The electronic and chemical properties of graphene can be modulated by chemical doping foreign atoms and functional moieties. The general approach to the synthesis of nitrogen-doped graphene (NG), such as chemical vapor deposition (CVD) performed in gas phases, requires transitional metal catalysts which could contaminate the resultant products and thus affect their properties. In this paper, we propose a facile, catalyst-free thermal annealing approach for large-scale synthesis of NG using low-cost industrial material melamine as the nitrogen source. This approach can completely avoid the contamination of transition metal catalysts, and thus the intrinsic catalytic performance of pure NGs can be investigated. Detailed X-ray photoelectron spectrum analysis of the resultant products shows that the atomic percentage of nitrogen in doped graphene samples can be adjusted up to 10.1%. Such a high doping level has not been reported previously. High-resolution N1s spectra reveal that the as-made NG mainly contains pyridine-like nitrogen atoms. Electrochemical characterizations clearly demonstrate excellent electrocatalytic activity of NG toward the oxygen reduction reaction (ORR) in alkaline electrolytes, which is independent of nitrogen doping level. The present catalyst-free approach opens up the possibility for the synthesis of NG in gram-scale for electronic devices and cathodic materials for fuel cells and biosensors.

Boron atoms, with strong electron-withdrawing capability, are doped into graphene frameworks forming boron doped graphene (BG) via a catalyst-free thermal annealing approach in the presence of boron oxide. Atomic force microscopic (AFM) and transmission electron microscopic (TEM) characterizations reveal that the as-prepared BG has a flake-like structure with an average thickness of ca. 2 nm. X-ray photoelectron spectroscopy (XPS) analysis demonstrates that boron atoms can be successfully doped into graphene structures with the atomic percentage of 3.2%. Due to its particular structure and unique electronic properties, the resultant BG exhibits excellent electrocatalytic activity towards oxygen reduction reaction (ORR) in alkaline electrolytes, similar to the performance of Pt catalysts. In addition, the non-metallic BG catalyst shows long-term stability and good CO tolerance superior to that of Pt-based catalysts. These results demonstrate that the BG, as a promising candidate in advanced electrode materials, may substitute Pt-based nanomaterials as a cathode catalyst for ORR in fuel cells as well as other electrochemical applications similar to the reported nitrogen doped graphene.

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A one-step electrochemical approach to the synthesis of highly dispersed Pt nanoparticles on graphene has been proposed. The resultant Pt NPs@G nanocomposite shows higher electrocatalytic activity and long-term stability towards methanol electrooxidation than the Pt NPs@Vulcan.

A graphene-based electrochemical sensing platform for sensitive determination of explosive nitroaromatic compounds (NACs) was constructed by means of electrochemical reduction of graphene oxide (GO) on a glassy carbon electrode (GCE). The electrochemically reduced graphene (ER-GO) adhered strongly onto the GCE surface with a wrinkled morphology that showed a large active surface area. 2,4-Dinitrotoluene (2,4-DNT), as a model analyte, was detected by using stripping voltammetry, which gave a low detection limit of 42 nmol  L(-1) (signal-to-noise ratio=3) and a wide linear range from 5.49×10(-7) to 1.1×10(-5)  M. Further characterizations by electrochemistry, IR, and Raman spectra confirmed that the greatly improved electrochemical reduction signal of DNT on the ER-GO-modified GC electrode could be ascribed to the excellent electrocatalytic activity and high surface-area-to-volume ratio of graphene, and the strong π-π stacking interactions between 2,4-DNT and the graphene surface. Other explosive nitroaromatic compounds including 1,3-dinitrobenzene (1,3-DNB), 2,4,6-trinitrotoluene (TNT), and 1,3,5-trinitrobenzene (TNB) could also be detected on the ER-GO-modified GC electrode at the nM level. Experimental results showed that electrochemical reduction of GO on the GC electrode was a fast, simple, and controllable method for the construction of a graphene-modified electrode for sensing NACs and other sensing applications.

Size-tunable nanofluidic devices coupled to an electrochemical detector have been designed and then used to study glucose oxidase (GOx) reaction kinetics confined in nanospaces. The devices are fabricated via a photochemical decomposition reaction, which forms nanochannels covered with carboxyl groups. The generated carboxyl groups enable us to chemically pattern biological molecules on the polymer surfaces via covalent bonding. With this approach, the activity of the immobilized biological molecules confined in nanospaces with different sizes has been investigated. GOx species are chemically immobilized on the surface of the nanochannels, catalyzing the oxidation of substrate glucose as it flows through the channels. The enzyme reaction product, hydrogen peroxide, passing through the nanochannels, reaches an electrochemical detector, giving rise to an increase in anodic current. This steady-state electrochemical current, which responds to various glucose concentrations, can be used to evaluate the GOx activity under confinement conditions. The results show significant nanoconfinement effects that are dependent on the channel size where the reaction occurs, demonstrating the importance of spatial confinement on the GOx reaction kinetics. The present approach provides an effective method for the study of enzyme activity and other bioassay systems, such as cell assays, drug discovery, and clinical diagnosis.

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