Browsing by Author "Jeong Won Ryu"

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Band Energy Modulation in an Fe-Mn-ZnO Nanowire-Nanosheet Catalyst for Efficient Overall Water Splitting
(American Chemical Society, 2024) Rajneesh Kumar Mishra; Gyu Jin Choi; Jeong Won Ryu; Ranjana Verma; Dhananjay Mishra; Santosh Kumar; Jay Singh; Yogendra Kumar Mishra; Jin Seog Gwag
Here, we studied a simple, scalable, and in situ hydrothermal method to prepare an Fe-Mn-doped ZnO nanowire-nanosheet on a three-dimensional (3D) Ni-foam substrate for electrocatalytic overall water splitting. Attractively, the doping of Fe and Mn in ZnO plays a significant role in mobilizing the electron from Fe and Mn toward ZnO in the Fe-Mn-doped ZnO nanowire-nanosheet due to different vacuum levels of Fe, Mn, and ZnO, facilitating the development of more active sites on the surface of the catalyst, which plays a crucial role in improving the catalytic performances during overall water splitting. Consequently, the Fe-Mn-doped ZnO nanowire-nanosheet shows a lowermost overpotential of 230 mV and a lowermost Tafel slope of 115.2 mV dec-1 during the hydrogen evolution reaction (HER) and 248 mV overpotential and a short Tafel slope of 109.1 mV dec-1 during the oxygen evolution reaction (OER) in a 1.0 M KOH electrolyte. Besides, the Fe-Mn-doped ZnO nanowire-nanosheet depicts low charge transfer and series resistances of 3.7 and 0.41 Ω during the HER and 0.36 and 1.66 Ω during the OER, respectively. Also, it elucidates outstanding durability at −10 mA cm-2 for 12 h (HER) and 10 mA cm-2 for 12 h (OER) using chronopotentiometry and 1000 cycles. In addition, the Fe-Mn-ZnO
Recent advances in ZnO nanostructure as a gas-sensing element for an acetone sensor: a short review
(John Wiley and Sons Ltd, 2023) Rajneesh Kumar Mishra; Vipin Kumar; Le Gia Trung; Gyu Jin Choi; Jeong Won Ryu; Rajesh Bhardwaj; Pushpendra Kumar; Jay Singh; Seung Hee Lee; Jin Seog Gwag
Air pollution is a severe concern globally as it disturbs the health conditions of living beings and the environment because of the discharge of acetone molecules. Metal oxide semiconductor (MOS) nanomaterials are crucial for developing efficient sensors because of their outstanding chemical and physical properties, empowering the inclusive developments in gas sensor productivity. This review presents the ZnO nanostructure state of the art and notable growth, and their structural, morphological, electronic, optical, and acetone-sensing properties. The key parameters, such as response, gas detection limit, sensitivity, reproducibility, response and recovery time, selectivity, and stability of the acetone sensor, have been discussed. Furthermore, gas-sensing mechanism models based on MOS for acetone sensing are reported and discussed. Finally, future possibilities and challenges for MOS (ZnO)-based gas sensors for acetone detection have also been explored. © 2022 John Wiley & Sons Ltd.
Recent progress in gas sensing based on 2D SnS2 and its heterostructure platforms: A review
(Elsevier B.V., 2024) Rajneesh Kumar Mishra; Hyeon Jong Choi; Jeong Won Ryu; Gyu Jin Choi; Vipin Kumar; Pushpendra Kumar; Jay Singh; Santosh Kumar; Jin Seog Gwag
The surface and electronic engineering of the 2D SnS2 have recently attracted substantial courtesies in various applications due to the abundant active oxygen sites and high transport properties because of electronic modulation. Herein, we reviewed the recent signs of progress in the morphological, structural, elemental properties, and gas-detection characteristics of the two-dimensional SnS2. Furthermore, it also offers information on recent advancements and developments of various types of gas sensors prepared using the SnS2 and its heterostructures. Numerous influential gas recognition parameters have also been discussed. The gas sensing mechanisms are also discussed on NH3, NO2, H2S, and VOCs to explore the interactions of the test gas with the sensor surface, elucidating the crucial role of active surface and electronic features of SnS2 and its heterostructures on the rapid response and recovery profiles. Besides, it provides insight into the adsorption/desorption chemistry on the sensor's surface and eco-friendly environment. However, it is found that there is still vast scope for SnS2 sensors to detect several other gases, which are still not studied and reported in the literature. Therefore, it opens up a new opportunity to develop various types of gas sensors to discriminate the particular gas at optimum working temperature and concentrations. Finally, the review clinches with the future perspectives and positions of the SnS2-based gas sensors. © 2023 Elsevier B.V.
Unveiling the Transformative Potential of SWCNT/In2O3 Heterostructures as High-Performance Catalysts for Overall Water Splitting
(American Chemical Society, 2023) Rajneesh Kumar Mishra; Gyu Jin Choi; Jeong Won Ryu; Jay Singh; Santosh Kumar; Yogendra Kumar Mishra; Seung Hee Lee; Jin Seog Gwag
In this paper, we studied the synthesis of In2O3/SWCNT heterostructure catalysts by blending single-walled carbon nanotubes (SWCNTs) in In2O3 nanomaterial during an in situ and facile one-step hydrothermal method for the application of electrocatalytic overall water splitting (OWS). Interestingly, it is predictable that the SWCNTs and In2O3 have different vacuum levels, which could play a crucial role in charge transfer by band engineering when both are brought into direct contact (surface or interface or both) to form the In2O3/SWCNT heterostructure. Remarkably, we discussed the possibilities of surface and interface engineering during In2O3/SWCNT heterostructure formation, which regulates and enhances the hydrogen and oxygen reaction kinetics. Consequently, the In2O3/SWCNT-4 catalyst illustrates the lowest overpotential values of 337 and 141 mV during the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively, compared with other catalysts in an alkaline medium. It may be because adding SWCNTs accelerates the mass transport and segregation of water molecules and enriches the adsorption and desorption free energy of hydrogen intermediates, providing more active sites and improving intrinsic catalytic activities. The Tafel slope values of the OER are 175.1 and 116.1 mV dec-1 for the pure In2O3 catalyst and In2O3/SWCNT-4 (5.0 mL of SWCNTs) heterostructure catalyst, suggesting that the SWCNTs can regulate the charge-transfer rate, which can play a crucial role in determining the rate-controlling steps of oxygen and hydrogen evolution reactions. The In2O3/SWCNT-4 catalyst shows excellent stability over 24 h of the HER (at −10 mA cm-2) and 24 h of the OER (at 10 mA cm-2) using chronopotentiometry (CP). Further, the overall water splitting of the In2O3/SWCNT-4