Tailored design of an oxygen-rich stable Co-MOF integrated with MXene nanofibers as an advanced heterostructure for high-performance ammonium-ion supercapacitors

Ammonium ions (NH₄ ⁺) are promising non-metallic charge carriers for sustainable and cost-effective advanced electrochemical energy storage. However, the development of electrode materials with well-defined structural features to facilitate rapid NH₄ ⁺ diffusion kinetics remains a significant challenge. In this study, we demonstrate the design of a novel oxygen-rich cobalt-based metal-organic framework (Co-MOF) showcasing unique (O₄-CoN₂) coordination geometry. This distinctive structure of Co-MOF contributes to high stability, abundant active sites, and enhanced electrochemical performance. To further boost performance, Co-MOF nanoflowers were uniformly integrated with Ti₃C₂T _<i>x</i> MXene carbonized nanofibers (MXCNF), forming advanced Co-MOF@MXCNF heterostructures. These heterostructures exhibit a highly porous, nanofibrous morphology, delivering a notable specific capacitance of 980 F g^-1 at a current density of 1 A g^-1 and excellent cycling stability, retaining 91.1% capacitance after 16 000 cycles. When paired with a porous MXCNF anode, the ammonium-ion hybrid supercapacitors (AIHSCs) delivered an impressive energy density of 41.5 mW h kg^-1 with the corresponding power density of 800 mW kg^-1, retaining 87% of their capacitance after 16 000 cycles. This study highlights the synergistic advantages of integrating stable MOFs with MXene nanofibers for remarkable ammonium-ion storage. It establishes a framework for designing high-performance energy storage materials, paving the way for next-generation sustainable energy storage devices.