Catalysis of hydrogen evolution

Grass, V., Lexa, D., Saveant, J.-M. (1997). Electrochemical generation of thodium porphyrin hydrides. Catalysis of hydrogen evolution, J. Am, Chem. Soc, 119 7526. 

It was noted above that one should seek electrode materials where the overpotential for chlorine evolution is as low as possible but where there is a considerable oxygen overpotential. In addition, for diaphragm and membrane cells there is the requirement for cathodes with a low hydrogen overpotential. Catalysis of hydrogen evolution was discussed in Chapter 1 and it was shown that strong catalysis is promoted by metals where the free energy of adsorption of hydrogen atoms has an intermediate value. This allows mechanisms such as... 

Detection of metallothionein is connected with specific structure of MT, i.e. the absence of aromatic amino acids in the native state and disulfide bonds. However, its structure is adapted to incorporate heavy metal ions by sulfhydryl groups, thus, these specific features may be used for the electrochemical determination. The protection by reduction agents is required, because sulfbydryl groups have a tendency to be oxidized. On the other hand, this property allows an application of electrochemical determination. The other opportunity how to detect metallothionein is the catalysis of hydrogen evolution from a supporting electrolyte [38-41]. 

In summary, a good catalyst for an electron transfer step should have a d band that spans the Fermi level and interacts strongly with the valence level of the reactant. On the basis of these principles, we have explained the trends in the catalysis of hydrogen evolution on pure metals... 

Linkous, C.A., Slattery, D.K., and Mraz, M.E., Hydrogen production via photocatalysis. Catalysis of 02 evolution, Proc. 15th World Hydrogen Energy Conf., Yokohama, Japan, 2004. 

As a result, it is to be expected that the maximum rate of hydrogen evolution will occur at intermediate values of AG ds which lead to a significant but not monolayer coverage by adsorbed hydrogen atoms. This is indeed observed and Fig. 1.16 shows a volcano plot of exchange current density vs AG ds for a series of metal cathodes. Similar dependences of rate parameters on the free energy of adsorption of an intermediate are common in gas-phase catalysis. 

S. Trasatti, Electrode kinetics and electro-catalysis of hydrogen and oxygen electrode reactions. 4. The oxygen evolution reaction, in Electrochemical Hydrogen Technologies (Ed. H. Wendt), Elsevier, Amsterdam, 1990, pp. 104-135. 

Finally, attention has been drawn to currents of hydrogen evolution which in the presence of some substances occurs at more positive potentials than in their absence. Such substances catalyze hydrogen evolution and result in high currents which are denoted catalytic hydrogen waves. Such waves are observed in the presence either of platinum group metals (57,58), where the catalysis is attributed to clusters of metals deposited on mercury or of compounds which possess acid-base properties. Catalytic effects of the latter type in solutions of simple buffers have been observed for low molecular weight compounds (59,60), as well as for proteins (61,62). Similar catalytic effects in ammoniacal cobalt (III)-solutions (63) found utilization in Brdicka reaction (64-66), used in cancer diagnosis. 

Shen Y, Liu J, Jiang J, Liu B, Dong S. Fabrication of a metallopoyphyrin-polyoxometalate hybrid film by a layer-by-layer method and its catalysis for hydrogen evolution and dioxygen reduction. J Phys Chem B 2003 107 9744-8. 

It is recognized, that the overall process consists of the catalysis of reaction 1, an intermediate step being the reduction of water. Reaction 4 can be treated as hydrogen evolution on a compact silver electrode at negative potential. Silver has a small overpotential for evolution Of the two steps of which reaction 4 is composed... 

Maeda, K., Terashima, H., Kase, K., and Domen, K. (2009) Nanoparticulate precursor route to fine particles of TaON and Zr02-TaON solid solution and their photocatalytic activity for hydrogen evolution under visible light. Applied Catalysis A General, 357 (2), 206—212. 

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—... 

Benzyl acetate was prepared by addition of benzyl chloride (containing 0.6% pyridine as stabiliser) to preformed sodium acetate at 70°, followed by heating at 115°, then finally up to 135°C to complete the reaction. On one occasion, gas began to be evolved at the end of the dehydration phase, and the reaction accelerated to a violent explosion, rupturing the 25 mm thick cast iron vessel. This was attributed to presence of insufficient pyridine to maintain basicity, dissolution of iron by the acidic mixture, and catalysis by ferric chloride of a Friedel-Craft type polycondensation reaction to polybenzyls, with evolution of hydrogen chloride, which at 130°C would produce an overpressure approaching 100 bar. Previously the chloride had been supplied in steel drums containing 10% sodium carbonate or 3% sodium hydroxide solutions as... 

From a catalysis point of view, the hydrogen evolution reaction can in principle be catalyzed perfectly, and in reality, it is seen that there is almost no overpotential on... 

In heterogeneous electro catalysis, the catalyst is immobilized on the electrode surface, or the electrode itself plays the role of a catalyst. Catalytic effects of various electrode materials on the hydrogen evolution reaction are typical examples of heterogeneous electro -catalysis [iii]. Further examples are electrode mechanisms involving hydrogen evolution at a mercury electrode catalyzed by adsorbed organic bases, microparti-... 

Attempts to support models of the catalytic activity and the operative mechanism with results of theoretical considerations have been reported for the oxygen reduction [iii] and hydrogen oxidation [iv]. Electrocatalytic electrodes are indispensable parts of fuel cells [v]. A great variety of electrocatalytic electrodes has been developed for analytical applications [vi]. See also electro catalysis, catalytic current, -> catalytic hydrogen evolution, catalymetry. 

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