Insights into the potentiometric response behaviour vs. Li+ of LiFePO4 thin films in aqueous medium

The potentiometric response of PLD-made LiFePO4 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-FePO4 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.