Fabrication of VOOH hollow spheres for ammonium-ion supercapacitors

The performance of vanadium hydroxide (VOOH) in ammonium-ion (NH4+) storage is currently unknown and attractive. Herein, low crystallinity VOOH hollow spheres are synthesized by a template-free hydrothermal method for investigating NH4+-storage properties. The hollow structure of VOOH, unlike the precursor V(OH)(2)NH2 solid spheres, promotes NH4+-insertion/extraction, resulting in improved NH4+-storage performance. The specific capacitance of VOOH hollow spheres is 221 F<middle dot>g(-1) (265 C<middle dot>g(-1)) at 0.1 A<middle dot>g(-1). The quasi-solid-state VOOH//AC hybrid supercapacitor (HSC) device exhibits the capacitance of 67 mF<middle dot>cm(-2) at 0.147 mA<middle dot>cm(-2). The above results indicate that VOOH aims to become an excellent electrode material for NH4+-storage.