In situ time resolved studies of hydride and deuteride formation in Pd/C electrodes via energy dispersive X-ray absorption spectroscopy

The electrochemical formation of β-hydride and β-deuteride phases of a carbon supported palladium nanoparticle catalyst has been investigated using time resolved in situ energy dispersive X-ray absorption spectroscopy (EDE) and the simultaneously collected chronoamperometric data. For the β-hydride formation the rate of the phase transition was found to be limited by the rate of diffusion of H through the bulk of the Pd particles, while for β-deuteride formation the interfacial reduction of D+ was found to contribute more significantly to the kinetics. The composition of the hydride and deuteride phases formed was determined using both the lattice parameters obtained by fitting the EDE data and from linear sweep voltammograms, the former giving compositions of PdH0.83 and PdD0.63, which are consistent with the β-hydride and deuteride phases. Hyperstoichiometric compositions were obtained from the linear sweep voltammograms and the excess attributed to H or D spill-over on to the carbon support or re-oxidation of H2 or D2 trapped in the porous structure of the catalyst electrode.