Electrocatalysis of hydrogen evolution

Trasatti, S. (1992) Electrocatalysis of hydrogen evolution progress in cathode activation, in Advances in Electrochemical Science and Engineering (eds H. Gerischer and C.W. Tobias), VCH Verlag GmbH, Weinheim. 

Electrocatalysis of Hydrogen Evolution Progress in Cathode Activation... 

Trasatti, Electrocatalysis of Hydrogen Evolution Progress in Cathode Activation A. Hammou, Solid Oxide Fuel Cells... 

Fleischmann, M. and Grenness, M. (1972) Electrocrystallisation of ruthenium and electrocatalysis of hydrogen evolution. Journal of the Chemical Society, Faraday Transactions I, 68, 2305. 

Electrol3dic hydrogen evolution in acid solutions. J Electroanal Chem 39 163-184. Trasath S. 1977. Electrocatalysis of hydrogen evoluhon. Adv Elechochem Electrochem Eng 10 213. 

A complete theory of electrocatalysis leading to volcano curves has been developed only for the process of hydrogen evolution and can be found in a seminal paper by Parsons in 1958 [26]. The approach has shown that a volcano curve results irrespective of the nature of the rate-determining step, although the slope of the branches of the volcano may depend on the details of the reaction mechanism. 

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 the case of hydrogen evolution, the theory of electrocatalysis on single individual metals was established about thirty years ago [32, 33]. However, no decisive advances have been made since then from the point of view of the theory of composite materials. It is probably for this reason that a great deal of applied research has been conducted thus far following the always convenient approach of try and see . In one case [34], it has been explicitly reported that more than 400 different materials have been tested in a few years with the purpose of finding the best one. 

Electrocatalysis at metal electrodes in aqueous (1.2) and non-aqueous ( ) solvents, phthalocyanine ( ) and ruthenium ( ) coated carbon, n-type semiconductors (6.7.8),and photocathodes (9,10) have been explored in an effort to develop effective catalysts for the synthesis of reduced products from carbon dioxide. The electrocatalytic and photocatalytic approaches have high faradaic efficiency of carbon dioxide reduction (1,6). but very low current densities. Hence the rate of product formation is low. Increasing current densities to provide meaningful amounts of product, substantially reduces carbon dioxide reduction in favor of hydrogen evolution. This reduction in current efficiency is a difficult problem to surmount in light of the probable electrostatic repulsion of carbon dioxide, or the aqueous bicarbonate ion, from a negatively charged cathode (11,12). 

It is difficult to present all applications of EIS some applications (such as those to solid materials and PEM fuel cells, corrosion and passivity, batteries see Sect. 1.3) may be found in available books. As examples, Mott-Schottky plots obtained for semiconductors, the impedance of coating and paints, and electrocatalysis of hydrogen adsorption, absorption and evolution were presented as they are well known in the electrochemical literature. Additionally, newer and developing applications such as the impedance of self-assembled monolayers, biological bilayers, and biosensors were also shown. 

Besides hydrogenation reactions, Raney-type catalysts derived from intermetallic compounds can also be used in electrocatalysis as hydrogen evolution electrodes. Ni-based electrodes were produced by leaching NiAls with an aqueous NaOH solution (32). An improvement in the electrodes in form of a lower overvoltage could be achieved by not leaching NiAla but (Nij Moj,Ti2)Al3, which in addition showed a higher corrosion resistance (33). 

The nature of the adsorbed intermediate (Hajs) and its impact on the mechanism of hydrogen evolution has been a major concern in HER electrocatalysis. Platinum has long been known to form adsorbed hydrogen [4], and the adsorption of hydrogen holds a particular significance in the overall development of modern electrochemical surface science. 

Research in electrocatalysis was strongly stimulated in the early 1960s by efforts toward the development of various types of fuel cells. Studies were initiated on the various factors influencing the rates not only of hydrogen evolution but also of other reactions, particularly cathodic oxygen reduction and the complete oxidation of simple organic substances ( fuels ) to carbon dioxide. The... 

Medvedev IG. 2004. To a theory of electrocatalysis for the hydrogen evolution reaction The hydrogen chemisorption energy on the transition metal alloys within the Anderson-Newns model. Russ J Electrochem 40 1123-1131. 

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 ... 

Pt is, of course, not a good electrocatalyst for the O2 evolution reaction, although it is the best for the O2 reduction reaction. However, also with especially active oxides of extended surface area, the theoretical value of E° has never been observed. For this reason, the search for new or optimized materials is a scientific challenge but also an industrial need. A theoretical approach to O2 electrocatalysis can only be more empirical than in the case of hydrogen in view of the complexity of the mechanisms. However, a chemical concept that can be derived from scrutiny of the mechanisms mentioned above is that oxygen evolution on an oxide can be schematized as follows [59] ... 

The chemistry of electrochemical reaction mechanisms is the most hampered and therefore most in need of catalytic acceleration. Therefore, we understand that electrochemical catalysis does not, in principle, differ much fundamentally and mechanistically from chemical catalysis. In addition, apart from the fact that charge-transfer rates and electrosorption equilibria do depend exponentially on electrode potential—a fact that has no comparable counterpart in chemical heterogeneous catalysis—in many cases electrocatalysis and catalysis of electrochemical and chemical oxidation or reduction processes follow very similar if not the same pathways. For instance as electrochemical hydrogen oxidation and generation is coupled to the chemical splitting of the H2 molecule or its formation from adsorbed hydrogen atoms, respectively, electrocatalysts for cathodic hydrogen evolution—... 

Saturating the electrolyte with iron(lll) hydroxide (e.g., by addition of aqueous solutions of ferric nitrate) and simultaneously adding cobaltous salts leads to in situ formation of a mixed Fe(llI)/Co(ll)/Co(IIl) deposit, which exhibits catalytic activity comparable to that of Fe304 shown by the current voltage curve in Fig. 11. Such mixed oxidic catalyst coatings are composed of very small oxide crystals, which evidently are dissolved upon current interruption due to dissociative oxide dissolution. The transfer of dissolved metal ions to the cathode followed by cathodic deposition of the metal, however, can be completely prohibited, if the potential of the cathode due to optimal electrocatalysis of cathodic hydrogen evolution proceeds with an over-... 

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. 

Hydrogen evolution is the only reaction for which a complete theory of electrocatalysis has been developed [33]. The reason is that the reaction proceeds through a limited number of steps with possibly only one type of intermediate. The theory predicts that the electrocatalytic activity depends on the heat of adsorption of the intermediate on the electrode surface in a way giving rise to the well known volcano curve. The prediction has been verified experimentally [54] (Fig. 2) and the volcano curve remains the main predictive basis on which the catalytic activity is discussed [41, 55],... 

Ion implantation is often recommended as an efficient tool to enhance electrocatalysis either by disrupting the surface structure of the catalyst or by placing active atoms on an inactive (or less active) matrix. The latter possibility (which links this section with Section 3.3 devoted to adatoms) offers also a way to the use of extremely small amounts of active but expensive materials. In order to investigate the effect of surface damages, self-implantation or ion beam bombardment is the most appropriate approach. Implantation of Ni on Ni has led to a modest enhancement of the surface area, but not to electrocatalytic effects [279]. On the other hand, Pt bombarded with neutrons has shown an increase in the activity for hydrogen evolution [280]. However, it has been suggested that this is not related to the formation of surface defects, but rather to the effect of the radioactivity induced on the electrode and on the electrolyte. 

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