Interlayer Engineered Covalently Functionalized Graphene Oxide-Bimetallic MOF Hybrids for Efficient Ammonium-Ion Storage

Ammonium ion-based energy-storage systems are emerging as propitious alternatives to conventional metal-ion devices due to their cost-effectiveness, environmental friendliness, and ionic mobility. Herein, we report the design and fabrication of a series of covalently functionalized graphene oxide (GOBDC)/Mn–Ni bimetallic metal–organic framework heterostructures (BDC, 1,4-benzenedicarboxylic acid) for efficient NH4+ storage. The direct covalent linkage spacer results in interlayer expansion and thus preserves the effective surface area by preventing the restacking between the layers. Among the hybrids, MNG (Mn–Ni MOF:GOBDC) 1:2 demonstrated the highest specific capacitance of 265 F g–1 at 0.5 A g–1 and superior rate capability. An NH4+ asymmetric supercapacitor comprising MNG 1:2 as the positive electrode and molybdenum disulfide (MoS2) as the negative electrode exhibited an energy density of 14.6 Wh kg–1 along with a good capacitance retention. This study highlights a strategic approach for interlayer engineering in MOF/GO systems, offering a viable route for next-generation NH4+-based energy-storage devices.