Reduced Graphene Oxide Cathode Research Articles

3D hierarchically fractal structure stabilized anode for achieving long-term cycle life of aqueous Zn-ion batteries

The cycling stability of aqueous Zn-ion battery (AZIB) is a serious issue for their successful application, mainly due to the considerable growth of Zn dendrites and the existence of side effects during operation. Herein, the hierarchically three-dimensional (3D) fractal structure of the ZnO/Zn/CuxO@Cu (ZZCC) anode is prepared by a two-step process, where CuxO nanowires are prepared on Cu foam by thermal oxidation method and Zn layer and ZnO surface are formed by plating. This fractal structure increases the electrodynamic surfaces and reduces the local current density, which can regulate Zn plating and inhibit dendritic growth and side effects. Apparently, the symmetric ZZCC-based cell shows a long-term operation time of 3000 h at 1 mA cm−2 with 1 mAh cm−2, and an operation time of more than 1000 h with a discharge depth of 15.94%. Compared with the bare Zn foil anode, the AZIB assembled with the composite of Mn-doped vanadium oxide and reduced graphene oxide cathode and ZZCC anode (MnVO@rGO//ZZCC) exhibits significantly improved cyclability (i.e. with 88.5% capacity retention) and achieves a Coulomb efficiency of 99.4% at 2 A g-1. This hierarchically 3D structure strategy to design anodes with superior cyclic stability contributes to the next generation of secure energy.

Metal organic framework derived NiCo layered double hydroxide anode aggregated with biomass derived reduced graphene oxide cathode: A hybrid device configuration for supercapattery applications

Metal-organic frameworks (MOFs), due to its exceptional characteristics like high specific surface area and design diversity, serve as an outstanding sacrificial template in forming layered double hydroxides (LDHs) for highly efficient electrodes in supercapattery devices. In this work, we have prepared bimetallic layered Nickel Cobalt LDH via in-situ etching of Co-ZIF, in different Nickel concentrations directly on Ni foam that enhances the interfacial contact between substrate and the material. The optimised NiCo LDH-2 sample exhibited remarkable electrochemical behaviour with fast electrolyte ion diffusion kinetics ideal for supercapattery device and delivered a high specific capacitance of 2567 Fg−1 at 1 Ag−1. Further, the supercapattery device assembled with Ni-Co LDH as anode and rGO derived from a sustainable source as cathode demonstrated an energy density of 21 Whkg−1, power density of 0.307 kWkg−1 and good cyclic stability with capacitance retention of 88.89 % along with coulombic efficiency of 90.58 % over 1500 cycles. This work proposes an effective approach for designing layered NiCo-LDH that can be further extended to the synthesis of other transition metal-derived LDH for supercapattery devices.

Phenothiazine/reduced graphene oxide composite as a pseudocapacitive cathode for lithium ion capacitors

The specific capacity of cathode in lithium-ion capacitors is greatly lower than that of anode, resulting in the energy density of device is limited. In this work, to enhance the specific capacity of cathode, redox-active phenothiazine is introduced and a superior-performance phenothiazine/reduced graphene oxide composite cathode is synthesized under hydrothermal condition. Owing to the production of pseudocapacitance by phenothiazine, the optimized composite cathode can give rise to higher discharge specific capacity (86.6 mAh g–1 under 0.5 A g–1) than reduced graphene oxide cathode (36.2 mAh g–1), even though the lower specific surface area. In addition, outstanding cyclic performance is presented by this composite cathode with capacity retention ability of 80.4% at the end of 700 cycles in Li-half cell under 0.5 A g–1. Furthermore, when paired with a carbon tube anode, the constructed lithium-ion capacitor possesses a larger energy density (114.4–17.8 Wh kg–1) than the device (57.0–1.9 Wh kg–1) without phenothiazine in the cathode. And it is found that the introduction of phenothiazine doesn't decrease the power density of device. Additionally, this composite cathode based device has good cycling stability with capacity fade ratio as low as 12.7% even after 8000 cycles.

Effect of annealing temperature on the performance of dye-sensitized solar cell using nickel sulphide–reduced graphene oxide cathode

Effect of annealing temperature on the performance of dye-sensitized solar cell using nickel sulphide–reduced graphene oxide cathode

In situ thermal conversion of graphene oxide films to reduced graphene oxide films for efficient dye-sensitized solar cells

Severe aggregation of reduced graphene oxide nanosheets and their weak adhesion to the conductive substrate largely restricts the electrocatalytic property. To overcome this flaw, we propose a simple strategy for fabrication of efficient reduced graphene oxide film through in-situ thermal conversion of graphene oxide film that is first adsorbed onto the conductive substrate. As compared to the reduced graphene oxide film prepared from the direct adsorption of reduced graphene oxide nanosheets, the reduced graphene oxide film obtained from the in-situ thermal conversion of graphene oxide film exhibits much higher electrocatalytic activity on the reduction of I3− due to the stronger adhesion to the conductive substrate and better film quality without aggregation. The thermal-converted reduced graphene oxide cathode produces much higher power conversion efficiency (6.35%) than that (1.20%) for the directly adsorbed reduced graphene oxide cathode. This work opens up a new avenue for preparation of simple and low-cost cathodes.

A 3D Printed Enzymatic Biofuel Cell Based on Reduced Graphene Oxide Para Amino Benzoic Acid Modified Anode and Electrodeposited Reduced Graphene Oxide Cathode

Para amino benzoic acid is used in the synthesis of folic acid by bacteria. It is biologically important for the survival of bacteria in the human intestinal tract. This biological and physiologically important molecule can be used to achieve immobilization of glucose oxidase on nanomaterial modified electrodes. This work focuses on the grafting of pABA on graphene oxide modified carbon fabric electrode. The immobilized enzymes have been used to generate electrons from glucose through direct electron transfer at a potential of -490 mV. Electrochemically deposited reduced graphene oxide was used as the cathode with an oxygen reduction potential of -200mV. The anode and the cathode were inserted into a 3D printed electrode holder with an inter electrode distance of 50mm and an OCV of 107mV was obtained. The compact design of the fuel cell combined with it’ s eco-friendly nature makes this an ideal construction for use as a biolfuel cell.

High‐Performance All‐Solid‐State Lithium–Sulfur Batteries Enabled by Amorphous Sulfur‐Coated Reduced Graphene Oxide Cathodes

Safety and the polysulfide shuttle reaction are two major challenges for liquid electrolyte lithium–sulfur (Li–S) batteries. Although use of solid‐state electrolytes can overcome these two challenges, it also brings new challenges by increasing the interface resistance and stress/strain. In this work, the interface resistance and stress/strain of sulfur cathodes are significantly reduced by conformal coating ≈2 nm sulfur (S) onto reduced graphene oxide (rGO). An Li–S full cell consisting of an rGO@S‐Li10GeP2S12‐acetylene black (AB) composite cathode is evaluated. At 60 °C, the all‐solid‐state Li–S cell demonstrates a similar electrochemical performance as in liquid organic electrolyte, with high rate capacities of 1525.6, 1384.5, 1336.3, 903.2, 502.6, and 204.7 mA h g−1 at 0.05, 0.1, 0.5, 1.0, 2.0, and 5.0 C, respectively. It can maintain a high and reversible capacity of 830 mA h g−1 at 1.0 C for 750 cycles. The uniform distribution of the rGO@S nanocomposite in the Li10GeP2S12‐AB matrix generates uniform volume changes during lithiation/delithiation, significantly reducing the stress/strain, thus extending the cycle life. Minimization of the stress/strain of solid cells is the key for a long cycle life of all‐solid‐state Li–S batteries.

Conductive porous vanadium nitride/graphene composite as chemical anchor of polysulfides for lithium-sulfur batteries

Although the rechargeable lithium–sulfur battery is an advanced energy storage system, its practical implementation has been impeded by many issues, in particular the shuttle effect causing rapid capacity fade and low Coulombic efficiency. Herein, we report a conductive porous vanadium nitride nanoribbon/graphene composite accommodating the catholyte as the cathode of a lithium–sulfur battery. The vanadium nitride/graphene composite provides strong anchoring for polysulfides and fast polysulfide conversion. The anchoring effect of vanadium nitride is confirmed by experimental and theoretical results. Owing to the high conductivity of vanadium nitride, the composite cathode exhibits lower polarization and faster redox reaction kinetics than a reduced graphene oxide cathode, showing good rate and cycling performances. The initial capacity reaches 1,471 mAh g−1 and the capacity after 100 cycles is 1,252 mAh g−1 at 0.2 C, a loss of only 15%, offering a potential for use in high energy lithium–sulfur batteries.

In Situ Analysis of the Li–O2 Battery with Thermally Reduced Graphene Oxide Cathode: Influence of Water Addition

The Li–O2 battery technology holds the promise to deliver a battery with significantly increased specific energy compared to today’s Li-ion batteries. As a cathode support material, reduced graphene oxide has received increasing attention in the Li–O2 battery community due to the possibility of increased discharge capacity, increased battery cyclability, and decreased charging overpotential. In this article we investigate the effect of water on a thermally reduced graphene oxide cathode in a Li–O2 battery. Differential electrochemical mass spectroscopy reveals a decreased electron count for batteries with 1000 ppm water added to the electrolyte in comparison to dry batteries, indicating additional parasitic electrochemical or chemical processes. A comparable capacity of the wet and dry batteries indicates that the reaction mechanism in the Li–O2 battery also depends on the surface of the cathode and not only on addition of water to the electrolyte as demonstrated by the solution-based mechanism. In situ s...

Oxygen-containing Functional Groups Enhancing Electrochemical Performance of Porous Reduced Graphene Oxide Cathode in Lithium Ion Batteries

Exploring high performance and environment-friendly electrode materials is highly desirable for the sustainable Li-ion batteries (LIBs) system. In this study, a facile approach of the modified Hummers’ method combining with special thermal reduction was proposed to synthesize nanostructured reduced graphene oxide (RGO) with abundant oxygen-containing functional groups. The resultant RGO showed high specific capacity and excellent cyclability as cathode materials for LIBs. The specific capacity of about 220mAhg−1 at a current density of 50mAg−1 was achieved after 100 cycles. More importantly, it was demonstrated that the capacity increased with the increase of the amount of oxygen functional groups, highlighting the significant effects of oxygen-containing functional groups of RGO on high lithium storage performance.

Slurryless Li2S/reduced graphene oxide cathode paper for high-performance lithium sulfur battery.

Lithium sulfide (Li2S) is a promising cathode material for Li-S batteries with high capacity (theoretically 1166 mAh g(-1)) and can be paired with nonlithium-metal anodes to avoid potential safety issues. However, the cycle life of coarse Li2S particles suffers from poor electronic conductivity and polysulfide shuttling. Here, we develop a flexible slurryless nano-Li2S/reduced graphene oxide cathode paper (nano-Li2S/rGO paper) by simple drop-coating. The Li2S/rGO paper can be directly used as a free-standing and binder-free cathode without metal substrate, which leads to significant weight savings. It shows excellent rate capability (up to 7 C) and cycle life in coin cell tests due to the high electron conductivity, flexibility, and strong solvent absorbency of rGO paper. The Li2S particles that precipitate out of the solvent on rGO have diameters 25-50 nm, which is in contrast to the 3-5 μm coarse Li2S particles without rGO.

Reduced graphene oxide for Li–air batteries: The effect of oxidation time and reduction conditions for graphene oxide

Reduced graphene oxide (rGO) has shown great promise as an air-cathode for Li–air batteries with high capacity. In this article we demonstrate how the oxidation time of graphene oxide (GO) affects the ratio of different functional groups and how trends of these in GO are extended to chemically and thermally reduced GO. We investigate how differences in functional groups and synthesis may affect the performance of Li–O2 batteries. The oxidation timescale of the GO was varied between 30min and 3days before reduction. Powder X-ray diffraction, micro-Raman, FE-SEM, BET analysis, and XPS were used to characterize the GO’s and rGO’s. Selected samples of GO and rGO were analyzed by solid state 13C MAS NMR. These methods highlighted the difference between the two types of rGO’s, and XPS indicated how the chemical trends in GO are extended to rGO. A comparison between XPS and 13C MAS NMR showed that both techniques can enhance the structural understanding of rGO. Different rGO cathodes were tested in Li–O2 batteries which revealed a difference in overpotentials and discharge capacities for the different rGO’s. We report the highest Li–O2 battery discharge capacity recorded of approximately 60,000mAh/gcarbon achieved with a thermally reduced GO cathode.

Ultrathin PdTe nanowires anchoring reduced graphene oxide cathodes for efficient hydrogen evolution reaction.

The design and synthesis of efficient electrocatalysts for hydrogen evolution reaction under all pH conditions is extremely desirable but still remains a challenge. Here a facile method to decorate PdTe nanowires on reduced graphene oxide nanosheets (PdTe NWs/rGO) has been developed. As a robust integrated 2D hydrogen-evolving cathode catalyst, the Pd3.02Te NWs/rGO shows a low onset potential of -7 mV and maintains its catalytic activity for at least 48 h in alkaline media. It requires overpotentials (η) of 97 and 355 mV to afford current densities of 10 and 100 mA cm(-2), respectively. The Pd3.02Te NWs/rGO also exhibits a high activity and excellent durability in acidic media.

Effect of the reduction process on the field emission performance of reduced graphene oxide cathodes

The effect of the reduction process and oxygen-contained functional groups on the field emission performance of reduced graphene oxide cathodes.

Free Standing Reduced Graphene Oxide Film Cathodes for Lithium Ion Batteries

We report the fabrication and electrochemical activity of free-standing reduced graphene oxide (RGO) films as cathode materials for lithium ion batteries. The conducting additive and binder-free RGO electrodes with different oxygen contents were assembled by a simple vacuum filtration process from aqueous RGO colloids prepared with the aid of cationic surfactants. The gravimetric capacity of RGO film cathodes showed clear dependence on the oxygen contents controlled by the thermal reduction process. The capacity increased with the increase of the amount of oxygen functional groups, indicating that the main lithium capturing mechanism of RGO cathodes is Li(+) ion interaction with the surface oxygen functionalities. The hydroxyl groups (C-OH) as well as carbon-oxygen double bonds have been identified as the lithiation-active species. The RGO cathodes achieved excellent rate capability due to the fast surface Faradaic reaction, suggesting that self-supported RGO films are promising cathodes for high power application. The graphene oxide (GO)/RGO composite films showed inferior performance to those of RGO only. The poor electronic conductivity of GO might result in inefficient utilization of redox active oxygen functional groups despite the higher oxygen content and higher theoretical capacity of GO/RGO composite films. Further optimization on the amount of oxygen functional groups for higher capacity and better electronic conductivity would lead to the development of RGO based high energy-high power cathodes.