A highly stable membrane with hierarchical structure for wide pH range flow batteries

A membrane with high stability and ion conductivity in wide pH range is essential for energy storage devices. Here, we report a novel membrane with hierarchical core–shell structure, which demonstrates high stability and ion conductivity, simultaneously under a wide pH range applications. Spectral characterizations and theoretical calculation indicate that the non-solvent induces the chain segment configuration and eventually leads to polymer–polymer phase separation, thus forming hierarchical porous core–shell structure. Benefiting from this structure, an acidic vanadium flow battery (VFB) with such a membrane shows excellent performance over 400 cycles with an energy efficiency (EE) of above 81% at current density of 120 mA cm−2 and an alkaline zinc-iron flow battery (AZIFB) delivers a cycling stability for more than 200 cycles at 160 mA cm−2, along with an EE of above 82%. This paper provides a cost-effective and simple way to fabricate membranes with high performance for variety of energy-related devices.