Deprotonation and Cation Adsorption on the NiOOH/Water Interface: A Grand-Canonical First-Principles Investigation

Nickel-based oxides are highly active, cost effective materials for the oxygen evolution reaction in alkaline conditions. Recent experimental studies have revealed the importance of surface deprotonation and alkali metal cation adsorption on the activity of Ni oxide surfaces, in contact with aqueous alkaline electrolyte. As a first step to elucidate the role of the alkali adsorption for the activity, we performed first-principles electronic structure calculations to address the stable surface structures of beta-NiOOH(0001) as a function of the operating conditions in an electrochemical environment. We present a grand-canonical approach to compute the surface Pourbaix diagram of the beta-NiOOH/water interface for the processes of deprotonation and alkali metal cation adsorption. The results of this study emphasize the importance of double layer effects, including the adsorbate-induced change of surface dipole moments and the rearrangement of water molecules due to their strong interaction with the adsorbed species, for the most stable interface structure.