Electrocatalysis for hydrogen electrode reactions in the light of Fermi dynamics and structural bonding factors - I. Individual electrocatalytic properties of transition metals

The Brewer valence-bond theory for bonding in metals and intermetallic phases has been employed, together with Fermi dynamics, to correlate with the electrocatalytic properties of both individual and composite transition metal catalysts for the hydrogen electrode reactions (HELR). It has been inferred that the electrocatalytic activity of both individual transition metals and their intermetallic phases and alloys for both hydrogen evolution (HER) and its oxidation (HOR), primarily correlates with the electronic density of states and obeys typical laws of catalysis reflected in the first place in the existence of volcano plots along the Periodic Table: Since the bonding effectiveness of both individual and intermetallic hypo-hyper-d-electronic transition metal composite electrocatalysts correlates in a straightforward manner with their electrocatalytic activity, such evidence strongly suggests Fermi energy, as a typical elementary binding energy, which otherwise stays in the linear relation with cohesive energy, this forms the basis in investigation and correlation of electrocatalytic activity. Due to the fact that the Fermi wave-vector represents the individual and collective (alloys and intermetallic phases) bulk property of the available electronic number density (or its concentration, n, i.e., k(F) = (3 pi(2)n)(1/3)), and in a straightforward manner correlates with the electronic;density of states at the Fermi lever, and thereby defines all metallic properties of a metal (and intermetallics) as "a solid with a Fermi surface", including electrocatalytic features, it has been taken as the main parameter to correlate with the exchange current density in the hydrogen electrode reactions. (C) 1998 International Association for Hydrogen Energy.