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Shrestha, Nabeen K.,Bui, Hoa Thi,Yoon, Seog Joon,Patil, Supriya A.,Bathula, Chinna,Lee, Kiyoung,Noh, Yong-Young,Han, Sung-Hwan Elsevier 2019 Journal of electroanalytical chemistry Vol.847 No.-
<P><B>Abstract</B></P> <P>This work reports a facile solution based chemical transformation of thin film of CdCO<SUB>3</SUB> cuboids into Cd-based Prussian blue analogue structured thin film with controlled redox-state by manipulating the anion exchange reaction between the solid film and the aqueous solution of K<SUB>3</SUB>[Fe(CN)<SUB>6</SUB>] at 60°C. The progress of the transformation reaction is monitored <I>via</I> electron microscopy, X-ray difractometry and X-ray photoelectron spectroscopy. Based on the scenario of the reaction progress revealed by these analysis, the CdCO<SUB>3</SUB> cuboids are first found to be transformed into the smaller cuboids of cadmium ferricyanide, which, on further reaction, are transformed into the cadmium ferrocyanide cuboids. Thus, by controlling the redox-state of the Fe-metal center on the frameworks, the electrocatalytic activity of the frameworks on oxygen reduction reaction (ORR) is studied. The electrocatalytically inert CdCO<SUB>3</SUB> cuboids after transformation to the frameworks with Fe<SUP>3+</SUP>-centers demonstrate an enhanced catalytic activity on ORR, while the Fe<SUP>2+</SUP>-centers of the frameworks are found to relegate the catalytic activity, thereby manifesting the redox-sate modulated ORR activity of the frameworks. To the best of the authors' knowledge, this is the first report of this kind on redox-state specific ORR activity.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Conversion of CdCO<SUB>3</SUB> cuboid film into Cd-HCF frameworks <I>via</I> anion exchange </LI> <LI> Controlling reaction time to achieve Fe (III)-or Fe(II)- based Cd-HCF frameworks </LI> <LI> Fe(III) based Cd-HCF frameworks demonstrate electrocatalytic activity towards ORR. </LI> <LI> Fe(II) based Cd-HCF frameworks relegate the ORR catalytic activity. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
이수정,이유정,( Nabeen K. Shrestha ),윤석준 한국공업화학회 2020 한국공업화학회 연구논문 초록집 Vol.2020 No.-
For the next-generation solar cell, the energy payback is also important factor to use the renewable energy, solar light. However, unfortunately, high-energy required processes are still being used to make photosensitizers for the solar cells, such as II-IV, III-V, I-III-VI semiconductors, quantum dots (QD, synthesized through hot-injection process), polymers, and so on. To reduce the energy payback time significantly, instead of high-temperature and inert gas based synthetic procedure, we propose brand new strategy: perovskite quantum dot synthesis at room temperature in ambient condition. Through in-situ and ex-situ spectroscopic tools, we proposed the formation mechanism of the QDs made through new synthetic process. Furthermore, the intrinsic problem of perovskite - instability against to humidity/water - has been solved by coating silica. We observed the perovskite QDs@SiOx is stable in water during several weeks.
Bui, Hoa Thi,Shrestha, Nabeen K.,Khadtare, Shubhangi,Bathula, Chinna D.,Giebeler, Lars,Noh, Yong-Young,Han, Sung-Hwan American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.21
<P>One of the challenges in obtaining hydrogen economically by electrochemical water splitting is to identify and substitute cost-effective earth-abundant materials for the traditionally used precious-metal-based water-splitting electrocatalysts. Herein, we report the electrochemical formation of a thin film of nickel-based Prussian blue analogue hexacyanoferrate (Ni-HCF) through the anodization of a nickel substrate in ferricyanide electrolyte. As compared to the traditionally used Nafion-binder-based bulk film, the anodically obtained binder-free Ni-HCF film demonstrates superior performance in the electrochemical hydrogen evolution reaction (HER), which is highly competitive with that shown by a Pt-plate electrode. The HER onset and the benchmark cathodic current density of 10 mA cm(-2) were achieved at small overpotentials of 15 mV and 0.2 V (not iR-corrected), respectively, in 1 M KOH electrolyte, together with the long-term electrochemical durability of the film. Further, a metal-HCF-electrode-based full water-splitting device consisting of the binder-free Ni-HCF film on a Ni plate and a one-dimensional Co-HCF film on carbon paper as the electrodes for the HER and the oxygen evolution reaction (OER), respectively, was designed and was found to demonstrate very promising performance for overall water splitting.</P>
Bui, Hoa Thi,Shrestha, Nabeen K.,Cho, Keumnam,Bathula, Chinna,Opoku, Henry,Noh, Yong-Young,Han, Sung-Hwan Elsevier 2018 Journal of electroanalytical chemistry Vol.828 No.-
<P><B>Abstract</B></P> <P>The present work reports on the morphological influence of catalyst on oxygen reduction reaction (ORR). As a catalyst, Prussian blue analog structured nickel hexacyanoferrate (Ni-HCF) with two distinct morphologically controlled frameworks, <I>viz.</I> granular crystalline bulk film and rose-petal like structured thin film having smooth surface, are synthesized <I>via</I> controlled anodization route, and their morphological influence on the ORR is investigated. In addition, the influence of addition of carbon black, which is commonly used as catalytic dispersing support, is also studied on the catalytic mechanism for the ORR. Based on the hydrodynamic voltammetry of the electrocatalytic films on rotating disk electrode, the number of electrons involved in the reduction of an O<SUB>2</SUB> molecule, and the kinetic current density of the reaction are estimated. While the pristine Ni-HCF frameworks based catalyst, regardless of their morphology, demonstrates the direct reduction of O<SUB>2</SUB> with participation of 4 electrons, the frameworks when mixed with carbon black as support diverts the reduction <I>via</I> two steps with participation of 2 electrons at each step. A larger kinetic current density is, however, obtained in the case of granular crystalline bulk film of the Ni-HCF frameworks.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Morphologically controlled Ni-HCF frameworks are synthesized <I>via</I> anodization route. </LI> <LI> Electrocatalytic behavior of the frameworks towards ORR is studied. </LI> <LI> The pristine frameworks show the direct 4e<SUP>−</SUP> reduction of O<SUB>2</SUB> into OH<SUP>−</SUP>. </LI> <LI> After mixing with carbon black support, the ORR path is diverted to 2 + 2e<SUP>−</SUP> process. </LI> <LI> Compared to thin film, the bulk film of the frameworks reveals faster rate of ORR. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Patil, Supriya A.,Kim, Eun-Kyung,Shrestha, Nabeen K.,Chang, Jinho,Lee, Joong Kee,Han, Sung-Hwan American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.46
<P>Metal telluride nanostructures have demonstrated several potential applications particularly in harvesting and storing green energy. Metal tellurides are synthesized by tellurization process performed basically at high temperature in reducing gas atmosphere, which makes the process expensive and complicated. The development of a facile and economical process for desirable metal telluride nanostructures without complicated manipulation is still a challenge. In an effort to develop an alternative strategy of tellurization, herein we report a thin film formation of self-standing cobalt telluride nanotubes on various conducting and nonconducting substrates using a simple binder-free synthetic strategy based on anion exchange transformation from a thin film of cobalt hydroxycarbonate nanostructures in aqueous solution at room temperature. The nanostructured films before and after ion exchange transformation reaction are characterized using field emission scanning electron microscope, energy dispersive X-ray analyzer, X-ray photoelectron spectroscopy, thin film X-ray diffraction technique, high resolution transmission electron microscope, and selected area electron diffraction analysis technique. After the ion exchange transformation of nanostructures, the film shows conversion from insulator to highly electrical conductive semimetallic characteristic. When used as a counter electrode in I<SUB>3</SUB><SUP>–</SUP>/I<SUP>–</SUP> redox electrolyte based dye-sensitized solar cells, the telluride film exhibits an electrocatalytic reduction activity for I<SUB>3</SUB><SUP>–</SUP> with a demonstration of solar-light to electrical power conversion efficiency of 8.10%, which is highly competitive to the efficiency of 8.20% exhibited by a benchmarked Pt-film counter electrode. On the other hand, the telluride film electrode also demonstrates electrocatalytic activity for oxygen evolution reaction from oxidation of water.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2015/aamick.2015.7.issue-46/acsami.5b08501/production/images/medium/am-2015-085018_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5b08501'>ACS Electronic Supporting Info</A></P>