Hydrogen absorption and diffusion into and in palladium: ac-impedance analysis under impermeable boundary conditions
✍ Scribed by Tae-hyun Yang; Su-il Pyun
- Book ID
- 103067681
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 613 KB
- Volume
- 41
- Category
- Article
- ISSN
- 0013-4686
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✦ Synopsis
The hydrogen absorption reaction (bar) and diffusion into and in palladium electrode has been investigated in 0.1 M NaOH solution under impermeable boundary conditions by using ac-impedance, open-circuit potential transient and current transient techniques. The UC-impedance measurements were carried out in the overpotential range of -0.10 to 0.25 V,,. Measured impedance spectra were analyzed by using complex non-linear least squares (CNLS) fitting method on the basis of Faradaic admittance equations for hydrogen absorption under impermeable boundary conditions. From the occurrence of plateau region of the open-circuit potential transients and hydrogen content below 0.03 determined from the current transients it is suggested that a thin p-phase palladium hydride layer is formed beneath the electrode surface. The indirect to direct bar transition in mode occurs at the overpotential of 0.08 V,h, below which the direct hat is predominant From the hydrogen diffusivity reduced with decreasing overpotential, it is indicated that the thin /J-phase palladium hydride layer acts as a barrier for hydrogen diffusion in the electrode. The formation of the thin B-phase palladium hydride layer between the electrode surface and subsurface accounts for the predominant direct bar mode and hydrogen diffusion impeded by the phase boundary between L-Z-and /?-phase palladium hydride below 0.08 V,h,.