Due to the rapid development of energy storage systems from the goal of carbon neutrality, rechargeable aqueous Zn-MnO 2 batteries have attracted growing attention. While the controversy surrounding various mechanisms, such as Zn 2+ insertion, Zn 2+ /H + co-insertion and Mn dissolution/deposition, leads to limitation of MnO 2 cathodes, especially for the β-MnO 2 . Though showing promising performance in recent works, the reaction process and influence factors of β-MnO 2 cathodes are still under debate. In this work, a complete MnO 2 /Mn 2+ redox chemistry is proposed to explain the abnormal electrochemical behaviors of β-MnO 2 cathodes, which indicates the reversible dissolution/deposition of layered manganese oxides appears after the initial MnO 2 dissolution reaction. The revealed effects of interfacial environment in regulating the electrochemical reactions also provide a new perspective for studying the working mechanism of aqueous Zn-MnO 2 batteries. Besides, the high specific capacity shown in the MnO 2 /Mn 2+ redox chemistry also contributes to designing high-performance cathodes for AZIBs.
Aqueous batteries are facing big challenges in the context of low working voltages and energy density, which are dictated by the narrow electrochemical window of aqueous electrolytes and low specific capacities of traditional intercalation-type electrodes, even though they usually represent high safety, low cost, and simple maintenance. For the first time, this work demonstrates a record high-energy-density (1503 Wh kg −1 calculated from the cathode active material) aqueous battery system that derives from a novel electrolyte design to expand the electrochemical window of electrolyte to 3 V and two high-specific-capacity electrode reactions. An acid-alkaline dual electrolyte separated by an ion-selective membrane enables two dissolution/deposition electrode redox reactions of MnO 2 /Mn 2+ and Zn/Zn(OH) 4 2− with theoretical specific capacities of 616 and 820 mAh g −1 , respectively. The newly proposed Zn–Mn 2+ aqueous battery shows a high Coulombic efficiency of 98.4% and cycling stability of 97.5% of discharge capacity retention for 1500 cycles. Furthermore, in the flow battery based on Zn–Mn 2+ pairs, more excellent stability of 99.5% of discharge capacity retention for 6000 cycles is achieved due to greatly improved reversibility of the Zn anode. This work provides a new path for the development of novel aqueous batteries with high voltage and energy density.
Proton exchange membrane water electrolysis (PEMWE) holds substantial promise for effectively utilizing renewable energy to produce green hydrogen. However, it faces critical durability challenges due to acid-driven catalyst degradation under intermittent renewable power. Here, this study reports a dynamic dissolution-deposition equilibrium that achieves exceptional hydrogen evolution reaction (HER) stability through rational design of a high-entropy alloy-derived architecture. Dealloying FeCoNiNbPt HEA creates a porous scaffold with dual-functional components: an amorphous NbOx buffer suppressing metal dissolution, while multicomponent Pt 3 (FeCoNi) nanocrystals synergistically enhancing HER activity (137 mV@1 A cm −2 , 2.5 × lower than Pt/C) that thermodynamically favors redeposition. This dynamic self-adaptive mechanism maintains equilibrium under harsh operating conditions, demonstrating exceptional durability (>2200 h @1 A cm −2 and 1 000 000 cycles). The self-supported catalysts can be easily mass-produced with 8.87 wt.% Pt loading (60% reduction vs Pt/C), indicating its industrial applicability. The equilibrium-driven design paradigm opens new avenues for industrial proton-exchange-membrane devices operating under fluctuating power.
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