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Choi, Mihwa,Ahn, Chi-Yeong,Lee, Hyunjoon,Kim, Jong Kwan,Oh, Seung-Hyeon,Hwang, Wonchan,Yang, Seugran,Kim, Jungsuk,Kim, Ok-Hee,Choi, Insoo,Sung, Yung-Eun,Cho, Yong-Hun,Rhee, Choong Kyun,Shin, Woonsup Elsevier 2019 Applied Catalysis B Vol.253 No.-
<P><B>Abstract</B></P> <P>Formic acid is a chemical with a simple molecular structure containing hydrogen. This liquid at room temperature is easy to handle and has a low toxicity, and is thus in the spotlight as a fuel. In particular, formic acid is an excellent fuel candidate because it can be operated at low temperatures when applied as a fuel in fuel cells with a high theoretical open-circuit voltage (1.48 V). However, it has a drawback in that the electrode catalyst is deactivated due to the generation of CO intermediates when formic acid is oxidized during cell operation. Therefore, to prevent this, an irreversibly adsorbed Bi on Pt catalyst is applied to a direct formic acid fuel cell (DFAFC) anode because it is easy to synthesize and economical. Physical analyses such as transmission electron microscopy (TEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) were conducted, and electrochemical evaluations were performed through half-cell and single-cell level tests. The results revealed that the formic acid oxidation reaction activity of the Bi-modified Pt/C was 13 times higher than that of the conventional catalyst at 0.58 V. Further, a DFAFC stack was fabricated using the Bi-modified Pt/C, which yielded a power of 300 W. These results suggest that a simple synthesis method can be applied to fabricating industrially available DFAFC stacks.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Bi-modified Pt catalyst is applied to a direct formic acid fuel cell (DFAFC) anode. </LI> <LI> Bi was irreversibly adsorbed on Pt catalyst by a simple synthetic strategy. </LI> <LI> Bi-modified Pt/C showed significantly high formic acid oxidation reaction activity. </LI> <LI> A DFAFC stack fabricated using Bi-modified Pt/C yielded a power of 300 W. </LI> <LI> The simple synthetic strategy can be applied to achieving DFAFC stacks commercially. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
물류센터 근로자의 안전인식에 대한 요인분석 및 집단간 인식 비교
최현준 ( Hyunjoon Choi ),문상영 ( Sangyoung Moon ),옥승용 ( Seung Yong Ok ) 한국안전학회(구 한국산업안전학회) 2015 한국안전학회지 Vol.30 No.4
This study is to examine the workers’ awareness of the safety in logistic centers. For that purpose, the exploratory factor analysis of workers’ safety awareness in logistic centers was performed at first, and the 6 variables extracted from the factor analysis were then used to investigate the difference in intergroup awareness of the safety environment in the logistic centers. We administered a survey to 147 workers attending the logistic centers and collected data from them. The results of the study showed that the intergroup awareness of the safety environment turned out to be statistically different from each other in terms of working environment, safe behavior, work risk, safety knowledge and effort, risk justification and compromising attitudes. Experiences in industrial accidents influenced awareness of working environment, work risk and risk justification. The group who experienced accidents is more likely to feel risky and unsatisfied with working place, and their awareness toward risk justification was high as well. It was also observed that there exists awareness difference between manager group and worker group. The group who manages the working place showed more positive awareness of working environment, safe behavior, work risk, safety knowledge and effort, risk justification and compromising attitudes than the worker group. On the contrary, the worker group showed high recognition in risk of working place, and felt that they are willing to compromise on safety for increasing production. The scale of the logistic center produced negative influence on awareness of safety. The group in small logistic center showed the highest awareness in safety, whereas the group in large logistic center with more than 100 workers showed the highest awareness in risk. They are more likely to deviate from correct and safe work procedures due to over-familiarity with the job, as well. The findings suggest that there is a need for the safety management and education to change the workers`` understanding and attitudes towards safety.
Choi, Ji Yong,Nam, Ki Min,Song, Hyunjoon The Royal Society of Chemistry 2018 Journal of materials chemistry. A, Materials for e Vol.6 No.34
<P>Zn1−xCdxSe nanorods were synthesized with various compositions, and were employed as model catalysts for photocatalytic hydrogen generation. The hydrogen evolution rate was highly dependent upon the composition due to the conduction band edge potential and light absorption capacity. After the Pt deposition, however, the trend was altered remarkably with the quantum yield of the Pt-tipped Zn0.25Cd0.75Se reaching its maximum. This sudden change is mainly attributed to the mobility of electrons transferring to the metal tips, as well as light absorption and charge separation abilities.</P>
Effect of end-block chain length on rheological properties of ABA triblock copolymer hydrogels
Hyunjoon Jung,Taeshik Earmme,Soo-Hyung Choi 한국유변학회 2021 Korea-Australia rheology journal Vol.33 No.2
End-block length dependence of the hydrogel relaxation dynamics was investigated using PEO-based ABA triblock copolymer solutions in an aqueous solvent. Both ends of PEO were capped with hydrophobic poly(isopropyl glycidyl ether-co-ethyl glycidyl ether) exhibiting a lower critical solution temperature (LCST) behavior, resulting in the transition between sol and gel with temperature. Despite the nearly identical hydrophobicity of the end-blocks, the sol-to-gel transition temperature is found to be significantly dependent on the end-block length. Particularly, a small increment of the end-block length leads to significantly slower relaxation dynamics which is attributed to the thermodynamic barrier of end-block extraction. Hydrogels with an appropriate relaxation time show excellent injectability and self-healing ability, yet extremely slow relaxation dynamics result in brittle hydrogels. These results are discussed in terms of current understanding of the hydrogel relaxation dynamics and particular attention is paid to the issue of the chain dynamics between aggregated cores.
Engineering Reaction Kinetics by Tailoring the Metal Tips of Metal–Semiconductor Nanodumbbells
Choi, Ji Yong,Jeong, Dahyi,Lee, Seon Joo,Kang, Dong-gu,Kim, Sang Kyu,Nam, Ki Min,Song, Hyunjoon American Chemical Society 2017 NANO LETTERS Vol.17 No.9
<P>Semiconductor-metal hybrid nanostructures are one of the best model catalysts for understanding photocatalytic hydrogen generation. To investigate the optimal structure of metal cocatalysts, metal-CdSe-metal nanodumbbells were synthesized with three distinct sets of metal tips, Pt-CdSe-Pt, Au-CdSe-Au, and Au-CdSe-Pt. Photoelectrochemical responses and transient absorption spectra showed that the competition between the charge recombination at the metal CdSe interface and the water reduction on the metal surface is a detrimental factor for the apparent hydrogen evolution rate. For instance, a large recombination rate (k(rec)) at the Pt CdSe interface limits the quantum yield of hydrogen generation despite a superior water reduction rate (k(WR)) on the Pt surface. To suppress the recombination process, Pt was selectively deposited onto the Au tips of Au-CdSe-Au nanodumbbells in which the krec was diminished at the Au-CdSe interface, and the large k(WR) was maintained on the Pt surface. As a result, the optimal structure of the Pt -coated Au-CdSe-Au nanodumbbells reached a quantum yield of 4.84%. These findings successfully demonstrate that the rational design of a metal cocatalyst and metal-semiconductor interface can additionally enhance the catalytic performance of the photochemical hydrogen generation reactions.</P>
인공지능의 이미지 인식을 활용한 사용자 재료기반 요리추천 서비스 개발
박현준 ( Hyunjoon Park ),최재혁 ( Jaehyuk Choi ),김민철 ( Minchul Kim ),조요한 ( Yohan Jo ),문재현 ( Jaehyun Moon ) 한국정보처리학회 2019 한국정보처리학회 학술대회논문집 Vol.26 No.2
1인 가구의 비율은 계속하여 증가하고 있으며 요리정보를 얻기 위한 쿡(Cook)방, 먹방, 요리추천 애플리케이션 등의 인기도 계속되고 있다. 요리에 대한 관심이 높아지면서 1인 가구 또한 요리에 많은 시간을 투자하는 것을 확인할 수 있었다. 한편, 기존 요리추천 애플리케이션에서는 사용자의 기호만 고려하기 때문에 사용자가 가지고 있는 재료를 고려하지 않은 문제가 있다. 본 논문은 이러한 요리정보의 수요를 충족시킴과 동시에 인공지능 이미지 인식 기술을 활용하여 현재 가진 재료로 지금 당장 만들 수 있는 요리와 레시피를 추천하는 서비스를 제공하여 1인 가구에 최적화된 솔루션을 제공한다.