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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]

A deuterium-labeled temperature-programmed desorption (TPD) technique was developed to accurately characterize functional groups on the surface of carbon-based materials. After the protic hydrogen of the functional groups on activated carbons was substituted by deuterium, TPD analysis revealed the desorption of deuterium compounds (D 2 O, DHO, D 2 , DH). The functional groups were estimated from the predicted desorption mechanisms of these deuterium compounds, which can be distinguished according to the functional groups and their surrounding chemical structures. Thus, this technique provides information on not only the type of functional groups but also the extensive chemical structure around them. The phenolic group, ether, and edge hydrogen formed on the activated carbons were separately quantified, and the functional groups were further classified into 12 types by the nearby chemical structures. Comparison with IR spectra indicated that the deuterium-labeled TPD gave qualitatively reasonable results. This technique is useful for obtaining a deeper understanding of the surface chemical structure of carbon-based materials. Image 1 [ABSTRACT FROM AUTHOR]

In polymer electrolyte fuel cells, the oxygen reduction reaction (ORR) rate increases at high temperatures. Therefore, ORR catalysts must be designed for use at high temperatures and require evaluation. To address the problem of decreased dissolved oxygen concentrations in conventional channel flow double electrode (CFDE) systems, this study develops a CFDE system capable of electrochemical measurement at 120 °C that can evaluate the ORR activity of Pt-supported carbon (Pt/C) and carbon-based non-precious metal catalysts (NPMC). The ORR activity increased with an increasing reaction temperature, regardless of the catalyst, and the current density ratios at 120 °C and room temperature were estimated to be 2.4 and 5.4 for Pt/C and NPMC, respectively. This indicates that the NPMC ORR activity increased significantly with the increasing reaction temperature. This increased activation energy, which is approximately 2.3 times greater than that of Pt/C at the overpotential of 0.38 V, contributes to a significant increase in the ORR activity at higher temperatures. [Display omitted] • An improved channel flow double electrode system is developed. • Kinetic analysis of ORR up to 120 °C was performed by using the system. • The activation energy of NPMC is higher than Pt/C catalyst. • ORR activity of NPMC increased significantly with the increasing reaction temperature. [ABSTRACT FROM AUTHOR]

Presents information on a study which investigated the photoconductive effect of carbon films prepared by plasma decomposition of propylene for infrared radiation. Deposition of carbon films; Configurations of electrodes; Observations on carbon films on glass substrates; Photovoltaic effect both for infrared radiation and visible radiation; Ratios of the photocurrent for the infrared radiation to the dark current.

Presents a study which investigated the relation between electrical conductivity and an infrared absorption parameter of carbons derived from polymers. Details on the experiment; Results; Conclusion.

Focuses on a study which investigated the iron containing carbon films for the effect of iron on the photoresponse of a light emitting diode. Experiment; Dependence of photocurrent on iron content; State of iron in carbon matrix.

Bromanil (BA) doping of a naphthalene pitch, a kind of soluble carbonaceous material, enhanced the photoresponse of the junction between this material and a ρ-type silicon substrate by about tenfold. Morphological and spectroscopic studies revealed that the enhancement was partly caused by an increase in the surface roughness of the carbonaceous films, and by the enhanced dissociation of excitons in the carbonaceous films upon the BA doping. [ABSTRACT FROM AUTHOR]

Abstract: C6-hydrocarbons, namely, n-hexane, 1-hexene, cyclohexane, and benzene, were selected as surrogate tar in low-temperature gasification (LTG) of biomass in the study of carbon deposition of organic compounds on a Ni/Al2O3 catalyst. All the compounds showed a two-stage weight increase due to carbon deposition; the two stages were the low-temperature stage (LTS: 300–650°C) and high-temperature stage (HTS: above 650°C). The LTS is the focus of this study. The susceptibility of the catalyst to carbon deposition was measured by the temperature (T max) giving maximum rate of weight increase (r max). 1-hexene was found to be the most influential compound with the lowest T max and the highest r max, followed by benzene. The saturated hydrocarbons, n-hexane and cyclohexane, were the least influential compounds for carbon deposition. The morphology of the deposits was found to be mainly herringbone-type carbon nanofibers, determined by transmission electron microscopy. Thermodynamic calculation revealed that 1-hexene was the most reactive compound for carbon deposition, while benzene was the most stable compound. The factors determining the carbon deposition of hydrocarbon compounds were explained in terms of both thermodynamic and adsorptive properties of the compounds. [Copyright &y& Elsevier]

Abstract: To obtain uniformly and finely dispersed nanoshell structures in nanoshell carbons (NSCs), we synthesized three oxine–polymer (OFR)/cobalt complexes with different ligand/metal ratios (L/M) (xOFR(Co), x =L/M=1, 2, and 3) as the starting materials of NSCs by polycondensation of 8-hydroxyquinoline (oxine) and formaldehyde. The formation of polymeric structures and coordination bonds was confirmed by infrared spectroscopy. Thermogravimetry revealed that the thermal decomposition temperature increased with the L/M ratio. Carbonization of xOFR(Co) (x =2 and 3) at 1000°C resulted in the uniform formation of nanoshells with diameters of 30nm, while carbonization of 1OFR(Co) resulted in the formation of nanoshells with a broader size distribution including some with diameters over several hundred nm. The results indicate that the fixation of metal atoms in the starting polymers is an effective method for the preparation of uniformly and finely dispersed nanoshells in NSCs. The carbon from 3OFR(Co), i.e., 3OFR(Co)/C, showed the highest electrocatalytic activity for the oxygen reduction reaction (ORR). The linear shape of the voltammograms were understood in terms of the distribution of active sites for ORR with different activation energies. [Copyright &y& Elsevier]

Abstract: Nanoshell carbon is a type of catalytically grown nanocarbon with a hollow, round, shell-like structure, with a diameter in the range of approximately 20–50nm. It has been shown to possess the electrocatalytic activity for oxygen reduction reaction (ORR) and is also expected to be a non-Pt catalyst for polymer electrolyte fuel cells. This paper reports the synergetic enhancement of the ORR activity of nanoshell carbons caused by the coexistence of nitrogen atoms. The nanoshell carbons were prepared by the carbonization of furan resin in the presence of acetylacetonates (AAs) and of phthalocyanines (Pcs), which contained Fe, Co, and Ni. The Pc-derived nanoshells (MP-T series; M=Co or Fe, T=carbonization temperature) showed higher ORR activities than the AA-derived nanoshells (MA-T series; M=Co or Fe, T=carbonization temperature) when the same metal elements were employed. An XPS study revealed that nitrogen species were introduced to the surface of the nanoshells when Pcs were used as the nanoshell-forming catalysts, and that no metal species remained on the nanoshells. Principally, the ORR activity of the carbons was governed by the presence of the nanoshells and further enhancement could be achieved by the introduction of nitrogen atoms. 0.78V of OCV and 0.21Wcm−2 of the maximum power density were observed for a fuel cell whose MEA consisted of 3CoP1000 cathode and a commercial Pt/C anode, when it was operated at 80°C under a pressurized condition of 0.35MPa. [Copyright &y& Elsevier]

Abstract: B-, N- and BN-doped carbons were prepared by the carbonization of poly(furfuryl alcohol) containing either BF3–MeOH complex, melamine or both. Various characterization techniques were conducted in order to understand the controlling factors for the electrocatalytic activity of carbons for oxygen reduction reaction (ORR). Analytical inspections of the obtained XRD profiles, such as the Diamond and the Hirsch methods, revealed that the doping of boron and nitrogen broadened the graphene size distribution; while it did not influence the stacking manner of graphenes. All doped carbons showed reductions in electrical conductivity by the factors of a quarter to a hundredth of the pristine carbons. Development of porosity was observed for the doped carbons. B1s and N1s XPS analyses revealed the presences of B–C bonds and B–N–C moieties in the BN-doped carbons. The oxygen reductive activity, which was assessed by the ORR current density normalized by BET surface area, was increased by the factors of 4–5 for B-doped and N-doped carbons, while a factor of 20 was attained for the BN-doped carbons. The ORR activity of the prepared carbons was found to be controlled by the presence of both the edge-N and B–N–C moieties, which were distinguished by XPS. [Copyright &y& Elsevier]

Abstract: In this study, we prepared a type of arylacetylene, poly(p-phenylene butadiynylene), PPPB, and studied its pyrolysis behavior. A pellet of PPPB maintained its shape and provided a carbonization yield of 94% by heat-treatment at 1000°C, although it experienced exothermal reaction and partial fusion at approximately 200°C. It was also found that PPPB did not show graphitization even when it was heat-treated at 3000°C. X-ray diffraction (XRD) study revealed the breakdown of the initial crystal structure of PPPB at 200°C and a formation of the carbon structure at above 650°C. By combining the results of TG–MS, FT-IR, and 13C NMR, a mechanism for pyrolysis of PPPB including the cross-link formation was proposed, which included a Diels–Alder type reaction between the terminal acetylene and the diene structure comprising of diacetylene and phenyl groups, which is facilitated by increased mobility due to the partial fusion and the presence of the terminal acetylene groups. [Copyright &y& Elsevier]

Abstract: Influences of the pore structure and the surface functionality of carbon substrates on the formation of ZSM-5 nanoparticles were studied. The inorganic substance formed on these carbons were identified as ZSM-5 by X-ray diffraction, which also revealed the presence of an amorphous silica phase. The fraction of crystalline phase, which was evaluated from XRD, was not affected by the pore structure; however, inorganic content depended on the pore structure of carbon: i.e. 14–17% for non- and microporous carbons, and 40–55% for mesoporous carbons. TEM observation revealed that the ZSM-5 deposited on these carbon substrates was in the form of nanoparticles with 10–20nm of diameters. The influence of the surface functionality on the formation of ZSM-5 nanoparticles was also studied with an activated carbon, of which surface functionality was modified by heat-treatment and nitric acid-treatment. A strong dependence of the fraction of crystalline phase on the treatments was observed; i.e. the heat-treatment increased the fraction and the acid-treatment decreased it. Finally, we clarified the controlling factors for the formation of ZSM-5 on carbon materials; the mesoporous surface area of carbon strongly affects the inorganic content and the total acidity of carbon influences the selectivity to ZSM-5 formation. [Copyright &y& Elsevier]

The structure, physicochemical properties and oxygen reduction abilities of carbons prepared by the carbonization of mixtures of ferrocene and poly(furfuryl alcohol) were studied. X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM) studies revealed that the carbons thus prepared consisted of two components; amorphous and turbostratic shell-like components. The fraction, f sharp, obtained by the analysis of the (002) peak in XRD was found to be a parameter that represented the degree of formation of the shell-like components. The formation of the shell-like components induced an increase in the mesopore volumes. Electrical conductivity increased exponentially with f sharp, which indicated that the conduction process was governed by a percolation process of the conductive shell-like components. The amount of CO-desorption by O2-TPD technique showed a maximum desorption at f sharp=0.3, and the further development in the sharp component led to a decrease in the CO-desorption. Mössbauer spectroscopy technique revealed the presence of α-Fe, γ-Fe, Fe1- x O and Fe3C in the prepared carbons, which were soluble species to acids. The oxygen reduction activity was studied in a oxygen saturated sulfuric acid solution by rotating disk electrode voltammetry. The oxygen reduction potential varied with f sharp; initially it increased by f sharp=0.3 and then it decreased at higher f sharp values. This behavior was similar to that of CO-desorption, which meant the presence of an adequate degree of the development of the shell-like structure for maximizing oxygen adsorption. Removal of the surface metal component from the carbons by acid-washing resulted in no decrease in the oxygen reduction activities of the carbons. The nature of the active sites on the carbon materials is discussed. [ABSTRACT FROM AUTHOR]

The warped graphene layer (WGL) has garnered attention as a potential alternative to Pt for oxygen reduction reaction (ORR) catalysts and as a platform for enhancing the activity of Pt or molecular catalysts through interactions. We propose an in-situ nano-templating method for the preparation and mass production of WGLs and demonstrate its efficiency. The in-situ nano-templating method facilitates the synthesis of materials with three-dimensional curvature by concurrently generating nanoparticles and carbonizing. The synthesized WGLs exhibited high ORR activity in acidic conditions. Although the ORR activity was not correlated with the surface area, it was strongly correlated with the curvature radius of the WGLs. This activity was considered to arise owing to the optimization of oxygen adsorption ΔG 0 with the decrease in the curvature radius of the WGLs; furthermore, the physicochemical characteristics of WGL possesses continuity of carbon layers and exhibit a Fermi level higher than the O 2 /H 2 O reduction potential. This report elucidates experimentally that WGLs contribute to ORR activity, suggesting the importance of incorporating WGLs in the development of non-precious metal catalysts. [Display omitted] [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]

Abstract: Crystalline mesoporous carbon was prepared from nanoshell-containing carbon (NSCC) by a sculpturing technique, i.e., the selective oxidation of amorphous carbon moieties (ACM) in NSCC using hydrogen peroxide (H2O2) treatment. The carbon structures of the NSCC and the H2O2-treated NSCC were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) measurement and N2 adsorption–desorption. Multiple repetitions of the treatment resulted in an increase of nanoshell fraction by the selective oxidation of the ACM intrinsically included in NSCC. This was confirmed by TEM, SEM and XRD measurements. N2 adsorption–desorption measurement showed that the treatment caused remarkable increases in mesopore volumes and the mesopore ratios. In particular, when the treatment was repeated five times the highest mesopore ratio of approximately unity was observed. [Copyright &y& Elsevier]

Abstract: Nanoshell carbon (NS) have properties such as hollow shell like structure, size range of primary particle (20–50nm in diameter), high rate of electron transfer and excellent dispersivity in aqueous solutions without surface modification. Investigation of cytochrome c (cyt c) adsorption was performed against NSs prepared by varying carbonization catalysts (Co, Fe) and temperatures (800, 1000°C). Higher carbonization temperature and the selection of Fe as the carbonization catalyst seemed to lead to better adsorptive abilities of carbons toward cyt c. Quinone groups on NS surface might play an important role on the adsorption of cyt c. The results obtained in this study suggest that NSs have the potential for use as novel electrode materials for immobilization of cyt c. [Copyright &y& Elsevier]

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]

The activity of non-precious metal catalysts (NPMCs) has now reached a stage at which they can be considered as possible alternatives to Pt for some proton exchange membrane fuel cell (PEMFC) applications. However, despite significant efforts over the past 50 years on catalyst development, only limited studies have been performed on NPMC-based cathode catalyst layer (CCL) designs. In this work, an extensive ionomer study is performed to investigate the impact of ionomer equivalent weight on performance, which has uncovered two crucial findings. Firstly, it is demonstrated that beyond a critical CCL conductance, no further improvement in performance is observed. The procedure used to determine this critical conductance can be used by other researchers in this field to aid in their design of high performing NPMC-based CCLs. Secondly, it is shown that the stability of NPMC-based CCLs can be improved through the use of low equivalent weight ionomers. This represents a completely unexplored pathway for further stability improvements, and also provides new insights into the possible degradation mechanisms occurring in NPMC-based CCLs. These findings have broad implications on all future NPMC-based CCL designs. [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]

Hard carbons emerge as one of the most promising candidate for an anode of Na-ion batteries. This research focuses on the carbon monolith derived from resorcinol-formaldehyde (RF) gels as a model hard carbon electrode. A series of binder-free monolithic carbon electrodes heat-treated at varied temperatures allow the comparative investigation of the correlation between carbon nanotexture and electrochemical Na + -ion storage. The increase in carbonization temperature exerts a favorable influence on electrode performance, especially in the range between 1600 °C and 2500 °C. The comparison between Li + - and Na + -storage behaviors in the carbon electrodes discloses that the Na + -trapping in nanovoids is negligible when the carbonization temperature is higher than 1600 °C. On the other hand, the high-temperature sintering at 2500–3000 °C enlarges the resistance for Na + -insertion into interlayer spacing as well as Na + -filling into nanovoids. In addition, the study on the effect of pore size clearly demonstrates that not the BET surface area but the surface area related to meso- and macropores is a predominant factor for the initial irreversible capacity. The outcomes of this work are expected to become a benchmark for other hard carbon electrodes prepared from various precursors. [ABSTRACT FROM AUTHOR]

A major hurdle to the widespread commercialization of proton exchange membrane fuel cells (PEMFCs) is the high loading of noble metal (Pt/Pt-alloy) catalyst at the cathode, which is necessary to facilitate the inherently sluggish oxygen reduction reaction (ORR). To eliminate the use of Pt/Pt-alloy catalysts at the cathode of PEMFCs and thus significantly reduce the cost, extensive research on non-precious metal catalysts (NPMCs) has been carried out over the past decade. Major advances in improving the ORR activity of NPMCs, particularly Fe- and Co-based NPMCs, have elevated these materials to a level at which they can start to be considered as potential alternatives to Pt/Pt-alloy catalysts. Unfortunately, the stability (performance loss following galvanostatic experiments) of these materials is currently unacceptably low and the durability (performance loss following voltage cycling) remains uncertain. The three primary mechanisms of instability are: (a) Leaching of the metal site, (b) Oxidative attack by H 2 O 2 , and (c) Protonation followed by possible anion adsorption of the active site. While (a) has largely been solved, further work is required to understand and prevent losses from (b) and/or (c). Thus, this review is focused on historical progress in (and possible future strategies for) improving the stability/durability of NPMCs. [ABSTRACT FROM AUTHOR]

By using non-graphitizable and graphitizable carbons prepared from poly(furfulyl alcohol) and poly(vinyl chloride), respectively, an attempt is made to determine the number of carbon edge sites by analyzing their hydrogen content and the amounts of surface oxygen complexes and localized spins. It is found that, at the present preparation conditions, the number of hydrogen-terminated edges is much higher than the number of surface oxygen complexes regardless of the type of carbon and the heat-treatment temperature, but the contribution of the localized spins derived from σ free radicals in closed spaces and/or triplet carbene/carbyne species may become comparable to the hydrogen content when the heat-treatment temperature is higher. Moreover, the average sizes of graphene layers in these carbons are estimated from the total number of edge sites. This analysis suggests that the actual size in the poly(furfulyl alcohol)-derived carbons is much larger than the size detected with transmission electron microscopy. This large difference is discussed in relation to a real structure of graphene layers in non-graphitizable carbons. [ABSTRACT FROM AUTHOR]

A catalyst support can improve the catalytic activity of metal catalysts, and this phenomenon is well known as the support effect. The effective use of this support effect is considered important for improving catalytic activity. However, the factors affecting this phenomenon are complex. It is, therefore, important to understand the interaction between the support and metal catalyst as well as the surface characteristics of the support for elucidating this phenomenon. Carbon is a useful support material because of its high chemical and thermal stability and electroconductivity. Moreover, its surface properties can be controlled by doping the carbon structure with heteroatoms. In this study, the catalytic activity of metal particles supported on heteroatom-doped carbon materials was evaluated to investigate the support effect of the doped carbon. The catalytic activity of carbon-supported Ni particles in benzene hydrogenation was improved by introducing N and B into the carbon support. In particular, Ni supported on N-doped carbon showed a two-fold improvement in activity compared to that supported on undoped carbon. A compensation effect was confirmed for the catalytic activity of Ni particles. The results suggest that the introduction of heteroatoms into the carbon support changed the adsorption energy of the reactant on Ni, thereby improving the Ni catalytic activity. [Display omitted] • A catalyst support can improve the catalytic activity of metal catalysts. • Ni on B- and N-doped carbons has better activity than Ni on undoped carbon. • Heteroatoms on carbon change the energy of reactant adsorption onto Ni. • A compensation effect was confirmed for the activity of Ni on doped carbon. [ABSTRACT FROM AUTHOR]

Abstract: Recently carbon-based catalysts have attracted much attention for its high ability to catalyze oxygen reduction reaction (ORR) in a cathode for polymer electrolyte fuel cells. Among active site models of the catalyst, edge region of sp 2 carbon network is expected to demonstrate high ORR activity comparable to platinum catalysts. However, it is difficult to directly identify the chemical structure of the edge sites by applying conventional structural or electronic probes to actual catalysts. Here, we used C 1s X-ray absorption spectroscopy to observe electronic structure of carbon in iron phthalocyanine-based catalysts, and found a signature of edge exposure below the π* edge, whose intensity is well correlated with the ORR activity. Combined with information about the chemical structure of nitrogen, ORR activity of the catalyst is characterized in terms of the edge exposure. [Copyright &y& Elsevier]

Abstract: The influences of the heat-treatment of Ketjen Black EC300J in the temperature range 1000–2000 °C on the catalytic activity of loaded Pt for oxygen reduction reaction (ORR) were studied. A maximum enhancement in the specific ORR activities (SOA) was observed for the carbon heat-treatment at 1500 °C. The heat-treatment of carbon induced decreases in porosity and the development of graphitic structures; however, no direct correlations were observed between these properties and the SOA. Transmission electron microscopy and X-ray photoelectron spectroscopy, respectively, showed enhancements in the uniformity of the Pt particle size distribution and of the extent of surface reduction of Pt with increasing heat-treatment temperature (HTT). Cyclic voltammetry in 0.5 M H2SO4 aqueous solution detected changes in the hydrogen adsorption at 0.12 V vs. a reversible hydrogen electrode, depending on the HTT of the carbon support, and this was ascribed to hydrogen adsorption on the Pt(110) surface, the most active crystal face of Pt for ORR. The fraction of Pt atoms belonging to the (110) surface out of the total surface Pt atoms showed an excellent correlation with the SOA. Heat-treatment of the carbon support was therefore concluded to be an effective treatment for enhancing the SOA of Pt. [Copyright &y& Elsevier]

Abstract: A technique to determine a trace amount of hydrogen in carbon materials heat-treated above 1000°C was developed. Three types of carbons prepared from poly(furfulyl alcohol), poly(vinyl chloride) and mesophase carbon microbeads were heat-treated at various temperatures ranging from 1000 to 1800°C. Then they were gasified by O2 in a fixed bed flow reactor, and the H2O gases formed during the gasification processes were carefully monitored with a Karl Fischer moisture analyzer. As a result, this method makes it possible to determine the hydrogen contents in the carbons down to three places of decimals as a weight percent and can detect even a trace amount of hydrogen as low as 0.002wt.%. A possible chemical structure of carbon edge sites was also discussed based on the experimentally determined hydrogen contents. [Copyright &y& Elsevier]

Abstract: The electronic structure of the residual metal atoms in Fe phthalocyanine (FePc)-based carbon catalysts, prepared by pyrolyzing a mixture of FePc and phenolic resin polymer at 800°C, before and after acid washing have been investigated using X-ray absorption fine structure (XAFS) spectroscopy to clarify the role of Fe in the oxygen reduction reaction (ORR) activity. The Fe K X-ray emission intensity suggests that the acid washing process reduces 36% of the total amount of residual Fe in the FePc-based catalysts. The decomposition analyses for the XAFS spectra reveal that the composition ratio of each Fe component is unaltered by the acid washing, indicating that the residual Fe components were removed by the acid washing irrespective of their chemical states. Because the oxygen reduction potential was approximately unchanged by the acid washing, the residual Fe itself does not seem to contribute directly to the ORR activity of the samples. The residual Fe is composed mainly of metallic Fe components (Fe metal and iron carbide Fe3C), which can act as a catalyst to accelerate the growth of the sp2 carbon network during pyrolysis. The results imply that light elements such as C and N are components of the ORR active sites in the FePc-based carbon catalysts pyrolyzed at high temperatures where the metal-N4 structures in the macrocycles are mostly decomposed. [Copyright &y& Elsevier]

Abstract: The electronic structure of Co atoms in cobalt phthalocyanine (CoPc)-based carbon catalysts, which were prepared by pyrolyzing a mixture of CoPc and phenol resin polymer up to 1000°C, has been investigated using X-ray absorption fine structure (XAFS) analysis and hard X-ray photoemission spectroscopy (HXPES). The CoK XAFS spectra show that most of the Co atoms are in the metallic state and small quantities of oxidized Co components are present in the samples even after acid washing to remove Co atoms. Based on the difference in probing depth between XAFS and HXPES, it was found that after acid washing, the surface region with the aggregated Co clusters observed by transmission electron microscopy is primarily composed of metallic Co. Since the electrochemical properties remain almost unchanged even after the acid washing process, the residual metallic and oxidized Co atoms themselves will hardly contribute to the oxygen reduction reaction activity of the CoPc-based carbon cathode catalysts, implying that the active sites of the CoPc-based catalysts primarily consist of light elements such as C and N. [Copyright &y& Elsevier]

Abstract: We report on the electronic structure of three different types of N-containing carbon-based cathode catalysts for polymer electrolyte fuel cells observed by hard X-ray photoemission spectroscopy. Prepared samples are derived from: (1) melamine and poly(furfuryl alcohol), (2) nitrogen-doped carbon black and (3) cobalt phthalocyanine and phenolic resin. C 1s spectra show the importance of sp 2 carbon network formation for the oxygen reduction reaction (ORR) activity. N 1s spectra of the carbon-based cathode catalysts are decomposed into four components identified as pyridine-like, pyrrole- or cyanide-like, graphite-like, and oxide nitrogen. Samples having high oxygen reduction reaction activity in terms of oxygen reduction potential contain high concentration of graphite-like nitrogen. O 1s spectra are similar among carbon-based cathode catalysts of different oxygen reduction reaction activity. There is no correlation between the ORR activity and oxygen content. Based on a quantitative analysis of our results, the oxygen reduction reaction activity of the carbon-based cathode catalysts will be improved by increasing concentration of graphite-like nitrogen in a developed sp 2 carbon network. [ABSTRACT FROM AUTHOR]

Abstract: ‘Carbon Alloy Catalysts’ (CAC), non-precious metal catalysts for the oxygen reduction reaction (ORR), were prepared from various kinds of nitrogen-containing rigid-rod aromatic polymers, polyimides, polyamides and azoles, by carbonization at 900°C under nitrogen flow. The catalytic activity for ORR was evaluated by the onset potential, which was taken at a current density of −2μAcm−2. Carbonized polymers having high nitrogen content showed higher onset potential. In particular, CACs derived from azole (Az5) had an onset potential of 0.8V, despite being was prepared without any metals. [Copyright &y& Elsevier]

Abstract: Pyrolysis of a mixture of Fe phthalocyanine and phenolic resin (FePc/PhRs) was studied to clarify the details of the preparation protocol of nitrogen-doped carbon-based materials for cathode catalysts in polymer electrolyte membrane fuel cells. TEM images show that nanoshell carbon is formed by the pyrolysis of FePc/PhRs in the temperature range of 600–800°C. The optimum pyrolysis temperature for the FePc/PhRs mixture was 600°C, where moderate conductivity and high nitrogen content of the prepared carbon were both satisfied. This catalyst showed a promising fuel cell performance with 1.01V open-circuit voltage and 0.33Wcm−2 maximum output, at 0.2MPa absolute pressure and 80°C. A detailed study of the carbonization process suggests that the presence of Fe species during carbonization process contributes to higher nitrogen content and growth of nanoshell structure of the resulting carbon. [Copyright &y& Elsevier]

Abstract: The activities of various metal catalysts were tested in steam reforming of acetic acid for the production of H2, using conventional metal oxides and transition metal-incorporated mesoporous smectite-like materials as supports. It has been found that Pt is superior to Ni, Co, and Fe among Al2O3 supported catalysts, Al2O3 is more effective than ZrO2 and SiO2 as support for Pt, Ni incorporated smectite (SM(Ni)) support is more effective than Fe and Co incorporated ones for Pt, and SM(Ni) is also active in the absence of Pt. The total activity for the conversion of acetic acid is in the order of Pt/Al2O3 >Pt/SM(Ni)>SM(Ni) but the ability of H2 production is comparable among these catalysts. These catalysts (and the other ones) were observed to lose their activities during the reforming reactions. The activity of Pt/Al2O3 decreased during the whole course of reaction up to 10h. In contrast, the activity of SM(Ni) also decreased within 2h but it showed a stable activity in the following stage of reaction. The initial activity of the used Pt/SM(Ni) and SM(Ni) was able to be almost completely restored by thermal treatment with H2 but less effectively for the used Pt/Al2O3. The catalyst deactivation was shown to occur by the formation and deposition of carbon materials on the catalysts (XRD, TEM, thermal analysis). The properties of carbon deposits formed on Pt/Al2O3 and SM(Ni) catalysts should be different and this may be responsible for the differences in the extent of deactivation and in the regeneration behavior between the two catalysts. [Copyright &y& Elsevier]

Abstract: This study examined the influence of different types of silane coupling agents on the dispersion of nanosilica particles with diameters of ca. 10nm and 25nm in two organic solvents, methylisobutylketone (MIBK) and cyclohexanone (CXN). The nanosilicas were prepared by the sol–gel process, and the following coupling agents were used: 3-glycidylpropyltrimethoxysilane (EpoSi), N-phenyl-3-aminopropyltrimethoxysilane (AmiSi), 3-mercaptopropyltrimethoxysilane (MerSi), and alkyltrimethoxysilane (AlkSi). While the 25-nm silica particles displayed dispersibility similar to that of submicron silica particles (ca. 150nm and 250nm), the dispersibility of the 10-nm silica particles proved to be dependent on the combinations of the agents and solvents; for example, EpoSi and MerSi were found to be suitable agents for MIBK and CXN, respectively. The slurries were also subjected to heating at 40°C for 24h, which resulted in a considerably higher stability of the dispersion state when CXN was employed as the solvent, regardless of which silica coupling agents were used. FTIR measurement revealed the presence of unreacted free Si–OH at 3740cm−1 for some nanosilicas. Combustion of the organic moieties introduced onto the silica surfaces also proved that the amount of organic groups present in a unit surface area of the nanosilicas were only 1/3 or 1/2 of that found on submicron silicas. From these observations, the low dispersibility of the nanosilicas was inferred to be due to the imperfect coverage of the silanol groups by the silane coupling agents. [Copyright &y& Elsevier]

Abstract: The electronic structure of nitrogen introduced into various carbon-based cathode catalysts for the polymer electrolyte fuel cell (PEFC) is investigated using X-ray absorption spectroscopy (XAS). The profile of π* peaks at the pre-edge of N 1s XAS spectra is used to determine the chemical state of nitrogen, which can be an indicator of oxygen reduction reaction (ORR) activity. It is found that catalysts with a relatively larger amount of graphite-like nitrogen exhibit a higher ORR activity than those with a relatively larger amount of pyridine-like nitrogen. We propose that effective doping with graphite-like nitrogen is a practical guideline for the synthesis of active carbon alloy catalysts. [Copyright &y& Elsevier]

Pt-free cathode catalysts for polymer electrolyte membrane fuel cells have been prepared by multi-step pyrolysis of FePc and PhRs, in the best of which show extensively high initial cell performance and good durability compared to other present precious-metal-free cathode catalysts to date. [ABSTRACT FROM AUTHOR]