As the interfacial NiOH, NiO -, and NiOH2 + groups cannot flip their net orientation, we subtract 𝜒 ?#@ (;) (1.1 x 10 -22 x 10 -22 m 2 V -1 ) from the 𝜒 (;) values obtained at each applied potential to compute the change in the second-order nonlinear susceptibility, ∆𝜒 (;) . The aim is to estimate the 𝜒 (;) contribution from the mobile Stern lay water molecules, which can change their orientation distribution in response to the applied potential. When Φ(0) !"! is zero, we find that ∆𝜒 (;) is near zero (Fig. ), which indicates a largely isotropic arrangement of the Stern layer water molecules, in which an approximately equal number of interfacial water molecules point their dipole moments up vs down or are all fully disordered. In other words, 𝒩 . <a (2) >=0, where 𝒩 is the total number of Stern layer water molecules and . <a (2) > is water's orientationally averaged molecular hyperpolarizability), consistent with the small negative z-potential at pH 12 .