Heterogeneous nanocarbon materials are being increasingly investigated and deployed in numerous new technologies and devices for sustainable energy conversion and storage. Nanocarbons often consist of fullerene, graphene and carbon nanotubes. Their derivatives include quantum dots, nanofibres, nanoribbons, nanospheres/capsules and other nanostructured morphologies. The heterogeneous forms of these nanocarbons stem from the implantation of alien atoms into the aromatic carbon lattice or the covalent grafting of functional groups onto the carbon basal plane or edge sites. Heterogeneous nanocarbons have shown remarkable advantages in solar cells, water splitting, supercapacitors, lithium ion batteries and catalysis. This review focuses on recent progress in the experimental and computational studies of the roles of heteroatoms in heterogeneous nanocarbons for electrocatalytic oxygen reduction reaction (ORR). Critical perspectives are devoted to the ambiguous phenomena in this emerging research area. The long standing debate about the active sites is discussed with an emphasis on more rational development of advanced nanocarbon-based electrocatalysts for ORR. Broader contextThe emerging demand for next generation renewable and sustainable energy conversion technologies requires diverse catalytic and electrochemical methods and reactors. In terms of energy density, metal-air batteries exhibit the greatest promise for delivering compact energy by reducing oxygen from the air and oxidizing the implanted metal electrodes. Compared with metal oxidation, the kinetics of oxygen reduction is rather slow and inhibits the overall power capability of these promising devices. Platinum is the most active electrocatalyst for oxygen reduction and its high cost is urging the development of non-noble oxygen reduction electrocatalysts. Metal-free heterogeneous carbon nanotubes and many other nanocarbons have been increasingly studied in recent years. It has been greatly expected that by modifying the heteroatoms in nanostructured carbon materials their electrocatalytic activity towards oxygen reduction can be potentially increased to approaching that of platinum. However, many fundamental issues, particularly the specic functions of the heteroatoms in the oxygen reduction reaction on heterogeneous nanocarbons, are unclear. We expect to address some of these questions in this review and to propose some ideas for future research.

The classical strong metal–support interaction between TiO2 and IB metals was demonstrated.

Gold nanoparticle/alkanedithiol films were prepared via layer-by-layer self-assembly. For the assembly process, dodecylamine-stabilized Au nanoparticles with an average size of 4 nm and alkanedithiols with different alkylene chain lengths (C 6 , C 9 , C 12 , C 16 ) were used. The thickness of the films was determined by AFM and ranged between 26 and 34 nm. FE-SEM and TEM images indicate that the particle size within the film materials was similar to that of the dodecylamine-stabilized particles used for film preparation. The composition of the films was analyzed by XPS. The absence of the nitrogen signal indicated that the dodecylamine ligands were quantitatively exchanged by alkanedithiol molecules during film assembly. Two sulfur signals were observed, which could be assigned to sulfur bound to gold (S-Au) and to free thiol groups (S-H). As indicated by the relative signal intensities, about 60% of the alkanedithiol molecules were bound with both ends to the nanoparticles, whereas 40% were bound with only one thiol group. The C/S ratio was in good agreement with the stoichiometry of the alkanedithiol molecules. All films showed linear current-voltage characteristics. Conductivity measurements at variable temperature were consistent with an Arrhenius-type activation of charge transport. Using an activated tunneling model for describing the charge transport properties, we obtained an electron tunneling decay constant of β N ) 0.61 or 0.71, depending on the method used for data analysis. When the films were dosed with vapors of toluene and tetrachloroethylene, the resistance of the films increased reversibly. This response increased exponentially with increasing length of the alkanedithiol molecules. The chemical selectivity of the films corresponded essentially to the solubility properties of the alkanedithiol molecules.

Ammonia is synthesized directly from water and N at room temperature and atmospheric pressure in a flow electrochemical cell operating in gas phase (half-cell for the NH synthesis). Iron supported on carbon nanotubes (CNTs) was used as the electrocatalyst in this half-cell. A rate of ammonia formation of 2.2×10 gNH3  m h was obtained at room temperature and atmospheric pressure in a flow of N , with stable behavior for at least 60 h of reaction, under an applied potential of -2.0 V. This value is higher than the rate of ammonia formation obtained using noble metals (Ru/C) under comparable reaction conditions. Furthermore, hydrogen gas with a total Faraday efficiency as high as 95.1 % was obtained. Data also indicate that the active sites in NH electrocatalytic synthesis may be associated to specific carbon sites formed at the interface between iron particles and CNT and able to activate N , making it more reactive towards hydrogenation.

In order to expand the range of high-quality nanosized semiconductor materials that can be obtained as quantum dots through a wet chemical route a series of oxidize-stable CdTe nanoclusters with narrow size distributions and extremely small particle sizes ranging from 1.3 to 2.4nm has been prepared in aqueous solution using 2-mercaptoethanol and 1 -thioglycerol as stabilizers. It has been investigated by means of UV-vis absorption and photoluminescence spectroscopy, X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and energy dispersive x-ray analysis (EDX).

Developing highly efficient, low-cost oxygen reduction catalysts, especially in acidic medium, is of significance toward fuel cell commercialization. Although pyrolyzed Fe-N-C catalysts have been regarded as alternatives to platinumbased catalytic materials, further improvement requires precise control of the Fe-N x structure at the molecular level and a comprehensive understanding of catalytic site structure and the ORR mechanism on these materials. In this report, we present a microporous metal−organic-framework-confined strategy toward the preferable formation of single-atom dispersed catalysts. The onset potential for Fe-N-C is 0.92 V, comparable to that of Pt/C and outperforming most noble-metal-free catalysts ever reported. A high-spin Fe 3+ -N 4 configuration is revealed by the 57 Fe Mossbauer spectrum and X-ray absorption spectroscopy for Fe L-edge, which will convert to Fe 2+ -N 4 at low potential. The in situ reduced Fe 2+ -N 4 moiety from high-spin O x -Fe 3+ -N 4 contributes to most of the ORR activity due to its high turnover frequency (TOF) of ca. 1.71 e s −1 sites −1 .

An important goal in the preparation of highly active supported metal particles is the enhancement of the metal support interaction, providing a more stable catalyst, especially for liquid phase reactions as the leaching and reconstruction of the active phase causes deactivation. In this work, a covalent triazine framework (CTF) as support for Pd nanoparticles is compared to activated carbon (AC), the typical support used in liquid phase reactions. The results indicate that the presence of the N-heterocyclic moieties on the surface of the frameworks is beneficial for improving the stability of Pd nanoparticles during the liquid phase glycerol oxidation. Pd/CTF showed better activity and in particular better stability when compared to Pd supported on activated carbon (AC).

Ketonic carbonyl groups are catalytic active sites for oxidative dehydrogenation (ODH) reactions on carbon nanotubes. The quantity of these groups could be calculated from chemical titration with hydrazine compounds. ODH catalytic activity of nanocarbon is directly correlated with surface concentration of ketonic carbonyl groups, and the turnover frequency normalized by the number of active sites reflects the intrinsic activity of nanocarbon catalysts.