Effect of non-stoichiometry of KxFe[Fe(CN)6] as inner solid-contact layer on the potential response of all-solid-state potassium ion-selective electrodes

Abstract

In the current study, we synthesized Prussian blue analogues, KxFe[Fe(CN)6] (KFeHCF) having different [Fe(CN)6] vacancies, potassium contents (x), and crystal system, and investigated the effect of the difference on ion-sensor performance by using the KFeHCF as the solid-contact layer of all-solid-state ion-selective electrodes (ASS-ISEs). Cubic-KFeHCF shows slopy potential curve during galvanostatic K+ extraction/insertion because the reaction proceeds in single-phase regime, which deteriorates the long-term potential stability as internal reference electrode of ASS-ISEs. On the other hand, monoclinic-KFeHCF exhibits flat potential plateau during galvanostatic K+ extraction/insertion through two-phase reaction, providing superior potential stability. While the potential of an ISE is primarily determined by the membrane potential of the ion-sensitive membrane, it is discovered that the different crystal structure of the KFeHCF introduced into the solid-contact layer affects the long-term stability of ISE.