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Synthesis and Electrochemical Evaluation of Graphene-Ni/Cu/Zn Nanocomposite Coating Modified by Pt/Ru Nanoparticles

Yaghoubinezhad, Yadollah | 2015

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 47236 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Afshar, Abdollah
  7. Abstract:
  8. In this research,Graphene Oxide nanoplatelets (GO) were synthesized by chemically modified Hummer's method.After the GO nanosheets electrochemically reduced to graphene, nanoparticles imposed to this thin film.This optimized nanostructure coating was utilized for investigating the Hydrogen Evolution Reaction (HER) over the copper substrate. In order to optimize the kinetic of electrodeposition and reduction, diverse electrochemical approaches such as cyclic voltammetry, chronoamperometic and potentiometric as well as pulse electrodeposition methods were employed. Electrochemical procedures were aligned by Design of Experiment (DOE) software. The best condition for pulse reverse GO electrodeposited in PBS electrolyte resulted at pH about 802, pulse current density of231mA/cm2and anodic and cathodic times of105ms and802ms respectively as well as total electrodeposition time equal to238s.3D electrodeposited graphene with a thickness exceeding 42μm, roughness factor equal to 111 and cathodic Tafel slope of 14mV/decade in 1M KOH demonstrates the high potential of this carbon allotrope is HER study.Graphene coatings in terms of corrosion resistance, proper electrochemical impedance and a higher active surface area were optimized for HER by DOE and response surface methodology.Linear polarization resistance of the graphene at a proper condition was measured about 108kΩ.cm2.Moreover,the electrochemical impedance of the layer was equal to 2304Ω.cm2 and charge transfer was recorded around 128094mC/cm2.To improve the kinetics of hydrogen evolution, graphene coating produced by pulse electrodeposition method was optimized by mixing the Ni/Cu/Zn nanoparticles with graphene matrix as a nanocomposite.Zinc element used as an intermediate for replacing the noble metals (Pt/Ru) via cathodic corrosion approach. In the best nanocomposite coating corrosion current density was reduced to 131nA/cm2 and Tafel slop was declined to 23mV/decade in KOH solution.Because of the graphene porosities were filled by nanoparticles of transition nanoparticles, defects of the coating were reduced and consequently the roughness factor of the optimized coating declined to 5104.In this state coating impedance was recorded about 11Ω.cm2, which suggests increasing the layer charge transfer.However, platinum and ruthenium nanoparticles were replaced by cathodic corrosion.Further reduction of Tafel slope until 19mV/decade was demonstrated in the modified nanocomposite coating. In the modified coating,because of the noble nanoparticles effect, corrosion current density more reduced to 1103nA/cm2, the polarization coating impedance was more increased to23kΩ.cm2 and charge transfer was improved to 112099 mC/cm2 which are the main component in the hydrogen production electrodes. In this thin film, the prominent mechanism is Tafel-Heyrovsky
  9. Keywords:
  10. Hydrogen Evolution Reaction ; Transition Metal Oxides ; Graphene Oxide ; Nano-Composite Coating ; Electrochemical Reduction

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