Template-free synthesis of ordered mesoporous NiO/poly(sodium-4-styrene sulfonate) functionalized carbon nanotubes composite for electrochemical capacitors

We report the first example of a practical and efficient template-free strategy for synthesizing ordered mesoporous NiO/poly(sodium-4-styrene sulfonate) (PSS) functionalized carbon nanotubes (FCNTs) composites by calcining a Ni(OH)₂/FCNTs precursor prepared by refluxing an alkaline solution of Ni(NH₃) _x ²⁺ and FCNTs at 97 °C for 1 h. The morphology and structure were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Thermal decomposition of the precursor results in the formation of ordered mesoporous NiO/FCNTs composite (ca. 48 wt% NiO) with large specific surface area. Due to its enhanced electronic conductivity and hierarchical (meso- and macro-) porosity, composite simultaneously meets the three requirements for energy storage in electrochemical capacitors at high rate, namely, good electron conductivity, highly accessibleelectrochemical surface areas owing to the existence of mesopores, and efficient mass transport from the macropores. Electrochemical data demonstrated that the ordered mesoporous NiO/FCNTs composite is capable of delivering a specific capacitance (SC) of 526 F/g at 1 A/g and a SC of 439 F/g even at 6 A/g, and show a degradation of only ca. 6% in SC after 2000 continuous charge/discharge cycles.