Ammonium-Ion Storage Using Electrodeposited Manganese Oxides.

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Ammonium ions (NH₄⁺) are emerging as viable charge carriers for aqueous rechargeable batteries.
• Manganese oxide (MnO_x) is investigated as a potential host material for NH₄⁺ storage.

Purpose of the Study:

• To explore the NH₄⁺ storage chemistry of electrodeposited manganese oxide (MnO_x) for the first time.
• To understand the role of electrolyte concentration and material transformations in NH₄⁺ storage within MnO_x.
• To elucidate the mechanism of NH₄⁺ insertion/deinsertion in layered MnO_x.

Main Methods:

• Electrochemical deposition of MnO_x.
• Charge/discharge cycling in ammonium acetate (NH₄ Ac) electrolyte.
• Spectroscopy studies (e.g., XRD, XPS) to analyze material transformations.
• Theoretical calculations to support mechanism elucidation.

Main Results:

• MnO_x undergoes morphology and phase transformations during cycling in NH₄ Ac.
• A transformed layered MnO_x structure delivers a high specific capacity of 176 mAh g^-1 at 0.5 A g^-1.
• The material exhibits excellent cycling stability over 10,000 cycles in 0.5 M NH₄ Ac.
• Evidence suggests solid-solution behavior and NH₄⁺ migration in layered MnO_x.
• Spectroscopy and calculations reveal reversible NH₄⁺ insertion/deinsertion linked to hydrogen bonding.

Conclusions:

• Electrodeposited MnO_x is a promising prototype for NH₄⁺-based aqueous rechargeable batteries.
• The study provides fundamental insights into the NH₄⁺ storage mechanism in metal oxides.
• Optimized NH₄⁺ storage in MnO_x is dependent on electrolyte concentration and achieved through structural transformations.