Wenbin Zhong

High performance nitrogen-doped porous graphene/carbon frameworks for supercapacitors

Nitrogen-doped porous graphene/carbon (NPGC) framework electrode materials have been synthesized via chemical activation of graphene oxide/polypyrrole (GOP) composites with KOH. The effects of the mass ratio of KOH/GOP and activation temperature on the electrochemical performance of NPGC have been discussed. It is found that the NPGC prepared by activating GOP (GO : Py = 1 : 40) with 3.5 times mass of KOH at 650 °C (NPGC650) exhibits the highest specific capacitance of 405 F g−1 at a current density of 0.2 A g−1. Particularly, the specific capacitance still remains at 249 F g−1 even at a current density as high as 10 A g−1. Moreover, 96% of the capacitance can be retained after 1000 cycles even under a high operation current of 10 A g−1. The present work provides a novel strategy to synthesize NGPC electrode material for supercapacitors.

Mechanically robust double-crosslinked network functionalized graphene/polyaniline stiff hydrogels for superior performance supercapacitors

To extend the applications of supercapacitors, it is important and challenging to develop structural/stiff supercapacitors with excellent mechanical and electrochemical performance. In this work, high performance double-crosslinked network functionalized graphene/polyaniline stiff hydrogels (DN-PGH/PANIPA) have been successfully synthesized by polymerization of aniline in a confined functionalized graphene (PGH) hydrogel framework. A unique polyaniline (PANI) morphology with a combination of nanodot protrusions and nanofibers is obtained, where nanodot protrusions are tightly anchored to graphene walls and nanofiber crosslinked graphene sheets. The as-prepared DN-PGH/PANIPA hydrogel, consisting of a continuous conductive closely combined double-crosslinked network and PANI nanofibers, together with a high crystallization degree of the PANI structure, is both stiff and mechanically robust with a high tensile strength of 1.39 MPa at a small ruptured elongation of 0.42%. Meanwhile, the DN-PGH/PANIPA stiff hydrogels are assembled into symmetric supercapacitors and achieve a superior areal specific capacitance of 3488.3 mF cm−2 and a volumetric specific capacitance of 872 F cm−3, remarkable rate capability, and excellent cycling stability, resulting in a notable energy density of 155 μW h cm−2 at 200 μW cm−2 and an outstanding power density of 20 015 μW cm−2 at 67.5 μW h cm−2. This novel double-crosslinked network design strategy establishes a promising approach towards the development of other stiff electrode materials as high performance structural supercapacitors.

Hydrothermal direct synthesis of polyaniline, graphene/polyaniline and N-doped graphene/polyaniline hydrogels for high performance flexible supercapacitors

Electroactive hydrogels have been considered as flexible solid-state supercapacitor electrode materials. Herein, a novel strategy has been proposed to directly prepare polyaniline (PANI) hydrogels from soluble PANI dispersion by self-crosslinking of molecules during the hydrothermal process. The PANI hydrogel single-electrode shows high specific capacitance (325 F g−1) and superior rate capability. To achieve more excellent electrochemical performance, the graphene/PANI hydrogel (GPH7) is prepared using graphene oxide (GO) and soluble PANI dispersion. However, a slightly enhanced specific capacitance (375 F g−1) is achieved for the GPH7 single-electrode, due to the strong interactions between GO and PANI molecules. It is of particular interest that the incorporation of m-phenylenediamine (mPD) into the GO and PANI system could protect the inherent conjugated structure of PANI, and thereby the as-prepared N-doped graphene/PANI hydrogels (GMPH7) show significantly improved specific capacitance (514.3 F g−1). Moreover, the assembled flexible solid-state supercapacitors based on the PANI hydrogel, GPH7 and GMPH7 exhibit excellent areal specific capacitance (484, 519.2 and 584.7 mF cm−2, respectively), approximately 100% capacitance retention after 2000 mechanical bending cycles and favorable energy density (42.96, 60.9 and 81.28 μW h cm−2, respectively). Such hydrogel assembled supercapacitors with robust capacitive behavior and outstanding flexibility are promising for applications in flexible and wearable electronics.

High-Performance Biomass-Based Flexible Solid-State Supercapacitor Constructed of Pressure-Sensitive Lignin-Based and Cellulose Hydrogels

Employing renewable, earth-abundant, environmentally friendly, low-cost natural materials to design flexible supercapacitors (FSCs) as energy storage devices in wearable/portable electronics represents the global perspective to build sustainable and green society. Chemically stable and flexible cellulose and electroactive lignin have been employed to construct a biomass-based FSC for the first time. The FSC was assembled using lignosulfonate/single-walled carbon nanotubeHNO3 (Lig/SWCNTHNO3) pressure-sensitive hydrogels as electrodes and cellulose hydrogels as an electrolyte separator. The assembled biomass-based FSC shows high specific capacitance (292 F g-1 at a current density of 0.5 A g-1), excellent rate capability, and an outstanding energy density of 17.1 W h kg-1 at a power density of 324 W kg-1. Remarkably, the FSC presents outstanding electrochemical stability even suffering 1000 bending cycles. Such excellent flexibility, stability, and electrochemical performance enable the designed biomass-based FSCs as prominent candidates in applications of wearable electronic devices.

Nacre-like laminate nitrogen-doped porous carbon/carbon nanotubes/graphene composite for excellent comprehensive performance supercapacitors

A nitrogen-doped porous carbon/carbon nanotubes/graphene (PGMC) composite was prepared through a process of hydrothermal treatments, polymerization of o-phenylenediamine (OPD), and pyrolysis. The as-prepared PGMC composite was found to be of a nacre-like laminate porous structure, constructed with alternatively stacked two-dimensional (2D) graphene sheets and porous carbons, and also interspersed within one-dimensional (1D) multi-walled carbon nanotubes (MWNTs). The MWNTs effectively suppressed agglomeration of graphene sheets during the hydrothermal process and were interspersed in PGMC to help construct more networks with excellent conductivity. The PGMC possessed an enriched nitrogen doping ratio of 15.67 at% and relative high density of 1.39 g cm-3. The electrode composed of PGMC provided high gravimetric capacitance of 562.9 F g-1 and volumetric capacitance of 782.4 F cm-3 at current density of 1 A g-1, as well as excellent rate capability and cycling stability. The symmetric supercapacitors mounted with the as-prepared PGMC electrode were stably operated in a wide potential range of 0-1.3 V and demonstrated a superb gravimetric energy density of 19.79 W h kg-1 at high power density of 650 W kg-1, and a high volumetric energy density of 27.51 W h L-1 with a power density of 904 W L-1. The outstanding electrochemical performance enables this as-prepared nacre-like laminate PGMC composite to be a promising candidate for energy storage application.