Articulo
Electrochemical study of hydrogen absorption in polycrystalline palladium
Autor
Salvarezza, Roberto Carlos
Montemayor, M. C.
Fatas, E.
Arvia, Alejandro Jorge
Institución
Resumen
The hydrogen reactions on polycrystalline Pd in 0.1 M NaOH at 25°C have been studied by using transients at constant potential, and by impedance spectroscopy and X-ray diffraction techniques. At potentials, E<sub>s</sub>, more positive than the reversible potential, E<sub>r</sub>, for the H<sub>2</sub> evolution reaction, the current-time response and the impedance data indicate H atom diffusion into the bulk Pd. The X-ray diffraction pattern of electrodes cathodized during 20 min at these potentials are similar to those obtained for Pd. At Es < Er, the current transients exhibit a current maximum which increases as E<sub>s</sub> moves in the negative direction. The Nyquist plot for the rising part of the transients indicates the H atom diffusion into the bulk metal and H<sub>2</sub> evolution on the Pd surface at high frequencies. The X-ray diffraction pattern of the electrodes cathodized at E<sub>s</sub> < E<sub>r</sub>, shows the presence of the βPdH phase and Pd. The experimental results indicate that different reactions take place simultaneously in this potential range: (i) H<sub>s</sub> evolution, (ii) H diffusion into the bulk Pd, (iii) nucleation and diffusion-controlled growth of the βPdH phase. Taking into account the contribution of these reactions, a model, which is able to reproduce the experimental current transients, is presented. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas