Insights into the potentiometric response behaviour vs. Li + of LiFePO 4 thin films in aqueous medium

Abstract

The potentiometric response of PLD-made LiFePO 4 thin films versus Li + ions in aqueous solutions has been investigated, and a sensitivity of 54 mV dec −1 has been observed in a Li + concentration range of 1–10 −4 M. Physical and electrochemical measurements of electrodes aged in aqueous medium show a slight surface oxidation with formation of heterosite-FePO 4 that we show to be responsible for the stable potential response measured. Cyclic voltamperometry measurements operated in different Li + concentration clearly highlight the key relation between the material lithium ion insertion/de-insertion capability and its potentiometric sensing response implying a faradaic-governed sensing mechanism. Based on such a finding, selection criteria (enlisting among others the potential of the redox couple, the nature of the insertion process) are herein underlined in the search for new sensitive materials.