Redox-Active 2D Layers Metal–Organic Framework as Ion Highways toward Fast and Reversible Ammonium-Ion Supercapacitors

The design of advanced materials for ammonium-ion (NH4+) energy storage systems is gaining momentum due to their environmental benignity and fast ion mobility. In this work, we introduce a two-dimensional cobalt metal–organic framework (2D Co-MOF) composed of redox-active organic linkers and cobalt centers, which adopts a crystallographically defined 2D layered architecture. The intrinsic planar structure offers extensive surface accessibility, uniform pore channels, and abundant redox-active sites conducive to efficient NH4+ intercalation. It exhibits a high specific capacitance of 564 F g–1 at 1 A g–1, excellent rate capability, and a capacity retention of 91% over 10,000 charge–discharge cycles. Furthermore, the ammonium-ion supercapacitors (AISc) exhibited an outstanding energy density of 42.5 Wh kg–1, maintaining 88% capacitive retention after 10,000 cycles. This study highlights the potential of crystal-engineered, redox-active 2D layered MOFs as high-performance NH4+ ion storage materials. It offers a rational strategy for developing advanced coordination frameworks for next-generation green energy storage technologies.