Electrochemical study of hydrogen absorption in polycrystalline palladium

• Autores: Salvarezza, Roberto Carlos; Montemayor, M. C.; Fatas, E.; Arvia, Alejandro Jorge
• Año de publicación: 1991
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: Ciencias Exactas; Química; Hydrogen absorption; Polycrystalline palladium
• Institución: Universidad Nacional de La Plata

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_s, more positive than the reversible potential, E_r, for the H₂ 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_s 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 H₂ evolution on the Pd surface at high frequencies. The X-ray diffraction pattern of the electrodes cathodized at E_s < E_r, 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_s 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