Reduced graphene oxide/tin oxide composite as an enhanced anode material for lithium ion batteries prepared by homogenous coprecipitation

Reduced graphene oxide/tin oxide composite is prepared by homogenous coprecipitation. Characterizations show that tin oxide particles are anchored uniformly on the surface of reduced graphene oxide platelets. As an anode material for Li ion batteries, it has 2140 mAh g⁻¹ and 1080 mAh g⁻¹ capacities for the first discharge and charge, respectively, which is more than the theoretical capacity of tin oxide, and has good capacity retention with a capacity of 649 mAh g⁻¹ after 30 cycles. The simple synthesis method can be readily adapted to prepare other composites containing reduced graphene oxide as a conducting additive that, in addition to supporting metal oxide nanoparticles, can also provide additional Li binding sites to, perhaps, further enhance capacity.     

Tungsten-molybdenum oxide nanowires/reduced graphene oxide nanocomposite with enhanced and durable performance for electrocatalytic hydrogen evolution reaction

Hydrogen has attracted huge interest globally as a durable, environmentally safe and renewable fuel. Electrocatalytic hydrogen evolution reaction (HER) is one of the most promising methods for large scale hydrogen production, but the high cost of Pt-based materials which exhibit the highest activity for HER forced researchers to find alternative electro-catalyst. In this study, we report noble metal free a 3D hybrid composite of tungsten-molybdenum oxide and reduced graphene oxide (GO) prepared by a simple one step hydrothermal method for HER. Benefitting from the synergistic effect between tungsten-molybdenum oxide nanowires and reduced graphene oxide, the obtained W-Mo-O/rGO nanocomposite showed excellent electro-catalytic activity for HER with onset potential 50 mV, a Tafel slope of 46 mV decade^?1 and a large cathodic current, while the tungsten-molybdenum oxide nanowires itself is not as efficient HER catalyst. Additionally, W-Mo-O/rGO composite also demonstrated good durability up to 2000 cycles in acidic medium. The enhanced and durable hydrogen evolution reaction activity stemmed from the synergistic effect broadens noble metal free catalysts for HER and provides an insight into the design and synthesis of low-cost and environment friendly catalysts in electrochemical hydrogen production.     

Effect of reduced graphene oxide addition on cathode functional layer performance in solid oxide fuel cells

Solid oxide fuel cells (SOFCs) operating at high temperatures are highly efficient electrochemical devices since they convert the chemical energy of a fuel directly into heat and electrical energy. The electrochemical performance of an SOFC is significantly influenced by the materials and microstructure of the electrodes since the electrochemical reactions in SOFCs take place at three/triple phase boundaries (TPBs) within the electrodes. In this study, graphene in the form of reduced graphene oxide (rGO) is added to cathode functional layer (CFL) to improve the cell performance by utilizing the high electrical properties of graphene. Various cells are prepared by varying the rGO content in CFL slurry (1–5 wt %), the number of screen printing (1–3) and the cathode sintering temperature (900–1100 °C). The electrochemical behavior of the cells is evaluated by electrochemical performance and impedance tests. It is observed that there is a ∼26% increase in the peak performance of the cell coated with single layer CFL having 1 wt % graphene and 1050 °C sintering temperature, compared to that of the reference cell.     

Facile synthesis of reduced graphene oxide supported PtAg nanoflowers and their enhanced electrocatalytic activity

In this work, a simple and facile method is developed in the synthesis of well-dispersed PtAg nanoflowers on reduced graphene oxide nanosheets (PtAg/RGOs) under solvothermal conditions, using ethylene glycol as a reducing agent and hexadecyl trimethyl ammonium bromide (CTAB) as capping and stabilizing agents. The as-prepared nanocomposites show a superior electrocatalytic activity, good tolerance, and better stability toward the oxidation of formic acid and ethylene glycol in alkaline media, compared with the commercial Pt/C (10 wt%) catalyst. For the oxidation of formic acid, the PtAg nanoflowers own thirty times higher of the catalytic currents than those of the commercial Pt/C catalyst. Meanwhile, for the oxidation of ethylene glycol, the ratio of forward current (j_F) to reverse current (j_R) is high up to 8.4, which is almost four times higher than that of the commercial Pt/C catalyst. This strategy provides a promising platform for direct formic acid and ethylene glycol fuel cells.     

Enhanced hydrogen storage performance in Pd3Co decorated nitrogen/boron doped graphene composites

In order to harness the potential of hydrogen as an alternative energy carrier, overcoming the barrier related to its storage is of utmost importance. In this direction, it has been shown that dissociation of hydrogen molecules into atoms followed by their adsorption onto high surface area nanomaterials like reduced graphene oxide is a promising pathway. In the present study, we have exploited this pathway, commonly known as the “spillover mechanism” and achieved a hydrogen storage capacity of ～4.6 wt% at 30 bar and 25 °C in Pd₃Co decorated boron doped graphene composite. We demonstrate that optimum loading of transition metal alloy nanoparticles coupled with heteroatom (nitrogen or boron) doped graphene support is an efficient, easy and cost effective avenue towards meeting the US department of energy (DOE) targets for gravimetric hydrogen storage capacity at room temperature and moderate pressures.     

Significant enhancement of the electrochemical hydrogen uptake of reduced graphene oxide via boron-doping and decoration with Pd nanoparticles

Development of advanced hydrogen storage materials with high capacity and stability is vital to achieve an envisaged hydrogen economy. Here, we report a uniformly dispersed Pd nanoparticles on the boron-doped reduced graphene oxide (Pd/B-rGO) as a novel nanocomposite for efficient hydrogen storage. The effects of the incorporation of Pd NPs and the substitution of boron atoms into the graphene-based nanomaterial matrix on the electrochemical hydrogen up-taking and releasing were comparatively studied using electrochemical techniques, and duly supported by density functional theory (DFT) calculations. The discharge capacities of the Pd-rGO and Pd/B-rGO nanocomposites were determined to be over 45 and 128 times higher than that of the Pd NPs, respectively, showing that the B doping and the rGO support played significant roles in the enhancement of the hydrogen storage capability. Moreover, the galvanostatic charging and discharging cycling tests demonstrated a high stability and efficient kinetics of the Pd/B-rGO nanocomposite in the H₂SO₄ electrolyte for hydrogen up-taking and release.     

Fe3+-assistantly carbon-impregnated porous SiO2 mesoscale tubes as Li-ion battery anode materials with highly enhanced performances

Porous SiO₂ mesoscale tubes (SiO₂-pMT) impregnated with carbon in the pores within their tube walls were successfully prepared for the first time by making use of the Fe³⁺ assisted anchoring of dopamine (DA) on the surface of SiO₂ as carbon source, and thereby endowed with highly enhanced anode performances for Li-ion batteries. Typically, a reversible specific capacity of 512.8 mAh g^?1 was achieved after 500 cycles at 1 A g^?1 when the SiO₂-pMT impregnated with carbon by Fe³⁺ assistance was used as anode material, which is about 10 times that of SiO₂-pMT with no carbon impregnation and 25% higher than that of the SiO₂-pMT with carbon impregnated at double the concentration of dopamine but in the absence of Fe³⁺ cations. It has been found that the carbon impregnation of the SiO₂-pMT may be achieved more easily and homogeneously with the assistance of Fe³⁺ cations and, as a result, 3-dimensional porous carbon-networks with higher connectivity can be built up, which greatly facilitate the transport of electrons to more potential reaction sites where Li-ions are available and provide fast channel for Li-ions diffusion, leading to enhanced electrochemical kinetics, as unveiled by the differential capacity curves and electrochemical impedance spectra acquired at different intervals during the initial cycle. Furthermore, as shown by XPS data, such benefitial assistance of Fe³⁺ cations is believed to arise from their coupling effects between the phenolic hydroxyl groups of dopamine molecules and the surface of SiO₂ through the chemical bondings of C-O-Fe and Fe-O-Si.     

Facile scalable manufacture of improved electrodes using structured surface coatings of nickel oxide as cathode and reduced graphene oxide as anode for evaluation in a prototype development on microbial fuel cells

Improvement of the microbial fuel cell performance is highly required in energy production associated with domestic sewage treatment. For this objective, metal electrodes coated with specific materials for anode and cathode were manufactured. Materials such as reduced graphene oxide (rGO) as an anode, with high electrical conductivity, and structured nickel oxide (sNiO), which act as air cathode, could be the key to obtaining substantial improvements in the production of energy and treatment of domestic sewage. In this work, simple methods were developed to coat the stainless steel meshes with rGO and sNiO, used in MFC prototypes. The results show that the methodologies developed for the coating of the electrodes aid to improve the performance of the MFC in the delivery of potential, current density and power density up to 220%, 140% and 700% respectively, compared to the blank stainless steel electrodes; while the COD levels in the water purified by the MFC with covered electrodes reached a decrease of 36% compared to the same system without covered electrodes. Additionally, the built MFCs prototypes were tested as a power supply for a digital clock and an LED light.     

Improved electrochemical performance of nickel-cobalt hydroxides by electrodeposition of interlayered reduced graphene oxide

Efficient, economical, and eco-friendly water splitting catalysts are in priority to replace the fossil fuels. In the presented work, reduced graphene oxide is formed through electrochemical reduction and applied as an effective interlayer between nickel foam substrate and nickel-cobalt hydroxide catalyst to augment its activity toward hydrogen evolution reaction. Through subsequent cyclic voltammetry deposition of nickel-cobalt hydroxide over the surface of supported interlayer, the prepared electrocatalyst exhibited remarkable performance by reaching a current density of 10 mA cm⁻² at a small overpotential of 60 mV in 1.0 M KOH electrolyte, much lower than that of the same electrocatalyst without interlayer (78 mV). The proposed strategy made the active metallic catalyst phase acquiring a small Tafel slope and superior durability for hydrogen production in alkaline medium. By utilizing the reduce graphene oxide interlayer, the electrical conductivity of the final nickel-cobalt hydroxide electrode was boosted. Furthermore, a clear transition from ordered reticulated arrays of nanosheets to roughened and disordered nanosheet-comprised nanospheres is demonstrated for surface morphology of nickel-cobalt electrocatalyst that indeed prompts the increase in its electrochemically active surface area.     

Monodisperse rutheniumcopper alloy nanoparticles decorated on reduced graphene oxide for dehydrogenation of DMAB

In this study, we report a superior dehydrogenation catalyst for dimethylamine borane, which exhibited one of the best catalytic activities. The newly formed catalyst system contains well dispersed ruthenium-copper nanomaterials on reduced graphene oxide (3.86 ± 0.47 nm), which was prepared by using the ultrasonic double reduction technique. The characterization of monodisperse ruthenium-copper alloy nanoparticles was performed using some advanced analytical methods such as TEM, HRTEM, XPS, Raman spectroscopic analysis. The experiments results revealed that the monodisperse ruthenium-copper alloy catalyst (RuCu@rGO) has one of the highest catalytic activity compared to previous studies, having a high turnover frequency value (256.70 h⁻¹). The detailed kinetic parameters such as activation energy, enthalpy, and entropy values were also calculated for the dehydrogenation of dimethylamine borane at room temperature. Also, the results showed that the monodisperse RuCu@rGO catalyst has high durability and reusability as retained its 81% initial catalytic activity even after 4th runs for the dehydrogenation of dimethylamine borane.     

Growth control of cobalt oxide nanoparticles on reduced graphene oxide for enhancement of electrochemical capacitance

The high capacitance and cyclic stability of graphene nanosheets decorated with Co₃O₄ nanoparticles as a material for supercapacitor electrodes are reported here. Hydrothermal method is adopted to deposit cobalt oxides on the reduced graphene oxide (RGO) sheets in a mixture of water and dimethylformamide (DMF) as the solvent with different volume ratios. The water volume ratio presents a crucial factor in the nucleation and growth process. In addition, it affects dispersion, particle size and the amount of nucleated cobalt oxide particle on the graphene sheets. By decreasing the water volume, the nucleation and growth occur mainly on graphene rather than in solution. According to the obtained results from transmission electron microscopy, scanning electron microscopy and thermogravimetric analysis, a model for growth of nanoparticles on graphene sheets is proposed. Based on the obtained results, the presented model can also be used for the synthesis of other graphene-metal (oxide) composites. Electrochemical measurements indicate that water volume ratio in the mixture solvent influences on capacitance of the RGO/Co₃O₄ composite electrodes. The highest obtained specific capacitance is 440.4 F g⁻¹ with 50% volume ratio of water at current density of 5 A g⁻¹.     

Exploring the impact of doping and co-doping with B and N on the properties of graphene oxide and its photocatalytic generation of hydrogen

The photocatalytic production of hydrogen was studied in graphene oxide materials doped with nitrogen or/and boron by hydrothermal treatments. Characterization of the materials was carried out by XRD, FTIR, XPS, Raman, UV–Vis, and photoluminescence spectroscopies, FESEM and TEM. The study of hydrogen evolution in the water splitting reaction was done using UV light as source of irradiation and methanol as hole scavenger. Boron-doped graphene oxide with the highest bulk electrical resistance exhibited the highest photocatalytic hydrogen generation, due to interstitial positioning of boron in the graphene lattice, which improved the light absorption coefficient, formation of inter-gap states and reduced charge recombination. This phenomenon is hypothesized for the first time as “decentralized reaction clusters”, which spread across the graphene lattice and produce hydrogen independently. Nitrogen-doped graphene oxide showed high electrical conductivity due to a significant removal of oxygen functional groups, and improved carrier density. Partially reduced nitrogen and boron co-doped graphene oxide showed the highest electrical conductivity, due to the presence of more electron-donating nitrogen configurations, such as pyrrolic N and pyridinic N. Nitrogen and boron co-doping of graphene oxide allows to modify the conduction band and valence bands, thus improving the electrical conductivity.     

Insight into effects of graphene and zinc oxide in Li4Ti5O12 as anode materials for Li-ion full-cell battery

Programmable design of nanocomposites of Li₄Ti₅O₁₂ (LTO) conducted through hydrothermal route in the presence of ethylenediamine as basic and capping agent. In this work, effect of ZnO and Graphene on the Li₄Ti₅O₁₂ based nanocomposites as anode materials investigated for Li-Ion battery performances. The full cells battery assembled with LTO based nanocomposites on Cu foil as the anode electrode and commercial LMO (LiMn₂O₄) on aluminum foil as cathode electrode. X-Ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FT-IR), along with Field Emission Scanning Electron Microscopy (FE-SEM) and Transmission electron microscopy (TEM) images was applied for study the composition and structure of as-prepared samples. The electrochemical lithium storage capacity of prepared nanocomposites was compared with pristine LTO via chronopotentiometry charge-discharge techniques at 1.5–4.0 V and current rate of 100 mA/g. As a result, the electrode which is provided by LTO/TiO₂/ZnO and LTO/TiO₂/graphene nanocomposites provided 765 and 670 mAh/g discharge capacity compared with pristine LTO/TiO₂ (550 mAh/g) after 15 cycles. Based on the obtained results, fabricated nanocomposites can be promising compounds to improve the electrochemical performance of lithium storage.     

A graphite sheet modified with reduced graphene oxide-hyper-branched gold nanostructure as a highly efficient electrocatalyst for hydrogen evolution reaction

Hydrogen is considered as the most important energy carrier for the future. Water electrolysis is a green method for hydrogen production and simple technology that produces very clean gases. However, the main problems with this method are that this process possesses slow kinetic, consumes many energies and its common electrocatalyst is platinum (Pt) based which is an expensive and rare substance. The use of accessible electrocatalyst materials with new shape or structure, which can reduce the overpotential for the hydrogen evolution reaction (HER) is one of the ways to increase the efficiency of the electrolyzers. Herein, first, a graphite sheet was modified with graphene oxide (GO) and then a hyperbranched structure of gold was electrodeposited on it by controlling the electrodeposition conditions. The electrode surface was characterized by scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT-IR). The HER performance of the prepared electrodes was evaluated using linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) methods in 0.5 M H₂SO₄ solution. The as-prepared electrode revealed outstanding HER performance with a near-zero onset overpotential (4.7 mV), overpotential of 44 mV at 10 mA cm⁻², a high current density of 127.9 mA cm⁻² at 200 mV and also satisfactory stability. Such results suggest that this electrocatalyst is promising for generating clean energy on an industrial scale.     

Effect of surface functional groups on hydrogen adsorption properties of Pd dispersed reduced graphene oxide

Pd/reduced graphene oxide (Pd-RGO) composites were successfully prepared from graphite and PdCl₂ precursors using wet impregnation and reverse micro emulsion methods. From hydrogen adsorption studies it is confirmed that spillover of hydrogen from Pd to graphene layers occurs at room temperature. However, at low temperatures there is negligible spillover effect and this is explained based on lower kinetic energy available with hydrogen atoms to overcome the activation barrier involved in diffusion. Detailed ¹³C MAS NMR and Raman spectroscopic studies confirmed that small amounts of structural units (functional groups) like carboxylate and polyacetylenic linkages are retained in Pd-RGO samples prepared by wet impregnation and reverse micro-emulsion methods, respectively. Such structural moieties facilitate the atomic scale mixing of Pd with the graphene layers thereby improving the spillover efficiency.     

Facile synthesis of well dispersed Pd nanoparticles on reduced graphene oxide for electrocatalytic oxidation of formic acid

In present study, we report a facile synthesis of crystalline, small size Pd nanoparticles (NPs) on reduced graphene oxide (RGO) abbreviated as Pd/RGO for electrocatalytic oxidation of formic acid (FA). Here, first graphene oxide (GO) was reduced by the green method using l-ascorbic acid and citric acid and further Pd NPs were decorated on RGO by a facile method without using any reducing agents. The reduction of GO to RGO and synthesis of Pd NPs was confirmed by the X-ray diffraction (XRD) and X-ray photoelectrons (XPS) techniques. Surface morphology of Pd/RGO nanocomposite was evaluated by the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The electrocatalytic behavior of Pd/RGO nanocomposite was tested by using of cyclic voltammetric (CV) technique for electro-oxidation of FA in mixed solution of 0.5 M HCOOH + 0.5 H₂SO₄ at RT. Results shows that the higher electrocatalytic activity of Pd/RGO nanocomposite compare to Pd NPs.     

Soybean milk derived carbon intercalated with reduced graphene oxide as high efficient electrocatalysts for oxygen reduction reaction

Exploring high-performance and low-cost metal-free oxygen reduction reaction (ORR) catalysts from biomass-derived materials is vital to the development of novel energy conversion devices such as fuel cells, etc. Herein, nitrogen-enriched soybean milk derived carbon (BDC/rGO-HT-NH₃) intercalated with reduced graphene oxide (rGO) electrocatalyst is prepared via one-pot hydrothermal synthesis method followed with nitridation by NH₃. The resultant catalyst with high surface area, good conductivity and high content of N (9.4 at.%) shows high electrocatalytic activity towards ORR in alkaline medium, which mainly happens through the direct 4-electron pathway. The onset potential of BDC/rGO-HT-NH₃ catalyzed ORR is 0.96 V vs RHE, which is only 0.11 V lower than that of the commercial Pt/C (20 wt%) catalyst. In addition, the BDC/rGO-HT-NH₃ catalyst shows superior long-term running durability. The desirable catalytic performances enable the facile synthesis approach of BDC/rGO-HT-NH₃ to be a promising methodology for transforming other biomass materials to N-enriched carbon based materials as low-cost and environmental friendly catalysts for ORR.     

Hydrothermal synthesis of three dimensional reduced graphene oxide-multiwalled carbon nanotube hybrids anchored with palladium-cerium oxide nanoparticles for alcohol oxidation reaction

The synergistic effect of 3D carbon support on Pd-based catalyst and its performance toward direct alcohol oxidation reaction is reported here. The surface of 3DrGO-MWCNTs support was modified by loading different amounts (5–20 wt%) of cerium oxide (CeO₂) by wet impregnation method. Further, Pd nanoparticles were dispersed over CeO₂/3DrGO-MWCNTs nanocomposites by chemical reduction method. The synthesized nanocomposites were characterized by various techniques such as XRD, XRF, SEM, TEM, Raman, and XPS analysis. The electro-oxidation performance and long-term stability of the Pd/CeO₂/3DrGO-MWCNTs electro-catalyst were measured by CV, LSV, and CA analysis. The modification of the catalyst's surface by cerium oxide Pd/10CeO₂/3DrGO-MWCNTs leads to a higher anodic peak current of about138.43 mA/cm² and 91.72 mA/cm² when compared to the Pd/3DrGO-MWCNTs and Pd/C for ethanol and methanol electro-oxidation. In addition, the catalyst showed the highest electro chemical active surface area. The present work demonstrates a possible way to fabricate a nanostructure catalyst to improve the performance of electro-catalytic reactions.     

Kinetic performance of TiO2/Pt/reduced graphene oxide composites in the photocatalytic hydrogen production

Among the different alternatives to generate hydrogen, photocatalysis can play an important role since it is based on the use of solar radiation and a suitable semiconductor. Starting from the most commonly researched TiO₂ catalyst, many efforts have been devoted to improve its efficacy. This work, based on the potential of reduced graphene oxide (rGO) to carry charges and platinum nanoparticles to act as efficient traps for photogenerated electrons, assesses the performance of synthesized binary and ternary photocatalysts (TiO₂/rGO, TiO₂/Pt and TiO₂/rGO/Pt) for hydrogen generation. The addition of rGO to TiO₂ almost duplicates (1.95 factor) the hydrogen production rate compared to bare TiO₂. Moreover, the binary TiO₂/Pt photocatalyst reported the best performance, with an increase in the hydrogen production rate by a factor of 15.26 compared to TiO₂. However, the ternary catalyst performed worse than the binary TiO₂/Pt probably due to the use of non-optimized co-catalyst ratios. Since the addition of rGO reduces the cost of the catalyst, the trade-off between the catalyst performance and cost is worth of future research.