Hydrogen evolution reaction single-crystal surfaces

Figure 3.16 Volcano plot for the hydrogen evolution reaction (HER) for various pure metals and metal overlayers. Values are calculated at 1 barof H2 (298K) and at a surface hydrogen coverage of either 0.25 or 0.33 ML. The two curved lines correspond to the model (3.24), (3.25) transfer coefficients (not included in the indicated equations) of 0.5 and 1.0, respectively, have also been added to the model predictions in the figure. The current values for specific metals are taken from experimental data on polycrystalline pure metals, single-crystal pure metals, and single-crystal Pd overlayers on various substrates. Adapted from [Greeley et al., 2006a] see this reference for more details.

Our article has concentrated on the relationships between vibrational spectra and the structures of hydrocarbon species adsorbed on metals. Some aspects of reactivities have also been covered, such as the thermal evolution of species on single-crystal surfaces under the UHV conditions necessary for VEELS, the most widely used technique. Wider aspects of reactivity include the important subject of catalytic activity. In catalytic studies, vibrational spectroscopy can also play an important role, but in smaller proportion than in the study of chemisorption. For this reason, it would not be appropriate for us to cover a large fraction of such work in this article. Furthermore, an excellent outline of this broader subject has recently been presented by Zaera (362). Instead, we present a summary account of the kinetic aspects of perhaps the most studied system, namely, the interreactions of ethene and related C2 species, and their hydrogenations, on platinum surfaces. We consider such reactions occurring on both single-crystal faces and metal oxide-supported finely divided catalysts. 

One conclusion is clear. The instability of a metal with surface cracks will tend to be greater than that of a surface without such cracks. The metal-dissolution and hydrogen-evolution reactions tend to occur indiscriminately on the normal surface of a homogeneous single crystal. When, however, there is a crack, the metal dissolution will occur preferentially inside the crack and the hydrogen evolution on the surface outside the crack (Fig. 12.78). But this implies that the electron-source area AH is very large compared with the area AM inside the crack, i.e., compared with the area over which there is metal dissolution. It is essential, however, that the corrosion current (not the current density) be equal to the electronation current ... 

Figure 10.9 In-situ IR spectra (SNIFTIRS) of high-index planes of Pt in 0.5 M H SO,. All spectra recorded atOV (RHE) with a reference potential of 0.8 V [16], Reprinted from Surface Science, Vol. 605, Nakamura, M. Kobayashi, T Hoshi, N. Structural dependence of intermediate species for the hydrogen evolution reaction on single crystal electrodes of Pt, pages 1462-1465, copyright 2011, with permission from Elsevier.

Bai L, Harrington DA, Conway BE. Behavior of overpotential-deposited species in Faradaic reactions-II. AC Impedance measurements on H2 evolution kinetics at activated and unactivated Pt eathodes. Electrochim Acta 1987 32(12) 1713-31. Markovic NM, Grgur BN, Ross PN. Temperature-dependent hydrogen electrochemistry on platinum low-index single-crystal surfaces in acid solutions. J PhysChemB 1997 101(27) 5405-13. 

Kita H, Ye S, Gao Y. Mass transfer effect in hydrogen evolution reaction on Pt single-crystal electrodes in acid solution. J Electroanal Chem 1992 334 1—2) 351—7. Protopopoff E, Marcus P. Effect of chemisorbed sulfur on the hydrogen adsorption and evolution on metal single-crystal surface. J Chim Phys 1991 88 1423-52. 

Schmidt, T.J., Ross, P.N., Jr., and Markovic, N.M. (2002) Temperature dependent surface electrochemistry on Pt single crystals in alkaline electrolytes Part 2. The hydrogen evolution/ oxidation reaction. Journal of Electroanalytical Chemistry, 524-525, 252-260. 

Schmidt, J., Ross Jr., N. Markovic, M. (2002). Temperature Dependent Surface Electrochemistry on Pt Single Crystals in Alkaline Electrolytes Part 2. The Hydrogen Evolution/Oxidation Reaction. Journal of Electroanalytical Chemistry, Vol.524-525, No.3, (May 2002), pp. 252-260, ISSN 00220728... 

---