about twice that of Ni at a given oxidation potential. X-ray analyses showed that the oxidation state of Ni in NiCu alloys was increased with the content of Cu by lattice expansion. Ni components in alloys with higher oxidation state were more effective in the oxidation of glucose.
    Bulletin- Korean Chemical Society 07/2014; 35(7):2019-2024. DOI:10.5012/bkcs.2014.35.7.2019 · 0.80 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A membrane electrode assembly (MEA) for use in an alkaline water electrolyzer is fabricated by sandwiching an anion exchange membrane (AEM) between two electrodes prepared by the electrodeposition of Ni (used as a catalyst) on carbon papers (CPs) acting as gas diffusion layers. The conditions for Ni electrodepositon are determined on the basis of the results of half-cell tests for hydrogen and oxygen evolution reactions. An MEA fabricated by the direct electrodeposition of an extremely low Ni amount of 8.5 mu g(Ni) cm(-2) exhibits a high cell performance of 150 mA cm(-2) at 1.9 V when a 1.0 M KOH solution is supplied to the cathode. Electrodeposited Ni is uniformly distributed on the surface of CP fibers, thereby providing a large electrochemical surface area for gas evolution reactions and thus maintaining high catalyst utilization. It is suggested that control of bubble generation and AEMs with higher ionic conductivity would further increase MEA performance. (c) 2014 Elsevier B.V. All rights reserved.
    Applied Catalysis B Environmental 07/2014; s 154–155:197–205. DOI:10.1016/j.apcatb.2014.02.021 · 7.44 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: As a catalyst for the hydrogen evolution reaction (HER) in alkaline water splitting, NiCo alloys of various compositions were prepared through electrodeposition onto Cu substrates. The composition of each alloy catalyst was varied by controlling the molar ratio of Co2+ ions in the electrolyte. With an increase in the Co content, the morphologies of the NiCo alloys were progressively changed from a round to polygonal shape. The NiCo alloys all exhibited a Ni rich surface, as confirmed by the bulk-to-surface compositional ratio and degree of alloying. The catalytic activities of the NiCo alloys toward the HER of water splitting were electrochemically tested in a KOH electrolyte, and the specific activities were characterized by considering the electrochemical surface areas of Ni and Co. The effect of alloying was demonstrated to be a significant enhancement of HER activity, resulting from a change in the electronic structures of Ni and Co.
    Applied Surface Science 07/2014; 307:146–152. DOI:10.1016/j.apsusc.2014.03.197 · 2.71 Impact Factor
  • Sang Hyun Ahn · Insoo Choi · Oh Joong Kwon · Jae Jeong Kim ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Silicon-based micro-reactors for the fuel processing of liquefied natural gas (LNG) were fabricated using silicon technologies. The micro-LNG steam reformer achieves a LNG conversion of 77.4%, and the hydrogen composition of the product was 73.3% at 600 degrees C. The product gas was supplied to consecutive micro-reactors to carry out carbon monoxide removal through a high-temperature water gas shift (HTS) reaction and a low-temperature water gas shift (LTS) reaction. Under operating conditions we investigated, the micro-HTS and LTS reactors demonstrated the highest carbon monoxide conversion of 61.5% at 450 degrees C and 77.5% at 300 degrees C, respectively. The final product gas of the micro-fuel processor was composed of 75.7% hydrogen and 0.7% carbon monoxide.
    The Chemical Engineering Journal 07/2014; 247:9–15. DOI:10.1016/j.cej.2014.02.108 · 4.32 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Objectives Although diffuse splenic 18F-fluorodeoxyglucose (F-18 FDG) uptake exceeding hepatic activity, is considered abnormal, its clinical significance is rarely discussed in the literature. The aim of this study was to determine the contributing factors causing diffusely increased splenic FDG uptake in patients with cholangiocarcinoma. Methods From January 2010 to March 2013, 140 patients (84 men, 56 women) were enrolled in this study. All patients had been diagnosed with cholangiocarcinoma and underwent F-18 FDG positron emission tomography/computed tomography (PET/CT) for the pretreatment staging work up. Clinical records were reviewed retrospectively. Various hematological parameters, C-reactive protein (CRP) level, CEA, CA19-9, pancreatic enzymes and liver function tests were conducted within 2 days after the F-18 FDG PET/CT study. Results Diffuse splenic uptake was observed in 23 patients (16.4%). Of those, 19 patients (82.6%) underwent endoscopic retrograde cholangiopancreastography (ERCP) 7 days before F-18 FDG PET/CT. The CRP level (p < 0.001) and white blood cell count (p = 0.023) were significantly higher in the group of patients with diffuse splenic FDG uptake. The hemoglobin (p < 0.001) and the hematocrit (p < 0.001) were significantly lower in patients with diffuse splenic FDG uptake. Pancreatic enzymes, liver function test results, and tumor markers were not significantly different between the patients who did or did not have diffusely increased splenic FDG uptake. The significant factors for diffuse splenic F-18 FDG uptake exceeding hepatic F-18 FDG uptake on multivariate analysis included: performing ERCP before F-18 FDG PET-CT (odds ratio [OR], 77.510; 95% CI, 7.624-132.105), and the presence of leukocytosis (OR, 12.436; 95% CI, 2.438-63.445) or anemia (OR, 1.211; 95% CI, 1.051-1.871). Conclusion In conclusion, our study demonstrated that concurrent inflammation could be associated with diffusely increased splenic FDG uptake. We suggest that performing ERCP before F-18 FDG PET/CT could cause acute inflammation which may induce splenic FDG activity.
    06/2014; 48(2):137-143. DOI:10.1007/s13139-013-0246-0
  • Insoo Choi · Sang Hyun Ahn · Myeong Ho Kim · Oh Joong Kwon · Jae Jeong Kim ·
    [Show abstract] [Hide abstract]
    ABSTRACT: A Pt-shell-Pd-core/C catalyst is prepared via electroless deposition and galvanic displacement. The catalyst is active toward the electro-oxidation of methanol and is more stable against COad-poisoning than a commercial Pt/C catalyst. The stable activity of Pt-shell-Pd-core/C is ascribed to the tuned electronic property of the Pt over-layer in the Pt-shell-Pd-core/C, which leads to weak binding with COad and increases the kinetics of OHad formation. The weakened binding property of the surface Pt with COad and the facile oxidation of COad by OHad were confirmed by a spectroscopic analysis and in a COad-stripping experiment, respectively. The electro-oxidation of COad by Had is the rate-determining step of methanol oxidation. Therefore, the accelerated formation of OHad contributes to the overall oxidation reaction, preventing COad-poisoning. In addition, Pt-shell-Pd-core/C maintains its activity longer than Pt/C does during a prolonged cycle experiment. Copyright
    International Journal of Hydrogen Energy 03/2014; 39(8):3681–3689. DOI:10.1016/j.ijhydene.2013.12.118 · 3.31 Impact Factor
  • Source
    Sang Hyun Ahn · Sung Hoon Kim · Gi Hong Choi · Jin Sub Choi · Kyung Sik Kim ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Although many patients with hepatocellular carcinoma experience recurrence within 2 years after hepatectomy, some patients with T1 and T2 hepatocellular carcinoma show recurrence-free survival for more than 5 years after surgery. This study was designed to analyze the optimal follow-up period on patients with T1 and T2 hepatocellular carcinoma (HCC) showing recurrence-free survival 5 years after surgery. One hundred seventy patients underwent hepatectomy from January 1995 to December 1999. Numbers of patients with T1 and T2 HCC were 76 and 73, respectively. The recurrence patterns of patients experiencing recurrence more than 5 years after liver resection were analyzed in aspect of clinicopathological features and follow-up period. Thirteen patients experienced recurrence more than 5 years after surgery. Only age was found as a significant factor for recurrence. Eight patients were checked regularly with 6-month intervals and the others were checked with 12-month or more intervals. The size of the recurrent tumors in the 6-month interval group had a median of 1.1 cm (range, 1 to 4.2 cm) and the size of the recurrent tumors in the 12-month or more interval group had a median of 3 cm (range, 1.6 to 4 cm). The tumor size was significantly smaller in the 6-month interval group. Though the patients with early stage HCC showed high overall survival, some patients experienced a late recurrence of more than 5 years after surgery. Patients less than 60 years old with early stage HCC should be checked regularly with 6-month intervals even over 5 years after liver resection.
    Journal of the Korean Surgical Society 12/2013; 85(6):269-74. DOI:10.4174/jkss.2013.85.6.269 · 0.73 Impact Factor

Publication Stats

293 Citations
175.55 Total Impact Points


  • 2013-2015
    • Korea Institute of Science and Technology
      • Fuel Cell Research Center
      Sŏul, Seoul, South Korea
    • Wonkwang University
      • Division of Mechanical and Automotive Engineering
      Riri, North Jeolla, South Korea
    • National Institute of Standards and Technology
      • Material Measurement Laboratory (MML)
      GAI, Maryland, United States
    • Wonju Severance Christian Hospital
      Genshū, Gangwon-do, South Korea
  • 2014
    • Pusan National University
      • Department of Nuclear Medicine
      Tsau-liang-hai, Busan, South Korea
  • 2008-2014
    • Seoul National University
      • • Institute of Chemical Processes
      • • Department of Chemical and Biological Engineering
      • • Department of Surgery
      Sŏul, Seoul, South Korea
  • 2009-2013
    • Hanyang University
      • Division of Chemical Engineering and Bioengineering
      Sŏul, Seoul, South Korea
  • 2012
    • Yonsei University Hospital
      • Department of Internal Medicine
      Sŏul, Seoul, South Korea
  • 2009-2010
    • University of Seoul
      • School of Computer Science
      Sŏul, Seoul, South Korea
  • 2007
    • Dongguk University
      Sŏul, Seoul, South Korea