Fluorinated reduced graphene oxide as a protective layer on the metallic lithium for application in the high energy batteries

International audienceMetallic lithium is considered to be one of the most promising anode materials since it offers high volumetric and gravimetric energy densities when combined with high-voltage or high-capacity cathodes. However, the main impediment to the practical applications of metallic lithium is its unstable solid electrolyte interface (SEI), which results in constant lithium consumption for the formation of fresh SEI, together with lithium dendritic growth during electrochemical cycling. Here we present the electrochemical performance of a fluorinated reduced graphene oxide interlayer (FGI) on the metallic lithium surface, tested in lithium symmetrical cells and in combination with two different cathode materials. The FGI on the metallic lithium exhibit two roles, firstly it acts as a Li-ion conductive layer and electronic insulator and secondly, it effectively suppresses the formation of high surface area lithium (HSAL). An enhanced electrochemical performance of the full cell battery system with two different types of cathodes was shown in the carbonate or in the ether based electrolytes. The presented results indicate a potential application in future secondary Li-metal batteries

Reduced graphene oxide as efficient carbon support for Pd-based ethanol oxidation catalysts in alkaline media

The sluggish kinetics of the ethanol oxidation reaction (EOR) and the related development of low-cost, highly active and stable anode catalysts still remains the major challenge in alkaline direct ethanol fuel cells (ADEFCs). In this respect, we synthesized a PdNiBi nanocatalyst on reduced graphene oxide (rGO) via a facile synthesis method. The prepared composite catalyst was physicochemically characterized by SEM, STEM, EDX, ICP-OES and XRD to analyze the morphology, particle distribution and size, elemental composition and structure. The electrochemical activity and stability towards EOR in alkaline media were examined using the thin-film rotating disk electrode technique. The results reveal well-dispersed and strongly anchored nanoparticles on the rGO support, providing abundant active sites. The PdNiBi/rGO presents a higher EOR activity and stability compared to a commercial Pd/C ascribed to a high ECSA and synergistic effects between Pd, Ni and Bi and the rGO material. These findings suggest PdNiBi/rGO as a promising anode catalyst in ADEFC applications

Electrode configurations study for alkaline direct ethanol fuel cells

The direct electrochemical conversion of ethanol, a sustainable fuel, is an alternative sustainable technology of the future. In this study, membrane electrode assemblies with different electrode configurations for an alkaline direct ethanol fuel cell were fabricated and tested in a fuel cell device. The configurations include a catalyst-coated substrate (CCS), a catalyst-coated membrane (CCM), and a mixture of these two fabrication options. Two different anion exchange membranes were used to perform a comprehensive analysis. The fabricated CCSs and CCMs were characterized with single cell measurements, electro­chemical impedance spectroscopy and scanning electron microscopy. In addition, the swelling behavior of the membranes in alkaline solution was investigated in order to obtain information for CCM production. The results of the experimental electrochemical tests show that the CCS approach provides higher power densities (42.4 mW cm-2) than the others, regardless of the membrane type

Green Synthesis of Immobilized CuO Photocatalyst for Disinfection of Water

A green method for depositing a CuO layer with good adhesion and a large surface area on a support of activated alumina (Al2O3) was evaluated. The relatively simple method consists of adsorption of a copper salt on the surface of Al2O3, formation of Cu(OH)2, and subsequent decomposition of the hydroxide to CuO. The XRD confirmed that the deposited photocatalyst crystalized at low temperatures (80 °C). Furthermore, BET measurements show a surface area of about 90 m2/g. The large surface area is the result of the speed of the conversion and decomposition reactions. The photokilling properties of the prepared photocatalyst were evaluated using E. coli cells and the leaching of copper ions was determined using ICP-MS. The photocatalytic efficiency was also evaluated by the degradation of an organic azo dye. The prepared photocatalyst shows good activity in the purification and disinfection of treated water. The described method is economical, fast, and can be considered green, since the only byproducts are water and NaCl

Effect of PdNiBi Metal Content: Cost Reduction in Alkaline Direct Ethanol Fuel Cells

In this work, the metal content of Pd85Ni10Bi5/C catalysts for the alkaline ethanol-oxidation reaction was reduced from 40 wt.% (PdNiBi/C (40/60)) to 30 wt.% (PdNiBi/C (30/70)), 20 wt.% (PdNiBi/C (20/80)) and 10 wt.% (PdNiBi/C (10/90)), while increasing performance. The synthesized catalysts were examined using physicochemical measurements and electrochemical measurements. The best performing catalysts were used to fabricate membrane electrode assemblies for carrying out single-cell tests and to determine the influence of the metal/carbon ratio of the electrode. The electrochemical surface area (695 cm2 mg−1) and activity were increased, resulting in high peak-current densities for the ethanol oxidation reaction (3.72 A mg−1) by the resulting more accessible metal particles. The electrode produced with the PdNiBi/C (30/70) catalyst reached a maximum power density of 34.8 mW mg−1 at 50 °C. This successfully demonstrated a doubling of the power density compared with the performance of the PdNiBi/C (40/60) electrode, while simultaneously reducing the costs

Highly sensitive amperometric detection of hydrogen peroxide in saliva based on N-doped graphene nanoribbons and MnO2_2 modified carbon paste electrodes

Four different graphene-based nanomaterials (htGO, N-htGO, htGONR, and N-htGONR) were synthesized, characterized, and used as a modifier of carbon paste electrode (CPE) in order to produce a reliable, precise, and highly sensitive non-enzymatic amperometric hydrogen peroxide sensor for complex matrices. CPE, with their robustness, reliability, and ease of modification, present a convenient starting point for the development of new sensors. Modification of CPE was optimized by systematically changing the type and concentration of materials in the modifier and studying the prepared electrode surface by cyclic voltammetry. N-htGONR in combination with manganese dioxide (1:1 ratio) proved to be the most appropriate material for detection of hydrogen peroxide in pharmaceutical and saliva matrices. The developed sensor exhibited a wide linear range (1.0–300 µM) and an excellent limit of detection (0.08 µM) and reproducibility, as well as high sensitivity and stability. The sensor was successfully applied to real sample analysis, where the recovery values for a commercially obtained pharmaceutical product were between 94.3% and 98.0%. Saliva samples of a user of the pharmaceutical product were also successfully analyzed

Highly Sensitive and Selective Graphene Nanoribbon Based Enzymatic Glucose Screen-Printed Electrochemical Sensor

A simple, sensitive, cost effective, and reliable enzymatic glucose biosensor was developed and tested. Nitrogen-doped heat-treated graphene oxide nanoribbons (N-htGONR) were used for modification of commercially available screen-printed carbon electrodes (SPCEs), together with MnO2 and glucose oxidase. The resulting sensors were optimized and used to detect glucose in a wide linear range (0.05–5.0 mM) by a simple amperometric method, where the limit of detection was determined to be 0.008 mM. (lifetime), and reproducibility studies were also carried out and yielded favorable results. The sensor was then tested against potential interfering species present in food and beverage samples before its application to real matrix. Spiked beer samples were analyzed (with glucose recovery between 93.5 and 103.5%) to demonstrate the suitability of the developed sensor towards real food and beverage sample applications

Influence of the ultrasound cavitation intensity on reduced graphene oxide functionalization

Graphene is a valuable and useful nanomaterial due to its exceptionally high tensile strength, electrical conductivity and transparency, as well as the ability to tune its materials properties via functionalization. One of the most important features needed to integrate functionalized graphene into products via scalable processing is the effectiveness of graphene dispersion in aqueous and organic solvents. In this study, we aimed to achieve the functionalization of reduced graphene oxide (rGO) by sonication in a one-step process using polyvinyl alcohol (PVA) as a model molecule to be bound to the rGO surface. We investigated the influence of the sonication energy on the efficacy of rGO functionalization. The correlation between the performance of the high-intensity ultrasonic horn and the synthesis of the PVA functionalized rGO was thoroughly investigated by TGA coupled with MS, and IR, Raman, XPS, Laser diffraction, and SEM analysis. The results show that the most soluble PVA-functionalized rGO is achieved at 50% of the ultrasonic horn amplitude. Analysis of cavitation dynamics revealed that in the near vicinity of the horn it is most aggressive at the highest amplitude (60%). This causes rGO flakes to break into smaller domains, which negatively affects the functionalization process. On the other hand, the maximum of the pressure pulsations far away from the horn is reached at 40% amplitude, as the pressure oscillations are attenuated significantly in the 2-phase flow region at higher amplitudes. These observations corelate well with the measured degree of functionalization, where the optimum functionalized rGO dispersion is reached at 50% horn amplitude, and generally imply that cavitation intensity must be carefully adjusted to achieve optimal rGO functionalization