Continuous porous aromatic framework membranes with acid-/base-induced reversible isomerization for switchable ion conductivity

Abstract

Stimuli-responsive ion conductor materials are highly sought after in the fields of biological systems, clean energy, and smart devices. However, it remains a huge challenge to achieve acid/base switchable ion conductors owing to their stringent requirements of structural responsive behaviors, high stability and porosity. In this study, porous aromatic frameworks (PAFs) are utilized as a favorable platform to successfully design and prepare ion conductive powders and its continuous membranes based on a commercially available pH indicator. Interestingly, these PAFs possessed structural reversibility in response to acidic and alkaline environments, followed by an apparent ion-conducting switch of about 4 orders of magnitude (from 3.36 × 10⁻⁷ S cm⁻¹ to 4.59 × 10⁻³ S cm⁻¹) under the conditions of 25 °C and 98% RH. Moreover, the continuous PAF membrane exhibited an ultrahigh ion conductivity of 7.29 × 10⁻¹ S cm⁻¹ after 1 mol per L NaOH treatment and good acid/base switchable cycle stability. To our knowledge, this is the first report on exploring ion-conductive porous frameworks and continuous membranes that dynamically respond to acid/base chemical stimuli. This work provides a new research strategy for the application of ion conductors as so-called “smart materials” even in extremely harsh chemical environments.