Electrocatalysis and Catalyst Screening from Density Functional Theory Calculations - Fuel Cell Catalysis: A Surface Science Approach - page 80

Figure 3.16 Volcano plot for the hydrogen evolution reaction (HER) for various pure metals
and metal overlayers. Values are calculated at 1 bar of H 2 (298K) and at a surface hydrogen cov-
erage 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.

3.6.5 Surface Alloys

Having established a descriptor and a reliable computational procedure for determining
HER activity trends, we are in a position to begin our computational catalyst search. To
start the search, we create a pool of alloys that we will later analyze for stability and
activity properties. For our present purposes, we selected a pool of binary transition
metal surface alloys. These alloys are composed of a homogeneous, pure substrate
element (also called the “host”), with an alloying element (the “solute”) incorporated
into the surface layer of the host. Solute coverages of 3 ,

2

3 , and 1 ML are considered for
each solute/host pair, and, in all cases, the lattice constant of the alloy is naturally con-
strained to adopt the lattice constant of the pure host element (additional computational
details are given in [Greeley and Nørskov, 2007]). In total, binary combinations of 16
elements (Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, Au, Re, Cd, As, Sb, and Bi) are con-
sidered; these metals are chosen because they are not thermodynamically favored to
form bulk oxides in water at zero applied potential with respect to a standard hydrogen
electrode. In total, 736 such surface alloys are considered.

3.6.6 Results of Combinatorial DFT Calculations

Using periodic DFT calculations [Greeley and Nørskov, 2007], we calculate the value of
the HER descriptor DG H on all of the surface alloys of interest. The results are