Résumé
Electrochemical hydrogen oxidation and reduction reaction catalysed by noble metals are essential for hydrogen conversion technologies. When a Pd electrode is in contact with H2 and polarized to hydrogen reaction region such superimposed phenomena as H absorption into Pd, H adsorption/desorption, H evolution reaction and H2 oxidation reaction occur making in situ electrochemical measurements tricky. The operando measurements of the PdHx lattice parameters with wide-angle X-ray scattering (WAXS) allow the quantification of H atoms inserted into the Pd lattice and thus, help to resolve contribution from hydrogen absorption. This experiment thus aims at (i) exploring the H/Pd ratio dependency on the potential, (ii) distinguishing the two distinctive Pd hydride phases: the α-phase at low hydrogen content and the lattice-expanded β-phase at high hydrogen concentrations, (iii) showing that the Pd lattice can be saturated at low potentials, and (iv) investigating the stability of the β-phase.