Browsing by Author "Gupta, Rupali"

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    Effect of structural modifications on the oxygen reduction reaction properties of metal-organic framework-based catalysts
    (Elsevier, 2022) Yadav, Dharmendra Kumar; Gupta, Rupali; Ganesan, Vellaichamy; Ramaraj, Ramasamy
    In the present era, technological advancements are significantly progressed due to the rapid depletion of traditional energy resources. These energy resources are anticipated to be drained out due to their limited availability and nonrenewable nature in the near future. Therefore, intense research has to be carried out to explore alternative energy resources. A judicious solution to this menace is the exploitation of alternative energy sources which have minimum hazards to the environment. A very impactful method could be the use of electrochemical energy conversion systems such as fuel cells, metal-air batteries, etc. For these electrochemical energy conversion systems, oxygen reduction reaction (ORR) is the essential half-cell reaction that takes place at the cathode. However, the major hindrance which results in slow kinetics of the ORR is the conversion of O-O bond to O-H bond which requires high activation energy. Such a high energy barrier associated with this conversion limits its efficiency and conversion rates. Additionally, the high cost and mediocre durability of precious-metal-based catalysts such as platinum which made a benchmark for ORR put a limit on their commercial application. Therefore, it becomes very much essential to design and implement efficient and cost-effective electrocatalysts which can facilitate this conversion by alleviating the energy barrier. In the recent past, a unique class of functional material, known as metal-organic frameworks (MOFs) and their derivatives has gained limelight among the researchers worldwide, on account of its prominent efficiency as electrocatalysts for various electrochemical processes. MOFs are composed of metal ions or clusters bridged by organic linker molecules. The periodic structural design offers them a crystalline nature with high surface area and porosity. Meanwhile, on account of the hybrid nature of the structural components (i.e., organic as well as inorganic), MOFs display tailorable pore size and chemical environment rendering them variable physical and chemical properties. The porous nature of these MOFs results in the rapid diffusion of substrates through them thereby enhancing the number of active sites for the catalytic process. As the metal ion/cluster sites are isolated in the MOFs, they are analogical to the molecular catalysts. The structural design offers stability and robustness to the MOFs. Moreover, a careful approach toward structural and functional modification paves new ways of their utility for a large number of applications. Despite all these advantages, MOFs suffer from serious drawbacks of poor electrical conductivity and stability which hinders their utility as electrocatalysts for ORR. However, these shortcomings can be overcome by integrating these MOFs with highly conductive, advanced materials such as graphene, metal nanoparticles, nanocarbons, carbon nanotubes which results in the formation of MOF-based composites with improved electrical conductivity and stability. Additionally, thermal treatment methods like carbonization and pyrolysis can also be employed to convert MOFs and their composites to inorganic derivatives which find their applicability as ORR electrocatalyst on account of their superior conductivity and improved stability. Here, in this chapter, the ORR process and the role of MOFs as electrocatalysts for the ORR are described. In addition, different processes employed for the structural modifications of MOF and their successful utilization as the electrocatalysts for the ORR process are also described. � 2022 Elsevier Inc. All rights reserved.
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    Enhanced Four-Electron Selective Oxygen Reduction Reaction at Carbon-Nanotube-Supported Sulfonic-Acid-Functionalized Copper Phthalocyanine
    (John Wiley and Sons Inc, 2023) Yadav, Mamta; Kumar Singh, Devesh; Kumar Yadav, Dharmendra; Kumar Sonkar, Piyush; Gupta, Rupali; Ganesan, Vellaichamy
    In the present work, the oxygen reduction reaction (ORR) is explored in an acidic medium with two different catalytic supports (multi-walled carbon nanotubes (MWCNTs) and nitrogen-doped multi-walled carbon nanotubes (NMWCNTs)) and two different catalysts (copper phthalocyanine (CuPc) and sulfonic acid functionalized CuPc (CuPc-SO3?)). The composite, NMWCNTs-CuPc-SO3? exhibits high ORR activity (assessed based on the onset potential (0.57 V vs. reversible hydrogen electrode) and Tafel slope) in comparison to the other composites. Rotating ring disc electrode (RRDE) studies demonstrate a highly selective four-electron ORR (less than 2.5 % H2O2 formation) at the NMWCNTs-CuPc-SO3?. The synergistic effect of the catalyst support (NMWCNTs) and sulfonic acid functionalization of the catalyst (in CuPc-SO3?) increase the efficiency and selectivity of the ORR at the NMWCNTs-CuPc-SO3?. The catalyst activity of NMWCNTs-CuPc-SO3? has been compared with many reported materials and found to be better than several catalysts. NMWCNTs-CuPc-SO3? shows high tolerance for methanol and very small deviation in the onset potential (10 mV) between the linear sweep voltammetry responses recorded before and after 3000 cyclic voltammetry cycles, demonstrating exceptional durability. The high durability is attributed to the stabilization of CuPc-SO3? by the additional coordination with nitrogen (Cu-Nx) present on the surface of NMWCNTs. � 2023 Wiley-VCH GmbH.
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    Mesoporous carbon nitride supported 5,10,15,20-tetrakis(4-methoxyphenyl)-21H,23H-porphine cobalt(ii) as a selective and durable electrocatalyst for the production of hydrogen peroxideviatwo-electron oxygen reduction
    (Royal Society of Chemistry, 2021) Singh, Devesh Kumar; Ganesan, Vellaichamy; Yadav, Dharmendra Kumar; Yadav, Mamta; Sonkar, Piyush Kumar; Gupta, Rupali
    Mesoporous carbon nitride (MCN) is synthesized using a mesoporous silica material (MCM-41) as a sacrificial template. 5,10,15,20-Tetrakis(4-methoxyphenyl)-21H,23H-porphine cobalt(ii) (cobalt tetramethoxyphenylporphyrin, CoTMPP), which consists of methoxy groups as the electron-rich center is integrated with MCN and the resulting composite material (CoTMPP@MCN) without any further heat treatment is used for the electrocatalytic reduction of oxygen. CoTMPP@MCN shows a higher onset potential (0.65 and 0.84 V, respectively, in 0.1 M HClO4and 0.1 M KOH) for the oxygen reduction reaction (ORR) than the bare MCN (0.34 and 0.60 V, respectively, in 0.1 M HClO4and 0.1 M KOH). The ORR onset potential exhibited by CoTMPP@MCN is comparable to several non-pyrolyzed mono-nuclear metal porphyrin integrated on carbon-based supports in both acidic and basic media. Kinetic measurements of CoTMPP@MCN show high selectivity for two-electron oxygen reduction to H2O2in both media. The H2O2yield in terms of faradaic efficiency is measured to be 87.6 and 89.0%, respectively, in 0.1 M HClO4and 0.1 M KOH. CoTMPP@MCN exhibits amazingly high durability (minute changes in the onset potential and current density at high reduction potentials after 3000 CV cycles) facilitated by the surface coordination of CoTMPP through the nitrogen present on the MCN surface. Being highly selective and outstandingly durable, CoTMPP@MCN fulfills all necessary requirements for an economically efficient electrocatalyst for industrial hydrogen peroxide synthesis and related commercial applications. � The Royal Society of Chemistry 2020.
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    Phenosafranine encapsulated mesoporous silica as efficient electrocatalyst for Cr(VI) reduction and its subsequent sensitive determination
    (Elsevier Inc., 2023) Gupta, Rupali; Ganesan, Vellaichamy; Sonkar, Piyush Kumar; Yadav, Dharmendra Kumar; Yadav, Mamta
    This work presents an easy, highly specific, and sensitive route for the electrochemical reduction of Cr(VI) by phenosafranine (PSF+) integrated sulfonic acid functionalized mesoporous silica microspheres (MS-SO3?), denoted as PSF+-MS-SO3?. The synthesized material is characterized using various spectroscopic and microscopic methods. The glassy carbon electrode (GCE) is modified with this material (represented as GCE/PSF+-MS-SO3?) and employed for electroanalytical applications. The electrochemical characteristics of PSF+-MS-SO3? are established by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. Further, it is exploited for the electrocatalytic reduction of, Cr(VI). Superior electron transfer kinetics and stable electrochemical response for Cr(VI) are observed at the GCE/PSF+-MS-SO3? electrode. Moreover, the quantitative estimation of Cr(VI) at the GCE/PSF+-MS-SO3? done using linear sweep voltammetry (LSV). Dual linear calibration ranges (1 to 20 �M and 20 to 100 �M) is obtained from the LSV response. A low limit of detection (0.5 �M) and superior sensitivity (1.1 �A �M?1 cm?2) are recognized at this electrode. In addition, significant selectivity in the existence of other interfering ions is also shown by fabricated sensing scaffold. The precise measurement of Cr(VI) in spiked water samples with simple matrix is also demonstrated successfully with sufficient durability and reproducibility. � 2023 Elsevier B.V.
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    The Characterization Analysis of Graphene
    (Springer Science and Business Media Deutschland GmbH, 2023) Gupta, Rupali; Yadav, Dharmendra Kumar; Deka, Sasanka; Ganesan, Vellaichamy
    This chapter describes various state-of-the-art fabrication routes for high-quality graphene included: chemical vapour deposition (CVD), mechanical exfoliation, chemical exfoliation, electrochemical exfoliation, arc discharge, epitaxial growth, and pyrolysis. CVD is a widely used technique for growing high-quality graphene films on metal catalyst substrates, and copper foil has shown promising results. Mechanical exfoliation involves peeling graphite flakes from highly oriented pyrolytic carbon (HOPG) platelets using Scotch tape, resulting in single-layer graphene. Chemical exfoliation has two methods: solution-assisted and low-temperature chemical exfoliation. Electrochemical exfoliation involves the intercalation and exfoliation of graphite into graphene nanosheets through electrolyte solutions. Arc discharge is a plasma deposition technique for synthesizing high-quality graphene sheets using alternating current arc-discharge processes. Epitaxial growth involves growing single-layer or multilayer graphene on a SiC substrate using high-temperature sublimation growth. Pyrolysis is a 6-step process of poly(methyl methacrylate) composite that results in carbon derivatives that dissolve in the Ni catalyst surface, resulting in the epitaxial growth of graphene. Each method has its unique features, advantages, and disadvantages, making them suitable for different applications. For example, mechanical exfoliation remains one of the most reliable ways of producing high-quality graphene and has led to the discovery of graphene's extraordinary physical properties. Chemical exfoliation can produce graphene on a large scale, and electrochemical exfoliation is effective in creating biocompatible and fluorescent carbon nanomaterials for biological labelling and imaging. CVD as well as epitaxial growth can produce high-quality graphene films, and pyrolysis produces graphene with a high degree of graphitization. The choice of the appropriate technique is crucial for specific applications. � 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.