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Acrylic fiber is one of three important synthetic fibers in the world. The disposal and reuse of large number of waste acrylic fibers from fabric manufacturers or waste recovery is an urgent economic and environmental issue. Here, a porous carbon was derived from waste acrylic fibers via pre-oxidized, carbonization and KOH activation. Furthermore, we adopted melamine as nitrogen source to dope the porous carbon materials. When used as the anode of lithium ion batteries, this nitrogen-doped porous carbon shows high reversible capacity of ca. 1200 mA h g−1 after 50 cycles at 0.1 A g−1. Reversible capacities of 550 and 370 mA h g−1 are obtained at higher current densities of 1 and 5 A g−1 after 500 cycles, respectively. The outstanding electrochemical performance are a result of its large mesopore volume, high-level N-doping (especially, pyridinic-N), large quantity of edge defects, and three-dimensional hierarchical porous architecture. This paper demonstrates that the reuse of waste industrial acrylic fibers as energy storage materials is a promising method for both energy and environmental fields.

Transition-metal oxide materials have gained significant attention as high-performance anode materials for lithium ion batteries. Great advances have been achieved in the development of micro/nanostructured materials with controllable shape and tunable pore size. In this work, a facile co-precipitation approach has been developed to fabricate the Ni-NiCo2O4@ZnCo2O4 yolk-shell nano-tetrahedron composites, which significantly improve the structural stability and conductivity of the material. The Ni-NiCo2O4@ZnCo2O4 is proven to exhibit excellent cycling and rate performance for lithium ion batteries, such as the charge capacity of 1571.9 mA h g−1 after 70 cycles at 0.1 A g−1, 1097.5 mA h g−1 after 600 cycles at 1.0 A g−1. This superior electrochemical performance may attribute to the yolk-shell architecture and the Ni-doping.

In terms of enhancing the energy storage performance of flexible MXene electrode, both heteroatom doping and introducing electroactive “spacers” are proved to be effective strategies. In this work, a facial protective hydrothermal method is explored to synthesis nitrogen doped porous MXene/TiO2 heterostructure in one pot, which enables a well preserved conductivity of porous N-doped MXene and controlled in-situ generation of uniformly dispersed electroactive TiO2 spacers. This unique hybridized structure provides a chance to integrate several physical and chemical advantages in a complementary easy way. As a result, the assembled freestanding film electrode based on the N-doped porous MXene/TiO2 heterogeneous layers demonstrates excellent energy storage performance with an outstanding specific capacitance value of 2194.33 mF cm−2 (918.69 F g−1), which outperforms most of the heteroatom-doped MXene electrodes reported previously. Besides, the film electrode delivers excellent cycling performance with a 74.39% capacitance retention after 10,000 cycles and the as fabricated flexible supercapacitor displays almost no changes on capacitive performance when subjected to mechanical deformations, indicating its excellent flexibility and stability. This work presents a simple way of modifying MXene with N doping and inserting “spacer” for enhancing the electrochemical performance, and builds up an exciting potential for applying to highly flexible and integrated energy storage devices.

The current information era has witnessed the fast development of flexible high-performance energy storage devices for portable and wearable smart electronics. Here, tough supercapacitor with high flexibility and tear resistance based on Ag-coated Tyvek/PEDOT:PSS/carbon nanotubes (Tyvek/Ag/PCNTs) composite electrodes has been well designed and fabricated for the first time via a facile and scalable method. In the supercapacitor, Ag-coated Tyvek substrate roles as the current collector through a polymer-assisted metal deposition method while the treatment of sulfuric acid on the electrode contributes to the removal of insulating PSS part and the increase of the crystallinity of the active materials. Due to the tough and flexible substrate and the increased conductivity of the electrodes, the supercapacitor exhibits excellent stability and rate capacity as well as brilliant mechanical strength and flexibility. The prepared supercapacitor can exhibit large specific mass capacitance (138.7 F/g) and specific volume capacitance (544.2 F/cm3) at the scan rate of 50 mV/s. As far as we can concern, the Tyvek/Ag/PCNTs-based supercapacitor owns higher energy density or power density than any other CNTs-based or PEDOT-related supercapacitors. In addition, after 1000 bending cycles, the capacitance of the supercapacitor can still reach to 91.2% of the initial value. This work will help to enlarge the study in the Tyvek-based supercapacitors for the flexible and tough energy storage devices.

In this work, we addresses the fabrication of a flexible film electrode based on 2D MXene wrapped 3D Ni-Fe oxide nanocube mixed analogous heterostructure. The resulted composite film electrode successfully inherits the merit of different building blocks: MXene layers works as binders and conductive additives that can connect cubic Ni-Fe oxide nanoparticals, facilitate the charge transfer and avoid a significant conductivity decrease in the resulting electrode. While cubic Ni-Fe oxide serves as an active spacer inside the adjacent MXene layers to increase the interlayer space, facilitate the electrolyte diffusion and enhance the electrochemical activity of the composite film. As a result, the optimized composite film manifests excellent specific capacitance of 1038.43 mF cm−2 at current density 0.5 mA cm−2. Meanwhile by assembling into all-solid-state flexible supercapacitor, an excellent specific areal capacitance of 328.35 mF cm−2 at 0.2 mA cm−2 was achieved. Additionally, the excellent energy storage performance is well maintained with a capacitance retention of 90.9% during 10,000 charging-discharging long cycles. Furthermore, a high mechanical robustness with 88.9% capacitance remained after subjected to bending at 90° for 50 cycles, suggesting great potentials for the applications in future flexible and wearable devices.

Zn-air batteries have received extensive attention because of their high energy density, environmental friendliness, low cost and safety. It is vital to develop cost-effective and stable electrocatalysts for oxygen reduction reaction for Zn-air batteries. Herein, Fe 3 O 4 encapsulated in porous carbon nanobowls (Fe 3 O 4 @PCN) for oxygen reduction reaction are prepared by simple soft-template approach and calcination subsequently. The optimized catalyst 4Fe 3 O 4 @PCN-800 with uniformly doped Fe 3 O 4 nanoparticles and large surface area exhibits excellent catalytic performance and long-term durability. It displays 66 mV higher half-wave potential (0.911 V) than that of 20 wt% Pt/C catalysts in 0.1 M KOH electrolyte. It also shows excellent durability, only 5 mV attenuation of halfwave potential after 10,000 potential cycles. In addition, 4Fe 3 O 4 @PCN-800 possesses better methanol resistance than Pt/C, negligible current density fluctuation in the basic electrolyte with 3 M methanol. Impressively, when being employed as a cathode catalyst in both aqueous and solid-state Zn-air batteries, 4Fe 3 O 4 @PCN-800 presents higher open-circuit voltage, higher capacity and peak power density, and more stable discharge voltage plateaus than those of Pt/C. Furthermore, the solid-state Zn-air batteries with the optimal synthesized catalyst exhibit encouraging flexibility, which have enormous potential in the application of flexible and wearable power sources.