Electrocatalysis and Catalyst Screening from Density Functional Theory Calculations - Fuel Cell Catalysis: A Surface Science Approach - page 83

To probe the stability properties of the surface alloys for the HER, we perform a
series of stability tests on all of the surface alloys that are predicted to have high
HER activity. First, we estimate the free energy change associated with surface
segregation events; such events can cause surface solute atoms to segregate into the
bulk. Second, we determine the free energy change associated with intrasurface
transformations such as island formation and surface dealloying. Third, we evaluate
the free energy of oxygen adsorption, beginning with splitting of liquid water;
facile oxygen adsorption can lead to surface poisoning and/or oxide formation.
Finally, we estimate the likelihood that the surface alloys of interest will corrode in
acidic environments ( pH ¼ 0). For the last test, we simply take the free energies of
dissolution as reported in the electrochemical series [Lide, 1996]. These stability
tests are summarized schematically in Fig. 3.19.
Figure 3.19 Schematic representation of surface alloy stability tests. White spheres denote
adsorbed hydrogen, black spheres denote solute metal atoms, and gray spheres denote host
metal atoms. Adapted from [Greeley and Nørskov, 2007]; see this reference for more details.