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Jeong, Beomgyun,Shin, Dongyoon,Lee, Jae Kwang,Kim, Dae Han,Kim, Young Dok,Lee, Jaeyoung The Royal Society of Chemistry 2014 Physical Chemistry Chemical Physics Vol.16 No.27
<P>Co oxides are known to be active and stable alternative anode electrocatalysts possessing the potential to replace the best performing but most expensive Ir and Ru oxides in alkaline water electrolysis. Of late, Co oxides loaded on various carbon supports have been reported as a way to outperform Ir or Ru catalysts by improving the utilization efficiency. In this study, we introduce Co and Fe nanoparticles embedded carbon nanofibers (CoFe-CNFs), fabricated through electrospinning and pyrolysis of a polymer mixed with Co and Fe precursors. This method is a facile route for simultaneously making Co and Fe nanoparticles as well as the stable accommodation of the CoFe nanoparticles in the carbon support. We demonstrate the potential of the CoFe-CNFs as active and stable electrocatalysts for the oxygen evolution reaction (OER) in alkaline media. We conducted detailed physico-chemical characterizations to elucidate the effect of the CNFs on the OER activity and stability of the CoFe-CNFs. It is suggested that the CNFs are a medium in which OER-active CoFe alloy nanoparticles are formed homogeneously, and that carbon layers surrounding the nanoparticles are beneficial to the stability of the CoFe-CNFs in the OER.</P> <P>Graphic Abstract</P><P>Non-precious metal electrocatalyst: CoFe particles surrounded by fibrous carbon for the elongated stability of oxygen evolution from water molecules. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4cp00385c'> </P>
Jeong, Beomgyun,Shin, Dongyoon,Choun, Myounghoon,Maurya, Sandip,Baik, Jaeyoon,Mun, Bongjin Simon,Moon, Seung-Hyeon,Su, Dangsheng,Lee, Jaeyoung American Chemical Society 2016 The Journal of Physical Chemistry Part C Vol.120 No.14
<P>Fe- and N-modified carbon nanofibers (Fe-CNF) were synthesized via electrospinning and pyrolysis as electrocatalysts for oxygen reduction reaction (ORR). In order to increase the exposed surface area with the active sites buried inside Fe CNF, we attempted water vapor activation for Fe CNF and observed a substantial improvement of ORR activity up to the comparable level with Pt/C. Unlike what was expected, however, water vapor activation did not significantly increase the specific surface area of Fe CNF; instead, it induced a depletion of surface N content, which makes it difficult to explain the improved ORR activity with the increase of surface area with N-based active sites. In water vapor activation, the chemical phase of embedded particles is changed from Fe3C to Fe3O4 and nitrogen-free Fe and C-based ORR active sites were exposed, which seemed to be related with hierarchical macro/mesopore structure and graphitic edge defects. This study demonstrates a facile activation method for better ORR activity of Fe-modified CNF and suggests a potential relationship of surface carbon structure with the catalytic activity toward ORR rather than the type and concentration of N in Fe CNF, which should be investigated further.</P>
Jeong, Beomgyun,Jeon, Hongrae,Toyoshima, Ryo,Crumlin, Ethan J.,Kondoh, Hiroshi,Mun, Bongjin Simon,Lee, Jaeyoung American Chemical Society 2018 The Journal of Physical Chemistry Part C Vol.122 No.4
<P>While model studies of surface science under ultrahigh vacuum (UHV) have made significant contributions to understanding electrochemistry, many issues related to electrochemical phenomena still remain unanswered due to the extreme environmental differences between UHV and liquid conditions. Electrochemical formic acid (HCOOH) oxidation is one such example. While the dehydration step in the indirect oxidation pathway (HCOOH → H<SUB>2</SUB>O + CO<SUB>ad</SUB> → 2H<SUP>+</SUP> + 2e<SUP>–</SUP> + CO<SUB>2</SUB>) is observed in the electrochemical oxidation of formic acid on Pt(111) surface, the surface science studies conducted in UHV condition reported the complete HCOOH dissociation to H<SUB>2</SUB> and CO<SUB>2</SUB> on Pt(111) surface with no adsorbed CO at room temperature. A dehydration mechanism may also exist in gas-phase HCOOH dissociation in some conditions different from UHV, but it has not been demonstrated with a surface science method due to pressure limitations. Using ambient pressure X-ray photoelectron spectroscopy (AP-XPS), we observed the dehydration mechanism of gas-phase HCOOH in unprecedented high pressure environment for the first time. This study is a demonstration of reconciling the disagreement between electrocatalysis and surface science by bridging the environment gap.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2018/jpccck.2018.122.issue-4/acs.jpcc.7b07735/production/images/medium/jp-2017-077355_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp7b07735'>ACS Electronic Supporting Info</A></P>
Excavated Fe-N-C sites for enhanced electrocatalytic activity in the oxygen reduction reaction.
Jeong, Beomgyun,Shin, Dongyoon,Jeon, Hongrae,Ocon, Joey D,Mun, Bongjin Simon,Baik, Jaeyoon,Shin, Hyun-Joon,Lee, Jaeyoung Wiley-VCH 2014 CHEM SUS CHEM Vol.7 No.5
<P>Platinum (Pt) is the best electrocatalyst for the oxygen reduction reaction (ORR) in hydrogen fuel cells, but it is an extremely expensive resource. The successful development of a cost-effective non-Pt ORR electrocatalyst will be a breakthrough for the commercialization of hydrogen-air fuel cells. Ball milling has been used to incorporate metal and nitrogen precursors into micropores of carbon more effectively and in the direct nitrogen-doping of carbon under highly pressurized nitrogen gas in the process of the preparation of non-noble ORR catalysts. In this study, we first utilize ball milling to excavate the ORR active sites embedded in Fe-modified N-doped carbon nanofibers (Fe-N-CNFs) by pulverization. The facile ball-milling process resulted in a significant enhancement in the ORR activity and the selectivity of the Fe-N-CNFs owing to the higher exposure of the metal-based catalytically active sites. The degree of excavation of the Fe-based active sites in the Fe-N-CNFs for the ORR was investigated with cyclic voltammetry, X-ray photoelectron spectroscopy, and pore-size distribution analysis. We believe that this simple approach is useful to improve alternative ORR electrocatalysts up to the level necessary for practical applications.</P>
Oxygen electrocatalysis in chemical energy conversion and storage technologies
이재영,Beomgyun Jeong,Joey D. Ocon 한국물리학회 2013 Current Applied Physics Vol.13 No.2
Oxygen electrocatalysis that we first defined is considered as the most important phenomenon in almost all electrochemical industries because it is the most sluggish reaction that governs the overall reaction rate in electrochemical cells. In this review, we cover two main areas of oxygenewater electrocatalysis, oxygen reduction to water and oxygen evolution from water. In particular, it aims to provide the readers with an understanding of the critical scientific challenges facing the development of oxygen electrocatalysts, various unique attributes of recent novel catalysts, the latest developments in electrode construction and the outlook for future generation of oxygen electrocatalysts. This review will be of value to both electrochemists and other applied scientists interested in this field of electrocatalysis.