Impact of surface mechanics on the reactivity of electrodes.

Theory links the reactivity of metal surfaces to the interatomic spacing and, hence, to the tangential strain. We point out that this proposition can be experimentally verified by exploiting a seemingly unrelated phenomenon, the mechanical deformation of solid bodies when charged in an electrolyte. Such experiments allow the strength of coupling between adsorption enthalpy and strain to be quantified. For hydrogen adsorption on Pd, the result agrees with ab initio computation and with trends that can be inferred from experiment on pseudomorphic layers strained by epitaxy with misfitting substrates. The data suggest that experimentally accessible strain values afford a variation of the adatom concentration by several orders of magnitude and a significant shift of the reaction along the 'volcano curve' of reactivity versus adsorption strength.

Surface stress-charge response of a (111)-textured gold electrode under conditions of weak ion adsorption.

We report a cantilever bending investigation into the variation of surface stress, f, with surface charge density, q, for (111)-textured thin films of gold in aqueous NaF and HClO 4. The graphs of f(q) are highly linear, and the surface stress-charge coefficients, d f/d q, are -1.95 V for 7 mM NaF and -2.0 V for 10 mM HClO 4 near the potential of zero charge. These values exceed some previously published experimental data by a factor of 2, but they agree with recent ab initio calculations of the surface stress-charge response of gold in vacuum.

Unique activity of Pd monomers: hydrogen evolution at AuPd(111) surface alloys.

Well-defined Au/Pd(111) alloy films have been prepared on a Ru(0001) substrate by electrochemical metal deposition and subsequent heating up to 700 degrees C. The electrochemical behaviour of the 20 monolayers thick epitaxially-grown films is in excellent agreement with both equilibrium surface composition and distribution for Au/Pd alloys on Mo(110) as previously reported (D. W. Goodman et al., J. Phys. Chem., 2005, B109, 18535). The electrocatalytic activity of the AuPd(111) surface alloys was studied for the hydrogen evolution in 0.1 M H(2)SO(4) as a function of surface composition. Maximum activities were found for Pd fractions of 0.2 +/- 0.1, where the population of Pd atoms surrounded by Au has its maximum. These Pd monomers are found to be about 20 times more active than Pd atoms in the Pd overlayer.