Fig. shows the second-order nonlinear susceptibility and the total interfacial potential as a function of externally applied potential. From -0.4 V applied to zero V applied, the total surface potential is near zero mV (± 100 mV from the -60° to -100° range in the phase relative to that of the glass:air interface), consistent with slight negative z-potentials at pH 11 and 12.5 of -12 mV and -15 mV, respectively, in 0.1 M NaNO3 (points of zero charge of nickel oxides are at or below pH 11) . We note that the total potential is sum of the Gouy-Chapman-Stern potential associated with the mobile charges (ions) and the contributions from the immobile charges (electrons bound to the molecules and ions), like from dipoles and quadrupoles . The total potential increases with increasingly positive applied potential until it plateaus near +0.8 V (±0.2