Counterion triple layer in solid/solution interface: Stirring and temperature effects on pH measurements

This paper reports on the pH glass electrode potential based on the double- capacitor theory and the discovery of a mobile counterion triple layer next to the double layer to explain the electrode potential changes caused by s tirring and temperature increase. This mobile triple layer behaves like a r ubberband, which may be loosened by stirring (or agitation) and temperature increase and tightened after stirring stops or temperature lowers. Stirrin g and temperature exert different effects on the potential of the pH and SC E electrodes via their different mechanisms. In contrast to the past, resul ts reported here were obtained from experiments designed with the glass ele ctrode and SCE in separate beakers connected with a conducting wire, so tha t one electrode could be stirred while keeping the other unstirred. There i s a weak charge attraction between the double and triple layers, not a stro ng covalent bonding for complexation, so that the latter can be removed by stirring or temperature increase. In light of present results and the new c oncept, the Boltzmann equation has been modified to include the net charge density and the triple-layer potential. The counterion triple layer concept will have a tremendous impact on our understanding of the interface struct ure and properties, and stimulate further studies and applications of ion-s elective electrodes. (C) 2001 Academic Press.