1,721,154 research outputs found
Hydrogen Evolution
No full textThe article begins with a brief presentation of the strategic importance of the hydrogen evolution reaction in various fields; this is followed by a discussion of its reversibility and of the factors on which reversibility depends. Adsorption of hydrogen atoms is a necessary step that depends on the interaction of metal surfaces with solvents. Thus, a correlation is found between M-H bond strength and hydrophilicity of metal surfaces. This point is discussed with the help of voltammetric curves for platinum-group metals. Besides being adsorbed, hydrogen atoms can also penetrate beneath the surface, thus affecting the adsorption energy on the surface. Hydrogen evolution is often accompanied by cathodic poisoning owing to the presence of metallic impurities. Ways to minimize this are discussed. The three most popular mechanisms of the electrode reaction for hydrogen liberation are discussed and kinetic parameters reported. The effect of the coverage of the electrode with the intermediate (H ad) is illustrated in detail. The effect of the nature of the electrode material (in electrocatalysis) is discussed using the so-called volcano curves depicting the dependence of the activity on M-H bond strength. A detailed analysis of electronic and geometric factors in electrocatalysis is also carried out. Finally, the findings of a survey of the most active materials in acidic and alkaline solutions are presented
Comment on "Trends in the exchange current for hydrogen evolution" [J. Electrochem. Soc., 152, J23 (2005)]
No full textWe compare the adsorption energies calculated by Norskov et al. with data derived from experimental values; except for Ni and Co, which absorb hydrogen strongly, there is a linear relation. We discuss the model proposed by these authors in the light of extensive previous work and of experimental data and find it overly simplistic
Recent developments in understanding factors of electrocatalysis
No full textAfter an introductory analysis of terms and concepts in the field of electrocatalysis, a number of experimental examples are reported to illustrate various factors. In particular, Tafel slope and PZC of oxide electrodes are shown to be able to disentangle electronic from geometric factors. The points under discussion are: effect of particle size and methods of preparation, surface vs. bulk composition, primary vs. secondary effects with redox systems depending on the molecular structure of the couple, single crystal vs. polycrystalline surfaces. The last case is particularly relevant since for the first time "vicinal" faces of RuO2 are shown to behave at the extremes of the usually observed experimental picture
Electrocatalytic activity for hydrogen evolution of polypyrrole films modified with noble metal particles
No full textPolypyrrole (Ppy) films of various thicknesses contg. particles of noble metals such as Pt, Ru and Ir were electrosynthesized on the surface of austenitic stainless steel (Ss). Two different approaches were applied: (i) electrodeposition of a polymer film from a soln. already contg. an anionic metal complex, followed by potentiodynamic or galvanostatic redn.; and (ii) presynthesized Ppy films modified by galvanostatic electrodeposition of noble metals from solns. of the metal complexes. Surface morphol. and compn. of the resulting layers were studied by means of SEM and XPS. The electrocatalytic activity of the modified electrodes for the hydrogen evolution reaction (her) was tested in 0.05 M H2SO4 by means of potentiodynamic techniques (0.5 mV s-1)
- …
