Bingsen Zhang

Unravelling the Structure of Electrocatalytically Active Fe–N Complexes in Carbon for the Oxygen Reduction Reaction

Non-precious Fe/N co-modified carbon electrocatalysts have attracted great attention due to their high activity and stability in oxygen reduction reaction (ORR). Compared to iron-free N-doped carbon electrocatalysts, Fe/N-modified electrocatalysts show four-electron selectivity with better activity in acid electrolytes. This is believed relevant to the unique Fe-N complexes, however, the Fe-N structure remains unknown. We used o,m,p-phenylenediamine as nitrogen precursors to tailor the Fe-N structures in heterogeneous electrocatalysts which contain FeS and Fe3 C phases. The electrocatalysts have been operated for 5000 cycles with a small 39 mV shift in half-wave potential. By combining advanced electron microscopy and Mössbauer spectroscopy, we have identified the electrocatalytically active Fe-N6 complexes (FeN6, [Fe(III)(porphyrin)(pyridine)2]). We expect the understanding of the FeN6 structure will pave the way towards new advanced Fe-N based electrocatalysts.

Topological Defects in Metal-Free Nanocarbon for Oxygen Electrocatalysis.

A bifunctional graphene catalyst with abundant topological defects is achieved via the carbonization of natural gelatinized sticky rice to probe the underlying oxygen electrocatalytic mechanism. A nitrogen-free configuration with adjacent pentagon and heptagon carbon rings is revealed to exhibit the lowest overpotential for both oxygen reduction and evolution catalysis. The versatile synthetic strategy and novel insights on the activity origin facilitate the development of advanced metal-free carbocatalysts for a wide range of electrocatalytic applications.

Macroporous ‘bubble’ graphene film via template-directed ordered-assembly for high rate supercapacitors

A three-dimensional bubble graphene film, with controllable and uniform macropores and tailorable microstructure, was fabricated by a facile hard templating strategy and exhibit extraordinary electrochemical capacitance with high rate capability (1.0 V s(-1)).

Sulfur and nitrogen co-doped carbon nanotubes for enhancing electrochemical oxygen reduction activity in acidic and alkaline media

Carbon materials have received an increasing amount of attention due to their low cost, long-term stability, and high electrocatalytic activity in catalyzing the cathodic oxygen reduction reaction (ORR). However, most of the carbon catalysts have exhibited their excellent activity only in alkaline media, which greatly hinders their practical application in polymer electrolyte membrane fuel cells (PEMFCs). In order to break the restriction of alkaline conditions, sulfur and nitrogen doped carbon nanotubes (SN-CNTs) were designed and successfully prepared via annealing of a mixture composed of nitrogen doped carbon nanotubes (N-CNTs) and sulfur. The result showed the as-prepared SN-CNTs have an enhanced ORR activity in both acidic and alkaline media compared with N doped CNTs (N-CNTs). This report also provides a new approach to explore low-cost electrocatalysts for practical fuel cell applications.

Oxidative Dehydrogenation on Nanocarbon: Identification and Quantification of Active Sites by Chemical Titration

Nanostructured carbon-based materials have shown high catalytic activity in several important reactions and related chemical industrial processes, such as direct or oxidative dehydrogenation of hydrocarbons and Friedel–Crafts reactions. Nanocarbon materials exhibit significant advantages over traditional metal or metal oxide based catalysts because of their tunable acidity/basicity, electron density, and convenient recycling and reusability, and they have been shown to be potential alternatives to conventional catalysts to meet the requirements of sustainable chemistry. As a result, the field of nanocarbon catalysis has been experiencing an unparalleled development of new catalyst synthesis or their applications in new reaction systems. However, there is only slow growth of mechanistic interpretation of carbon-catalyzed reactions, which is even more urgent to advance our knowledge in related fields. Present research on the mechanism of carbon catalysis suggests that oxygen containing functional groups, especially ketonic carbonyl groups on nanocarbon, which are rich in electrons, may act as the catalytic active sites for oxidative dehydrogenation (ODH) of alkanes to corresponding alkenes. The reaction process is assumed to be similar to that for transition-metal oxide catalysts. The C H bonds of alkanes dissociate at active oxygen functional groups, and the hydrogen atoms are abstracted by Lewis base sites. After the desorption of alkene products, gas-phase O2 reacts with the abstracted hydrogen to form H2O, then the active catalytic sites are regenerated to finish one catalytic cycle. The above unspecific catalytic mechanism is only based on the qualitative characterization of carbon catalysts, while the identity of the active sites or a detailed kinetic study has never been executed with direct and convincing chemical evidence. One of the most critical problems that limits the quantitative description of the catalytic mechanism is the uncertainty of the chemical structure of nanocarbon materials. The coexistence of several kinds of surface functional groups (such as hydroxyl, carbonyl, and carboxylic acid groups) is unavoidable, as the synthesis or the following surface modification procedures of nanocarbon catalysts are normally realized by a severe physical or chemical process, such as laser irradiation and oxidation by HNO3, O2, and O3. [8] There are still lack of reliable quantification methods for the surface functional groups on nanostructured carbon materials because of their complexity in type and quantity. As a result, turnover frequency (TOF), the ultimate parameter to evaluate the intrinsic activity of heterogeneous catalysts, is also rarely reported in the case of nanocarbon catalysts, making it impossible to study the detailed reaction kinetics or compare the activity of carbon catalysts bearing different structures fairly and objectively. The quantitative surface composition analysis is also desirable for the application of nanostructured carbon as a catalyst support or electrochemical devices, which takes an even larger proportion in the field of carbon materials, as the surface structure of nanocarbon materials is essential for their physical or chemical properties (for example, affinity for a certain metal or metal ion). In view of the quantification methods of oxygen functional groups, herein we propose a chemical titration method to determine the surface concentration of three kinds of typical oxygen functional groups ( C=O, C OH, and COOH) on the surface of carbon nanotubes (CNTs) (Scheme 1). Through selective deactivation of these specific oxygen functional groups and the assessment of the catalytic activity of different CNT derivatives for ethylbenzene (EB) ODH reactions, we provided chemical evidence to show that

Revealing the enhanced catalytic activity of nitrogen-doped carbon nanotubes for oxidative dehydrogenation of propane

Bulk nitrogen doping can efficiently improve the catalytic performance of carbon nanotubes (CNT) in oxidative dehydrogenation of propane (ODH). The graphitic nitrogen plays a determining role in enhancing their activity by speeding up the activation of oxygen and decreasing the overall activation energy of the reaction.

Low-cost SnS(x) counter electrodes for dye-sensitized solar cells.

SnS nanosheets (NSs), SnS nanowires (NWs) and SnS2 nanosheets were synthesized and investigated as counter electrode (CE) catalysts in a I3(-)/I(-) based dye-sensitized solar cell (DSC) system for the first time. It is found that the SnS NS based DSCs show comparable power-conversion efficiency (E(ff) = 6.56%) to Pt (7.56%), while the E(ff) of SnS NW and SnS2 NS based DSCs are 5.00% and 5.14% respectively, indicating the excellent catalytic activity of SnS(x) for the reduction of triiodide to iodide.

Nanosizing Intermetallic Compounds Onto Carbon Nanotubes: Active and Selective Hydrogenation Catalysts**

Therefore, nanosizing andsupporting the annealed metal products remain challenges.Another difficulty is in directly preparing supportedcatalysts while simultaneously obtaining good crystallite sizecontrol. A good catalyst support should be capable ofinhibiting sintering and loss of the catalyst during reaction.Fabrication of supported intermetallics catalysts in nanoscaledimensionsrequiresareliablemethodthatfacilitatesnotonlysize control but a thermally stable phase under reactionconditions. Since the work of Iijima in 1991,

Nitrogen-doped onion-like carbon: a novel and efficient metal-free catalyst for epoxidation reaction

Onion-like carbon (OLC) as a promising carbon material has attracted extensive interest in many fields. In this work, we report for the first time the controllable synthesis of nitrogen-doped OLC via nitric acid pretreatment, followed by different temperature calcination treatment under an ammonia atmosphere. The detailed physicochemical properties of the doped OLC samples are investigated by high resolution transmission electron microscopy (HRTEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), elemental analysis (EA) and electron energy loss spectroscopy (EELS). Moreover, the potential catalytic performance of such doped samples is evidenced by styrene epoxidation reaction, a kind of typical metal-related catalytic reaction. The results indicate that doped OLC samples exhibit more excellent catalytic performance than pristine OLC and some reported metal-related catalysts. The graphitic nitrogen species plays a key role in the catalytic reaction based on some control experiments and a good linear correlation between the content of this species and the activity results. Our work provides valuable information on the design and application of modified carbon materials in catalytic reactions.

Empirical strong-line oxygen abundance calibrations from galaxies with electron temperature measurements

Aims. Our aims are to estimate the validity of empirical methods, such as R 23 , R 23 - P, log([N II]/Hα) (N2), log[([O III]/Hβ)/ ([N II]/Hα)] (03N2), and log([S II]/Hα) (S2), and to re-derive (or add) the calibrations of R 23 , N2, 03N2, and S2 indices for oxygen abundances on the basis of a large sample of galaxies with T e -based abundances. Methods. We determined the gas-phase oxygen abundance for a sample of 695 galaxies and H II regions with reliable detections of [O III]4363, using the reliable and direct temperature-sensitive (T e ) method of measuring metallicity. We selected 531 star-forming galaxies from the SDSS-DR4 database with strong emission lines, including [O III]4363 detected at a signal-to-noise ratio higher than 5σ, as well as 164 galaxies and H II regions from the literature with T e measurements. The O/H abundances were derived from a two-zone model for the temperature structure, assuming a relationship between high ionization and low ionization species. Results. We compare our (O/H) Te measurements of the SDSS sample with the abundances obtained by the MPA/JHU group who used multiple strong emission lines and Bayesian techniques (Tremonti et al. 2004). For roughly half of the sample the Bayesian abundances are overestimated ∼0.34 dex, possibly due to the treatment of nitrogen enrichment in the models they used. The R 23 and R 23 - P methods systematically overestimate the O/H abundance by a factor of ∼0.20 dex and ∼0.06 dex, respectively. The N2 index, rather than the 03N2 index, provides more consistent O/H abundances with the T e -method, but with some scatter. The relations of N2, 03N2, and S2 with log(O/H) are consistent with the photoionization model calculations of Kewley & Doptita (2002), but R 23 does not match well. We derive analytical calibrations for O/H from R 23 , N2, 03N2, and S2 indices on the basis of this large sample, including the excitation parameter P as an additional parameter in the N2 calibration. These empirical calibrations are free of the systematic problems inherent in abundance calibrations based on photoionization models. Conclusions. We conclude that the N2, 03N2, and S2 indices are useful indicators for calibrating metallicities of galaxies with 12 + log(O/H) < 8.5 and that the R 23 index works well for the metal-poor galaxies with 12+log(O/H) < 7.9. For the intermediate metallicity range (7.9 < 12 + log(O/H) < 8.4), the R 23 and R 23 - P methods are unreliable for characterizing the O/H abundances.