Electrochemical Graphene Oxide Research Articles

UV‐Induced Synthesis of Graphene Supported Iridium Catalyst with Multiple Active Sites for Overall Water Splitting

AbstractCatalysts that can promote the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) are in demand for efficient water splitting. Here, a general and practical UV‐induced synthesis of noble metal catalysts supported on reduced electrochemical graphene oxide (M‐rEGO, M = Ir, Pt or Pd) is proposed. The use of EGO with a low degree of oxidation and the generation of the highly reducing isopropanol radical from added isopropanol and acetone are crucial for this one‐step, one‐pot synthesis. Using Ir as a model material, the vacancies of rEGO allow the interaction of undercoordinated C with Ir, forming multiple active Ir species including single atoms (SAs), dual‐atom pairs (DAs) and nanoparticles. This Ir‐rEGO catalyst exhibits overpotentials of only 42.3 and 294 mV to reach 10 mA cm−2 in 0.5 м H2SO4 for HER and 1 м KOH for OER, respectively, at an extremely low Ir loading (2.1 wt%). The water‐splitting cells featuring Ir‐rEGO catalyst outperform those using commercial Pt/C (20 wt%) and RuO2 catalysts in both acidic and alkaline electrolytes. Density functional theory calculations confirm the stabilization of SAs and DAs at the vacancies of graphene lattice as well as the high activity of DAs in both HER and OER.

Evaluation of Bactericidal Activity of Electrochemical GO Modified with TiO2 Nanoparticles

Evaluation of Bactericidal Activity of Electrochemical GO Modified with TiO2 Nanoparticles

Graphenization of graphene oxide films for strongly anisotropic thermal conduction and high electromagnetic interference shielding

A macroscopic carbon film that has a “graphenic” structure (defect-free in-plane graphene lattice yet absence of Bernal type graphitic stacking order), may inherit the exotic properties of rotated/slipped few-layer graphene (e.g., high flexibility and anisotropic transport properties). However, the fabrication of such a film remains challenging and unreported. Here we show that the annealing of reduced electrochemical graphene oxide (REGO), which has fewer in-plane defects than the conventional graphene oxide from Hummers’ method, leads to a nearly intact graphene lattice (Raman ID/IG down to 0.03) without restoring the graphitic stacking order (I2D/IG > 1 and a single Lorentzian 2D peak). Atomic resolution transmission electron microscopy verifies the unique graphenic structure with random interlayer rotations. Density functional theory calculations imply the low defect density of REGO can suppress the interplanar interaction between undercoordinated carbon atoms, therefore inhibiting cross-plane migration of vacancies and the consequent establishment of stacking order. The annealed, graphenic REGO film is highly flexible and has an in-plane to cross-plane thermal conductivity ratio of 835 (among the highest reported for anisotropic thermal conductors). This high anisotropic ratio is attributed to the inhibited through-plane heat transport (0.26 W m−1 K−1) by the interlayer rotations and the high in-plane thermal conductivity (218 W m−1 K−1) enabled by intact graphene lattice. The graphenic films show high electromagnetic interference shielding effectiveness of 80.3 dB at a thickness of 53 μm and 42.4 dB at 5.7 μm, with an absolute effectiveness (>70000 dB cm2 g−1) superior to two-dimensional metal carbides (MXenes) and Al foil.

Two-step thermal treatment of electrochemical graphene oxide films for high-performance electrical heating and electromagnetic interference shielding

Electric heaters have attracted growing interest due to their wide applications in healthcare, smart wear, and aerospace. Contrarily, conventional heaters fail to meet the expectations of flexibility, high temperature, and efficiency. The current protocol focus on the fabrication of a flexible, high-temperature, and high-performance heater through a multi-step strategy. The modified two-step electrochemical exfoliation approach facilitated the formation of electrochemical graphene oxide (EGO). The simple two-step thermal treatment of EGO produced graphene film. The EGO structure exhibits excellent flexibility, good electrical conductivity, and thermal stability after thermal treatment. Consequently, graphene film showed good flexibility and efficient electric heating performance. It only required 13 s to reach 401.2 °C at 3.5 V. Additionally, graphene film displays sufficient heating reliability, stability, and repeatability under heating cycles and prolonged heating. Moreover, it demonstrates electromagnetic interference shielding effectiveness of up to 30383.6 dB cm2/g. Therefore, graphene film has emerged as a promising alternative for developing intelligent clothes, wearable devices, and healthcare devices.

Controlling the Thermoelectric Behavior of La-Doped SrTiO3 through Processing and Addition of Graphene Oxide.

The addition of graphene has been reported as a potential route to enhance the thermoelectric performance of SrTiO3. However, the interplay between processing parameters and graphene addition complicates understanding this enhancement. Herein, we examine the effects of processing parameters and graphene addition on the thermoelectric performance of La-doped SrTiO3 (LSTO). Briefly, two types of graphene oxide (GO) at different oxidation degrees were used, while the LSTO pellets were densified under two conditions with different reducing strengths (with/without using oxygen-scavenging carbon powder bed muffling). Raman imaging of the LSTO green body and sintered pellets suggests that the added GO sacrificially reacts with the lattice oxygen, which creates more oxygen vacancies and improves electrical conductivity regardless of the processing conditions. The addition of mildly oxidized electrochemical GO (EGO) yields better performance than the conventional heavily oxidized chemical GO (CGO). Moreover, we found that muffling the green body with an oxygen-scavenging carbon powder bed during sintering is vital to achieving a single-crystal-like temperature dependence of electrical conductivity, implying that a highly reducing environment is critical for eliminating the grain boundary barriers. Combining 1.0 wt % EGO addition with a highly reducing environment leads to the highest electrical conductivity of 2395 S cm-1 and power factor of 2525μW m-1 K-2 at 300 K, with an improved average zT value across the operating temperature range of 300-867 K. STEM-EELS maps of the optimized sample show a pronounced depletion of Sr and evident deficiency of O and La at the grain boundary region. Theoretical modeling using a two-phase model implies that the addition of GO can effectively improve carrier mobility in the grain boundary phase. This work provides guidance for the development of high-performance thermoelectric ceramic oxides.

Electrochemical reduction of thin graphene-oxide films in aqueous solutions – Restoration of conductivity

Graphene oxide finds applications in different fields of science, including energy conversion. Electrochemical reduction of graphene oxide (GO) significantly improves its conductivity. However, the kinetics of this process depends on the solvent, supporting electrolyte, pH, and numerous other factors. Most studies report the macroscopic views and ex-situ properties of reduced GO. To expand the knowledge about GO reduction, in this study, we used cyclic voltammetry (CV), simultaneous 2 points and 4 points resistance measurement (s24), conductive atomic force microscopy (AFM), and theoretical calculations. Using CV, we demonstrated that the choice of supporting electrolyte (KCl or LiCl) influences the potential range in which electrochemical GO reduction occurs. The activation energy of this process was estimated to be below 30 kJ mol‒1 in both electrolytes, being significantly lower than that required for thermal reduction of GO. Simultaneous in situ s24 resistance measurements suggest that GO films reach a highly conductive state at deep negative potentials, with an abrupt, irreversible switch from non-conductive to the conductive state. However, conductive AFM presents a more exact picture of this process: the reduction of GO films starts locally while the formed conductive islands grow during the reduction. This mechanism was confirmed by theoretical calculations indicating that the reduction starts on isolated oxygen-functional groups over the GO basal plane, while clustered OH groups are more difficult to reduce. The presented results can help in tailoring reduced GO for a particular electrochemical application by precisely controlling the reduction degree and percentage of the conductive area of the reduced GO films.

Novel electrolyte additive of graphene oxide for prolonging the lifespan of zinc-ion batteries

Aqueous zinc-ion batteries have attracted the attention of the industry due to their low cost, good environmental friendliness, and competitive gravimetric energy density. However, zinc anodes, similar to lithium, sodium and other alkali metal anodes, are also plagued by dendrite problems. Zinc dendrites can penetrate through polymer membranes, and even glass fiber membranes which seriously hinders the development and application of aqueous zinc-ion batteries. To resolve this issue, certain additives are required. Here we have synthesized an electrochemical graphene oxide with novel electrolyte based on tryptophan, which allows to obtain few-layered sheets with a remarkably uniform morphology, good aqueous solution dispersion, easy preparation and environmental friendliness. We used this electrochemical graphene oxide as an additive to the electrolyte for aqueous zinc-ion batteries. The results of phase-field model combined with experimental characterization revealed that the addition of this material effectively promotes the uniform distribution of the electric field and the Zn-ion concentration field, reduces the nucleation overpotential of Zn metal, and provides a more uniform deposition process on the metal surface and improved cyclability of the aqueous Zn-ion battery. The resultant Zn∣Zn symmetric battery with the electrochemical graphene oxide additive affords a stable Zn anode, which provided service for more than 500 h at 0.2 mA cm−2 and even more than 250 h at 1.0 mA cm−2. The Coulombic efficiency (98.7%) of Zn∣Cu half-cells and thus cyclability of aqueous Zn-ion batteries using electrochemical graphene oxide is significantly better compared to the additive-free electrolyte system. Therefore, our approach paves a promising avenue to foster the practical application of aqueous Zn-ion batteries for energy storage.

Unlocking the energy storage potential of polypyrrole via electrochemical graphene oxide for high performance zinc-ion hybrid supercapacitors

Safe and low-cost zinc-ion hybrid supercapacitors using neutral aqueous electrolytes are promising for large scale and high power energy storage. A key challenge for Zn-ion hybrid supercapacitors is to increase their energy density without sacrificing the high power performance. Herein, we report a Zn-ion hybrid supercapacitor using a polypyrrole/electrochemical graphene oxide (PPy/EGO) composite cathode and aqueous 1 M ZnCl 2 or ZnBr 2 electrolytes. The Zn-PPy/EGO system with an operating cell voltage from 0.5 to 1.5 V exhibited high energy and high power densities of 117.7 and 72.1 Wh kg −1 at 0.34 and 12.4 kW kg −1 , respectively, outperforming the Zn-ion hybrid supercapacitors using carbon cathodes. This high performance is because of the facilitated electronic and ionic transport in the PPy/EGO composite. In brief, the EGO prepared via the electrochemical method we recently reported has good structure integrity and is easily reduced; the porous PPy/EGO composite from co-electrodeposition benefits fast ion diffusion in pores; the small, monovalent halides anions in the zinc halides electrolytes are highly mobile in bulk PPy for fast solid-phase anion insertion/de-insertion. Electrochemical characterization and ex-situ X-ray photoelectron spectroscopy confirmed the anion-dominated charge storage mechanism of PPy/EGO cathode in Zn-PPy/EGO system. • PPy/EGO composite electrodes were prepared by one-step co-electrodeposition. • Mildly oxidized EGO with less disrupted structure benefits electron conduction. • Porous structure of PPy/EGO composite electrode facilitate ion diffusion. • Zn-PPy/EGO system using ZnCl 2 or ZnBr 2 electrolyte show record high performance.

Laser solid-phase synthesis of single-atom catalysts

Single-atom catalysts (SACs) with atomically dispersed catalytic sites have shown outstanding catalytic performance in a variety of reactions. However, the development of facile and high-yield techniques for the fabrication of SACs remains challenging. In this paper, we report a laser-induced solid-phase strategy for the synthesis of Pt SACs on graphene support. Simply by rapid laser scanning/irradiation of a freeze-dried electrochemical graphene oxide (EGO) film loaded with chloroplatinic acid (H2PtCl6), we enabled simultaneous pyrolysis of H2PtCl6 into SACs and reduction/graphitization of EGO into graphene. The rapid freezing of EGO hydrogel film infused with H2PtCl6 solution in liquid nitrogen and the subsequent ice sublimation by freeze-drying were essential to achieve the atomically dispersed Pt. Nanosecond pulsed infrared (IR; 1064 nm) and picosecond pulsed ultraviolet (UV; 355 nm) lasers were used to investigate the effects of laser wavelength and pulse duration on the SACs formation mechanism. The atomically dispersed Pt on graphene support exhibited a small overpotential of −42.3 mV at −10 mA cm−2 for hydrogen evolution reaction and a mass activity tenfold higher than that of the commercial Pt/C catalyst. This method is simple, fast and potentially versatile, and scalable for the mass production of SACs.

Thermo-electro-rheological behaviour of vanadium electrolyte-based electrochemical graphene oxide nanofluid designed for redox flow battery

The use of electrolyte-based nanofluid is a new approach for enhancing the performance of Vanadium Redox Flow Batteries (VRFBs). This paper, for the first time in the literature, presents an experimental study to comprehensively investigate the rheological behaviour, electrical conductivity, and thermal conductivity of a newly prepared electrochemical graphene oxide (EGO)/ vanadium (IV) electrolyte-based nanofluid in different weight concentration and bulk temperatures. SEM, FT-IR and X-ray Diffraction (XRD) characterizations were performed and different functional groups, smooth 2D layered structures, and low crystallinity were detected in our tailored oxidation EGO which are amongst the enhancing features for VRFBs electrode materials. It was observed that the optimum weight concentration of nanoparticles in the electrolyte-based nanofluid is 0.05 wt% with strong colloidal stability, enhanced electrical and thermal conductivities, and an optimal viscosity. The maximum feasible enhancements in electrical and thermal conductivities that were achieved were 12%, and 4%, respectively, which can positively affect the performance of flow battery in terms of electrochemical activity on the electrode surface and thermal management of the flow battery system. In addition, the rheological evaluation showed that the behaviour of the electrolyte-based nanofluid tends to change from Newtonian to non-Newtonian for weight concentrations higher than 0.05%. The results obtained from rheological behaviour can provide useful insights in choosing an optimum pumping system of the flow batteries working with electrolyte-based nanofluid.

Facile Synthesis of Boron-Doped Reduced Electrochemical Graphene Oxide for Sodium Ion Battery Anode

Facile Synthesis of Boron-Doped Reduced Electrochemical Graphene Oxide for Sodium Ion Battery Anode

Laser Assisted Solution Synthesis of High Performance Graphene Supported Electrocatalysts

AbstractSimple, yet versatile, methods to functionalize graphene flakes with metal (oxide) nanoparticles are in demand, particularly for the development of advanced catalysts. Herein, based on light‐induced electrochemistry, a laser‐assisted, continuous, solution route for the simultaneous reduction and modification of graphene oxide with catalytic nanoparticles is reported. Electrochemical graphene oxide (EGO) is used as starting material and electron–hole pair source due to its low degree of oxidation, which imparts structural integrity and an ability to withstand photodegradation. Simply illuminating a solution stream containing EGO and metal salt (e.g., H2PtCl6 or RuCl3) with a 248 nm wavelength laser produces reduced EGO (rEGO, oxygen content 4.0 at%) flakes, decorated with Pt (≈2.0 nm) or RuO2 (≈2.8 nm) nanoparticles. The RuO2–rEGO flakes exhibit superior catalytic activity for the oxygen evolution reaction, requiring a small overpotential of 225 mV to reach a current density of 10 mA cm−2. The Pt–rEGO flakes (10.2 wt% of Pt) show enhanced mass activity for the hydrogen evolution reaction, and similar performance for oxygen reduction reaction compared to a commercial 20 wt% Pt/C catalyst. This simple production method is also used to deposit PtPd alloy and MnOx nanoparticles on rEGO, demonstrating its versatility in synthesizing functional nanoparticle‐modified graphene materials.

Investigation of sulfuric acid intercalation into thermally expanded graphite in order to optimize the synthesis of electrochemical graphene oxide

This paper is devoted to a detailed study of the electrochemical intercalation of sulfuric acid into the foil structure based on thermally expanded graphite, as the decisive stage in the process of producing electrochemical graphene oxide. In the work, the potentials of individual areas of anodic polarization were determined, passing without destroying the carbon electrode. The diffusion control characteristic of the entire range of intercalation potentials is shown. The effective capacities, characteristic times, and acid consumption for the electrochemical intercalation process are evaluated. The minimum termination potential of the intercalation process is found. It is shown that limiting the anodic polarization of thermally expanded graphite at the minimum potential for the termination of intercalation can significantly reduce the energy consumption of the entire method for producing electrochemical graphene oxide. A comparison is made of electrochemical graphene oxide with graphene oxide, obtained by a modified Hammers method, by a number of physicochemical methods.

The role of electrolyte acid concentration in the electrochemical exfoliation of graphite: Mechanism and synthesis of electrochemical graphene oxide

Electrochemistry has emerged as a major route for graphene and graphene oxide synthesis from graphite. Anodic graphite oxidation is commonly used with dilute mineral acid or aqueous salt electrolytes. In this system, the electrolyte acid concentration appears to be a critical parameter. However, the effect of the acid concentration, particularly at low concentrations, is still not fully understood. To address this issue, we used a packed bed electrochemical reactor to synthesize seven different electrochemical graphite oxide (EGO) products in 2–16 M sulfuric acid. Detailed XRD, XPS, Raman, conductivity and optical microscopy analysis of the products was carried out. We found dilute acid (<10 M) graphite oxides were less crystalline and less oxidized than those produced in stronger acids. The oxygen evolution reaction at the graphite surface appears to affect the structural changes, oxidation mechanism, and electrochemical corrosion of the anode. EGO conductivity is also strongly affected by the electrolyte’s acidity. We show that well oxidized, yet reasonably conductive, single layer graphene oxide can be produced from 7.1 M acid. These results broaden our understanding of graphite electrochemistry and will serve to inform future electrochemical graphene synthesis efforts.

Environmentally friendly route for graphene oxide production via electrochemical synthesis focused on the adsorptive removal of dyes from water

ABSTRACT This work shows a promising, environmentally friendly and greener alternative for the production and application of electrochemically produced Graphene Oxide (GO) for the adsorptive removal of Methylene Blue (MB) dye in an aqueous medium. During the adsorption tests, GO produced via electrochemical route reached the equilibrium in only 10 min of contact, exhibiting a percentage removal of MB over 97%. It could also be observed that the experimental data better fitted to the pseudo-second order kinetic model. By analysing the isotherms, it was verified the maximum adsorptive capacity was 500 mg g−1 (303.15 K) and that in overall, adsorptive capacity decreases with the increase in temperature. Experimental equilibrium data were better fitted to the Freundlich isotherms in all temperatures studied (303.15, 318.15 and 333.15 K). The thermodynamic analysis confirmed the exothermic nature of the process, and that MB adsorption onto GO occurs spontaneously. ΔH◦ and ΔG◦ values suggested that physisorption occurred, which is mainly due to π–π interactions and electrostatic interactions between MB and oxygen functional groups on the GO surface. Cost-effectiveness analysis showed there is a lower cost involved in the production of electrochemical GO, as compared to the Hummers method; and in the reusability study, even after 5 cycles GO removed ≥ 90% MB. Thus, the electrochemically produced GO seems to be an efficient, cost-effective and environmentally friendly alternative for colour removal from water, as it uses less hazardous and expensive reagents when compared to those applied in the traditional GO synthesis, without losing, however, the efficiency in colour removal from water.

Hollow ZnO microspheres functionalized with electrochemical graphene oxide for the photodegradation of salicylic acid.

Hollow ZnO microspheres were successfully synthesized by a hydrothermal method and then functionalized with graphene oxide (GO) flakes, previously obtained through electrochemical oxidation. Their photocatalytic activity toward the photodegradation of salicylic acid under UV light irradiation was evaluated by UV-Vis spectroscopy. Unfunctionalized microspheres and ZnO functionalized with chemically oxidized graphene were also studied as comparative terms. The hybrid materials of ZnO with both electrochemical and chemical GO gave a similar photodegradation yield of ∼28% against 18% of the non-functionalized microspheres. The similar degradation yields and rate constants obtained with the two GO synthetic methods indicate that electrochemical oxidation of GO represents an eco-friendly option over traditional methods for photocatalytic degradation systems.

Giant third-order nonlinearity from low-loss electrochemical graphene oxide film with a high power stability

Giant third-order nonlinear absorption and refraction of electrochemical graphene oxide (EGO) film were investigated in the femtosecond regime using the single beam Z-scan technique. The excellent chemical stability of the EGO film under high-power illumination up to 400 mJ/cm2 is demonstrated, which can be attributed to the low oxidation degree revealed by the optical and Raman spectroscopies. High and broadband linear transmission over 70% has been observed from the visible to the infrared range. The low-loss EGO film with giant third-order nonlinearity, excellent chemical stability, large-scale preparation and flexible integration has a great potential for high-power nonlinear optical applications.

Graphene Transistors via in Situ Voltage-Induced Reduction of Graphene-Oxide under Ambient Conditions

Here, we describe a simple approach to fabricate graphene-based field-effect-transistors (FETs), starting from aqueous solutions of graphene-oxide (GO), processed entirely under ambient conditions. The process relies on the site-selective reduction of GO sheets deposited in between or on the surface of micro/nanoelectrodes. The same electrodes are first used for voltage-induced electrochemical GO reduction, and then as the source and drain contacts of FETs, allowing for the straightforward production and characterization of ambipolar graphene devices. With the use of nanoelectrodes, we could reduce different selected areas belonging to one single sheet as well.