Computational Study to Assess the Influence of Elastic Strains on the Catalytic Activity of Au Surfaces for the HER and ORR Including the Effect of Coverage.

The influence of different surface coverages and the effect of biaxial elastic strains on the catalytic properties for the hydrogen evolution reaction (HER) and the oxygen reduction reaction (ORR) were analyzed using the example of a Au fcc(111) surface. The adsorption energies of H, O, and OH for the corresponding intermediate reactions were obtained by density functional theory calculations. While for H and O, the adsorption energy increased with coverage, for OH, the lowest adsorption energy was observed at 0.5 ML. Then, after elastic strains were applied, the trends observed for the unstrained slab were maintained for the three adsorbates. Although neither tension nor compression modified the optimum coverage, they did change the differences in relative energies. This is considered to be a consequence of the deformations promoted on the surface. Finally, the catalytic activity of the HER and ORR was computed for the distinct coverages and elastic strains. Catalytic activity plots confirmed for both reactions that the more favorable adsorption energy promoted by tensile strains leads to an increment of the activity and that the most active coverage is 0.25 ML. Furthermore, an analysis of the free energies of each step of the dissociative mechanism of the ORR unveils that both coverage and elastic strains can modify the rate-limiting step and, therefore, the catalytic activity of a material. The results presented in this work provide ample characterization of the Au fcc(111) surface as a catalyst for the HER and ORR and offer, for the first time, an analysis of the influence of both coverage and elastic strain engineering on the catalytic activity.