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Choun, Myounghoon,Hong, Sujik,Lee, Jaeyoung The Electrochemical Society 2018 Journal of the Electrochemical Society Vol.165 No.15
<P>We investigate the mechanistic origin of oxidation of HCOO<SUP>−</SUP> on Pd/C in alkaline media using H/D kinetic isotope effect studies and electrochemical experiments, such as cyclic voltammetry, step-linear sweep voltammetry, and stripping voltammetry. We reveal that HCOO<SUP>−</SUP> is oxidized to CO<SUB>2</SUB> through a direct pathway, and the oxidation of H<SUB>ads</SUB> is the rate determining step. The slow oxidation kinetics of H<SUB>ads</SUB>, which causes a site-occupying effect, suppress the oxidation of HCOO<SUP>−</SUP>, and a more distinct phenomenon is observed in the potential region for H<SUB>ads</SUB>. These observations provide clues to understanding the significant electrocatalytic activity of Pd and rational approaches for the development of more active catalysts for the oxidation of HCOO<SUP>−</SUP> in alkaline media.</P>
Catalytically active highly metallic palladium on carbon support for oxidation of HCOO<sup>−</sup>
Choun, Myounghoon,Ham, Kahyun,Shin, Dongyoon,Lee, Jae Kwang,Lee, Jaeyoung Elsevier 2017 CATALYSIS TODAY - Vol.295 No.-
<P><B>Abstract</B></P> <P>Catalytically active highly metallic palladium (A-I-Pd/C) catalyst for oxidation of formate (HCOO<SUP>−</SUP>) was synthesized via borohydride reduction method assisted by ammonia and iodine ion. The physico-chemical characterizations were conducted to investigate properties of the synthesized catalysts and we confirmed A-I-Pd/C is consisted with palladium hydride. The catalytic activity of the catalysts for oxidation of HCOO<SUP>−</SUP> are characterized by electrochemical analysis and A-I-Pd/C catalysts performed the best catalytic activity for oxidation of HCOO<SUP>−</SUP> in terms of Tafel slope and onset potential. The enhanced catalytic activity of A-I-Pd/C is explained by enhanced kinetics of oxidation of H<SUB>ads</SUB>, which is caused by weaken adsorption strength of H<SUB>ads</SUB> on Pd due to electron transfer from H to Pd. The enhanced performance of A-I-Pd/C was also confirmed and compared with the others in a single cell system.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Highly metallic Pd/C is synthesized by addition of NH<SUB>3</SUB> and iodine ion. </LI> <LI> Highly metallic Pd/C catalyst improves oxidation kinetics of H<SUB>ads</SUB>. </LI> <LI> Highly metallic Pd/C catalyst shows enhanced activity toward formate oxidation. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>The dependency of the state of Pd in carbon-supported palladium on synthesis process.</P> <P>[DISPLAY OMISSION]</P>
Choun, Young-Sun,Kim, Min-Kyu Korean Nuclear Society 2008 Nuclear Engineering and Technology Vol.40 No.4
This study evaluates the performance of a coil spring-viscous damper system for the vibration and seismic isolation of an Emergency Diesel Generator (EDG) by measuring its operational vibration and seismic responses. The vibration performance of a coil spring-viscous damper system was evaluated by the vibration measurements for an identical EDG set with different base systems - one with an anchor bolt system and the other with a coil spring-viscous damper system. The seismic performance of the coil spring-viscous damper system was evaluated by seismic tests with a scaled model of a base-isolated EDG on a shaking table. The effects of EDG base isolation on the fragility curve and core damage frequency in a nuclear power plant were also investigated through a case study.
Choun, Young-sun,Park, Junhee,Choi, In-Kil Korean Nuclear Society 2014 Nuclear Engineering and Technology Vol.46 No.5
The effects of variability of the mechanical properties of lead rubber bearings on the response of a seismic isolation system are investigated. Material variability in manufacturing, aging, and operation temperature is assumed, and two variation models of an isolation system are considered. To evaluate the effect of ground motion characteristics on the response, 27 earthquake record sets with different peak A/V ratios were selected, and three components of ground motions were used for a seismic response analysis. The response in an isolation system and a superstructure increases significantly for ground motions with low A/V ratios. The variation in the mechanical properties of isolators results in a significant influence on the shear strains of the isolators and the acceleration response of the superstructure. The variation provisions in the ASCE-4 are reasonable, but more strict variation limits should be given to isolation systems subjected to ground motions having low A/V ratios. For application of seismic isolation systems to safety-related nuclear structures, the variation in the material and mechanical properties of the isolation system should be properly controlled during the manufacturing and aging processes. In addition, special consideration should be given to minimize the accidental torsion caused by the dissimilarity in the stiffness variations of the isolators.
Polydimethylsiloxane treated cathode catalyst layer to prolong hydrogen fuel cell lifetime
Choun, M.,Nauryzbayev, D.,Shin, D.,Lee, J. Elsevier Science Publishers 2016 CATALYSIS TODAY - Vol.262 No.-
<P>In operation of hydrogen fuel cells for vehicle, carbon corrosion induced by frequent on/off operation significantly causes degradation of performance and durability of fuel cells, aggregating and losing Pt particles. It is critical to develop durable cathode and understand the mechanism of degradation in hydrogen fuel cells for commercialization. In this study, we prepared polydimethylsiloxane treated cathode, which is hydrophobic, for improving durability in hydrogen fuel cells. In addition, effect of hydrophobic cathode on durability was investigated by various analyses. We observed that the polydimethylsiloxane (PDMS) treated cathode contributed to limit both mass transfer limitation and carbon corrosion by efficient water withdrawal. Based on our results, we provide the possibility of PDMS treatment to decline the performance degradation in fuel cells. (C) 2015 Published by Elsevier B.V.</P>
Choun-sub Kim,Maengkyu Kim,Min-ju Kim,Hyeyoung Jung 한국영양학회 2020 Nutrition Research and Practice Vol.14 No.6
BACKGROUND/OBJECTIVES: Although some juices affect subjective sleep quality, there is a lack of information on the effect of a specific juice on objective sleep quality and heart rate variability (HRV) during sleep; thus the present study investigated whether a blended juice made from natural extracts influenced sleep quality and HRV during sleep in adults with disturbed sleep. SUBJECTS/METHODS: A randomized, crossover study was conducted on twenty-five adults (15/10, female/male) complaining of difficulty initiating or maintaining nighttime sleep (Pittsburgh sleep quality index [PSQI] ≥ 5). During feeding sessions (FS), subjects received sleep-inducing juice made of natural ingredients (250 mL/trial) twice a day for 8 weeks or non-FS (N-FS) for 8 weeks while maintaining normal activities. Sleep quality and parameters were recorded via wearable actigraph for 7 consecutive days, and PSQI scores were assessed before and after the intervention. HRV was also monitored at rest and during sleep. RESULTS: After receiving the sleep-inducing juice intervention (FS), PSQI scores were significantly decreased (P < 0.001) and correlated with a significant decline in fatigue severity scale and visual analogue scale levels (P < 0.05; both). HRV indices of vagal activity were significantly improved during FS (P < 0.05), and no significant differences in N-FS were observed. Sleep efficiency and total sleep time increased significantly (P < 0.05) and sleep latency, total counts, sleep fragmentation index, and movement index, decreased significantly (P < 0.05, all 4) during FS, with no significant differences-observed during N-FS. CONCLUSIONS: This study results demonstrated that an 8-week course of sleep-inducing juice has led to improve sleep quality, suggesting an enhanced cardiac vagal tone during sleep. Thus, it could be a well-tolerated option for adults with disturbed sleep.
Improvement in Catalytic Activity of Ag Catalyst via Simple Mixing with Carbon
Choun, Myounghoon,Baek, Ji Yun,Eom, Taehyoung Korea Electric Power Corporation 2019 KEPCO Journal on electric power and energy Vol.5 No.4
In this study we investigate catalytic activity and selectivity of mixture of Ag and ketjenblack according to their ratios by product analysis and electrochemical experiments, such as cyclic voltammetry, linear sweep voltammetry and chronoamperometry. We reveal that catalytic activity toward CO2 reduction to CO is improved by simple mixing Ag nanoparticle and ketjenblack because addition of ketjenblack suppresses aggregation of Ag nanoparticles and brings increase in electrochemical active surface area. However, excess amount of ketjenblack rather inhibit the CO2 reduction to CO. These observations provide clues to develop highly active Ag catalyst or electrode toward electrochemical reduction of CO2.