Iodine-doped Graphene Research Articles

Iodine-Doped Graphene Oxide: Fast Single-Stage Synthesis and Application as Electrocatalyst.

Iodine-doped graphene oxide is attracting great attention as fuel cell (FC) electrocatalysts with a high activity for the oxygen reduction reaction (ORR). However, most of the reported preparation techniques for iodine-doped graphene (I/rGO) could be transposed into practice as multiple step procedures, a significant disadvantage for scale-up applications. Herein, we describe an effective, eco-friendly, and fast technique for synthesis by a microwave-tuned one-stage technique. Structural and morphological characterizations evidenced the obtaining of nanocomposite sheets, with iodine bonded in the graphene matrix. The ORR performance of I/rGO was electrochemically investigated and the enhancement of the cathodic peak was noted. Based on the noteworthy electrochemical properties for ORR activity, the prepared I/rGO can be considered an encouraging alternative for a more economical electrode for fuel cell fabrication and commercialization. In this perspective, the iodine-based catalysts synthesis can be considered a step forward for the metal-free electrocatalysts development for the oxygen reduction reaction in fuel cells.

NO2 Gas Sensor Using Iodine Doped Graphene at Room Temperature With Electric Field Enhanced Recovery

A novel carbon-based material was synthesized by chemical doping of Iodine (I₂) into multilayer graphene (MLG) using photolysis method. Elemental analysis using Energy Dispersive X-ray (EDX) determined low amount of Iodine doping in the graphene. Raman spectroscopy demonstrated increase in number of layers of graphene. Iodine doped graphene (I-MLG) showed a sharp reduction in resistance when exposed to NO₂ gas at room temperature. It demonstrated sensing response of 69% for 100 ppm of gas in just 16 seconds at room temperature. When compared with other gases and vapours, I-MLG showed selective sensing towards NO₂ gas by reduction in resistance during exposure. Hybrid Material displayed reversible sensing but recovery after the removal of NO₂ gas source took 1380 seconds. An electric field assisting sensor element was fabricated to lower the recovery time to 156 seconds after applying negative gate voltage of −15V. Sensing and recovery mechanisms of I-MLG along with effect of electric field are presented.

Sensitive electrochemical detection of endocrine disruptor bisphenol A (BPA) in milk based on iodine-doped graphene

A novel electrochemical sensor for bisphenol A (BPA) detection was constructed on a glassy carbon electrode (GCE) coated with iodine-doped graphene (I-RGO). The I-RGO material was facilely prepared by simultaneous iodine-doping and reduction of graphene oxide (GO) with hydrogen iodide solution. The electrochemical performance of developed electrode was examined using electrochemical impedance spectra (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. Under the optimal experimental conditions, the sensor presented a good linear response between the current and the BPA concentration range of 0.04–4.5 μM, with a low detection limit of 0.02 μM (S/N = 3). The developed I-RGO/GCE sensor has high selectivity, good stability and excellent reproducibility. Moreover, it has been successfully applied for BPA detection in real milk samples with satisfying recovery results.

Bi2S3 nanorods encapsulated in iodine-doped graphene frameworks with enhanced potassium storage properties

Bismuth sulfide (Bi2S3) is a promising anode material for high-performance potassium ion batteries due to its high theoretical capacity. However, the poor conductivity and substantial volume expansion hinder its practical application. We proposed an iodine-doped graphene encapsulated Bi2S3 nanorods composite (Bi2S3/IG) as an efficient anode for PIBs. The uniform-sized Bi2S3 nanorods evenly in-situ encapsulated in iodine-doped graphene framework, facilitating the electron transportation and structural stability. The potassium storage performance was evaluated in three electrolytes, with the best option of 5 mol/L KFSI in DME. The reversible capacity of representative Bi2S3/IG reached 453.5 mAh/g at 50 mA/g. Meanwhile, it could deliver an initial reversible capacity of 413.6 mAh/g at 100 mA/g, which maintained 256.9 mAh/g after 200 cycles. The proposed strategy contributes to improving potassium storage performance of metal sulfide anodes.

Flexible asymmetric microsupercapacitor with high energy density based on all-graphene electrode system

The growing interest and rapid development of portable and flexible wearable electronics has significantly escalated the need of designing miniaturized on-chip energy storage and conversion units as power sources for smart electronic devices. Current aqueous microsupercapacitors suffer from a low energy density due to their small working potential, which limits their potential application. This study presents the fabrication of a 1.6 V flexible, aqueous asymmetric microsupercapacitor (AMSC) with 83% capacitance retention after 5000 cycles which designed by the integration and voltage balance of functionalized graphene-based cathode as a double-layer supercapacitive electrode and iodine-doped graphene anode as a pseudocapacitive electrode. The combination of electrostatic and faradic charge storage mechanism in this all-graphene-based AMSC enables the device to deliver an ultra-high energy–power density (4.75 mWh cm−3 at 61.55 W cm−3) and a stabilized performance even after 2000 repeated bending cycles, which suggests the promising potential of the all-graphene AMSC as a substantial power source for future flexible electronic devices.

Influence of catalyst structure on PEM fuel cell performance – A numerical investigation

Abstract The effect of the catalyst microstructure on a 5 cm2 PEM fuel cell performance is numerically investigated. The catalyst layer composition and properties (i.e. ionomer volume fraction, platinum loading, particle radius, electrochemical active area and carbon support type), and the mass transport resistance due to the ionomer and liquid water surrounding the catalyst particles, are incorporated into the model. The effects of the above parameters are discussed in terms of the polarization curves and the local distributions of the key parameters. An optimum range of the ionomer volume fraction was found and a gain of 39% in the performance was achieved. As regards the platinum loading and catalyst particle radius, the results showed that a higher loading and a smaller radius leads to an increase in the PEMFC performance. Further, the influence of the electrochemical active area produces an overall increase of 22% in current density and this was due to the use of a new material developed as support for Pt particles, an iodine doped graphene, which has better electrical contacts and additional pathways for water removal. Using this parameter, the numerical model has been validated and good agreement with experimental data was achieved, thus giving confidence in the model as a design tool for future improvements of the catalyst structure.

Hierarchical porous hollow FeFe(CN)6 nanospheres wrapped with I-doped graphene as anode materials for lithium-ion batteries.

Hierarchical porous hollow FeFe(CN)6 nanospheres were synthesized via a facile anisotropic chemical etching route at different temperatures. Herein, we integrated these FeFe(CN)6 nanospheres and conductive iodine-doped graphene (IG) into a lithium-ion battery (LIB) system, FeFe(CN)6@IG. The hollow Prussian-blue type FeFe(CN)6 nanospheres with an average particle size of 230 nm are uniformly and tightly encapsulated by IG sheets. As an anode material for LIBs, the fabricated FeFe(CN)6@IG exhibits high specific capacity, excellent rate properties, and superior cycling stability. A reversible capacity can be maintained at 709 mA h g-1 after 250 cycles at a current density of 1000 mA g-1. Even at a current rate of 2000 mA g-1, the capacity could reach 473 mA h g-1. This facile fabrication strategy may pave the way for constructing high performance Prussian blue-based anode materials for potential application in advanced lithium-ion batteries.

Direct and efficient conversion from low-quality graphite to high-quality graphene nanoplatelets

Low-quality graphite (L-graphite), containing various impurities (e.g., metals and inorganics), can be directly and efficiently converted into high-quality iodine-doped graphene nanoplatelets (HIGnPs) via mechanochemical ball-milling in the presence of iodine (I2) with subsequent work-up procedures. Despite using L-graphite, the resultant HIGnPs show high-quality characteristics, including large specific surface area (969 m2 g−1), lower metallic residues, and well-maintained graphitic structure. In addition, HIGnPs display remarkable electrocatalytic performance for oxygen reduction reaction (ORR), involving benefits such as higher selectivity, longer-term stability, and better tolerance to methanol crossover/CO poisoning effects. Therefore, simple mechanochemical ball-milling in solid state can produce high-quality graphene nanoplatelets in large quantity at low-cost for commercialization, regardless of the initial quality of the graphite.

Iodine-doped graphene – Catalyst layer in PEM fuel cells

Graphene base materials have received appreciable attention as substrate or nanocomposite with nonmetallic catalysts in alternative energy devices and technologies. The end application of iodine-doped (I-doped) graphene in fuel cells has been recently investigated as innovative nanomaterial for oxygen reduction reaction (ORR). Microscopic and spectroscopic techniques (SEM, FTIR, XRF, XPS) have been combined with structural investigation (BET) and electrochemical techniques for a comprehensive characterization of developed ORR catalysts. Moreover, the durability as ORR electrode have been evaluated in order to assess long-term performance. I-doped graphene was prepared by nucleophilic substitution of graphene oxide (GrO) by reduction with HI. The as-synthesized graphene with incorporation of iodine possesses unique structure revealing high surface area, mesopores and vacancies. The structural characteristics and their synergistic effects could not only improve the ions and electrons transportation but also limits the ohmic resistance. Thus the I-doped graphene exhibited superior electrochemical performances as well as long-term stability, which demonstrate that the I-doped graphene with great potential to be an efficient electrode material.

A Class of High Performance Electrocatalysts for Oxygen Reduction Reaction of Fuel Cells, using Iodine Doped Graphene

Low cost, sustainable and high performance electrocatalysts for oxygen reduction reaction (ORR) which can replace/reduce rare metals base catalysts are highly desirable for the effective commercial development of fuel cells. In this paper, we report a class of low cost electrocatalyst with highly performance for ORR, obtained by graphene doping with iodine precursor. It can be one of the most promising alternatives to Pt-based catalysts to date. Iodine doped graphene based materials were prepared by nucleophilic substitution and characterized by different techniques, including Scanning Electron Microscopy SEM, wavelength dispersive X-ray fluorescence WDXRF, that revealed the structure and morphology. The iodinated graphene was sprayed on gas diffusion layer (GDL) and tested in a single cell PEMFC. The electrochemical performances of fuel cell with/without iodinated graphene under typical experimental conditions were evaluated, namely current-voltage polarization and cyclic voltammetry curves, electrochemical impedance spectroscopy (EIS).

Center-iodized graphene as an advanced anode material to significantly boost the performance of lithium-ion batteries.

Iodine edge-doped graphene can improve the capacity and stability of lithium-ion batteries (LIBs). Our theoretical calculations indicate that center-iodization can further significantly enhance the anode catalytic process. To experimentally prove the theoretical prediction, iodine-doped graphene materials were prepared by one-pot hydrothermal and ball-milling approaches to realize different doping-sites. Results show that the center-iodinated graphene (CIG) anode exhibits a remarkably high reversible capacity (1121 mA h g-1 after 180 cycles at 0.5 A g-1), long-cycle life (0.01% decay per cycle over 300 cycles at 1 A g-1) and high-rate capacity (374 mA h g-1 after 800 cycles at 8 A g-1), which greatly improves the performance of the edge-iodinated graphene anode and these results are in good agreement with the theoretical analysis. More importantly, the CIG anode also delivers a high-rate capacity and excellent cycling stability (279 mA h g-1 after 500 cycles at 10 A g-1) in full-cells. Both the theoretical analysis and experimental investigation reveal the enhancement mechanism, in which the center-iodization increases the surface charge for fast electron transfer rate, improves the conductivity for charge transport and rationalizes the pore structure for enhanced mass transport and ion insertion/desertion, thus resulting in a high rate capacity and long cycle life. This work not only discloses the critical role of catalytic sites including both amounts and site positions but also offers great potential for high-power rechargeable LIB applications.

Sandwich-Type NbS2@S@I-Doped Graphene for High-Sulfur-Loaded, Ultrahigh-Rate, and Long-Life Lithium-Sulfur Batteries.

Lithium-sulfur batteries practically suffer from short cycling life, low sulfur utilization, and safety concerns, particularly at ultrahigh rates and high sulfur loading. To address these problems, we have designed and synthesized a ternary NbS2@S@IG composite consisting of sandwich-type NbS2@S enveloped by iodine-doped graphene (IG). The sandwich-type structure provides an interconnected conductive network and plane-to-point intimate contact between layered NbS2 (or IG) and sulfur particles, enabling sulfur species to be efficiently entrapped and utilized at ultrahigh rates, while the structural integrity is well maintained. NbS2@S@IG exhibits prominent high-power charge/discharge performances. Reversible capacities of 195, 107, and 74 mA h g-1 (1.05 mg cm-2) have been achieved after 2000 cycles at ultrahigh rates of 20, 30, and 40 C, respectively, and the corresponding average decay rates per cycle are 0.022%, 0.031% and 0.033%, respectively. When the area sulfur loading is increased to 3.25 mg cm-2, the electrode still maintains a high discharge capacity of 405 mAh g-1 after 600 cycles at 1 C. Three half-cells in series assembled with NbS2@S@IG can drive 60 indicators of LED modules after only 18 s of charging. The instantaneous current and power of the device reach 196.9 A g-1 and 1369.7 W g-1, respectively.

Low cost iodine doped graphene for fuel cell electrodes

In this work, iodine-doped graphene (I-Gr) was successfully prepared using the electrophilic substitution method and was characterized using micro-Raman spectroscopy, X-Ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. I-Gr was integrated into a cathode electrode, as microporous layer. A simple, time-efficient and reliable test protocol was employed for the screening of the new cathode catalyst layers for the PEM fuel cell. A new approach on an aggressive accelerated degradation testing (ADT) protocol along with the monitoring of electrochemical performances response was introduced in order to investigate the degradation. The 400 cycle's operation, totalizing 100 h, was performed for specific sequences of current cycling steps. Electrochemical performances, including polarization curves (I-V), electrochemical surface area (ECSA), and linear sweep voltammetry (LSV) were measured and analyzed every 25 h in order to investigate the performance decreasing trend during the proposed ADT. This reported 100 h test provides very limited information and requires further investigation.

One-step and low-temperature synthesis of iodine-doped graphene and its multifunctional applications for hydrogen evolution reaction and electrochemical sensing

Iodine (I) has emerged as a powerful heteroatom dopant for efficiently tailoring the electrocatalytic properties of graphene. However, the preparation methods of I-doped graphene (I-G) and its electrocatalysis applications remain largely unexplored. Herein, a one-step and low-temperature hydrothermal approach was developed for the successful synthesis of I-G with a high I-doping level (0.52 at.%). The resulting I-G was then applied as a metal-free catalyst for hydrogen evolution reaction (HER) and electrochemical sensing. It was shown that the I-G exhibited a dramatically enhanced HER activity compared to undoped graphene, attributed to the critical role of I-doping in offering large exposed active sites and high electron transfer capability. Furthermore, I-G also displayed attractive sensing performances for highly sensitive and selective detection of dopamine. These findings demonstrate that the hydrothermally synthesized I-G can be a promising electrocatalyst for multifunctional applications in water-splitting and electrochemical sensing.

Iodine-Doped Graphene for Enhanced Electrocatalytic Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cell Applications

We prepared iodine-doped graphenes by several techniques (electrophilic substitution and nucleophilic substitution methods) in order to incorporate iodine atoms onto the graphene base materials. The physical characterization of prepared samples was performed by using an array of different techniques, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and electrochemical methods. A series of cathodes using I-doped graphene were prepared and evaluated. Electrochemical performances of the cathodes with and without I-doped graphene indicated an effective improvement, resulting in a better mass transport in the catalyst layer.

DFT Simulation of Edge Halogenated Graphene Nanosheets As an ORR Catalyst in Fuel Cells

Edge halogenated graphene-nanosheets1have recently been discovered to be a low cost Oxygen Reduction Reaction (ORR) catalysts for alkaline fuel cells. Better understanding of ORR on these catalysts is needed to understand: i) why these doped catalysts form water in the preferred 4e-ORR mechanism over the peroxide formation found in undoped graphene. ii) how to improve these catalysts, so that ORR can occur in the preferred acidic environment. We used the PBE flavor density functional theory (DFT) with the SeqQUEST code2to calculate the binding energies, onset potential, and reaction barriers for ORR using either bromine, chlorine or iodine as the hetero-atom dopants on edge halogenated graphene-nanosheets. We examined both the zig-zag and armchair edges and find that the ORR intermediates bind to the zig-zag edges more strongly than the armchair. We find that the ORR intermediate species HOO does not bind to the basal plane. Thus, the ORR occurs on the graphene edges and not on the basal plane surface. We also find that the halide doped graphene zig-zag and armchair edges lead to a skewed geometry due to nonbonded interactions of the halogen with each other on the adjacent edge sites. Although the ORR intermediate species bind more strongly on the zigzag edges, our results predict that ORR occurs in the armchair edges based on the predicted onset potential calculation that agree well with experiments (Cl: 0.95 V, Br: 0.70 V, I: 0.72 V). We used nudged elastic band (NEB) calculations in conjunction with the CANDLE water solvation method3 to predict the potential dependent barriers4of the ORR. The dissociation of O2 in the second step of the ORR indicates that halogen doped graphene favor the 4e- pathway. In addition, the barrier to form –OH is much lower on the halide graphene edges than undoped graphene. Based on the calculated barriers, we conclude that iodine-doped graphene has the lowest thresholds water formation (0.56 eV at 0.72 V), which we find to be the rate determine step (RDS). This is in agreement with ORR activity of experimental results indicating iodine doped graphene performs better than bromine-doped, chlorine-doped, and undoped1.

Polyiodide-Doped Graphene

Iodine-doped graphene has recently attracted significant interest as a result of its enhanced conductivity and improved catalytic activity. Using density functional theory calculations, we obtain the formation energy, desorption rate, and electronic properties for graphene systems doped with polyiodide chains consisting of 1–6 iodine atoms in the low-concentration limit. We find that I3 and I5 act as p-type surface dopants that shift the Fermi level 0.46 and 0.57 eV below the Dirac point, respectively. For these two molecules, molecular orbital theory and analysis of the charge density show that doping transfers electronic charge to iodine π* molecular orbitals oriented perpendicular to the graphene sheet. For even-length polyiodides, we find that I6 and I4 decompose to I2, which readily desorbs at 300 K. Adsorption energy calculations further show that I3 acts as an effective catalyst for the oxygen reduction reaction on graphene by stabilizing the rate-limiting OOH intermediate.

Iodinated carbon materials for oxygen reduction reaction in proton exchange membrane fuel cell. Scalable synthesis and electrochemical performances

Doped graphene-based cathode catalysts are considered as promising competitors for ORR, but their power density has been low compared to Pt-based cathodes, mainly due to poor mass-transport properties. A new electrocatalyst for PEMFCs, an iodine doped grahene was prepared, characterized, and tested and the results are presented in this paper. We report a hybrid derived electrocatalyst with increased electrochemical active area and enhanced mass-transport properties. The electrochemical performances of several configurations were tested and compared with a typical Pt/C cathode configuration. As a standalone catalyst, the iodine doped graphene gives a performance with 60% lower than if it is placed between gas diffusion layer and catalyst layer. If it is included as microporous layer, the electrochemical performances of the fuel cell are with 15% bigger in terms of power density than the typical fuel cell with the same Pt/C loading, proving the beneficial effect of the iodine doped graphene for the fuel cell in the ohmic and mass transfer region. Moreover, the hybrid cathode manufactured by commercial Pt/C together with the material with best proprieties, is tested in a H2-Air fuel cell and a power density of 0.55Wcm−2 at 0.52V was obtained, which is superior to that of a commercial Pt-based cathode tested under identical conditions (0.46Wcm−2).

Semimetallic-to-metallic transition and mobility enhancement enabled by reversible iodine doping of graphene.

We demonstrate that a reversible semimetallic-to-metallic transition can be realized in monolayer graphene by iodine doping and dedoping processes. Upon iodine doping, the charge transfer from graphene to iodine creates a high hole density up to 4.75 × 10(13)cm(-2), well beyond that realized by applying gate voltages. Iodine-doped graphene shows metallic behaviour, as evidenced by the resistance variation with temperature and magnetic field. We further introduce an iodine dedoping method to completely remove the iodine anions from graphene surfaces. Transport measurements show that after dedoping treatments, the mobility of graphene is significantly enhanced, much higher than that of pristine graphene. The improvement in graphene electronic properties is attributed to the corrosive characteristic of iodine that it can react with and remove absorbed atoms on graphene surfaces. Our work not only opens a facile and effective way to tune the properties of monolayer graphene reversibly, but also demonstrates a new method to increase the quality of graphene.

Cytotoxicity of halogenated graphenes

Graphene and its family of derivatives possess unique and remarkable physicochemical properties which make them valuable materials for applications in many areas like electronics, energy storage and biomedicine. In response to the possibility of its large-scale manufacturing as commercial products in the future, an investigation was conducted to determine the cytotoxicity of one particular family of graphene derivatives, the halogenated graphenes, for the first time. Halogenated graphenes were prepared through thermal exfoliation of graphite oxide in gaseous chlorine, bromine or iodine atmospheres to yield chlorine- (TRGO-Cl), bromine- (TRGO-Br) and iodine-doped graphene (TRGO-I) respectively. 24 h exposure of human lung carcinoma epithelial cells (A549) to the three halogenated graphenes and subsequent cell viability assessments using methylthiazolyldiphenyl-tetrazolium bromide (MTT) and water-soluble tetrazolium salt (WST-8) assays revealed that all the halogenated graphenes examined are rather cytotoxic at the concentrations tested (3.125 μg mL(-1) to 200 μg mL(-1)) and the effects are dose-dependent, with TRGO-Cl reducing the cell viability to as low as 25.7% at the maximum concentration of 200 μg mL(-1). Their levels of cytotoxicity can be arranged in the order of TRGO-Cl > TRGO-Br > TRGO-I, and it is suggested that the amount of halogen present in the graphene material is the determining factor for the observed trend. Control experiments were carried out to test for possible nanomaterial-induced interference as a consequence of reaction between the halogenated graphenes and the viability markers (MTT/WST-8 reagent) or binding of the formazan products under cell-free conditions. The data obtained eliminate the probability of significant influence by these interferents as the change in the normalized percentage of formazan formed is relatively small and thorough washings were performed prior to the viability assessments to reduce the amount of halogenated graphenes that could eventually interact with the MTT/WST-8 assays. More studies need to be carried out in the future to complement the results obtained in this initial study in an attempt to develop a better understanding of the health hazards that the halogenated graphenes pose.