https://oak.ulsan.ac.kr/handle/2021.oak/410 2026-03-27T07:00:51Z https://oak.ulsan.ac.kr/handle/2021.oak/19973 Title: Engineering phosphorous doped graphene quantum dots decorated on graphene hydrogel as effective photocatalyst and high-current density electrocatalyst for seawater splitting Author(s): Tran Van Tam; Kailash Chandra Bhamu; Min Jae Kim; Sung Gu Kang; Jin Suk Chung; Seung Hyun Hur; Won Mook Choi Abstract: Designing metal-free catalyst with outstanding activity for both photocatalytic and electrocatalytic seawater splitting is highly demand and still remained challenge. This work demonstrates the synthesis of P-doped graphene quantum dots (PGQDs) containing different P-configuration bonding of PC3, PO4 and PO3 via synthesis temperature controlled simple hydrothermal process. Specifically, PGQDs having PC3-bonds (PGQD3) shows effectively tunable electronic structure, significant enhancing visible light absorption, then their hybrid composite with graphene hydrogel (PGQD3/GH) is prepared. The PGQD3/GH composite possesses excellent photocatalytic hydrogen production with yield of 20.47 mmol·g-1·h-1 in seawater splitting. Furthermore, the PGQD3/GH composite performs superior electrochemical activities of hydrogen evolution reaction (HER) toward seawater with an overpontetial of 41 mV at 10 mA·cm-2 as well as oxygen evolution reaction (OER) with 262 mV at 10 mA·cm-2. In seawater electrolysis cell, the PGQD3/GH composite delivers small overall voltage of 1.62 V to obtain high current density of 500 mA·cm-2 with excellent stability for 1000 h continuous operation, outperforming the commercial Pt/C and IrO2. This work demonstrates the role of PC3-bond in modulating the band gap and active site for photocatalytic and electrocatalytic seawater splitting reaction that may provide new idea for developing porous non-metal all-carbon catalyst for seawater splitting by both photocatalysis and electrocatalysis. 2023-12-31T15:00:00Z https://oak.ulsan.ac.kr/handle/2021.oak/19968 Title: The Effect of Different Polyol Precursors on Disordered Spinel ZnAl2O4 Structure Prepared by the Polymeric Citrate Complex Method and the Corresponding Catalytic Behavior in the Glycerolysis of Urea Author(s): Nhiem Pham-Ngoc; Huy Nguyen-Phu; Youngil Lee; and Eun Woo Shin Abstract: ZnAl2O4 is a cubic close-packed oxide with tetrahedral and octahedral sites in the lattice structure. The catalytic activity of ZnAl2O4 is strongly connected with the surface properties caused by the partially inverse spinel ZnAl2O4 structure. In this research, ZnAl2O4 catalysts are prepared for the glycerolysis of urea via the polymeric citrate complex method using polymeric templates made of citric acid with a different polyol precursor. Depending on the polyol precursor, the partial inversion parameters representing the disordered bulk ZnAl2O4 structure are controlled, which results in different surface AlO4/AlO6 ratios and surface acidity. The specific surface areas of the prepared ZnAl2O4 catalysts are proportional to the molecular weight of the polyol precursor. The s-ZnAl2O4 (polyol precursor = sorbitol) prepared via two pathways from citrate complex and polymeric citrate complex shows the highest inversion parameter and surface acidity, leading to the highest glycerol carbonate (GC) yield and glycerol conversion in the glycerolysis of urea. A relationship between the GC yield and the surface properties, such as the acidity and inversion parameters, is established. 2023-12-31T15:00:00Z https://oak.ulsan.ac.kr/handle/2021.oak/19960 Title: Ni-foam supported Ni(OH)2 sheets decorated by MXene quantum dots for high performance supercapacitors Author(s): Jinjie Wang; Yiwen Hong; Yongqi Pan; Jiaying Zhu; Xiaoqing Xu; Won Mook Choi; Jingxia Yang Abstract: The MXene quantum dots (MQDs) were prepared by microwave-sonication exfoliation, and further loaded on Ni(OH)2 sheets using Ni form as substrate by one-pot solvothermal synthesis. Three different exfoliation mediums (ethanol-EtOH, N,N-dimethylformamide-DMF, dimethyl sulfoxide-DMSO) were changed to investigate their influences on the structure of MQDs and MQDs-Ni(OH)2 composites. The DMF medium is better than the other two due to its good reducibility and small polarity, and the obtained MDQf from DMF exfoliation has less oxidation and higher quantum yield, while the prepared MQDf-Ni(OH)2 composites possessed large Ni(OH)2 sheet, high Ni3+ ratio and high N doping content. All these material changes caused by DMF can promote the charge-discharge process during the supercapacitor application, resulting in the best electrochemical performance of 1660 F/g at 1 A/g using MQDf-Ni(OH)2 composites as electrodes. Moreover, the asymmetric supercapacitors using MQDf-Ni(OH)2 composites and active carbon as electrodes possessed a maximum specific capacitance of 98 F/g, and a maximum energy density of 30.6 Wh/kg (with a power density of 750 W/kg). 2023-12-31T15:00:00Z https://oak.ulsan.ac.kr/handle/2021.oak/19959 Title: Effect of active sites distributions on temperature dependent-coke formation over Ni/CexZr1-xO2-Al2O3 catalysts for ethanol steam reforming: Coke precursor gasification Author(s): Mingyan Wang; Sang Yoon Kim; Azam Jamsaz; Nhiem Pham-Ngoc; Yong Men; Dong Hwi Jeong; Eun Woo Shin Abstract: Understanding coke formation routes over Ni-based catalysts is essential in determining the catalytic performance in ethanol steam reforming. In this study, we focused on optimizing the active sites distribution via the metal-support interactions and understanding the coke precursor gasification in Ni/CexZr1-xO2-Al2O3 (CZA) catalysts for ethanol steam reforming. We found that the optimized active sites distribution could minimize coke formation by enabling efficient gasification of a coke precursor on Ni. In the 20Ni/40CZA catalyst, the crystalline CZ exhibited a strong interaction with Ni, maintaining a uniform distribution of highly dispersed Ni nanoparticles and creating abundant oxygen vacancies on CZ, even at 20 wt% of Ni loading. Consequently, the resistance to coking over 20Ni/40CZA was significantly enhanced due to the efficient delivery of active oxygen atoms from steam on the abundant oxygen vacancies to the coke precursor on the Ni surface, resulting in fast gasification of the coke precursor. 2023-12-31T15:00:00Z