Positron Annihilation in Copper Hydrogen-Charged Electrochemically

Atomic–electronic structure of copper foils is studied by a positron annihilation method directly in the course of electrochemical hydrogen sorption and after switching the current off. The shape of the curve of angular correlation of the annihilation radiation (ACAR) alters: the intensity of the broad Gaussian component, which is connected with the positron annihilation on the ionic core, is found to increase. The simultaneous increase in the Fermi energy points to an increase in the concentration of free electrons in the conduction band. The latter results from an increased number of electronic states following the formation of a solid solution of incorporation of hydrogen into the crystal lattice of copper. After switching the current off, the ACAR curve resumes its former shape, indicating that hydrogen leaves the crystal lattice and undergoes molization in caverns and on the grain boundaries. The discovered phenomena explain the increase observed in the size of cathodes—the “swelling” of copper foils during hydrogen sorption.