NH₄ ⁺-mediated interfacial chemistry for collaborative dual-pathway high-mass-loading energy storage

The deposition/dissolution mechanism of MnO₂ with two-electron transfer is promising for high-energy aqueous energy storage. However, this reaction is severely limited by the kinetically unfavorable dissolution step, a challenge that is greatly exacerbated as the deposit thickens. Herein, by refining NH₄ ⁺-mediated interface chemistry, we achieve the precise configuration of MnO₂ with controlled hydroxylation, which guides the reversible MnO₂/Mn²⁺ conversion under high-mass-loading conditions. The partially hydroxylated surface further creates a kinetically favorable microenvironment for NH₄ ⁺ storage, ultimately leading to energetic dual-pathway storage behaviors. This enables a remarkable areal capacitance of 13.8 F cm^-2 and sound cycling stability over 6000 cycles under high-mass-loading conditions (27.1 mg cm^-2). Theoretical calculations reveal that the controlled partial hydroxylation of MnO₂ promotes electronic conduction and lowers the adsorption energy of NH₄ ⁺, outperforming both highly hydroxylated and pure MnO₂. The adsorbed NH₄ ⁺ delivers intimate interfacial electronic interaction with partially hydroxylated MnO₂ to trigger local charge redistribution, substantially lowering the MnO₂/Mn²⁺ conversion energy barrier of the nonspontaneous rate-determining step at the NH₄ ⁺-proximal site. Our findings highlight the significance of the interfacial microenvironment governing the collaborative dual-pathway storage chemistry, which provides guidance for boosting high-mass-loading energy storage.