Jizhen Zhang

Fabrication of an arbitrary-shaped and nitrogen-doped graphene aerogel for highly compressible all solid-state supercapacitors

Herein, we report a new template method for fabricating an arbitrary-shaped compressible nitrogen-doped graphene aerogel (GA). The as-prepared GA remains stable under a maximum compressive strain of 90% or after 50 compression/release cycles at a strain of 80%. The compressible nitrogen-doped GA is used as an electrode to fabricate an all solid-state graphene aerogel supercapacitor (GASC). The as-assembled GASC shows a specific capacitance of 150 F g−1 at a current density of 0.3 A g−1 and a long cycle life with 85.1% capacitance retention after 10 000 cycles at 1 A g−1. In addition, the compressible GASC displays stable electrochemical performance under different compressive strains (0%, 25%, 50% and 75%) or after 100 compression/release cycles under a compressive strain of 50%. The present work highlights the first example of fabricating an arbitrary-shaped compressible GA. Furthermore, the as-obtained GASC overcomes the limitation of previous work which required the assistance of other materials to maintain the mechanical properties. This simple template method for the fabrication of compressible and robust GA electrodes could have enormous potential for high performance compressible energy storage devices.

A highly conductive porous graphene electrode prepared via in situ reduction of graphene oxide using Cu nanoparticles for the fabrication of high performance supercapacitors

Herein, a new graphene/Cu nanoparticle composite was prepared via the in situ reduction of GO in the presence of Cu nanoparticles which was then utilized as a sacrificing template for the formation of flexible and porous graphene capacitor electrodes by the dissolution of the intercalated Cu nanoparticle in a mixed solution of FeCl3 and HCl. The porous RGO electrode was characterized by atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). The as-prepared graphene/Cu nanoparticle composite and the pure graphene film after removal of Cu nanoparticles possessed high conductivity of 3.1 × 103 S m−1 and 436 S m−1 respectively. The porous RGO can be used as the electrode for the fabrication of supercapacitors with high gravimetric specific capacitances up to 146 F g−1, good rate capability and satisfactory electrochemical stability. This environmentally friendly and efficient approach to fabricating porous graphene nanostructures could have enormous potential applications in the field of energy storage and nanotechnology.

Quantifying the Tunable Conjugated Area of Graphene Oxide by Using Pyrene as a Fluorescent Probe

The determination of oxygenous groups, conjugated area ratio, and reduction efficiency of graphene oxide (GO) is a difficult task because of its heterogeneous structure. Herein, a novel approach is described for a detailed understanding of the surface chemistry of GO by using pyrene as a fluorescent probe through π-π stacking interactions.

A simple and large-scale method to prepare flexible hollow graphene fibers for a high-performance all-solid fiber supercapacitor

Herein, we develop a spray deposition process for the production of flexible and conductive hollow graphene fibers (HGFs). Firstly, a graphene oxide suspension is spray-coated on silk fibers, which act as a template, followed by the reduction of GO into RGO using HI as the reductant. This simple method gets rid of the picky conditions and complicated process for the fabrication of graphene fibers (GFs) which possess good flexibility, conductivity and a hollow structure. A flexible all-solid hollow graphene fiber supercapacitor (HGFS) is assembled using the as-prepared HGFs and shows an excellent specific capacitance of 76.1 F g−1 (127.4 mF cm−2, 48.5 F cm−3) at a current density of 1 A g−1, excellent rate capability (over 87% retention at 5 A g−1) and high cycling stability with only 9.5% capacitance decay over 2000 recycles at a scan rate of 100 mV s−1. This simple large-scale template method for the preparation of flexible and conductive HGF electrodes could promise broad prospects for high-performance energy storage applications, particularly for next-generation wearable electronic devices.

High-Performance Biscrolled MXene/Carbon Nanotube Yarn Supercapacitors

Yarn-shaped supercapacitors (YSCs) once integrated into fabrics provide promising energy storage solutions to the increasing demand of wearable and portable electronics. In such device format, however, it is a challenge to achieve outstanding electrochemical performance without compromising flexibility. Here, MXene-based YSCs that exhibit both flexibility and superior energy storage performance by employing a biscrolling approach to create flexible yarns from highly delaminated and pseudocapacitive MXene sheets that are trapped within helical yarn corridors are reported. With specific capacitance and energy and power densities values exceeding those reported for any YSCs, this work illustrates that biscrolled MXene yarns can potentially provide the conformal energy solution for powering electronics beyond just the form factor of flexible YSCs.

Elastic fiber supercapacitors for wearable energy storage

The development of wearable devices such as smart watches, intelligent garments, and wearable health-monitoring devices calls for suitable energy storage devices which have matching mechanical properties and can provide sufficient power for a reasonable duration. Stretchable fiber-based supercapacitors are emerging as a promising candidates for this purpose because they are lightweight, flexible, have high energy and power density, and the potential for easy integration into traditional textile processes. An important characteristic that is oftentimes ignored is stretchability-fiber supercapacitors should be able to accommodate large elongation during use, endure a range of bending motions, and then revert to its original form without compromising electrical and electrochemical performance. This article summarizes the current research progress on stretchable fiber-based supercapacitors and discusses the existing challenges on material preparation and fiber-based device fabrication. This article aims to help researchers in the field to better understand the challenges related to material design and fabrication approaches of fiber-based supercapacitors, and to provide insights and guidelines toward their wearability.