Anion Mobility Renormalization Reveals Backbone‐Dependent Tortuosity in Anion Exchange Membranes

Understanding ion transport in anion exchange membranes (AEMs) requires establishing quantitative links between polymer chemistry, nanoscale morphology, and the effective tortuosity of hydrated ion‐conducting pathways. In this work, we analyze a broad set of literature data for polysulfone‐ (PSU) and poly(2,6‐dimethyl‐1,4‐phenylene oxide)‐based (PPO) AEMs to generalize a mobility‐based framework for extracting membrane tortuosity. By combining ion exchange capacity, water uptake, and hydroxide conductivity to deduce the concentration‐dependent anion mobility, we determine the anion mobility at infinite dilution and compare it to its value in pure water to obtain the porosity/tortuosity ratio (π/τ). Using the Bruggeman relation, we derive tortuosity values for a wide range of AEMs and show that PPO‐based membranes exhibit significantly lower tortuosity (τ approximately 1.2) than PSU‐based analogs (τ approximately 1.6). This difference arises from the higher intrinsic hydrophilicity of PSU, which suppresses hydrophilic–hydrophobic nanophase separation and yields narrower, more tortuous aqueous channels. The exponential decrease of anion mobility with increasing anion concentration further reflects restricted connectivity within these domains. These results highlight backbone polarity as a key determinant of nanophase separation and tortuosity, providing actionable design rules for next‐generation AEMs with enhanced ion transport and structural stability.