DFT-MD of the (110)-Co3O4 cobalt oxide semiconductor in contact with liquid water, preliminary chemical and physical insights into the electrochemical environment.

Abstract

Within the general context of the electrochemical oxygen evolution reaction of the water oxidation/electrolysis, we focus on one essential aspect of electrochemical interfaces, i.e., the comprehension of the interaction and organisation of liquid water at the (semiconductor) (110)-Co3O4 surface using density functional theory-molecular dynamics simulations. A detailed characterization of the chemical and physical properties of the aqueous interface is provided in terms of structure, dynamics, electric field, work function, and spectroscopy, as a preliminary step into the modelling of the (110)-Co3O4 aqueous surface in more relevant electrochemical conditions. The water at the aqueous B-termination is, in particular, shown more dynamical than that at the A-termination and more "undisciplined": the water is indeed mostly an HB-acceptor with the solid, with an orientation of their dipole moments found opposite the field generated by the negative surface charge. At both aqueous interfaces, the work function is twice lower than that at the bare (non-hydroxylated) surfaces. The SFG (Sum Frequency Generation) spectroscopy is shown dominated by the water in the diffuse layer, while the SFG signal from the binding interfacial layer reflects the single orientation of water at the aqueous A-termination and the two orientations of water at the aqueous B-termination.