Potentiometric measurements and impedance characteristics of Li0.30La0.57TiO3 membrane in lithium anhydrous solutions

The potentiometric response of the Li+ ion-selective electrode based on the fast ion conductor Li3xLa2/3−xTiO3 (x = 0.10) membrane (named LLTO) as well as the impedance of the LLTO membrane/Li+ solution in either anhydrous or hydrated PC solvent have been carried out. A four-electrode configuration has been used for the investigation of the interfacial phenomenon. It has been shown that the LLTO membrane can be used to detect the Li+ activity in anhydrous solutions through a Li+ ion exchange mechanism. The potentiometric response shows a Nernstian behavior with a Li+ sensitivity of −72 mV/decade at 25 °C. This high sensitivity can be correlated to a localised hydroxylation of the oxide surface with the residual water present in the solution in combination to the Li+ exchange reaction. An apparent standard current density of 12 μA/cm2 and a charge-transfer coefficient of 0.29 have been determined. However, as water content in the electrolyte increases, the activity domain of the detection decreases to lead to the disappearance of the Li+ ion exchange mechanism in Li+ aqueous solution. This annihilation of the exchange process may be due to the predominant catalytic reaction of [Ti–O]− with H2O and/or to the formation of a water layer on the oxide surface.