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

Abstract

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.

Proton-Trapping Agent for Mitigating Hydrogen Evolution Corrosion of Zn for an Electrolytic MnO2/Zn Battery

“…To distinguish the currents of Zn plating/stripping and HEC, the LSV test was implemented in a mixed solution composed of H 2 SO 4 , Na 2 SO 4 , NaAc, and NaCl. The corresponding corrosion currents were evaluated using a Tafel extrapolation approach. , As shown in Figure f, the fitted corrosion currents of Zn electrodes in the PTA-regulated electrolytes (0.621 mA cm –2 for 20% NaAc electrolyte, 0.681 mA cm –2 for 60% NaAc electrolyte, and 0.782 mA cm –2 for 100% NaAc electrolyte) were 6–8 times lower than that of the Zn electrode in the Na 2 SO 4 electrolyte (4.931 mA cm –2 ). Furthermore, the working mechanisms of the PTAs were investigated by DFT calculation.…”

“…During the discharge process, the dissolution reaction of MnO 2 requires protons, so that an acidic electrolyte with plenty of protons can facilitate the dissolution of MnO 2 , improving the reversibility of the Mn 2+ /MnO 2 reaction. , However, the preferred electrolyte environment for the Zn anode is a proton-free condition . Excessive protons in the electrolyte not only cause severe HEC on the Zn anode (Figure and eq ) but also increase the activity of the competitive reaction of H + /H 2 during the charge process. , Besides, the side reactions of HEC and the competitive reaction of H + /H 2 will, in turn, cause a decrease in the proton concentration in the electrolyte, which deteriorates the reversibility of the Mn 2+ /MnO 2 reaction.…”

High‐Capacity Zinc Anode with 96 % Utilization Rate Enabled by Solvation Structure Design

“…[17,18,26] These side effects result in low Coulombic efficiency (CE), poor cycle stability and low Zn utilization rate (ZUR) of the Zn anode. [12,19,[27][28][29] To solve the issues of Zn anodes in AZBs, various strategies have been proposed to improve the reversibility of Zn anodes through regulation of the electrode-electrolyte interface [25,[30][31][32] via electrode modification and electrolyte optimization. For instance, Zhi et al achieved a cycle life of 700 h at 3 mAh cm À 2 by designing a gradient fluorinated alloy for Zn anode.…”

Nanoscale Ultrafine Zinc Metal Anodes for High Stability Aqueous Zinc Ion Batteries

“…This is important as many of the problems associated with AZBs are exacerbated by the higher reactivity of metallic Zn in water-based electrolytes (−0.762 V vs standard hydrogen electrode (SHE)). , According to the Nernst equation (Δ G m = − nFE θ ), the Gibbs free-energy (Δ G m = −147 kJ mol –1 ) of the reaction (Zn + 2H + = Zn 2+ + H 2 ) is < 0, meaning the spontaneity of Zn metal corrosion in zinc salt solutions triggers a series of side reactions, including HER and inert byproducts (eqs s1 and s2 in Figure S1a). Our prior work , explored the use of a passivation layer to alter electrolyte surface tension, impede proton induced HER and protect the Zn metal from corrosion. But a simple and scalable method to controllably modulate electrolyte surface free energy and inhibit the activity of metallic zinc, thereby reducing side reactions and promoting uniform zinc deposition, is still required.…”