A nitrogen-doped graphene electrocatalyst for selective oxygen reduction in presence of glucose and D-gluconic acid in pH-neutral media

Elucidating the structural, catalytic, and antibacterial traits of Ficus carica and Azadirachta indica leaf extract-mediated synthesis of the Ag/CuO/rGO nanocomposite

The present exploration demonstrates the efficient, sustainable, cost-effective, and environment-friendly green approach for the synthesis of silver (Ag)-doped copper oxide (CuO) embedded with reduced graphene oxide (rGO) nanocomposite using the green one-pot method and the green deposition method. Leaf extracts of Ficus carica and Azadirachta indica were used for both methods as reducing and capping agents. The effect of methodology and plant extract was analyzed through different characterization techniques such as UV-visible spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), x-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM). The lowest band gap of 3.0 eV was observed for the Ag/CuO/rGO prepared by the green one-pot method using F. carica. The reduction of graphene oxide (GO) and the formation of metal oxide was confirmed through functional group detection using FT-IR. Calculation of thermodynamic parameters showed that all reactions involved were nonspontaneous and endothermic which shows the stability of nanocomposites. XRD studies revealed the crystallinity, phase purity and small average crystallite size of 32.67 nm. SEM images disclosed that the morphology of the nanocomposites was spherical with agglomeration and rough texture. The particle size of the nanocomposites calculated through HRTEM was found in agreement with the XRD results. The numerous properties of the synthesized nanocomposites enhanced their potential against the degradation of methylene blue, rhodamine B, and ciprofloxacin. The highest percentage degradation of Ag/CuO/rGO was found to be 97%, synthesized using the green one-pot method with F. carica against ciprofloxacin, which might be due to the lowest band gap, delayed electron-hole pair recombination, and large surface area available. The nanocomposites were also tested against the Gram-positive and Gram-negative bacteria. RESEARCH HIGHLIGHTS: Facile synthesis of Ag/CuO/rGO nanocomposite using a green one-pot method and the green deposition method. The lowest band gap of 3.0 eV was observed for nanocomposite prepared by a green one-pot method using Ficus carica. Least average crystallite size of 32.67 nm was found for nanocomposite prepared by a green one-pot method using F. carica. Highest antibacterial and catalytic activity (97%) was obtained against ciprofloxacin with nanocomposite prepared through green one-pot method using F. carica. A mechanism of green synthesis is proposed.

Cobalt and Nitrogen Codoped Carbon Nanosheets Templated from NaCl as Efficient Oxygen Reduction Electrocatalysts

The oxygen reduction reaction (ORR) in a cathode is an essential component of many electrochemical energy storage and conversion systems. Two-dimensional materials are beneficial for electron conduction and mass transport with high density, showing prominent electrochemical catalytic performance towards the ORR. Herein, a simple NaCl-assisted method to synthesize cobalt-nitrogen-doped carbon materials (CoNC), which present prominent performance towards the ORR in alkaline media, is described. The utilization of the NaCl template endows the product with a large specific surface area of 556.4 m²  g^-1 , as well as good dispersion of cobalt nanoparticles. CoNC-800@NaCl (800 indicates the calcination temperature in °C) displays an excellent onset potential of 0.94 V (vs. a reversible hydrogen electrode), which is close to that of commercial Pt/C. Additionally, CoNC-800@NaCl also exhibits better long-term durability and methanol tolerance than that of Pt/C. The high-performance CoNC-800@NaCl catalyst provides a hopeful alternative to noble-metal catalysts for the ORR in practical applications.

Nitrogen-doped graphene and graphene quantum dots: A review onsynthesis and applications in energy, sensors and environment

Doping of nitrogen is a promising strategy to modulate chemical, electronic, and structural functionalities of graphene (G)and graphene quantum dots (GQDs) for their outstanding properties in energy and environmental applications.This paper reviews various synthesis approaches of nitrogen-doped graphene (N-G) and nitrogen-doped graphene quantum dots (N-GQDs).;Thermal, ultrasonic, solvothermal, hydrothermal, and electron-beam methods have been applied to synthesize N-G and N-GQDs.These nitrogen-doped carbon materials are characterized to obtain their structural configurations in order to achieve better performance in their applications compared to only either graphene or graphene quantum dots.Both N-G and N-GQDs may be converted into functional materials by integrating with other compounds such as metal oxides/nitrides, polymers, and semiconductors.These functional materials demonstrate superior performance over N-G and N-GQDs materials.Examples of applications of N-G and N-GQDs include supercapacitors, batteries, sensors, fuel cells, solar cells, and photocatalyst.

Platinum nanowires anchored on graphene-supported platinum nanoparticles as a highly active electrocatalyst towards glucose oxidation for fuel cell applications

The limited performance of platinum-based electrocatalysts for glucose electrooxidation is a major concern for glucose fuel cells, since glucose electrooxidation is characterized by slow reaction kinetics and low diffusion coefficient. Here, the presented graphene-supported platinum-based hierarchical nanostructures attain highly enhanced electrocatalytic activity towards glucose oxidation. Platinum nanoparticles electrodeposited on graphene support retain mechanical stability and act as junctions allowing a reliable, smooth and dense growth of platinum nanowires with extremely small diameters (>10 nm) on graphene. The electrode's surface roughness was increased by factors up to 4000 to the geometrical surface area enabling maximized exploitation of the electrocatalytic activity of platinum and efficient electron transfer between nanowires and the substrate. The unique three-dimensional geometry of these hierarchical nanostructures has a significant impact on their catalytic performance offering short diffusional paths for slow glucose species, thus, mass transport limitations are optimized leading to lower polarization losses. This was examined by galvanostatic measurements of the operation as anodes in glucose half-cells under conditions corresponding to implantable glucose fuel cells. The presented hierarchical nanostructures show remarkably enhanced catalytic performance for glucose electrooxidation, i.e. a negatively shifted open circuit potential of -580 mV vs. Ag/AgCl, hence, representing appropriate electrocatalysts for use as anodes in glucose fuel cells. In combination with a non-metal N-doped graphene cathode, a cell potential of 0.65 V was achieved at a galvanostatic load of 17.5 μA cm^-2 which noticeably surpasses the performance of state of the art catalysts for the aforementioned operation conditions.

Control over fuel cell performance through modulation of pore accessibility: investigation and modeling of carbon nanotubes effects on oxygen reduction at N-graphene-based nanocomposite

The lack of performance of graphene-based electrocatalysts for oxygen reduction (ORR) is a major concern for fuel cells which can be mastered using nanocomposites. This work is highlighted by the optimization of nitrogen(N)-doped graphene/carbon nanotubes (CNTs) nanocomposite's ORR performance examined by galvanostatic measurements in realistically approached glucose half-cells. Obtained results mark an essential step for the development of nanocarbon-based cathodes, as we specifically evaluate the electrode performance under real fuel cell conditions. The 2D simulations exclusively represent an important approach for understanding the catalytic efficiency of the nanocomposite with unique structure. The kinetics features extracted from simulations are consistent with the experimentally determined kinetics. The morphology analysis reveals a 3D porous structure. The results demonstrate that the incorporation of CNTs implements mesoscale channels for improved mass transport and leads to efficient 4-electron transfer and enhanced overall catalytic activity in pH-neutral media. The nanocomposite shows increased specific surface area of 142 m² g^-1, positively shifted ORR onset potential of 67 mV and higher open circuit potential of 268 mV versus Ag/AgCl compared to N-graphene (11 m² g^-1, -17, 220 mV). The findings are supported by 2D simulations giving qualitative evidence to the significant role of CNTs for achieving better accessibility of pores, i.e. enabling improved transfer of oxygen and OH^-, and providing more reaction sites in the nanocomposite. The nanocomposite demonstrates better ORR performance than constituent components regarding potential application in miniaturized single-compartment glucose-based fuel cells.

Effect of the aromatic precursor flow rate on the morphology and properties of carbon nanostructures in plasma enhanced chemical vapor deposition

Understanding the effects of the synthesis parameters on the morphology and electrochemical properties of nanocarbon layers is a key step in the development of application-tailored nanostructures.