Designing Proton‐Selective Pathway on MnO 2 Surface Toward Sustainable Protonation Electrochemistry

Manganese dioxide (MnO 2 ), known for its low‐cost, high‐theoretical capacity, and environmental friendliness, has garnered great attention in developing mild aqueous Zn‐MnO 2 batteries (AZMBs). However, Mn 2+ dissolution severely compromises cycling stability and practical viability; moreover, the ambiguity of charge storage mechanisms (e.g., Zn 2+ vs. H + ) makes the direction of strategic engineering uncertain. Herein, via advanced electron microscopy, we show that the charge storage in MnO 2 is dominated by H + intercalation rather than Zn 2+ insertion. Inspired by this finding and by referring to the recipe of proton exchange membrane, we uniformly coat individual MnO 2 particles with a proton‐selective surface, that is, Nafion, which successfully suppresses Mn 2+ dissolution as an “ion filter” and simultaneously facilitates reversible H + insertion/extraction as a “proton channel”. Therefore, the MnO 2 @Nafion cathode exhibits an outstanding specific capacity (277 mAh g −1 after 100 cycles at 0.2 A g −1 ) and remarkable cycling stability, retaining 91.7% of its capacity after 3000 cycles at 2 A g −1 . These results outperform previously reported manganese‐based cathodes, demonstrating the potential of MnO 2 @Nafion as a high‐performance and durable cathode material for AZMBs. This work rationalizes the rising endeavors in the mechanism understanding of MnO 2 ‐based aqueous battery systems and provides new insights for developing more sustainable aqueous battery materials.