Trends in the HER are studied on selected metals (M= Cu, Ag, Au, Pt, Ru, Ir,
Ti) in acid and alkaline environments. We found that with the exception of
Pt, Ir and Au, due to high coverage by spectator species on non-noble metal
catalysts, experimentally established positions of Cu , Ag, Ru and Ti in the
observed volcano relations are still uncertain. We also found that while in
acidic solutions the M-Hupd binding energy most likely is controlling the
activity trends, the trends in activity in alkaline solutions are controlled
by a delicate balance between two descriptors: the M-Had interaction as well
as the energetics required to dissociate water molecules. The importance of
the second descriptor is confirmed by introducing bifunctional catalysts
such as M modified by Ni(OH); e.g. while the latter serves to enhance
catalytic decomposition of water, the metal sites are required for
collecting and recombining the produced hydrogen intermediates.
Electrocatalysis of the HER in acid and alkaline media
