Graphene Cathode Research Articles

Microwave Exfoliated Few-Layered Graphene Cathode for Aluminum Batteries

Microwave Exfoliated Few-Layered Graphene Cathode for Aluminum Batteries

A Study on the Mechanism and Properties of a Self-Powered H2O2 Electrochemical Sensor Based on a Fuel Cell Configuration with FePc and Graphene Cathode Catalyst Materials.

Conventional electrochemical sensors use voltammetric and amperometric methods with external power supply and modulation systems, which hinder the flexibility and application of the sensors. To avoid the use of an external power system and to minimize the number of electrochemical cell components, a self-powered electrochemical sensor (SPES) for hydrogen peroxide was investigated here. Iron phthalocyanine, an enzyme mimetic material, and Ni were used as a cathode catalyst and an anode material, respectively. The properties of the iron phthalocyanine catalyst modified by graphene nanoplatelets (GNPs) were investigated. Open circuit potential tests demonstrated the feasibility of this system. The GNP-modulated interface helped to solve the problems of aggregation and poor conductivity of iron phthalocyanine and allowed for the achievement of the best analytical characteristics of the self-powered H2O2 sensor with a low detection limit of 0.6 µM and significantly higher sensitivity of 0.198 A/(M·cm2) due to the enhanced electrochemical properties. The SPES demonstrated the best performance at pH 3.0 compared to pH 7.4 and 12.0. The sensor characteristics under the control of external variable load resistances are discussed and the cell showed the highest power density of 65.9 μW/cm2 with a 20 kOhm resistor. The practical applicability of this method was verified by the determination of H2O2 in blood serum.

Enhancing Electrochemical Performance of Aluminum-Ion Batteries with Fluorinated Graphene Cathode.

In pursuit of high-performance aluminum-ion batteries, the selection of a suitable positive electrode material assumes paramount importance, and fluorinated graphene (FG) nanostructures have emerged as an exceptional candidate. In the scope of this study, a flexible tantalum foil is coated with FG to serve as the positive electrode for aluminum-ion batteries. FG positive electrode demonstrates a remarkable discharge capacity of 109 mA h g-1 at a current density of 200 mA g-1, underscoring its tremendous potential for energy storage applications. Concurrently, the FG positive electrode exhibits a discharge capacity of 101 mA h g-1 while maintaining an impressive coulombic efficiency of 95 % over 300 cycles at a current density of 200 mA g-1, which benefiting from the significant structure of FG. The results of the in-situ Raman spectroscopy signified the presence of intercalation/de-intercalation processes of AlCl4 - behavior within the FG layers.

Binder-Free Three-Dimensional Porous Graphene Cathodes via Self-Assembly for High-Capacity Lithium-Oxygen Batteries.

The porous architectures of oxygen cathodes are highly desired for high-capacity lithium-oxygen batteries (LOBs) to support cathodic catalysts and provide accommodation for discharge products. However, controllable porosity is still a challenge for laminated cathodes with cathode materials and binders, since polymer binders usually shield the active sites of catalysts and block the pores of cathodes. In addition, polymer binders such as poly(vinylidene fluoride) (PVDF) are not stable under the nucleophilic attack of intermediate product superoxide radicals in the oxygen electrochemical environment. The parasitic reactions and blocking effect of binders deteriorate and then quickly shut down the operation of LOBs. Herein, the present work proposes a binder-free three-dimensional (3D) porous graphene (PG) cathode for LOBs, which is prepared by the self-assembly and the chemical reduction of GO with triblock copolymer soft templates (Pluronic F127). The interconnected mesoporous architecture of resultant 3D PG cathodes achieved an ultrahigh capacity of 10,300 mAh g-1 for LOBs. Further, the cathodic catalysts ruthenium (Ru) and manganese dioxide (MnO2) were, respectively, loaded onto the inner surface of PG cathodes to lower the polarization and enhance the cycling performance of LOBs. This work provides an effective way to fabricate free-standing 3D porous oxygen cathodes for high-performance LOBs.

Highly matched porous MXene anodes and graphene cathodes for high-performance aqueous asymmetric supercapacitors

Aqueous asymmetric supercapacitors (ASCs) provide promising prospects for electronic systems in the future that require high energy density, power density and cycling life, due to their advantages such as low cost, safe operation and environmental friendliness. However, developing well-matched anodes and cathodes with complementary potential windows and coordinated charge storage kinetics remains a significant challenge. Here, we constructed porous MXene- and graphene-based films with nitrogenous and phosphorous terminals as anodes and cathodes, respectively, alleviating the restacking of nanosheets, generating more electrochemical active sites and improving the electrolyte penetration. The assembled aqueous ASCs based on the porous MXene and graphene films could achieve an excellent energy density of 26.8 Wh kg−1 at 425 W kg−1, high rate performance, and remarkable cycling stability with 97.3 % retention after 20,000 cycles. This work demonstrates a novel concept to develop high-performance aqueous ASCs by surface engineering of two-dimensional porous electrodes with matched structural and electrochemical properties.

Aqueous Asymmetric Supercapacitors with Pyrenetetraone‐Derived Pseudocapacitive Polymer‐Functionalized Graphene Cathodes Enabling a 1.9 V Operating Window

Aqueous Asymmetric Supercapacitors with Pyrenetetraone‐Derived Pseudocapacitive Polymer‐Functionalized Graphene Cathodes Enabling a 1.9 V Operating Window

A Study on the Field Emission Characteristics of High-Quality Wrinkled Multilayer Graphene Cathodes.

Field emission (FE) necessitates cathode materials with low work function and high thermal and electrical conductivity and stability. To meet these requirements, we developed FE cathodes based on high-quality wrinkled multilayer graphene (MLG) prepared using the bubble-assisted chemical vapor deposition (B-CVD) method and investigated their emission characteristics. The result showed that MLG cathodes prepared using the spin-coating method exhibited a high field emission current density (~7.9 mA/cm2), indicating the excellent intrinsic emission performance of the MLG. However, the weak adhesion between the MLG and the substrate led to the poor stability of the cathode. Screen printing was employed to prepare the cathode to improve stability, and the influence of a silver buffer layer was explored on the cathode's performance. The results demonstrated that these cathodes exhibited better emission stability, and the silver buffer layer further enhanced the comprehensive field emission performance. The optimized cathode possesses low turn-on field strength (~1.5 V/μm), low threshold field strength (~2.65 V/μm), high current density (~10.5 mA/cm2), and good emission uniformity. Moreover, the cathode also exhibits excellent emission stability, with a current fluctuation of only 6.28% during a 4-h test at 1530 V.

Regulating the aspect ratio of bulk few-layer graphene to improve the field emission performance

Owing to its excellent electrical conductivity and local electric field enhancement capability from abundant electron tunneling edges, graphene is a promising material for field emission. However, graphene thin-film emitters mostly emit in planar structures, and due to the flexibility of the thin film, it is commonly challenging to achieve vertical structure emission with large aspect ratios. Therefore, the emission performance of current graphene field emitters is difficult to meet the requirements of high current applications. In the present investigation, bulk few-layer graphene cathodes are formed by cold pressing to achieve upright structural field emission, and the emission performance is enhanced by appropriately adjusting the aspect ratio. The obtained bulk few-layer graphene emitters exhibit a higher conductivity of 2498 S/cm and tensile strength of 6.02 MPa. The turn-on electric field (at 1 mA/cm2) and threshold electric field (at 10 mA/cm2) in order are determined to be 1.78 V/μm and 2.66 V/μm, with a maximum current density of 986 mA/cm2 (at 6.65 V/μm) and a maximum field enhancement factor of 14,891. Excellent emission stability is achieved over a continuous period of 110 h at 5 mA @ 526 mA/cm2. With the increase of emission current, the bulk few-layer graphene with large aspect ratios exhibits better emission stability. This work provides valuable insights into the application of graphene-based field emitters at high currents.

Electrochemical conversion from hydroxyl to carbonyl groups for improved performance of dual-carbon lithium ion capacitors

Pseudocapacitance from oxygen functional groups of carbon materials have been taken advantage to improve the capacity of lithium ion capacitors (LICs). However, the Li+ adsorption of hydroxyl groups and the Li+ desorption from lithiated hydroxyl groups remain poorly understood. Herein, density functional theory (DFT) calculations in combination with experimental characterizations of hydroxyl-rich graphene (HRG) cathodes at different lithiated states are performed. The calculation results predict that fully lithiated hydroxyl groups undergo Li+ desorption at a high potential of 4.45 V (vs. Li+/Li), and consequent conversion into carbonyl groups instead of return to hydroxyl groups. Experimental investigations through galvanostatic charge/discharge tests and ex-situ X-ray photoelectron spectra (XPS) analyses of HRG verify the predicted Li+ desorption potential and the conversion. This electrochemical conversion is effective to obtain carbonyl-rich graphene (CRG) with significantly improved specific capacities. The conversion process can be completed in LIC full cells assembled with pre-lithiated HRG cathodes, through which an HRG//N-doped porous carbon (NPC) LIC transforms into a CRG//NPC LIC with improved performance. The dual-carbon CRG//NPC LIC delivers an energy density of 206.2 Wh kg−1 at a power density of 169.5 W kg−1, and superior cycling stability.

Hierarchically Porous and Minimally Stacked Graphene Cathodes for High‐Performance Lithium–Oxygen Batteries (Adv. Energy Mater. 2/2024)

Hierarchically Porous and Minimally Stacked Graphene Cathodes for High‐Performance Lithium–Oxygen Batteries (Adv. Energy Mater. 2/2024)

Aqueous Asymmetric Supercapacitors with Pyrenetetraone‐Derived Pseudocapacitive Polymer‐Functionalized Graphene Cathodes Enabling a 1.9 V Operating Window

Pseudocapacitive polymers have garnered significant attention in the realm of supercapacitors due to their versatile molecular design capabilities, cost‐effectiveness, and impressive electrical conductivity. However, limited by the low capacity and short cycle life, the investigation on conducting polymers for potential electrode materials is still insufficient. Herein, a series of pyrenetetraone‐derived polymers with pyrazine units are designed and synthesized. Furthermore, UV–vis spectroscopy demonstrates the different interaction behavior between the polymers and reduced graphene oxide (rGO), which can further indicate the performance difference of the composite electrodes. As a result, the pseudocapacitive polymer/rGO composite electrode (2/1 PPYT/rGO) exhibits a high specific capacitance of 591 F g−1 at 1 A g−1 in a 1 m sulfuric acid electrolyte. The asymmetric supercapacitor (ASC) assembled by the 2/1 PPYT/rGO cathode and the annealed Ti3C2Tx anode (2/1 PPYT/rGO//A‐Ti3C2Tx) delivers an excellent energy density of 38.1 Wh kg−1 at a power density of 950 W kg−1. Additionally, both devices demonstrate outstanding stability, retaining over 90% of their capacity after 15 000 charge/discharge cycles. As a result, these carefully engineered organic polymers, with their well‐thought‐out structural designs, showcase exceptional electrochemical performance, positioning them as highly promising candidates for the next generation of high‐performance energy storage materials.

Chloroaluminate ionic liquids for low-temperature aluminum-ion batteries

The paper discusses the feasibility of 1-ethyl-3-methylimidazolium ([EMIm]Cl) and 1-butyl-3-methylimidazolium ([BMIm]Cl) chloroaluminate ionic liquids (ILs) as electrolytes for aluminum-ion batteries capable of delivering high performance at subzero temperatures. The melting temperatures of AlCl3–[EMIm]Cl and AlCl3–[BMIm]Cl ILs with the molar ratio of aluminum chloride to the chloride of imidazolium salt (N) equal to 1.3 and 1.5 were determined using DSC. The melting temperature of AlCl3–[EMIm]Cl is –21 and –32 °C at N = 1.3 and N = 1.5, respectively. The conductivity of AlCl3–[EMIm]Cl IL increases sharply at heating and decreases sharply near its melting temperature at cooling. The DSC curves for [BMIm]Cl-based ILs do not contain any peaks related to the melting or crystallization of the IL, and temperature dependences of conductivity contain no inflection points. Galvanostatic cycling and cyclic voltammetry demonstrated efficient performance of the aluminum-ion battery with an aluminum anode, graphene cathode and AlCl3–[BMIm]Cl IL, which delivered coulombic efficiency approaching 100 % at temperatures as low as –30 °C. The capacity of the graphene cathode was found to be 82.4, 63.0 and 48.5 mA∙h∙g−1 at 0, –20 and –30 °C, respectively.

Hierarchically Porous and Minimally Stacked Graphene Cathodes for High‐Performance Lithium–Oxygen Batteries

AbstractAlthough lithium–oxygen batteries have attracted attention due to their extremely high energy densities, rational design, and critical evaluation of high‐energy‐density cathode for practical Li–O2 batteries is still urgently needed. Herein, the multiscale, angstrom‐to‐millimeter, precisely controllable synthesis of binder‐free cathodes with minimally stacked graphene free from edge sites is demonstrated. The proposed Li–O2 battery, based on a hierarchically porous cathode with a practical mass loading of >4.0 mg cm−2, simultaneously exhibits an unprecedented specific areal (>30.0 mAh cm−2), mass (>6300 mAh g−1), and volumetric (>480 mAh cm−3) capacities. The battery displays the optimal energy density of 793 Wh kg−1 critically normalized to the total mass of all active materials including electrolytes and even discharge products Li2O2. Comprehensive in situ characterizations demonstrate a unique discharge mechanism in hierarchical pores which contributes to competitive battery performance. Superior rate performance in a current density range of 0.1 to 0.8 mA cm−2 and long‐cycle stability (>260 cycles) at a current density of 0.4 mA cm−2, outperforming state‐of‐the‐art carbon cathodes. This study yields insight into next‐generation carbon cathodes, not only for use in practical Li–O2 batteries, but also in other metal–gas batteries with high energy densities.

Lithium-ion and solvent co-intercalation enhancing the energy density of fluorinated graphene cathode

Fluorinated carbons CFx hold the highest theoretical energy density (e.g., 2180 W h kg−1 when x = 1) among all cathode materials of lithium primary batteries. However, the low conductivity and severe polarization limit it to achieve its theory. In this study, we design a new electrolyte, namely 1 M LiBF4 DMSO:DOL (1:9 vol.), achieving a high energy density in Li/CFx primary cells. The DMSO with a small molecular size and high donor number successfully solvates Li+ into a defined Li+-solvation structure. Such solvated Li+ can intercalate into the large-spacing carbon layers and achieve an improved capacity. Consequently, when discharged to 1.0 V, the CF1.12 cathode demonstrates a specific capacity of 1944 mA h g−1 with a specific energy density of 3793 W h kg−1. This strategy demonstrates that designing the electrolyte is powerful in improving the electrochemical performance of CFx cathode.

Fabrication of Self-Rolled Fluorinated Graphene Nanosheets and Cathode Application

A simple approach of self-rolled fluorinated graphene nanosheets (srFGN) was reported in this work. Notably, the preparation of the specific srFGN showed interesting solvent-sensitive characteristics. The research findings revealed that when an aprotic solvent was used, e.g., dimethyl sulfoxide (DMSO), the interesting srFGN was obtained readily, which was characterized by different technologies. Cathode application for primary lithium-ion batteries (LIBs) of the prepared srFGN nanoscrolls was also studied in this work, which exhibited elevated energy density (e.g., 2287.9 Wh·kg−1), excellent discharge specific capacity and reliable discharge platform, indicating it a cheap and hyperdensity cathode material for primary LIBs.

An Ion Exchange Membrane-Free, Ultrastable Zinc-Iodine Battery Enabled by Functionalized Graphene Electrodes

Global warming requires a shift in the energy economy towards renewable energy sources, such as solar and wind energy, to meet the ever-increasing worldwide energy demand while having lesser negative impact on the environment. The integration of such sustainable energy resources into the existing infrastructure, however, is challenging due to their fluctuations and intermittences requiring the development of efficient (intermediate) energy storage systems. The ultimate goal for these systems pertains to high performance, durability, safety, facile scalability, cost, and environmental-friendliness. The aqueous rechargeable zinc-iodine (Zn-I2) battery is promising due to the high theoretical capacities of Zn (820 mAh gZn -1) and I2 (211 mA h gI2 -1) along with the very high solubilities in aqueous media. Other advantages include the abundance of the electrode materials and the safety of the aqueous electrolyte. The high energy density of aqueous zinc-based batteries is a result of the multi-electron redox reactions and the low electrochemical potential of Zn (-0.763 V vs. RHE) in mildly acidic electrolytes such as in a Zn-I2 battery. In addition, compared to other alkali metals such as lithium, sodium, and potassium, metallic Zn is relatively stable in an aqueous environment over a wide temperature range.Several challenges need to be addressed for Zn-I2 batteries to be competitive; namely, self-discharge, sluggish kinetics, low practical energy density, as well as the dendrite formation on the Zn anode. In this work, we design a high-performance Zn-I2 battery with an unusual long-term stability which is based on a novel design of electrodes and electrolyte. In detail, a three-dimensional functionalized graphene cathode facilitates the iodide redox reactions and also immobilizes dissolved polyiodides; thus, suppressing the detrimental shuttling effect. Furthermore, we design a composite anode made of Zn coated with a film of reduced graphene oxide. This modification significantly enhances the performance and stabilizes the anode during repeated Zn stripping/plating preventing dendrite formation. The electrolyte is formulated in a way that, along with the graphene-based cathode, allows for the utilization of an economical glass fiber separator instead of the commonly employed ion-exchange membranes, which are expensive and have relatively high ohmic resistances. Our novel Zn-I2 battery design exhibit high current efficiencies of nearly 100%, along with stable specific capacities of 257, 186, 150, 84 mAh g-1 at corresponding current densities of 1, 2, 5, 10 A g-1. Furthermore, a long-term capacity retention of 96.7% at 5 A g-1 over 2000 cycles is achieved, outperforming most comparable aqueous batteries.

Ultra-Low Loading of Iron Oxide and Platinum on CVD-Graphene Composites as Effective Electrode Catalysts for Solid Acid Fuel Cells

We propose a new design for electrocatalysts consisting of two electrocatalysts (platinum and iron oxide) that are deposited on the surfaces of an oxidized graphene substrate. This design is based on a simple structure where the catalysts were deposited separately on both sides of oxidized graphene substrate; while the iron oxide precipitated out of the etching solution on the bottom-side, the surface of the oxidized graphene substrate was decorated with platinum using the atomic layer deposition technique. The Fe2O3-decorated CVD-graphene composite exhibited better hydrogen electrooxidation performance (area-normalized electrode resistance (ANR) of ~600 Ω·cm−2) and superior stability in comparison with bare-graphene samples (ANR of ~5800 Ω·cm−2). Electrochemical impedance measurements in humidified hydrogen at 240 °C for (Fe2O3|Graphene|Platinum) electrodes show ANR of ~0.06 Ω·cm−2 for a platinum loading of ~60 µgPt·cm−2 and Fe2O3 loading of ~2.4 µgFe·cm−2, resulting in an outstanding mass normalized activity of almost 280 S·mgPt−1, exceeding even state-of-the-art electrodes. This ANR value is ~30% lower than the charge transfer resistance of the same electrode composition in the absence of Fe2O3 nanoparticles. Detailed study of the Fe2O3 electrocatalytic properties reveals a significant improvement in the electrode’s activity and performance stability with the addition of iron ions to the platinum-decorated oxidized graphene cathodes, indicating that these hybrid (Fe2O3|Graphene|Platinum) materials may serve as highly efficient catalysts for solid acid fuel cells and beyond.

Graphene and biochar-based cathode catalysts for microbial fuel cell: Performance evaluation, economic comparison, environmental and future perspectives

Microbial fuel cells (MFCs) have been the prime focus of research in recent years because of their distinctive feature of concomitantly treating and producing electricity from wastewater. Nevertheless, the electrical performance of MFCs is hindered by a protracted oxygen reduction reaction (ORR), and often a catalyst is required to boost the cathodic reactions. Conventional transition metals-based catalysts are expensive and infeasible for field-scale usage. In this regard, carbon-based electrocatalysts like waste-derived biochar and graphene are used to enhance the commercialisation prospects of MFC technology. These carbon-catalysts possess unique properties like superior electrocatalytic activity, higher surface area, and high porosity conducive to ORR. Theoretically, graphene-based cathode catalysts yield superior results than a biochar-derived catalyst, though at a higher cost. In contrast, the synthesis of waste-extracted biochar is economical; however, its ability to catalyse ORR is debatable. Therefore, this review aims to make a side-by-side techno-economic assessment of biochar and graphene-based cathode catalyst used in MFC to predict the relative performance and typical cost of power recovery. Additionally, the life cycle analysis of the graphene and biochar-based materials has been briefly discussed to comprehend the associated environmental impacts and overall sustainability of these carbo-catalysts.

Holey Graphene/Ferroelectric/Sulfur Composite Cathodes for High-Capacity Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries have attracted considerable interest as next-generation high-density energy storage devices. However, their practical applications are limited by rapid capacity fading when cycling cells with high mass loading levels. This could be largely attributed to the inferior electron/ion conduction and the severe shuttling effect of soluble polysulfide species. To address these issues, composites of sulfur/ferroelectric nanoparticles/ho ley graphene (S/FNPs/hG) cathodes were fabricated for high-mass-loading S cathodes. The solvent-free and binder-free procedure is enabled using holey graphene as a unique dry-pressable electrode for Li-S batteries. The unique structure of the holey graphene framework ensures fast electron and ion transport within the electrode and affords enough space to mitigate the electrode's volume expansion. Moreover, ferroelectric polarization due to FNPs within S/hG composites induces an internal electric field, which effectively reduces the undesired shuttling effect. With these advantages, the S/FNPs/hG composite cathodes exhibit sustainable and ultrahigh specific capacity up to 1409 mAh/gs for the S/BTO/hG cathode. A capacity retention value of 90% was obtained for the S/BNTFN/hG battery up to cycle 18. The high mass loading of sulfur ranging from 5.72 to 7.01 mgs/cm2 allows maximum high areal capacity up to ∼10 mAh/cm2 for the S/BTO/hG battery and superior rate capability at 0.2 and 0.5 mA/cm2. These results suggest sustainable and high-yielding Li-S batteries can be obtained for potential commercial applications.

Uranium extraction by a graphene-based asymmetric electrode configuration through combined complexation, electro-adsorption, and photocatalytic reduction

Recently, capacitive deionization has become a promising approach for uranium extraction owing to its energy-efficiency and environmental benign. However, theadsorbedchargeduranium(VI)(U(VI))wouldrepulsetheincomingU(VI)ions,andmightre-enterintosolution,vastlyimpedingtheimprovementofelectro-adsorptionperformance. Reducing the adsorbed U(VI) ions into U(IV) precipitation is an ideal way to address above issues. Here, a coupling approach of photocatalytic reduction and electro-adsorption (PEA) was proposed. An asymmetric electrode configuration, composed of phosphate functionalized graphene (GP) cathode and graphene/TiO2 nanocomposite (GT) anode was rationally designed, and originally proved its enhanced U(VI) extraction via the PEA method. The asymmetric electrode device enables the fast transport of photo-electron and the rapidly directed migration of U(VI) ion to the GP cathode. More importantly, it combines three synthetic mechanisms of complexation, electro-adsorption, and photocatalytic reduction to extract U(VI) ions. As a consequence, the as-designed PEA method shows a higher removal rate of 91.3% in comparison with conventional photocatalytic reduction (PA) and electro-adsorption (EA) methods. Meanwhile, its kinetics rate is 225% and 50% faster than PA and EA methods. Furthermore, an enhanced reduction efficiency of U(VI) to U(IV), good selectivity as well as reusability for PEA method were also obtained. The results provide a potential approach to combine multiple mechanisms for efficient U(VI) extraction from aqueous solution by purposeful design of asymmetric electrodes.