Electrocatalysis hydrogen electrode reaction

Markovic NM (2003) The hydrogen electrode reaction and the electrooxidation of CO and H / CO mixtures on well-characterized Pt and Pt-bimetallic surfaces. In Vielstich W, Lamm A, Gasteiger HA (eds) Handbook of fuel cells fundamentals, technology and application, vol. 2 electrocatalysis. Wiley, Chichester, pp 368-393... 

HER/HOR electrocatalysis. In this sense, work conducted on single-crystal surface presented a starting point for the understanding of catalysis of hydrogen electrode reactions [3],... 

The theory of electrocatalysis is still in its infancy. It was developed first for the hydrogen evolution reaction in the second half of the 1900s. The grounds can be traced back in a seminal paper by Floriuti and Polanyi [25]. Accordingly, for a simple one-electron electrode reaction ... 

Trasatti, S. (1990) Electrode kinetics and electrocatalysis of hydrogen and oxygen electrode reactions. 1. Introduction, in Electrochemical Hydrogen Technologies (ed. 

Wendt, H. and Plzak, V. (1990) Electrode kinetics and electrocatalysis of hydrogen and oxygen electrode reactions. 2. Electrocatalysis and electrocatalysts for cathodic evolution and anodic oxidation of hydrogen, in Electrochemical Hydrogen Technologies (ed. H. Wendt), Elsevier, Amsterdam, Chapter 1. 2. 

In electrode reactions of the type H+/H2, 02/H20, and probably many organic redox systems, the electrode surface may be involved by virtue of the presence of adsorption sites where intermediates in the reaction mechanism, e.g. atomic hydrogen, are located. Generally, the reaction rate is higher at metals with a larger adsorptive capacity. This is a particular form of electrocatalysis, which is a subject of still-growing interest. 

Only two general reviews [38, 39] entirely devoted to the hydrogen evolution reaction have appeared after the start of the development of cathode activation [40]. In several other cases, hydrogen evolution has been discussed within the general frame of electrocatalysis [4, 41-47] or kinetics of electrode reactions [48, 49]. However, only one of the two reviews mentioned above discusses electrocatalytic aspects with literature coverage up to the late 70 s, when the field of cathode activation was at the beginning of its development. 

Examples are the oxygen electrode, Equation (1), or the hydrogen electrode (i.e. the H+/H2 reaction), Equation (2). Electron transfer proceeds regularly with the reacting species adsorbed at an electrode surface. In many cases, electrocatalysis by the electrode metal plays an important role. Associated chemical reactions, such as protonation and dissociation, render the reaction mechanisms complex. This is true in particular for the oxygen electrode. 

A special case of heterogeneous catalytic kinetics, that we will briefly discuss, is electrocatalysis, which is defined as the acceleration of an electrodic reaction by a substance that which is not consumed in the overall reaction. For a catalytic reaction with the following step Sads+Hads=>SHads this is only one of the possible mechanisms for the involvement of hydrogen in the catalytic reduction. Another mechanism is the electrochemical or ionic mechanism where the adsorbed hydrogen serves only as an electron source for the reduction process. This type of reaction is formulated by the following reaction steps ... 

A complete theory of electrocatalysis has been developed for hydrogen evolution reaction [12] because the reaction proceeds through a limited number of steps with possibly only one type of reaction intermediate. The theory predicts that the electrocatalytic activity depends on the heat of adsorption of the intermediate on electrode surface in a way giving rise to the well-known volcano curve [19], and prediction has been verified experimentally (Fig. 1). 

Steam electrolysis splits water in the form of steam into hydrogen and oxygen by use of electricity and thus can be used as a method to produce hydrogen. Unlike other types of electrolysis, e.g., alkaline water electrolysis and polymer electrolyte water electrolysis, the steam electrolysis operates typically at 700-1,000 °C since the electrolysis uses solid electrolyte that works at the high temperatures. Such high operation temperature leads to fast kinetics for the electrode reactions, so that precious metals are not necessary for the electrocatalysis. 

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