N-doped Graphene Oxide Research Articles

Photoconductivity from photochemical N-doped graphene oxide thin films

N-doped graphene oxide (NGO) thin film was synthesised by photochemical reduction method in an ammonia atmosphere. The NGO film obtained has high N content of 9·77 at.%. The photocurrent amplitude for the NGO film is ca. 8·29 μA at 5 mV. The NGO film exhibits significant photocurrent enhancement with a high-enhancement ratio of ∼1200% at 0·5 mV and enhancement ratio for NGO film is nearly twice of that for the reduced graphene oxide (RGO) film at all different bias voltage, which may attribute to the high content of N.

White-light photoconductivity of N-doped graphene oxide thin films

Photoconductivity of large-area graphene oxide thin film with high doping level of nitrogen in the basal plane of the graphene sheets are firstly demonstrated in this work. The N-doped graphene oxide thin film obtained by annealing reduction in NH3 atmosphere for 20 min (NRGO-20) has a high N content of 10.24 at.%, among which the predominant one is the pyridine-like N with the content of ~4.54 at.% in the basal plane of the graphene sheets. Compared to the reduced graphene oxide thin film obtained by annealing in Ar atmosphere for 20 min (RGO-20), the photocurrent of NRGO-20 thin film is significantly improved. The NRGO-20 film exhibits significant photocurrent enhancement with a high enhancement ratio of approximately 3,000 % under white-light irradiation at bias voltage of 0.5 mV. It might be attributed to its conjugation effect with the high content of pyridine-like N in the basal plane of the graphene sheets.

The carbonization of polyethyleneimine: facile fabrication of N-doped graphene oxide and graphene quantum dots

In this study, N-doped graphene oxide (N-GO) and graphene quantum dots (N-GQDs) were synthesized by the carbonization of branched polyethyleneimine (PEI) in the presence of H2O2.

Fabrication of nitrogen doped graphene oxide coatings: experimental and theoretical approach for surface protection

In this work, we present a simple strategy of fabricating an N-doped graphene oxide coating on stainless steel for protective applications.

Graphene-Oxide-Based Electrocatalysts for Oxygen Reduction Reaction

The commercialization of polymer electrolyte fuel cells (PEFCs) has been limited by the high cost of Pt-based catalysts used in both PEFC anode and cathode. Recently, non-precious metal catalysts (NPMCs) with high volumetric activity, low H2O2yield, and stability [1-2] have been developed as potential replacements for Pt-based oxygen reduction reaction (ORR) catalysts in the PEFC cathode.State-of-the-art NPMCs have typically been synthesized from highly heterogeneous precursors [1,3,4], making understanding of the ORR active site in such catalysts particularly arduous. Catalysts based on graphene and graphene-oxide (GO) are more homogeneous and possess properties such as good chemical stability, excellent conductivity, and more importantly, can potentially be functionalized in a controlled manner [5]. GO inherently has a high defect density and can be modified with various functional moieties, e.g.carboxyl, hydroxyl, and epoxy groups using various synthesis techniques such as Hummer’s or Hoffman’s methods. The desire to have a high defect density arises from the possibility that defect sites may serve as niches for the chemical doping of heteroatoms, such as nitrogen (N) that have been proven to play a critical role in the overall performance of NPMCs. Further, the N-doped sites might serve as anchors for the coordination of transition metal atoms such as Fe, leading to the formation of the ORR active sites.In this work, we have synthesized GO using different chemical routes and, subsequently, doped it with ammonia at various temperatures (500oC-900oC). Figures 1A and 1B display the respective SEM and HR-STEM images of the synthesized N-doped GO. The images indicate the preservation of graphene sheets after N doping, however, some amorphous content can also be seen in the sample. Figure 1C shows the electrochemical performance of the synthesized catalysts in oxygen reduction reaction measured using RDE. In a 0.5 M H2SO4electrolyte, a half-wave potential of 0.70 V and low peroxide formation were obtained. Conversely, in a 0.1 M NaOH electrolyte a half-wave potential of 0.85 V was observed. The catalyst is relatively stable in acidic conditions over 2000 cycles. A detailed ICP-MS study identified ppm levels of Mn and Fe in the sample, possibly due to the intrinsic GO synthesis method used. Results obtained using other characterization techniques, such as Raman and XPS, will be presented to further understand the role of the metal and nitrogen doping in the performance of GO-based catalysts.These first results indicate high performance of GO-based NPMCs in both acidic and alkaline media. Although, we have demonstrated effective oxygen reduction activity and have a better understanding of GO-based catalysts, we are now focusing our efforts on the synthesis of the model GO-based catalysts, free of any metal contaminants. Acknowledgment Financial support from the Los Alamos National Laboratory Laboratory-Directed Research and Development (LDRD) Program is gratefully acknowledged. References Wu, G., More, K. L., Johnston, C. M., Zelenay, P., Science, 332, 443-447 (2011).Bashyam, R., Zelenay, P., Nature, 443, 63-66 (2006).Chung, H. T., Johnston, C. M., Artyushkova, K., Ferrandon, M., Myers, D. J., Zelenay, P., Electrochem. Commun., 12, 1792-1795 (2010).Wu, G., Nelson, M., Ma, S. G., Meng, H., Cui, G. F., Shen, P. K., Carbon, 49, 3972-3982 (2011).Qu, L., Liu, Y., Baek, J.-B., Dai, L., ACS Nano, 4, 1321-1326 (2010).

Nitrogen-Doped Partially Reduced Graphene Oxide Rewritable Nonvolatile Memory

As memory materials, two-dimensional (2D) carbon materials such as graphene oxide (GO)-based materials have attracted attention due to a variety of advantageous attributes, including their solution-processability and their potential for highly scalable device fabrication for transistor-based memory and cross-bar memory arrays. In spite of this, the use of GO-based materials has been limited, primarily due to uncontrollable oxygen functional groups. To induce the stable memory effect by ionic charges of a negatively charged carboxylic acid group of partially reduced graphene oxide (PrGO), a positively charged pyridinium N that served as a counterion to the negatively charged carboxylic acid was carefully introduced on the PrGO framework. Partially reduced N-doped graphene oxide (PrGODMF) in dimethylformamide (DMF) behaved as a semiconducting nonvolatile memory material. Its optical energy band gap was 1.7-2.1 eV and contained a sp2 C═C framework with 45-50% oxygen-functionalized carbon density and 3% doped nitrogen atoms. In particular, rewritable nonvolatile memory characteristics were dependent on the proportion of pyridinum N, and as the proportion of pyridinium N atom decreased, the PrGODMF film lost memory behavior. Polarization of charged PrGODMF containing pyridinium N and carboxylic acid under an electric field produced N-doped PrGODMF memory effects that followed voltage-driven rewrite-read-erase-read processes.

Covalent Hybrid of Spinel Manganese–Cobalt Oxide and Graphene as Advanced Oxygen Reduction Electrocatalysts

Through direct nanoparticle nucleation and growth on nitrogen doped, reduced graphene oxide sheets and cation substitution of spinel Co(3)O(4) nanoparticles, a manganese-cobalt spinel MnCo(2)O(4)/graphene hybrid was developed as a highly efficient electrocatalyst for oxygen reduction reaction (ORR) in alkaline conditions. Electrochemical and X-ray near-edge structure (XANES) investigations revealed that the nucleation and growth method for forming inorganic-nanocarbon hybrids results in covalent coupling between spinel oxide nanoparticles and N-doped reduced graphene oxide (N-rmGO) sheets. Carbon K-edge and nitrogen K-edge XANES showed strongly perturbed C-O and C-N bonding in the N-rmGO sheet, suggesting the formation of C-O-metal and C-N-metal bonds between N-doped graphene oxide and spinel oxide nanoparticles. Co L-edge and Mn L-edge XANES suggested substitution of Co(3+) sites by Mn(3+), which increased the activity of the catalytic sites in the hybrid materials, further boosting the ORR activity compared with the pure cobalt oxide hybrid. The covalently bonded hybrid afforded much greater activity and durability than the physical mixture of nanoparticles and carbon materials including N-rmGO. At the same mass loading, the MnCo(2)O(4)/N-graphene hybrid can outperform Pt/C in ORR current density at medium overpotentials with stability superior to Pt/C in alkaline solutions.

Nanosized N-doped graphene oxide with visible fluorescence in water for metal ion sensing

Nanosized N-doped graphene oxide (GO) with visible fluorescence in water was prepared by cutting and unzipping of N-doped carbon nanotubes (NCNTs) and used to distinguish between normal and transition metal ions. It is found that the fluorescence is bathochromically shifted as the level of oxidation is increased.