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The Morphological Effects of Surface Modified Mos2 Nanosheets and Mos2 Qd/G-C3n4 Heterostructure Prepared by Chemical Methods in Hydrogen Evolution Reaction (Her)

Shaker, Tayebeh | 2022

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 55927 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Moshfegh, Alireza; Naseri, Naeimeh
  7. Abstract:
  8. The sustainable development in societies and the global energy challenge requires usage of clean energy systems that have attracted the attention of many researchers in recent decades. One of the major challenges in generating renewable resources is the problem of energy storage and imbalance between supply and demand cycles. Hydrogen as one of the clean energy carriers and due to having the highest energy density in terms of weight, is one of the important research topics. From this point of view, the preparation of electrocatalysts for hydrogen production, based on available materials, via simple and environmentally friendly production methods, was considered in this research. Electrocatalysts based on semiconductor MoS2 nanosheets were prepared from a scalable method without using intermediates such as Nafion. First, MoS2 bulk were exfoliated in different solvents and then the produced nanosheets were deposited on carbon cloth as a substrate by using electrophoretic method, at different voltages and deposition durations. The resulting structures were subjected to characterization and electrochemical analysis, which indicates high performance and good stability of these structures. The optimized structure at an overpotential of 137±1 mV reaches a current density of 10 mA/cm2 and the Tafel slope of the sample was measured as 77±3 mV/dec and the electrochemical active surface area of this sample was obtained as 53 with respect to bare carbon cloth. In addition, Gibss Energy of hydrogen adsorption, a unique indicator of electrocatalytic hydrogen production, was studied through density functional theory (DFT). In another study, by considering a significant electrocatalytic activity of two-dimensional materials towards hydrogen production reaction, the electrocatalysts based on heterostructure formation of g-C3N4 nanosheets and MoS2 quantum dots, through liquid phase exfoliation and then successive electrophoretic deposition were produced. The prepared structures were subjected to various characterization techniques as well as electrochemical measurements. The results showed that the combined structure of the MoS2 quantum dots/g-C3N4 nanosheets exhibits a significant electrocatalytic activity with an overpotential of 178±1 millivolts at the current density of 10 milliamperes per square centimeter. Furthermore, DFT study was used to evaluate the impact of the interface of MoS2 quantum dots and g-C3N4 nanosheets on hydrogen bonds and the nature of charge transfer across the interface. The results reveal that by considering the sulfur vacancy in the MoS2 QD ( which is common and well established by many experimentalists), the Gibbs free energy difference of hydrogen adsorption-desorption in the MoS2 QD/g-C3N4 nanosheets heterostructure will have a small value of -0.04 electronvolts, comparable with the platinum surface indicating excellent electrocatalytic activity of the heterostructure
  9. Keywords:
  10. Nanosheet ; Hydrogen Producing ; Electrocatalysts ; Density Functional Theory (DFT) ; Molybdenum Desulfide ; Quantum Dot ; Graphitic Carbon Nitride

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