Potentiometric measurements and impedance characteristics of Li0.30La0.57TiO3 membrane in lithium anhydrous solutions
Quoc Nghi Pham, Odile Bohnkea and Claude Bohnke
Electrochimica Acta, Volume 51, Issue 27, 25 August 2006, Pages 6186-6193
Abstract
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.