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Synthesis of Monoclinic Potassium Niobate Nanowires That Are Stable at Room Temperature
Kim, Seungwook,Lee, Ju-Hyuck,Lee, Jaeyeon,Kim, Sang-Woo,Kim, Myung Hwa,Park, Sungnam,Chung, Haegeun,Kim, Yong-Il,Kim, Woong American Chemical Society 2013 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.135 No.1
<P>We report the synthesis of KNbO<SUB>3</SUB> nanowires (NWs) with a monoclinic phase, a phase not observed in bulk KNbO<SUB>3</SUB> materials. The monoclinic NWs can be synthesized via a hydrothermal method using metallic Nb as a precursor. The NWs are metastable, and thermal treatment at ∼450 °C changed the monoclinic phase into the orthorhombic phase, which is the most stable phase of KNbO<SUB>3</SUB> at room temperature. Furthermore, we fabricated energy-harvesting nanogenerators by vertically aligning the NWs on SrTiO<SUB>3</SUB> substrates. The monoclinic NWs showed significantly better energy conversion characteristics than orthorhombic NWs. Moreover, the frequency-doubling efficiency of the monoclinic NWs was ∼3 times higher than that of orthorhombic NWs. This work may contribute to the synthesis of materials with new crystalline structures and hence improve the properties of the materials for various applications.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2013/jacsat.2013.135.issue-1/ja308209m/production/images/medium/ja-2012-08209m_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja308209m'>ACS Electronic Supporting Info</A></P>
김재연(Jaeyeon Kim),김혜옥(Hyeok Kim),김건휘(Geon Hwi Kim),김다솔(Dasol Kim),류한솔(Hansol Ryu),박태현(Taehyun Park) Korean Society for Precision Engineering 2020 한국정밀공학회지 Vol.37 No.7
This study reports on the feasibility of applying polymer electrolyte membrane fuel cells (PEMFCs) system to an energy storage system (ESS). We modeled each constituting system to compute the overall efficiency of the ESS. As a result, it was verified that the power plants’ electric powering capability can be curtailed. The amount of reduction is equal to that of 2nd Gori Nuclear Power Plant currently under construction. We calculated that approximately 320.85 L/day · MW of hydrogen is produced on a national scale. Also, Seoul’s demand output power of PEMFC and the requisite area of sites to install the PEMFC system are approximately 236 MW and 59059 m² respectively. This study can contribute to preventing the upsurge of the entire electric powering installed capability. Based on the present technology level, this study diagnoses the use of hydrogen-based ESS which will be introduced in the upcoming hydrogen economy period. Considering the water electrolysis by polymer electrolyte membrane water electrolyzers are currently at the beginning of commercialization and the energy density per mass of hydrogen is exceedingly high, we anticipate that the future of hydrogen base ESS’ effectiveness will reach greater levels than the analysis of this study.
Impact of cracked gas diffusion layer on performance of polymer electrolyte membrane fuel cells
Geon Hwi Kim,Dasol Kim,Jaeyeon Kim,Hyeok Kim,Taehyun Park 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.91 No.-
This paper reports the negative effect of the cracked gas diffusion layer (GDL) on the performance ofpolymer electrolyte membrane fuel cells (PEMFCs) under varyingflow channel width. The polarizationcharacteristics and the corresponding electrochemical impedance spectra of the PEMFCs with pristineGDLs and cracked GDLs were computed. The results showed that for PEMFCs with 1.0 mmflow channels,the power density rates of reduction between the PEMFCs with pristine GDLs and those with crackedGDLs were 2.8% under the condition of oxygen and 6.6% under the condition of air. On the other hand, forthe PEMFCs with 0.5 mmflow channels, these values were 10.3% under the oxygen condition and 14.2%under the air condition. This implies that the thinner theflow channels, the more severely the crackedGDLs influence the PEMFC performance in terms of concentration loss. The EIS data indicated that,compared to the PEMFCs with 1.0 mmflow channels, the cracks on GDLs had more impact on the PEMFCswith 0.5 mmflow channels with regard to activation overvoltage.