Designing an Interlayer-Widened MoS₂-Packed Nitrogen-Rich Carbon Nanotube Core–Shell Structure for Redox-Mediated Quasi-Solid-State Supercapacitors

Herein, we present a hierarchical structure consisting of an expanded interlayer, which comprises MoS2 dispersed onto and diffused into nitrogen-doped carbon nanotubes (MoS2-CNTPPys), as an electrode material for a symmetric supercapacitor device. Structural characterizations revealed the presence of expanded interlayer spacing as evidenced by the downshifting of the X-ray diffraction (XRD) peaks representing the (002) plane and an increased interlayer distance of ∼0.82 nm. Further transmission electron microscopy (TEM) measurements showed that the MoS2 nanosheets not only covered the surface of the CNTPPy but also penetrated the CNTPPy to form a core–shell structure. The MoS2-CNTPPy electrode delivers a high specific capacitance of 275 F g–1 at 1 A g–1 in aqueous 1 M H2SO4, which is 2.5 times higher than pristine CNTPPy. The MoS2-CNTPPy symmetrical supercapacitor (SSC) devices yield a high specific capacitance of 37.4 F g–1 with a pristine poly(vinyl alcohol) (PVA)/H2SO4 electrolyte. Surprisingly, the addition of Na2MoO4 to PVA/H2SO4 as a redox electrolyte further increases the specific capacitance of MoS2-CNTPPy SSC to three times (95.14 F g–1) that of the PVA/H2SO4 electrolyte, with outstanding capacity retention (95.6% over 5000 cycles). Overall, the excellent performance of the hierarchical MoS2-CNTPPy electrode, coupled with the PVA/H2SO4/Na2MoO4 redox polymer gel electrolyte, is expected to be a potent combination for energy storage device applications.