35
© Springer Nature Switzerland AG 2020
R. Adzic, N. Marinkovic, Platinum Monolayer Electrocatalysts,
https://doi.org/10.1007/978-3-030-49566-4_5
Chapter 5
Important Electrosorption Reactions
5.1 Hydrogen Adsorption on Platinum Metals
Determination of catalytic activity reflecting on a clean metal surface in a broad
potential range is not often possible. Water on the electrode surfaces in aqueous
solutions reacts with the noble metal surface at positive potentials resulting in H 2 O
oxidation and, in the case of Pt, Pt-OH formation, see Fig. 5.1. At negative potentials, H adsorption takes place in acid solutions before hydrogen evolution. In alkaline solutions, H 2 evolves from water. The potential range between Pt-OH formation
and H adsorption (no reaction takes place) is called the double-layer region. Metal
surface covered only with physisorbed water is available for reaction. Some nonnoble metals may dissolve at small positive potentials or they passivate covered by
oxide layer.
These adsorbates affect the reactivity of the electrode surface and the reaction
kinetics by participating in certain reaction steps, as spectators affect the surface
area accessible to the reactants or exert an electronic effect on the reacting species.
Cathodic reduction and evolution of hydrogen, together with the adsorption of
hydrogen, are some of the most studied processes in electrochemistry, not only
because of the scientific interest but because hydrogen can be a viable fuel. Renewed
interest in this fundamental process is stimulated by the growing environmental
concerns as well as the need to understand the process of surface hydrogen adsorption, which is important for the design of the electrocatalyst since it affects various
steps in the catalytic reaction.
In the gas phase, hydrogen adsorbs on the metallic surface by physisorption at
very low temperatures, creating weak van der Walls interactions that do not perturb
the covalent bond in hydrogen molecule because the amount of energy released by
the physisorption is much lower than that of the H-H bond. At higher temperatures,
a strong chemical interaction between H 2 and metal surface occurs, resulting in the
dissociation of the H–H bond and formation of a bond with the metal [1].
© Springer Nature Switzerland AG 2020
R. Adzic, N. Marinkovic, Platinum Monolayer Electrocatalysts,
https://doi.org/10.1007/978-3-030-49566-4_5
Chapter 5
Important Electrosorption Reactions
5.1 Hydrogen Adsorption on Platinum Metals
Determination of catalytic activity reflecting on a clean metal surface in a broad
potential range is not often possible. Water on the electrode surfaces in aqueous
solutions reacts with the noble metal surface at positive potentials resulting in H 2 O
oxidation and, in the case of Pt, Pt-OH formation, see Fig. 5.1. At negative potentials, H adsorption takes place in acid solutions before hydrogen evolution. In alkaline solutions, H 2 evolves from water. The potential range between Pt-OH formation
and H adsorption (no reaction takes place) is called the double-layer region. Metal
surface covered only with physisorbed water is available for reaction. Some nonnoble metals may dissolve at small positive potentials or they passivate covered by
oxide layer.
These adsorbates affect the reactivity of the electrode surface and the reaction
kinetics by participating in certain reaction steps, as spectators affect the surface
area accessible to the reactants or exert an electronic effect on the reacting species.
Cathodic reduction and evolution of hydrogen, together with the adsorption of
hydrogen, are some of the most studied processes in electrochemistry, not only
because of the scientific interest but because hydrogen can be a viable fuel. Renewed
interest in this fundamental process is stimulated by the growing environmental
concerns as well as the need to understand the process of surface hydrogen adsorption, which is important for the design of the electrocatalyst since it affects various
steps in the catalytic reaction.
In the gas phase, hydrogen adsorbs on the metallic surface by physisorption at
very low temperatures, creating weak van der Walls interactions that do not perturb
the covalent bond in hydrogen molecule because the amount of energy released by
the physisorption is much lower than that of the H-H bond. At higher temperatures,
a strong chemical interaction between H 2 and metal surface occurs, resulting in the
dissociation of the H–H bond and formation of a bond with the metal [1].