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Nowadays, materials that possess high activity and natural oxygen vacancy have garnered significant attention as potential electrode materials for supercapacitors. In this study, we successfully prepared the Hf 6 Ta 2 O 17 (HTO) nanofibres (NFs) with an orthorhombic superlattice structure using the electrospinning technique and sintering process. The characterization results indicate that the HTO NFs synthesized at 750 °C show good micro nanostructures and outstanding electrochemical properties. To enhance its energy storage performance, additional oxygen vacancies (OVs) were introduced through a carbothermal treatment under an Ar atmosphere. Although longer reduction reaction times can produce more OVs, the integration of grain boundaries and the growth of grain size caused by large annealing times may limit its electrochemical performance. Therefore, the HTO NFs treated for 1 h (HTO/C-1) exhibited the maximum C s of 925 F·g−1 at 1 A·g−1 with a larger voltage window of 2.1 V. Furthermore, a symmetric supercapacitor fabricated by two reduced HTO NFs electrodes and 1 M Na 2 SO 4 solution, recorded as r-HTO NFs//r-HTO NFs. The device demonstrated excellent energy density of 73.3 Wh·kg−1 (at power density of 1050 W·kg−1) and a long cycling life (81.8% retained after 5000 cycles). These results suggest that the optimized reduction process can provide appropriate oxygen vacancies in HTO NFs, thereby effectively enhancing its performance. [Display omitted] • The Hf 6 Ta 2 O 17 (HTO) nanofibres (NFs) are synthesized by electrospinning method. • The micro nanostructures and electrochemical property of HTO NFs can be designed by controlling the synthesis temperature. • The carbothermal treatment carried under Ar atmosphere is used to improve the amount of oxygen vacancies of HTO NFs. • The HTO NFs treated of 1 h (HTO/C-1) presents excellent capacitance of 925 F·g−1 at 1 A·g−1. • The r-HTO NFs//r-HTO NFs device shows high energy density of 73.3 Wh·kg−1 at power density of 1050 W·kg−1. [ABSTRACT FROM AUTHOR]

Flexible electrode materials play an important role in flexible portable energy storage devices. Carbon-based nanofiber has attracted numerous attentions due to its advantages on flexibility, safety, and reliability. Herein, we reported a novel and simple method to fabricate nitrogen-boron co-doped hollow porous carbon nanofiber (HPCNF) membranes as flexible supercapacitor electrodes. The higher specific surface area (413.98 m2/g) of HPCNF and the co-doping of N and B resulted in a high specific capacitance of 200.2 F/g (0.1 A/g). After 3000 cycles, NB-HPCNF still maintained high capacitance retention (104.81%). This study provides a new idea for electrochemical energy storage, which is beneficial to the deeper development of portable flexible devices. [Display omitted] • A novel and simple method was used to fabricate nitrogen-boron co-doped hollow porous carbon nanofiber membranes. • The well-developed hollow channels facilitated fast and efficient charge transport in carbon nanofibers. • A solid-state symmetric supercapacitor has good electrochemical properties and good mechanical stability. [ABSTRACT FROM AUTHOR]

Construction of hierarchically porous carbon electrode materials is considered as an efficient strategy for improving the performance of supercapacitors. Nevertheless, how to precisely control the pore structure for preferable improvement the capacitance performance and fabricate in a cost-efficient way is still a scientific challenge. In this paper, an industrial by-product of coal tar pitch is used as precursor to prepare interconnected hierarchically porous carbons, with another domestic waste of eggshell as a pore-forming template and an inner-activator, combined with KOH in-situ activation. The as-prepared porous carbons exhibit large specific surface area (S BET , 1398–2103 cm2 g−1), well-developed interconnected hierarchically architecture, and excellent electrochemical performance. Among them, the optimal TS-PCE-4 based symmetric supercapacitor possesses a high capacitance of 238 F g−1 at 0.5 A g−1 with an excellent rate capability, exhibits long cycle stability with capacitance retention of 95.85 % after 10,000 cycles, and delivers energy densities of 8.27–5.47 Wh kg−1 at power density in the range of 125–4925 W kg−1 in 6 M KOH aqueous electrolyte. This work offers a facile and low-cost route to construct interconnected hierarchically porous carbons for energy storage devices. [Display omitted] • An industrial by-product of coal tar pitch was used to fabricate the hierarchically porous carbons via a facile route. • The domestic waste of eggshell was served as a pore-forming template and an inner-activator. • The carbons show large specific surface area and well-developed interconnected hierarchically porous architecture. • The optimum sample displays outstanding supercapacitor performance. [ABSTRACT FROM AUTHOR]