Potassium cation induced ionic diode blocking for a polymer of intrinsic microporosity | nafion “heterojunction” on a microhole substrate

“Heterojunction” ionic diodes based on a Nafion cation conductor and a polymer of intrinsic microporosity (PIM) interfaced at a 6 μm thickness polyethylene-terephthalate (PET) film with 20 μm diameter microhole exhibit rectification effects in cation (K⁺) flux. When combined with the precipitation reaction of potassium cations with perchlorate anions to give insoluble KClO₄ (solubility product ca. 1.05 × 10⁻² M² at 25 °C) at the PIM | Nafion interface, inversion of the rectification/diode effect occurs and the formerly “open” state changes into a “closed” state due to blocking of ion flow. The localised interfacial precipitation reaction is due to up to three orders of magnitude accumulation of K⁺ at the PIM | Nafion interface and shown to be fast and reversible. The effects of K⁺/ClO₄ ⁻ concentration and of Na⁺ interference are considered. The blocking process within the heterojunction ionic diode is suggested to be dynamic/fast and potentially useful as a diode sensor mechanism based on solubility product dependent precipitation.