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This study aims to elucidate the role of hydrogen desorption profiles obtained through temperature programmed desorption (TPD) analysis of carbon materials for revealing their carbon edge sites. Accordingly, the H 2 desorption profiles of several carbon materials, such as activated carbon, carbon black, reduced graphene oxide (rGO), phenol resin carbon, graphite, high-temperature treated carbon, and carbon nanotubes (CNTs), were investigated. The kinetic analysis of the profiles revealed that H 2 desorption is a second-order reaction initiated by the association of edge hydrogen. Furthermore, the relationship between the total number of edge hydrogens in a sample and the peak temperature of H 2 desorption represents the spatial distribution of edge hydrogens in the carbon structure. Additionally, most of the activated carbons, carbon blacks, and rGOs exhibited a uniform distribution of edge hydrogen throughout their carbon structures. In contrast, the edge hydrogen in graphite, high-temperature treated carbon, and CNTs were heterogeneously distributed throughout their structures. [Display omitted] [ABSTRACT FROM AUTHOR]

Hard carbons have immense potential as anode materials for Na-ion batteries, because the expanded graphene interlayers and nanovoids between randomly stacked aromatic fragments can accommodate a substantial amount of sodium. However, the large irreversible capacity in the first cycle still remains as a significant issue in terms of a practicable battery technology. Here, we show that hard carbon electrodes derived from a common phenol resin deliver a high reversible capacity within the narrow potential range of 0.1-0.005 V (vs. Na+/Na) and an excellent initial coulombic efficiency up to 95 %. The former allows the sustainable high voltage, whereas the latter minimizes the amount of unavailable Na+ in a closed cell. The findings in this work put forward a guideline for manufacturing hard carbon electrodes, which goes against the current trend of nanostructuring and downsizing. [ABSTRACT FROM AUTHOR]

The control of the electronic states of carbon-based materials is of great importance for the widespread use of carbon materials as electronic devices and catalysts. This article reports a novel method of controlling the electronic states of carbon-based materials by establishing covalent bonds between inorganic support materials and carbon thin films. Carbon thin films of 1 nm thickness were grown on inorganic substrates (Al 2 O 3 , AlN, and ZrO 2) using chemical vapor deposition. Covalent bond formation was confirmed between the substrates and the carbon films. The investigations of field effect transistor characteristics and work function revealed the different relationships between the Dirac points and Fermi levels of carbon films depending on the type of substrate. The Fermi level of the films grown on Al 2 O 3 or ZrO 2 was found to be lower than the Dirac point energy level, with the ZrO 2 sample exhibiting the lowest Fermi level. In contrast, the Fermi level of the film grown on AlN was located at a higher energy than the Dirac point. The Fermi level of the carbon film depends on the inorganic substrate, and the change in the Fermi level can be explained by the nature of the covalent bonds between the substrate and the film. Controlling the energy levels of the valence electrons of carbon thin film depending on the composition of the substrate on which the carbon thin film is grown. [Display omitted] [ABSTRACT FROM AUTHOR]

Onion-like carbon (OLC) is known to form as an intermediate structure when nanodiamond (ND) is heat treated at 1100–1500 °C. In this letter, we report on the electrochemical activity of its oxygen reduction reaction (ORR) when prepared at temperatures from 1000 to 2000 °C. The ORR activity is found to exhibit excellent correlation with the degree of defects, with OLC prepared at 1400 °C found to have the highest activity. This is attributed to the formation of curved graphitic layers containing edges during ND-OLC transformation, which function as active sites for the adsorption and subsequent reduction of oxygen. [ABSTRACT FROM AUTHOR]

Trace amounts of edge sites in natural graphite, synthetic graphite and high-temperature treated coke are quantitatively analyzed from the numbers of hydrogen atoms and oxygen-containing functional groups at carbon edge sites. For the analysis of hydrogen content, a new analytical technique is developed. The oxygen-containing functional groups are analyzed with a highly sensitive temperature-programmed desorption (TPD) technique. These techniques allow us to estimate the trace amounts of edge sites in the range of 1–10 × 10 −4 at.% with extremely high accuracy and reveal that the concentration and the type of edges sites differ depending on the type and the particle size of these graphitized carbons. Moreover, the average sizes of graphene sheets in these carbons are estimated from the total number of edge sites. The graphene sheet size thus obtained is compared with the crystallite sizes, L a , and the average particle size, and such comparison provides deep insight into the understanding of carbon molecular structure in the graphitized carbons. [ABSTRACT FROM AUTHOR]

The use of carbon cathode catalysts in polymer electrolyte fuel cells instead of the current platinum catalysts is attracting increasing attention. We claim that two factors are important for enhancing the activity of carbon cathode catalysts in the oxygen reduction reaction (ORR): the formation of a nanoshell structure and co-doping with boron and nitrogen. Herein, we investigate the preparation and characterization of active ORR carbon catalysts that combine the above factors. Boron and nitrogen (BN)-doped nanoshell-containing carbon (BN-NSCC) was prepared by carbonizing a mixture of poly(furfuryl alcohol), cobalt phthalocyanine, melamine, and a trifluoroborane–methanol complex at 1000 °C. Transmission electron microscopy and X-ray photoelectron spectroscopy revealed the formation of nanoshell structures with distorted graphitic layers and the introduction of boron and nitrogen atoms, respectively. The ORR activity was evaluated in oxygen-saturated 0.5 mol dm −3 H 2 SO 4 using Koutecky–Levich analysis. The BN-NSCC showed an eight to ten times higher ORR activity than undoped NSCC, with an increased number of electrons participating in the reaction. Tafel analysis revealed a change in the rate-determining step caused by BN-doping. Thus, the combination of a nanoshell structure and co-doping with boron and nitrogen was found to improve the ORR activity of carbon catalysts. [ABSTRACT FROM AUTHOR]

This study reports the synergistic improvement of the oxygen reduction reaction (ORR) activity of a carbon catalyst prepared from a phenol–formaldehyde resin by simultaneous incorporation of Cu and Fe phthalocyanines. This carbon catalyst exhibited higher ORR activities than those prepared with either Cu or Fe phthalocyanines, with an approx. 28-fold maximum ORR current enhancement observed when Cu/Fe = 75:25 was incorporated into the carbon precursor. Surface and structural characterizations of these catalysts suggested that the incorporated Cu played a role in suppressing the catalytic activity of Fe, forming the reported nanoshell structure, and in keeping more nitrogen atoms attached to carbons. The incorporation of Cu in the carbon catalyst provided a doping effect for nitrogen into the carbon structure and inhibited catalytic graphitization caused by Fe species. These effects resulted in a distinctive carbon structure in the nanoshell. These multiple effects of Cu incorporation were considered key factors in the enhancement of ORR activity caused by Fe and Cu incorporation. [ABSTRACT FROM AUTHOR]

Carbon catalysts for the oxygen reduction reaction (ORR) were prepared from mixtures of humic acid and cobalt compounds. To examine the effects of cobalt and nitrogen on the ORR, cobalt phthalocyanine (CoPc), cobalt chloride (CoCl 2 ) and phthalocyanine (H 2 Pc) were mixed with the humic acid and carbonized at 800 °C. The carbons were washed with hydrochloric acid to remove metals on the surface of the carbons. The carbon prepared by mixing HA, CoCl 2 and H 2 Pc (HA–CoCl 2 –H 2 Pc) had the highest ORR activity, while the carbons, HA–CoPc and HA–H 2 Pc, had lower ORR activities. HA–CoCl 2 had moderate activity. The results imply that both of cobalt and nitrogen are important to obtain ORR catalysts with higher activities. A uniform distribution of Co atoms in the precursor is also important to obtain carbon alloy catalysts with higher ORR activities. TANSO 2015 (No. 267), 94–100. [ABSTRACT FROM AUTHOR]