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.

Recent studies on AuPd(111) alloy surfaces display unexpected hydrogen evolution reaction activities-a unique activity of AuPd alloys with surface fractions of~20% Pd was found. We investigated if this phenomenon also occurs with AgPd alloys. We first deposited Pd on a Ru (0001) substrate. After annealing, cyclic voltammetry investigations showed the same characteristics as Pd (111) single crystals. During Ag deposition, cyclic voltammetry experiments disclose underpotential deposition of Ag on the Pd film just as on Pd(111). AgPd alloys were formed by further annealing, and strong enrichment of Ag at the surface is observed. Using this approach, we prepared various bulk compositions at a film thickness of 20 monolayers. Most AgPd alloys show a higher electrocatalytic activity than Ag or Pd alone. The activity trends match those seen with AuPd alloys.