Freestanding XMoO4 nanosheet arrays@hollow porous carbon submicrofiber composites for flexible all-solid-state symmetric supercapacitors.

• A 3D freestanding hollow porous carbon submicrofibers (HPCMFs) network was prepared by electrospinning and carbonization. • The XMoO 4 (X Ni, Co) nanosheets were uniformly grown on HPCMFs through one-step solvothermal method. • The NiMoO 4 @HPCMFs electrode exhibts high specific capacitance of 1600 F g-1 at 1 A g-1 and good cyclic stability. • Six all-solid-state symmetric supercapacitors (ASSCs) in series can power a 'DHU' Logo consisted of 36 diodes. Exploring comwposite nanomaterials with novel and stable nanostructures is of great importance for high performance supercapacitors (SCs). Herein, the nanosheet-like XMoO 4 (X Ni, Co) were uniformly grown on the carbon submicrofibers (CMFs) by a facile hydrothermal route. The NiMoO 4 @CMFs exhibits higher specific capacitance of 1485.53 F g−1 and better cycling stability with 87.6% retention after 3000 cycles at 1 A g−1 than that of CoMoO 4 @CMFs (1407.1 F g−1, 80.6% retention after 3000 cycles at 1 A g−1). To further improve the electrochemical performance of NiMoO 4 @CMFs, the hollow porous carbon submicrofibers (HPCMFs) were designed and used as a substrate for NiMoO 4. Benefiting from the hollow porous structure, the HPCMFs can provide large specific surface area for electrolyte permeating and supply more ion channels in the charge-discharge process. Therefore, the NiMoO 4 @HPCMFs exhibits a high specific capacitance of 1600.0 F g−1 at 1 A g−1 and good cycling stability of 90.7% retention after 3000 cycles. The all-solid stated symmetric supercapacitors (ASSCs) were directly assembled by using NiMoO 4 @HPCMFs as electrode without any additives, which shows good flexibility and a high energy density of 55.33 Wh kg−1 at a power density of 999.89 W kg−1. Moreover, five series ASSCs can light 'DHU' logo, indicating potential application prospect in wearable electronics. [ABSTRACT FROM AUTHOR]