Dual-regulation tailoring of tunnel-structured hexagonal tungsten oxide for high-performance ammonium-ion hybrid supercapacitors

Ammonium-ion hybrid supercapacitors (A-HSCs) have emerged as promising candidates for next-generation energy storage owing to their inherent safety and environmental sustainability. Hexagonal tungsten oxide (h-WO3), with its well-defined tunnel structure, holds great promise as a negative electrode material for NH4+ storage. However, its practical application is hindered by structural instability and poor intrinsic electrical conductivity. To address these challenges, a dual-regulation strategy is proposed, integrating molybdenum (Mo) doping and NH4+ pre-intercalation to concurrently optimize the tunnel structure and electronic environment of h-WO3 (Mo-NWO). Comprehensive experimental and theoretical analyses reveal that Mo doping narrows the bandgap of WO3 and reduces the diffusion energy barrier, thereby accelerating NH4+ adsorption and diffusion. Simultaneously, NH4+ pre-intercalation stabilizes the tunnel framework via hydrogen bonding, ensuring structural reversibility. As expected, the Mo-NWO/AC electrode achieves a high areal capacitance of 13.6 F cm−2 at 5 mA cm−2 and retains 80.14 % of its capacitance after 5000 cycles, demonstrating exceptional rate capability and cycling stability. Moreover, the assembled Mn3O4//Mo-NWO/AC device delivers a high energy density of 3.41 mWh cm−2 and outstanding long-term stability (85.75 % retention after 12,000 cycles). This work provides a viable strategy for designing high-performance NH4+ storage materials and advances the development of sustainable energy storage systems.