Work function, electronegativity, and electrochemical behaviour of metals III. Electrolytic hydrogen evolution in acid solutions

The dependence of the exchange current for the electrolytic evolution of hydrogen on metals (i0,H) on the work function () is analyzed on the basic of a new list offor polycrystalline surfaces. It is shown that log i0,H is linearly related toirrespective of the detailed nature of the mechanism involved in the rate determining step (rds). i0,H on sp metals depends on the sign of the surface charge. Results confirm previous suggestions that the main difference in double layer structure between sp and transition metals arises as a result of hindered rotation of water molecules on the latter. If the strength of the M−H bond is taken into consideration, then metals divide into two groups: (a) sp metals, with slow discharge at usual overvoltages, and probably slow hydrogen removal close to equilibrium, and (b) transition metals, with slow hydrogen removal as the rate determining step. Mn is anomalous and cannot be assigned to either class in correlations. Dependence of M−H bond strength onis also shown and discussed.