Ammonium-Ion Storage Using Electrodeposited Manganese Oxides.

NH ions as charge carriers show potential for aqueous rechargeable batteries. Studied here for the first time is the NH -storage chemistry using electrodeposited manganese oxide (MnO ). MnO experiences morphology and phase transformations during charge/discharge in dilute ammonium acetate (NH Ac) electrolyte. The NH Ac concentration plays an important role in NH storage for MnO . The transformed MnO with a layered structure delivers a high specific capacity (176 mAh g ) at a current density of 0.5 A g , and exhibits good cycling stability over 10 000 cycles in 0.5 M NH Ac, outperforming the state-of-the-art NH hosting materials. Experimental results suggest a solid-solution behavior associated with NH migration in layered MnO . Spectroscopy studies and theoretical calculations show that the reversible NH insertion/deinsertion is accompanied by hydrogen-bond formation/breaking between NH and the MnO layers. These findings provide a new prototype (i.e., layered MnO ) for NH -based energy storage and contributes to the fundamental understanding of the NH -storage mechanism for metal oxides.