The adsorption of alcohols on strained Pt3Ni(111) substrates: a density functional investigation within the D3 van der Waals correction

Abstract

Experimental and theoretical studies have suggested the use of strain effects to design efficient catalysts for direct alcohol fuel cells. However, our atomistic understanding of the adsorption of alcohols on strained transition-metal (TM) catalysts is still far from satisfactory. Here, we report an ab initio investigation based on density functional theory within the van der Waals D3 correction to explore the adsorption properties of methanol, ethanol and glycerol on Pt₃Ni(111) alloys under different conditions. For that, we selected five TM substrates, namely, (i) Ni(111), (ii) Pt₁₂Ni₄/Pt₁₂Ni₄/Ni(111) (compressive strain), (iii) Pt₁₆/Pt₈Ni₈/Pt₃Ni(111) (without strain), (iv) Pt₁₆/Pt₈Ni₈/Pt(111) (tensile strain) and (v) Pt(111). As expected, the physical and chemical properties of the Pt₃Ni thin-layers are affected by the strain induced by the underlayer TM substrate, and hence, we can tune the adsorption properties of alcohols. In general, the magnitude of the alcohol adsorption energy increases in the following order Pt₁₆/Pt₈Ni₈/Pt₃Ni(111) < Pt₁₆/Pt₈Ni₈/Pt(111) < Pt₁₂Ni₄/Pt₁₂Ni₄/Ni(111), which correlates with the d-band center and the effective charge on the adsorption sites, i.e., the coulombic contribution plays an important role in the adsorption. Structural and electronic density analyses indicate that, upon adsorption, the O–H and C–H bonds weaken and their breaking should be the first steps in the decomposition of alcohols. From the Bader charge analysis, we found that the TM atom directly below the bonding O loses charge to neighboring atoms, which polarizes the surface and changes the substrate work function. Although a significant enhancement of energetic and structural properties was found, the addition of the D3 correction does not change our qualitative results except for improving the dependence of the adsorption energy with the alcohol size.