Grand-canonical approach. Our goal is to explore the thermodynamic stability of the NiOOH(0001)/water system for the processes of deprotonation and cation adsorption under varying electrode potential and pH. This can be achieved by employing the combination of periodic DFT calculations and the grandcanonical approach based on the computational hydrogen electrode (CHE) . In this approach, the change in the Gibbs free energy due to the formation of interface structure, normalized by the unit area, is given by,