Interface-Engineered 2H-MoS₂/MXene Heterostructures for High-Performance Ammonium-Ion Hybrid Supercapacitors

Aqueous ammonium-ion hybrid supercapacitors (AAHSCs) have received significant interest due to their environmental friendliness and excellent electrochemical performance. 2D transition metal carbides and nitrides (MXenes) are promising cathode candidates for AAHSCs owing to their high conductivity and redox activity. However, their tendency to restack severely limits ion accessibility and rate performance. To address this challenge, vertically aligned 2H-MoS₂ nanosheets are grown in situ on Ti₃C₂T_x MXene to form interfacial heterostructures (HS-2H-MS@MXene). The heterostructure interface forms a stable built-in electric field (BIEF), which accelerates the transport of electric charge driven by the electric field force. The perpendicular orientation of 2H-MoS₂ nanosheets effectively reduces charge transfer resistance, increasing surface area and providing abundant active sites for NH₄⁺ storage. As a single electrode, HS-2H-MS@MXene delivers a high specific capacitance of 722.13 F g⁻¹ at 1 A g⁻¹, excellent rate capability (61.6% retention at 20 A g⁻¹), and long-term cycling stability (90.1% retention after 5 000 cycles). When coupled with activated carbon (AC) in a full–cell configuration, the device achieves an energy density of 51.1 Wh kg⁻¹ at a power density of 750.6 W kg⁻¹, maintaining 95.6% capacitance after 10,000 cycles. This work provides an effective strategy for developing advanced cathode materials for next-generation AAHSCs.