Effect of hydrogen absorption on atomic-electronic structure of PdH system according to positron annihilation data

The positron annihilation technique is used to investigate the atomic-electronic structure of the electrochemically hydrogenated palladium. Curves of the angular correlation of the annihilation gamma-quanta radiation (ACAR) were recorded on the original Pd specimen, electrochemically hydrogenated Pd, and dehydrogenated Pd. EF Fermi levels and free-electron concentrations were estimated based on the experimental ACAR curves. A substantial increase in the free-electron concentration from N/V = 4.6 × 1022 [22] cm−3 to N/V = 6.0 × 1022 cm−3 was found in the hydrogenated Pd specimen compared to that of the original palladium. This change is accompanied by a decrease in the Gaussian half-width of the ACAR curves, which indicates a certain loosening of the palladium crystal lattice upon the hydrogenation. Upon the electrochemical removal of hydrogen from palladium, the annihilation characteristics of the metal are almost completely restored.