Graphene Paper Electrodes Research Articles

Freestanding Graphene/Carbide Derived Carbon Films As High-Performance Electrodes for Electrochemical Capacitors

Freestanding films of reduced graphene oxide (rGO) have attracted much attention as electrodes for electrochemical capacitor, especially for flexible device applications. However, graphene paper electrodes are usually limited in thicknesses to less than 10 μm, as increasing the electrode thickness hinders its performance due to restacking of rGO sheets and slow diffusion of ions [1]. To prevent this problem, carbon nanoparticels such as carbon nanotubes (CNTs) are frequently used as nanospacers between the rGO sheets to increase the electrolyte accessibility and electronic conductivity of the films [2]. However, CNTs have a much lower capacitance compared to rGO and their addition limits the overall capacitance of the freestanding electrodes. In this study, for the first time, we have used highly porous carbide derived carbon (CDC) nanoparticles as spacer between graphene sheets and fabricated thick rGO/CDC hybrid electrodes. The electrodes were made by thermal reduction of GO/CDC papers fabricated by vacuum-assisted filtration of aqueous solutions of GO and CDC containing 10, 20, and 30 wt. % of CDC. Utilizing the high surface area and conductivity of rGO and the accessible pores of the CDC [3], the hybrid electrodes showed specific capacitances as high as 200-210 F/g at a high scan rate of 100 mV/s in an aqueous electrolyte. The addition of CDC between the rGO layers increases the accessibility of active material to the electrolyte ions and we observed good performance of the electrodes with the thickness of 40-50 μm.

Flexible Graphene Paper as a Binder-Free Anode Material for Lithium Ion Batteries

Graphene paper (GP) with layered structure and highly conductive network is fabricated by a facile technique of vacuum filtration and studied as a single-component and binder-free anode of lithium ion batteries (LIBs). The process of fabrication of GP without any binder and high-temperature treatment, in the meantime, great improvement in both the capacity and cycling performance of the GP electrodes have compared with other kinds of traditional graphite electrode materials. Given the simplifying anode fabrication, low manufacturing costs and many electrochemical properties of the GP anode, it is regarded as an excellent anode material of LIB with great promise for its both excellent cycling performance and electrochemical properties. The specific capacity can reach to over 200 mAhg-1 after 60 charge-discharge cycles under the current rate of 50 mAg-1.

Carbon with ultrahigh capacitance when graphene paper meets K3Fe(CN)6.

For the first time, we have shown a novel supercapacitor system with a graphene paper electrode in the redox-electrolyte of K3Fe(CN)6 based on the system-level design principle. By combining electric double-layer capacitance and pseudocapacitance, the specific capacitance could be increased 5-fold compared with the conventional electrode-electrolyte system. This large improvement is attributed to the additional redox reactions on the graphene paper electrode via the constituent ions of K3Fe(CN)6 in the redox-electrolyte, during which the discharge process is highly enhanced. More importantly, the potential interval could reach as high as 1.6 V beyond the limited operating voltage of water (∼1.23 V). After 5000 continuous cycles, 94% of the initial capacitance was retained. The newly designed novel supercapacitor system is binder-free, conducting additive-free and can deliver higher capacitance. This designed graphene-paper-electrode/redox-electrolyte system can provide a versatile strategy for high-capacitance supercapacitor systems.

Water crystallization to create ice spacers between graphene oxide sheets for highly electroactive graphene paper

We proved that ice crystallized from water molecules within as-synthesized graphene oxide (GO) can be used as a spacer among individual GO sheets to form an expanded GO aerogel with a three-dimensional porous network structure. This designed specific structure can be retained during further processes to form graphene paper. Due to the fact that the as-fabricated graphene paper contains carbon defects and space in its infrastructure, this creates more electroactive surfaces and interfaces to significantly increase the Faradaic reaction efficiency. With the introduction of redox-electrolyte K3Fe(CN)6 into a KOH electrolyte, we can obtain a 95-fold increase in the specific capacitance compared with the value obtained in the traditional KOH electrolyte. The ice-crystallization formed graphene paper electrode showed high electroactivity because the specific porous structure can favor the fast transfer of electrolyte ions, such as Fe(CN)63− ions. The presented results prove that ice-crystallization formed GO can serve as a chemically tunable platform for electrochemical energy storage applications.

Novel graphene papers with sporadic alkyl brushes on the basal plane as a high-capacity flexible anode for lithium ion batteries

Graphene paper that exhibits an excellent stabilized capacity, as high as 1300 mAh g−1 at a current rate of 60mAg−1, as a lithium ion battery anode is fabricated and evaluated. The few-layer graphene used to make the graphene paper is prepared via the thermal reduction of graphite oxide. The graphene is then modified by a novel method utilizing inherent defects, namely epoxy groups, on the graphene as active sites for a reaction with methanol, 1-butanol, 1-hexanol, and 1-octanol. The density values and X-ray diffraction patterns obtained for the graphene paper demonstrate that the alkyl brushes on the graphene sheets expand the d-spacing and hinder close restacking of the sheets, thereby inducing the formation of extra cavities within the paper. This loose packing due to the alkyl brushes increases sensitively as the alkyl chain length of the alcohol becomes longer. The lithium ion insertion capacity of a graphene paper electrode at the first cycle also increases with the alkyl chain length. However, fading of the capacity at early charge/discharge cycles is accelerated by the modification process because of electrolyte penetration into the gallery and the acceleration of protective solid electrolyte interface film formation due to looser packing. The paper composed of graphene modified with 1-butanol rather than shorter or longer alcohols exhibits the best reversible storage capacity, more than two-fold higher when compared to that of pristine graphene paper, due to a compromise between two conflicting effects on the reversible storage capacity by long alkyl brushes. The tensile properties and electrical conductivity of the graphene papers are also examined.

Cellulosic Binder-Assisted Formation of Graphene-Paper Electrode with Flat Surface and Porous Internal Structure

We have reported the fabrication of flexible graphene-paper electrode (GPE) with a flat surface, whose internal structure has been formed with gradient porous build-up (from the surface to the 2-hydroxyethyl cellulose (HC)-coated paper). HC solution was used as a binder to form the gradient porous graphene layer, enabling it to create an anchoring force between the porous graphene layer and the filter paper. The morphology of GPE was investigated using a scanning electron microscope, and the surface resistance of the GPE as a function of graphene content was determined using four-probe method. The electrochemical performance of the GPE was evaluated using a three-electrode test cell by cyclic voltammetry. The gravimetric capacitance of GPE was found to be 120 F per gram of graphene, and the capacitance retention was within ca. 96% for over 500 cycles. This could be attributed to both the low surface resistance resulting from the flat surface and the high electrochemical activity caused by the gradient porous structure. This unique structure not only offers an enhanced conductivity and good electrical contact between the electrode and electrolyte but also helps GPE to maintain good cyclic stability, proving its potential for use in various rechargeable and portable energy-storage devices.

A Pyrene-Substituted Tris(bipyridine)osmium(II) Complex as a Versatile Redox Probe for Characterizing and Functionalizing Carbon Nanotube- and Graphene-Based Electrodes

We report the functionalization of nanostructured graphene-based electrode with an original (bis(2,2'-bipyridine)(4,4'-bis(4-pyrenyl-1-ylbutyloxy)-2,2'-bipyridine]osmium(II) hexafluorophosphate complex bearing pyrene groups. Graphene oxide (GO) and chemically reduced graphene oxide (c-RGO) paper electrodes were prepared by the flow-directed filtration method. After film transfer via the soluble membrane technique, the homogeneous and stable GO electrode was electrochemically reduced in water to achieve electrochemically reduced graphene oxide (e-RGO) film on the electrode. The electrochemical properties of GO, c-RGO, and e-RGO electrodes were characterized by scanning electron microscopy and electrochemistry. Cyclic voltammetry of the Ru(NH3)6(2+/3+) redox probe underlines the important influence of the RGO preparation method on electrochemical properties. We finally achieved the flexible functionalization of graphene-based electrodes using either supramolecular binding of the Os(II) complex bearing pyrene groups or its electropolymerization via the irreversible oxidation of pyrene. The properties of these functionalized graphene paper electrodes were compared to glassy carbon (GC) and multiwalled carbon nanotube (MWCNT) electrodes. Thanks to its divalent binding sites, the Os(II) complex constitutes a useful tool to probe the π-extended graphitic surface of RGO and MWCNT films. The Os(II) complex interacts strongly via noncovalent π-π interactions, with π-extended graphene planes, thus acting as a marker to quantify the electroactive surface of both MWCNT and RGO electrodes and to illustrate their ease of functionalization.

Impedimetric immunosensor based on gold nanoparticles modified graphene paper for label-free detection of Escherichia coli O157:H7

In this study, a low-cost and robust impedimetric immunosensor based on gold nanoparticles modified free-standing graphene paper electrode for rapid and sensitive detection of Escherichia coli O157:H7 (E. coli O157:H7) was developed. Graphene paper was prepared by chemical reduction of graphene oxide paper obtained from vacuum filtration method. Scanning electron microscope, Raman spectroscopy and X-ray diffraction techniques were employed to investigate the surface morphology and crystal structure of the prepared graphene paper. The gold nanoparticles were grown on the surface of graphene paper electrode by one-step electrodeposition technique. The immobilization of anti-E. coli O157:H7 antibodies on paper electrode were performed via biotin-streptavidin system. Electrochemical impedance spectroscopy was used to detect E. coli O157:H7 captured on the paper electrode. Results show that the developed paper immunosensor possesses greatly enhanced sensing performance, such as wide linear range (1.5×102–1.5×107cfumL−1), low detection limit (1.5×102cfumL−1), and excellent specificity. Furthermore, flexible test demonstrate the graphene paper based sensing device has high tolerability to mechanical stress. The strategy of structurally integrating metal nanomaterials, graphene paper, and biorecognition molecules would provide new insight into design of flexible immunosensors for routine sensing applications.

Flexible Holey Graphene Paper Electrodes with Enhanced Rate Capability for Energy Storage Applications

The unique combination of high surface area, high electrical conductivity and robust mechanical integrity has attracted great interest in the use of graphene sheets for future electronics applications. Their potential applications for high-power energy storage devices, however, are restricted by the accessible volume, which may be only a fraction of the physical volume, a consequence of the compact geometry of the stack and the ion mobility. Here we demonstrated that remarkably enhanced power delivery can be realized in graphene papers for the use in Li-ion batteries by controlled generation of in-plane porosity via a mechanical cavitation-chemical oxidation approach. These flexible, holey graphene papers, created via facile microscopic engineering, possess abundant ion binding sites, enhanced ion diffusion kinetics, and excellent high-rate lithium-ion storage capabilities, and are suitable for high-performance energy storage devices.