Demystifying Tunneled Niobium Molybdenum Oxide With Near‐Zero‐Strain for Hydrogen Bond‐Assisted Ammonium Ion Storage

ABSTRACT Aqueous ammonium‐ion batteries (AAIBs) have emerged as compelling contenders for sustainable large‐scale energy storage. However, the advancement is significantly impeded by the dearth of energetic electrode materials and unclear relationship between diffusion kinetics and channel size. Herein, we present a second‐level prepared 3D tunnel‐structured binary transition metal oxide—niobium molybdenum oxide (Nb 2 Mo 3 O 14 )—as a high‐performance anode material for AAIBs. Comparative electrochemical evaluations across various metal ion systems (Li + , Na + , K + , Mg 2+ , Ca 2+ ) reveal that Nb 2 Mo 3 O 14 exhibits superior storage performance specifically for NH 4 + ions with a near‐zero‐strain characteristic. In ammonium acetate electrolyte, Nb 2 Mo 3 O 14 electrode delivers a high specific capacity of 210.9 mAh g −1 , at a current density of 0.2 A g −1 , accompanied by an exceptional capacity retention of 88.9% after 14,000 cycles at 1 A g −1 . Furthermore, experimental and theoretical results demonstrate that the promotion of NH 4 ⁺ storage under hydrogen bond chemistry is dependent on the matched size of the tunnels. The relatively weak hydrogen bonds promote the efficient motion of bulky NH 4 + in 3D tunneled Nb 2 Mo 3 O 14 . These findings highlight 3D tunnel‐like binary transition metal oxides as valuable models for high‐performance ammonium‐ion storage, paving the way for the development of advanced AAIBs.