A Proton-Barrier Separator Induced via Hofmeister Effect for High-Performance Electrolytic MnO₂–Zn Batteries

Electrolytic MnO₂–Zn batteries with economic advantages and high energy density are viable candidates for large-scale energy storage. However, the spontaneous reactions between acidic electrolytes and Zn metal anode cause severe proton-induced hydrogen evolution which is difficult to avoid. Herein, a proton-barrier separator (PBS) based on poly(vinyl alcohol) (PVA) is fabricated via the Hofmeister effect for preventing hydrogen evolution. Experiments and theoretical calculations demonstrate that the concentrated sulfate enables PVA chains to form a discontinuous hydrogen bond network as well as isolated hydrophilic cavities. This unique feature can effectively obstruct proton migration to impede proton-induced hydrogen evolution, but allow for fast Zn²⁺ transfer with excellent stability. Electrolytic MnO₂–Zn batteries with PBS deliver high energy retention (91.2% after 200 cycles) and largely enhanced rate performance (20 C) in a high areal capacity of 6.67 mAh cm⁻² with a very low cost ($1 m⁻²) as compared to commercial anion exchange membranes (8 C). This work sheds light on new avenues for the development of stable electrolytic MnO₂–Zn batteries by deploying PBS for preventing hydrogen evolution through a cost-effective fabrication method, which is a universal approach that can be applied to design other stable aqueous metal-ion batteries.