Mo modulating the structure of monoclinic vanadium dioxide boosting the aqueous ammonium-ion storage for...

Supercapacitors (SCs) using ammonium-ion (NH₄⁺) as the charge carrier (NH₄⁺-SCs) have attracted continuous attention and vanadium-based materials are proved to have high-efficient NH₄⁺-storage properties. Monoclinic vanadium dioxide, VO₂(B), as an anode material applied to SCs has been rarely reported and modulating its electronic structure for boosted NH₄⁺-storage is full of challenge. In this work, molybdenum-doped VO₂(B) (Mo-doped VO₂(B)) is designed and synthesize to enhance its NH₄⁺-storage. The introduction of Mo atom into the crystal structure of VO₂(B) can modulate its crystal structure and bring in some defects. Experimental results manifest that Mo-doped VO₂(B) with 2 % Mo-doping shows the best electrochemical properties. Mo-doped VO₂(B) achieves the specific capacitance of 1403 F g^-1 (390 mAh g^-1) at 0.1 A g^-1 and the capacitance retention of about 98 % after 5000 cycle, superior to that of VO₂(B) (893 F g^-1, 248 mAh g^-1 at 0.1 A g^-1 and 60 % capacitance retention. The hybrid supercapacitor (HSC) assembled by Mo-doped VO₂(B) and active carbon delivers good electrochemical performance with the energy density of 38.6 Wh kg^-1 at power density of 208.3 W kg^-1. This work proves that the Mo-doping is an efficient strategy for boosted NH₄⁺-storage of VO₂(B) and this strategy is like a Chinese idiom "like adding wings to a tiger" to guide the design of electrode materials for high-efficient NH₄⁺-storage.