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

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Manganese dioxide (MnO2) offers potential for high-energy aqueous storage via a two-electron transfer mechanism.
• The dissolution step in MnO2 deposition/dissolution is kinetically challenging, especially with increasing deposit thickness.
• Developing strategies to overcome kinetic limitations is crucial for practical high-energy aqueous energy storage devices.

Purpose of the Study:

• To engineer the interface chemistry of MnO2 for improved aqueous energy storage performance.
• To address the kinetic limitations of the MnO2 dissolution step under high-mass-loading conditions.
• To achieve enhanced areal capacitance and cycling stability in energy storage devices.

Main Methods:

• Controlled hydroxylation of MnO2 surface using ammonium ion (NH4+)-mediated interface chemistry.
• Investigating the MnO2/Mn2+ conversion mechanism under high-mass-loading conditions.
• Utilizing theoretical calculations to understand the role of partial hydroxylation on electronic properties and ion adsorption.

Main Results:

• Achieved precise MnO2 configuration with controlled hydroxylation, enabling reversible MnO2/Mn2+ conversion.
• Demonstrated dual-pathway storage behaviors with a remarkable areal capacitance of 13.8 F cm-2.
• Attained sound cycling stability over 6000 cycles under high-mass-loading conditions (27.1 mg cm-2).
• Theoretical calculations confirmed that partial hydroxylation enhances electronic conduction and lowers NH4+ adsorption energy.

Conclusions:

• Controlled partial hydroxylation of MnO2 creates a favorable microenvironment for NH4+ storage and MnO2/Mn2+ conversion.
• The interfacial microenvironment plays a significant role in governing collaborative dual-pathway storage chemistry.
• Findings provide guidance for boosting high-mass-loading energy storage by optimizing interfacial chemistry.