Role of OH--ions in surface sites

One might here wonder/object, but what about OH--ions, especially at high pH, don’t they want to absorb? Take over the role of H+ and compete with H+ in occupying surface sites? We also find this a captivating question. We know we should not think like this, instead the OH--ion can and should be kept away from this analysis, it is only about the H+-ion and in the end this is only about thermodynamics. But it does not feel very convincing, admittedly. The (conceptual) problems with water self dissociation are manifold indeed (in a wholly different context: we know OH- and H+ are ions that are hydrated themselves, i.e., in a transport problem we must give them a volume. This would imply that the water self dissociation reaction creates solutes with volume out of nothing .. Their association, makes volume ‘disappear’ .. Via excess functions such as Carnahan-Starling, adding salt and increasing the osmotic pressure, would then ‘push’ on the water association equilibrium to push it ‘back to water’. (Though intriguing prospects, in reality this will not play a major role as only very near ‘pH 7’ do both ions exist simultaneously. Away from pH 7 we already have only one of the two types of ions in reality. In a charged membrane, in which we can have the high osmotic pressures for this effect to occur, we have a high membrane charge, and thus we already have only H+ or OH-.