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Electrochemical Fabrication and Analysis of Compositionally Graded Platinum-Cobalt Coatings

Namdar, Ashkan | 2025

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57869 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Dolati, Abolghasem
  7. Abstract:
  8. The high production costs of pure platinum electrodes, considered the gold standard for hydrogen evolution reactions, have made the development of compositionally graded coatings a notable solution. This study focuses on the electrochemical fabrication of compositionally graded Co-Pt coatings using the potential step method, with steps at -900 mV, -645 mV, and -450 mV, each applied for 450 s. To optimize the electrolyte bath, two separate baths containing cobalt (II) sulfamate and hexachloroplatinic acid were examined: one with 0.016 M Co²⁺ and another with 10 mM Pt⁴⁺, in the presence of boric acid and sodium saccharin. The baths underwent electrochemical tests, including LSV, CV, and chronoamperometry. The results indicated that increasing the pH shifted the reduction potential of Co from -0.7 V to -0.6 V. A similar trend was observed with increasing Pt concentration. The average diffusion coefficient of Co²⁺ was 7.67 × 10⁻7 cm²/s compared to that of Pt⁴⁺ at high concentration (1.43 × 10⁻6) and low concentration (8.43 × 10⁻7). The nucleation process in both individual baths followed an instantaneous mechanism, whereas in the case of the Co-Pt alloy, the reduction mechanism gradually shifted to progressive nucleation with increasing reduction potential. This phenomenon was confirmed by the FE-SEM images, which showed a needle-like sheet structure in the surface morphology of the three-layer sample. XRD analysis confirmed the presence of HCP CoPt, HCP CoPt₃, and FCC Co phases. With an increase in coating thickness from 8.89 μm to 22.44 μm, the Pt weight percentage, based on EDX analysis and elemental mapping of the cross-section, increased from 10% to 59.90%. The hydrogen evolution reaction results also demonstrated a reduction in the hydrogen generation potential from -0.93 V to -0.80 V. Consequently, compositionally graded Co-Pt coatings were successfully fabricated using the electrochemical method, effectively enhancing electrochemical performance and surface morphology
  9. Keywords:
  10. Multi-Layer Coating ; Hydrogen Evolution Reaction ; Nucleation ; Functionally Graded Coat (FGC) ; Cobalt-Platinum Alloys ; Potential Step

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