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A novel Co/Ni metal-organic framework (MOF)-derived three-dimensional (3D) nanoarchitecture in which graphene carbon-coated CoNi alloy nanoparticles grow on the tips of N-doped carbon nanotubes that are vertically-aligned on carbon nanofibers (Co/Ni@GC/NCNTs/CNFs) is fabricated. The Co/Ni@GC/NCNTs/CNFs electrode has a half-wave oxygen reduction reaction (ORR) potential of 0.80 V, a superior standing stability with 84.8% current retention after 175 000 s. The oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) reach a lower overpotential of 0.395 V and 0.15 V, respectively. Moreover, the resultant sample is an air cathode catalyst in a microbial fuel cell and indicates an utmost power density of 2100 ± 45 mW cm−2, which is much better than that of the Pt/C electrode (1334 ± 61 mW m−2). The density functional theory calculation demonstrates that the designed Co/Ni@GC/NCNTs/CNFs catalyst can remarkably promote OER, ORR, and HER performance. [Display omitted] • Co/Ni MOF-derived graphene carbon-coated CoNi alloy/NCNTs/CNFs was fabricated. • Co/Ni@GC/NCNTs/CNFs endows excellent ORR, OER and HER properties. • The as-prepared electrode exhibits high power density of 2100 ± 45 mW cm−2 in MFCs. • Superior property is due to the synergy of abundant active sites and 3D structure. [ABSTRACT FROM AUTHOR]

Here, we successfully synthesize three-dimensional (3D) callistemon-like hierarchical networks structural catalysts (CoNC/NCNTs@CNF) in which Co nanoparticles are encapsulated within N-doped carbon nanotubes apexes via electrospinning method combined with two-step pyrolysis process. Benefiting from the unique 3D callistemon-like structure, CoNC/NCNTs@CNF affords adequate surface area (261 m2 g−1) and the enhanced electronic conductivity (even superior to Pt/C and RuO 2). Due to the synergistic effect of the coupling between highly Co–N–C active sites and unique 3D callistemon-like structure, CoNC/NCNTs@CNF was explored as the trifunctional electrocatalysts for oxygen reduction reaction, oxygen evolution reaction, and hydrogen evolution reaction. Further, we assemble the catalysts as an air electrode for Zn-air batteries, demonstrating a maximum power density of 260 mW cm−2, and excellent cycling stability even after 43 h at 5 mA cm−2. Thus, this work offers a guide to the design of metal organic frameworks-derived 3D structure materials combined with electrospinning for wider application in renewable energy technologies. Image 1 • A ZIFs-derived callistemon-like 3D structure materials. • 1D carbon nanofibers were supported in situ forming carbon nanotubes. • Co nanoparticles coated with graphitic carbon were precisely encapsulated within the CNT apex. • The resultant catalyst displayed a multifunctional performance for ORR, OER, HER. • Catalyst was further constructed as overall water splitting and Zn-air batteries. [ABSTRACT FROM AUTHOR]

Carbon nanofibers (CNFs) have been continuously studied as a high performance electrode material due to their versatility in energy storage/conversion systems. The main concern of fabricating CNFs as electrode materials is to endow pristine carbon materials with adequate pore structure and active surface functional groups. Herein, we have fabricated porous hollow carbon nanofibers (PHCNF) with high nitrogen contents (13.4%) via co-axial electrospinning and subsequent phase separation process by using poly(styrene-co-acrylonitrile) (SAN) as core and polyacrylonitrile (PAN)/polyvinylpyrrolidone (PVP) mixture as shell. Simple etching process prior to carbonization has a significant effect on making hierarchical pore structure. Moreover, hollow characteristics allow efficient heat treatment for making high crystalline structure and favorable nitrogen functional group. Such an optimized structural and surface functional properties result in a remarkable supercapacitor performance. The designed structure achieves an energy density of 4.12 Wh kg−1 at power density of 15 kW kg−1, and a 92.33% retention rate in 10,000 charge/discharge cycles. The results offer a new strategy for developing advanced carbon material based electrode for high performance storage devices such as supercapacitors, lithium-ion batteries, and sensors. Porous hollow carbon nanofibers (PHCNFs), which have a textural surface and a high amount of nitrogen species, have been successfully developed via free-standing coaxial electrospinning and phase separation processes. PHCNFs show high specific capacitance and energy density at high power density due to its optimized physicochemical properties. Image 1 [ABSTRACT FROM AUTHOR]