Pulsed electrochemical fabrication of graphene/polypyrrole composite gel films for high performance and flexible supercapacitors

Construction of ion/electron transfer multi-channels for the composite film electrode from GO and cellulose derived porous carbon in supercapacitor

Due to excellent flexibility and dispersibility, 2D graphene oxide (GO) is regarded as one of the prospective materials for preparing self-supporting electrode material. Nevertheless, the self-stacking characteristic of GO significantly restricts the ion transmission and accessibility in GO-based electrodes, especially in the direction perpendicular to the electrode surface. Herein, a novel composite film was fabricated from GO and 3D porous carbon (PC) through vacuum filtration combined with thermal reduction strategy. The combination of GO and PC not only avoids the self-stacking of GO, but also exposes more active sites for ions in the inner. A massive released nitrogen and oxygen-containing gases during the thermal reduction endows the reduced graphene oxide (RGO) with abundant porous and CC, which contributes to the energy storage in the direction perpendicular to the electrode surface. Besides, the high specific surface area of the prepared composite film is favorable for the storage and release of charge on the electrode surface. Benefiting from the above characteristics, the electrode assembled by the as-prepared film exhibits ultrahigh areal/volumetric specific capacitance in supercapacitor and ZIHCs (Zinc ion hybrid capacitors). This work provides a promising approach for the development of advanced self-supported electrode materials with desirable electrochemical properties.

Newly graphene/polypyrrole (rGO/PPy) modified carbon felt as bio-cathode in bio-electrochemical systems (BESs) achieving complete denitrification

Nitrate reduction in bio-electrochemical systems (BESs) has attracted wide attention due to its low sludge yields and cost-efficiency advantages. However, the high resistance of traditional electrodes is considered to limit the denitrification performance of BESs. Herein, a new graphene/polypyrrole (rGO/PPy) modified electrode is fabricated via one-step electrodeposition and used as cathode in BES for improving nitrate removal from wastewater. The formation and morphological results support the successful formation of rGO/PPy nanohybrids and confirm the part covalent bonding of Py into GO honeycomb lattices to form a three-dimensional cross-linked spatial structure. The electrochemical tests indicate that the rGO/PPy electrode outperforms the unmodified electrode due to the 3.9-fold increase in electrochemical active surface area and 6.9-fold decrease in the charge transfer resistance (Rct). Batch denitrification activity tests demonstrate that the BES equipped with modified rGO/PPy biocathode could not only achieve the full denitrification efficiency of 100% with energy recovery (15.9 × 10-2 ± 0.14 A/m2), but also favor microbial attach and growth with improved biocompatible surface. This work provides a feasible electrochemical route to fabricate and design a high-performance bioelectrode to enhance denitrification in BESs.

One-Step Fabrication of Integrated Graphene/Polypyrrole/Carbon Cloth Films for Supercapacitor Electrodes

The facile and cost-effective preparation of supercapacitor electrodes is significant for the application of this kind of electrochemical energy-storing module. In this work, we designed a feasible strategy to fabricate a binary active material onto a current collector in one step. A colloidal mixture of graphene oxide and pyrrole layered on a carbon cloth could undergo a redox reaction through a mild hydrothermal process to yield a reduced graphene oxide/polypyrrole hydrogel film anchored onto the carbon cloth. The integrated electrode with the porous graphene/polypyrrole active material could be directly utilized as a freestanding working electrode for electrochemical measurements and the assembly of supercapacitor devices. The as-prepared electrode could achieve a high capacitance of 1221 mF cm-2 at 1 mA cm-2 (531 F g-1) with satisfactory cycling stability. The constructed symmetric supercapacitor with two optimal electrodes could provide an energy density of 70.4 μWh cm-2 (15.3 Wh kg-1). This work offers a feasible pathway toward the integration of graphene/conducting polymer composites as electrochemical electrodes.

Preparation of flexible and free-standing polypyrrole/graphene film electrodes for supercapacitors

A free-standing polypyrrole/graphene film (PGF) electrode with an excellent electrochemical performance was obtained using spin coating and hydrothermal methods.

Intertwined carbon networks derived from Polyimide/Cellulose composite as porous electrode for symmetrical supercapacitor

Designing intertwined porous structure is highly desirable to improve the electrochemical performance of carbon materials for supercapacitor. In this contribution, three-dimensional (3D) carbonized polyimide/cellulose (CPC) composite is fabricated via a facile "one-step" carbonization, in which cellulose as cross-linked agent is capable of modulating the molecular structure of polyamic acid, thus ensuring the formation of intertwined porous networks in the obtained carbon skeleton. Benefitting from the high specific surface area (951 m² g^-1) and uniformly distributed pores, the optimized CPC-5 electrode exhibits an outstanding specific capacitance of 300F g^-1 in 6.0 M KOH electrolyte. More impressively, the CPC-5 based symmetrical supercapacitor affords a high energy density of 22.6 Wh kg^-1 at power density of 800 W kg^-1, as well as an exceptional capacitance retention of 91.4% after 10,000 cycles. This work affords an effective strategy to yield a promising polyimide derived carbon material for high-performance supercapacitors.