Catalytic dissociation of a water molecule on the (1 1 1) surfaces of Pt0.5Ni0.5 bimetal: Density functional theory (DFT) study

Abstract

One of the biggest challenges for the transition towards renewable energy sources today is the development of affordable platinum (Pt) containing bifunctional bimetals as electrode materials for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Recently, the optimal ratio of a bimetal consisting of Pt and nickel (Ni) was studied. This study included the impact of bimetal mixing on the electronic and magnetic properties of the bimetal. However, the catalytic properties of the bimetal have not been studied and compared to that of the pure metals. In this study, spin-polarized density functional theory calculations were employed to investigate the surface properties of Pt0.5Ni0.5 bimetallic surfaces. Relaxation of the surface terminations showed that the 1.5(111) and 0.5(111) surface terminations are energetically the most favourable surfaces, while the 2.0(111) surface termination is energetically the least favourable surface. However, the 2.0(111) surface termination is energetically more favourable than pure Ni. The adsorption of single water (H2O) molecule onto various (111) surface terminations (0.0, 0.5, 1.0, 1.5 and 2.0) of the bimetallic surfaces was investigated. The H2O molecule was adsorbed onto the atop site in the most stable orientation, namely parallel to the surface (a flat geometry). The d-band centre revealed that the bonding of the H2O molecule on the 0.5(111) surface termination is stronger than on the pure Pt surface but weaker than on the pure Ni surface. Bond elongation of the OH bonds and an increase in the HOH bond angle were observed in the H2O molecule adsorbed on the 0.5(111) surface. The results show that the 1.5(111) surface termination, where the water adsorbs to a Ni atom, could potentially be used as an electrocatalyst for the water-splitting reaction. However, experimental data are needed to confirm these results.