Application of morphological instability to the analysis of physical parameters of a metal surface: Adsorption effect of hydrogen on galvanostatic electrodeposition

Using a newly developed method with which surface parameters of metals such as surface energy and surface diffusion coefficient of adatoms can be measured from the change of surface morphology, the effect of hydrogen adsorption on the crystal sizes formed in galvanostatic electrodeposition was studied. As a result, the reasons for the eccentric formation of minute, powdery crystals accompanied with hydrogen evolution was derived as follows: Since surface diffusion of metal adatoms is strongly hindered owing to saturated adsorption of hydrogen atoms, the supersaturation of the adatoms is violently promoted. Many small crystals resulting from nucleation growth, therefore, continuously appear at high growth velocity. At the same time, the surface energy of the crystals also increases and its value is mainly determined by saturatedly adsorbed hydrogen, so that the tendency for rapid formation of minute crystals are the more accelerated. On the other hand, when hydrogen adsorption can be disregarded, crystals grow more slowly and have relatively larger sizes. The transition from a hydrogen-nonadsorbed state to a hydrogen-adsorbed state is rather discontinuous; immediately after the electrode surface is saturatedly covered with hydrogen, the crystals suddenly reduce their sizes.