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Experimental Study of Oxygen Reduction Reaction (ORR) on Cu-alloys, Electrocatalysts in Alkaline Solution and Theoretical Investigation of Oxygen Adsorption on Cu-alloys Nano-clusters

Arab, Ramezan | 2011

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 41587 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Gobal, Fereydoon
  7. Abstract:
  8. In this study, electrochemical oxygen reduction reaction (ORR) was studied on Cu, Pd, Rh, Pd-Cu and Rh-Cu alloys in alkaline solution. Pd-Cu and Rh-Cu alloys were prepared by electrochemical methods. On copper electrode it is found that direct oxygen reduction is accompanied by the electrochemical reductions of copper oxides. Also, mechanism and kinetics of reaction change as the amount of copper oxides increase on the surface. For electrodeposited alloys, it is indicated that the reactivity of Pd-Cu and Rh-Cu alloys toward oxygen reduction is higher than pure Pd and pure Rh. The maximum reactivity among Pd-Cu alloys is related to the sample with 24.5% copper content while the maximum reactivity among Rh-Cu alloys is related to the sample with 68.7% copper content. The number of electrons exchanged per O2 for Rh and Rh-Cu alloys is equal to 4 at all potentials while for Pd and Pd-Cu alloys increased from 2 to 4 as the applied reducing potential was raised. Also, it is shown that the reactivity of Rh and Rh-Cu alloys toward oxygen reduction in the presence of ethanol decrease marginally and with increasing the copper contents of the alloys the activity for ORR in the presence of ethanol is less affected. For Pd and Pd-Cu alloys it is shown that while pure Pd has the least specific activity for ORR it possesses the highest selectivity towards oxygen reduction and least affected in the presence of ethanol. Theoretical studies based on density functional theory indicated that structure, stability and properties (chemical hardness, dipole moment, charge of atoms, vibrational frequencies and equilibrium distances) of nano-clusters strongly depend on spin multiplicity, charge and copper content of nano-cluster. Adding charge to the nano-cluster and increasing the copper content of nano-clusters change the adsorption modes of atomic and molecular oxygen as well as adsorption energies. Also, it is found that all nano-clusters prefer dissociative adsorption of oxygen and that Pd/Cu nano-clusters are more active than pure Pd nano-cluster for dissociative adsorption of oxygen while Rh/Cu and pure Rh nano-clusters show similar behavior
  9. Keywords:
  10. Alkaline Solution ; Density Functional Theory (DFT) ; Oxygen Reduction Reaction ; Palladium-Copper Alloy ; Rhodium-Copper Alloy ; Oxygen Adsorption ; Nano-Cluster

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