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Synthesis of N-Doped Graphene-Transition Metal Oxide Nanocomposites and Their Applications in Electrocatalytic Oxygen Evolution Reactions

Sadat Mousavi, Dorsa | 2022

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 56293 (48)
  4. University: Sharif University of Technology
  5. Department: Institute for Nanoscience and Nanotechnology
  6. Advisor(s): Shahrokhian Dehkordi, Saeed; Irajizad, Azam
  7. Abstract:
  8. Oxygen gas has many applications and is used in respiration, welding, methanol production, steel industry, rocket fuel and most importantly fuel cells. Today, due to the environmental pollution caused by fossil fuels, the use of clean energy production methods such as fuel cells has received much attention. In hydrogen fuel cells, electrical energy is generated using oxygen and hydrogen gases through an electrochemical process. One of the common methods of producing these gases is electrolysis of water in which the kinetics of anodic reaction (oxygen evolution) have led to many researches in the field of improving metal and non - metal electrocatalysts, especially based on carbon nanostructures. The best and most stable electrocatalysts for oxygen evolution reactions are ruthenium and iridium oxides, whose reaction kinetics are rapid. However, low availability of these materials and their high price hinder the commercialization of these electrodes. The aim of this dissertation is to improve the electrocatalytic parameters of the prepared electrodes, including overpotential and Tafel slope, for the oxygen evolution reaction by using simultaneously and asynchronously prepared nanocomposites of cheaper and more accessible transition metal oxides such as iron and titanium in graphene substrate with the use of hydrothermal, solvothermal, chemical and electrochemical methods. Structural, morphological and electrochemical characterization tests were performed to evaluate the properties of the electrodes and optimize them. The nanocomposites prepared in the first study included a three - dimensional hybrid of Fe2TiO5 and nitrogen-doped graphene by hydrothermal method with an overpotential of 0.382 V and Tafel slope of 0.111 (V/dec), solvothermal method (insitu preparation) with an overpotential of 0.360 volts and a Tafel slope of 0.071 (V/dec). Due to the fact that the methods in the first study require a lot of temperature, pressure and time, in the second study, an easier, faster and lower temperature method was selected. Electrocatalysts of the second study were prepared similar to the first study on a nitrogen doped graphene substrate with Fe2TiO5 nanoparticles but by chemical bath deposition method with an overpotential of 0.264 volts and a Tafel slope of 0.035 (V/dec). In this thesis, the addition of oxide of inexpensive single metals such as Fe₂O₃ to nitrogen doped graphene by electrochemical method was investigated and the overpotential of 0.313 volts and the Tafel slope of 0.081 (V/dec) were obtained. The electrochemical data of the prepared electrocatalysts are comparable to ruthenium oxide with an overpotential of 0.300 V and a Tafel slope of 0.042 (V/dec). All electrodes were fixed on the nickel foam substrate by immersion and electrochemical deposition without the use of polymeric adhesives and showed 22 - hour stability in one molar potassium hydroxide solution
  9. Keywords:
  10. Oxygen Evoloution Reaction (OER) ; Nitrogen Doped Graphene ; Hematite ; Water Electrolysis ; Iron Oxide Titanate ; Graphene-Based Electrocatalysts ; Composite Nanostructures

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