Browsing by Author "Jin Seog Gwag"

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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
Potentialities of nanostructured SnS2 for electrocatalytic water splitting: A review
(Elsevier Ltd, 2022) Rajneesh Kumar Mishra; Gyu Jin Choi; Hyeon Jong Choi; Jay Singh; Seung Hee Lee; Jin Seog Gwag
Evolving economically affordable, scalable, and effective electrocatalysts for producing viable hydrogen energy through electrocatalytic water splitting are highly desirable due to depleting fossil fuels and growing ecological and environmental concerns. Recently, layered SnS2 semiconductor nanomaterial has been recognized as a noteworthy electrocatalytic candidate due to its chemically stable, high effective surface area, low cost, and high stability. This review discussed how to boost hydrogen energy production using layered SnS2 nanostructure as catalysts through electrocatalytic water splitting, which essentially comprises morphological, doping, and nanocomposite/ heterostructural engineering. Further, various vital parameters for evaluating the electrocatalytic properties of layered SnS2 and reaction mechanisms are broadly discussed. Finally, we also discussed the summary and the future perspectives of evolving layered SnS2 nanostructure as a superior electrode nanomaterial for electrocatalytic hydrogen evolution reaction. © 2022 Elsevier B.V.
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.
Revolutionizing energy evolution: SnS-Sn2S3 layered structures as exceptional electrocatalytic materials for H2 and O2 generation
(Elsevier Ltd, 2024) Rajneesh Kumar Mishra; Gyu Jin Choi; Ranjana Verma; Sun Hun Jin; Rajesh Bhardwaj; Sandeep Arya; Jay Singh; Jin Seog Gwag
In this paper, we prepared the SnS-Sn2S3 layered structure using the in-situ solvothermal method for hydrogen evolution (HER) and oxygen evolution reaction (OER). XRD and HRTEM confirm the successful synthesis of the orthorhombic crystal structure of the SnS-Sn2S3. Further, SEM images demonstrate the layered shape of the SnS-Sn2S3 nanostructure, promoting the formation of more active sites on the surface for better electrocatalytic activities. Interestingly, during OER investigation, the SnS-Sn2S3 catalyst depicts an overpotential of 359 mV (10 mA cm−2) and a Tafel slope of 90.1 mV dec-1. However, during HER investigation, the SnS-Sn2S3 catalyst describes an overpotential of 162 mV (-10 mA cm−2) and a Tafel slope of 107.6 mV dec-1. Moreover, the SnS-Sn2S3 catalyst unveils superb stability for 2.3 h at 10 mA cm−2 for OER and 4.0 h at −10 mA cm−2 for HER. The OER and HER reaction mechanisms were also discussed to explore the kinetics rate of SnS-Sn2S3 catalyst. © 2024 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
Voltage holding and self-discharge phenomenon in ZnO-Co3O4 core-shell heterostructure for binder-free symmetric supercapacitors
(Elsevier B.V., 2022) Rajneesh Kumar Mishra; Gyu Jin Choi; Hyeon Jong Choi; Jay Singh; Fateme Sadat Mirsafi; Horst-Günter Rubahn; Yogendra Kumar Mishra; Seung Hee Lee; Jin Seog Gwag
We report an eco-friendly, in-situ, and one-step synthesis of ZnO-Co3O4 core-shell heterostructure (ZC-CSH) using the hydrothermal process as a transcendent nanomaterial for the supercapacitor applications. The ZC-CSH SSC showed a wide potential window (1.6 V), the excellent specific capacitance of 177.0F g−1 at 1.4 A g−1, high energy density (39.3 W h kg−1), and power density (19064.3 W kg−1). Further, the ZC-CSH SSC revealed excellent stability of 92.8 % after 10,000 cycles at 12.4 A g−1 using galvanostatic charging-discharging. Besides, the ZC-CSH SSC unraveled the outstanding stability of 96.1 % after the 8 h Voltage holding tests (VHT) at 1.6 V + 8 h Self-discharge tests (SDT). Moreover, the ZC-CSH SSC indicated a trivial leakage current of 0.06, 0.11, 0.15, and 0.17 mA during 2, 4, 6, and 8 h VHT, respectively. The ZC-CSH SSC demonstrated a voltage drop from 1.6 V to 0.39, 0.38, 0.37, and 0.36 V after 2, 4, 6, and 8 h VHT and SDT. To understand the ZC-CSH SSC's self-discharge behavior, this work explored the insights of the self-discharge mechanisms based on two thermodynamic processes, ionic concentration gradient (diffusion-control model) and potential difference (potential-driven model). Also, according to the tight-bonding (strong interactions) and loose-bonding (weak interactions), this work envisaged electrolyte ions' interactions with electrode materials to explore the coherent insights of the self-discharge behavior of the ZC-CSH SSC. It is concluded that this approach can lead to an unwavering performance of the ZC-CSH SSC for electronic portable futuristic gadgets. © 2021 Elsevier B.V.