Characterization of Fe/N-doped graphene as air-cathode catalyst in microbial fuel cells

This work proposed a simple and efficient approach for synthesis of durable and efficient non-precious metal oxygen reduction reaction(ORR) electro-catalysts in MFCs. The rod-like carbon nanotubes(CNTs)were formed on the Fe–N/SLG sheets after a carbonization process. The maximum power density of1210 ± 23 m W·m~(-2) obtained with Fe–N/SLG catalyst in an MFC was 10.7% higher than that of Pt/C catalyst(1080 ± 20 mW ·m~(-2)) under the same condition. The results of RDE test show that the ORR electron transfer number of Fe–N/SLG was 3.91 ± 0.02, which suggested that ORR catalysis proceeds through a four-electron pathway. The whole time of the synthesis of electro-catalysts is about 10 h, making the research take a solid step in the MFC expansion due to its low-cost, high efficiency and favorable electrochemical performance. Besides, we compared the electrochemical properties of catalysts using SLG, high conductivity graphene(HCG, a kind of multilayer graphene) and high activity graphene(HAG, a kind of GO) under the same conditions, providing a solution for optimal selection of cathode catalyst in MFCs.The morphology, crystalline structure, elemental composition and ORR activity of these three kinds of Fe–N/C catalysts were characterized. Their ORR activities were compared with commercial Pt/C catalyst.It demonstrates that this kind of Fe–N/SLG can be a type of promising highly efficient catalyst and could enhance ORR performance of MFCs.     

Structural and electronic properties of graphene nanotube-nanoribbon hybrids

The structural and electronic properties of a hybrid of an armchair graphene nanotube and a zigzag graphene nanoribbon are investigated by first-principles spin-polarized calculations. These properties strongly depend either on the nanotube location or on the spin orientation. The interlayer spacing, the transverse distance from the center of the ribbon and the stacking configuration affect the electronic structures. The antiferromagnetic configuration has a lower total energy than the ferromagnetic one. The interlayer atomic interactions between the two subsystems would change the low energy dispersions, open subband spacings, and induce more band-edge states. Moreover, such interactions create an energy gap and break the spin degeneracy in the antiferromagnetic configuration. The band-edge-state energies are sensitive to the nanotube location.     

Effects of heteroatoms on the electronic,sensor, and adsorption properties of graphene

The effects of doping heteroatoms on the structure, electronic and adsorption properties of graphene are investigated using density functional theory calculations. Six different doped graphenes (with Al, B, Si, N, P, and S) are considered, and to obtain the interaction and adsorption properties, three sulfur-containing molecules (H₂S, SO₂, and thiophene) were interacted with selected graphenes. The adsorption energies (E _ad) in the gas phase and solvents show the exothermic interaction for all complexes. The maximum E _ad values are observed for aluminum doped graphene (AG) and silicon doped graphene (SiG), and adsorption energies in the solvent are not so different from those in the gas phase. NBO calculations show that the AG and SiG complexes have the highest E ⁽²⁾ interaction energies and simple graphene (G) and nitrogen doped graphene (NG) have the least E ⁽²⁾ energies. Population analyses show that doping heteroatoms change the energy gap. This gap changes more during the interaction and these changes make these structures useful in sensor devices. All calculated data confirm better adsorption of SO₂ by graphenes versus H₂S and thiophene. Among all graphenes, AG and then SiG are the best adsorbents for these structures.     

Influence of borohydride concentration on the synthesized Au/graphene nanocomposites for direct borohydride fuel cell

Au/graphene nanocomposites are prepared via a one-pot chemical reduction process at room temperature, using graphene oxide (GO) and chloroauric acid (HAuCl₄) as precursors. The obtained Au/graphene nanocomposites are characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). TEM shows that the Au nanoparticles with size of approximately 8.7 nm disperse randomly on the surface of graphene. XPS confirms that the Au/graphene nanocomposites show a higher atomic percentage of C/O (6.3/1), in contrast to its precursor GO (2.2/1). Electrochemical studies reveal that the Au/graphene nanocomposites have electrochemically active surface area of 9.82 m² g^?1. Besides, the influence of borohydride concentration on the as-prepared Au/graphene nanocomposites is investigated in details by cyclic voltammetry, chronoamperometry, and chronopotentiometry. The results indicate that high concentration of borohydride can significantly improve the electrochemical performance of the Au/graphene catalyst.     

Structural and Conductive Characteristics of Fe/Co Nanotubes

The properties of Fe/Co nanotubes, which were fabricated by the method of electrochemical template synthesis, are studied. It is shown that the atomic ratio between the metals in the nanotubes shifts in the direction of cobalt with increasing potential difference during their synthesis; the geometric parameters of nanotubes, in particular, the wall thickness, also vary. Using the X-ray diffraction analysis, it was found that an increase in the concentration of cobalt in the crystal structure of nanotubes leads to a decrease in the interplanar distance and an increase in the conductivity.     

Use of Pd-Pt loaded graphene aerogel on nickel foam in direct ethanol fuel cell

A size customized binder-free bimetallic Pd-Pt loaded graphene aerogel deposited on nickel foam plate (Pd-Pt/GA/NFP) was prepared and used as an electrode for an alkaline direct ethanol fuel cell (DEFC) under room temperature. The effect of fuel concentration and metal composition on the output power density of the DEFC was systematically investigated. Under the optimum fuel concentration, the cell could achieve a value of 3.6 mW cm⁻² at room temperature for the graphene electrode with Pd/Pt ratio approaching 1:1. Such results demonstrated the possibility of producing a size customized metal loaded GA/NFP electrode for fuel cell with high performance.     

DFT computational study towards investigating Cladribine anticancer drug adsorption on the graphene and functionalized graphene

Structural Chemistry - Density functional theory calculations at the M06-2X/6-31G** level have been carried out to examine the adsorption behavior of Cladribine drug on the graphene and graphene...     

Effects of molecular adsorption on the electronic structure of single-layer graphene

The interaction of small molecules (CCl(4), CS(2), H(2)O, and acetone) with single-layer graphene (SLG) has been studied under steady-state conditions using infrared multiple-internal-reflection spectroscopy. Adsorption results in a broad and intense absorption band, spanning the ～200 to 500 meV range, which is attributed to electronic excitation. This effect, which has not previously been reported for SLG, has been further investigated using dispersion-corrected density functional theory to model the adsorption of H(2)O on SLG supported on an SiO(2) substrate. However, the ideal and defect-free model does not reproduce the observed adsorption-induced electronic transition. This and other observations suggest that the effect is extrinsic, possibly the result of an adsorption-induced change in the in-plane strain, with important differences arising between species that form liquid-like layers under steady-state conditions and those that do not. Furthermore, the C-H stretching modes of CH(2) groups, incorporated in the SLG as defects, undergo nonadiabatic coupling to the electronic transition. This leads to pronounced antiresonance effects in the line shapes, which are analyzed quantitatively. These results are useful in understanding environmental effects on graphene electronic structure and in demonstrating the use of the vibrational spectroscopy of H-containing defects in characterizing SLG structure.     

Transport properties of Nafion membranes modified with tetrapropylammonium ions for direct methanol fuel cell application

This work presents a study of transport properties (proton conductivity, methanol permeability, and water uptake) and acid-base properties of commercial Nafion-112, -115, and -117 membranes modified with tetrapropylammonium (TPA) cations. In the interaction between TPA hydroxide and protons of sulfonate groups in the Nafion matrix, some of the protons are shown to be bound to sulfonate groups and do not participate in transport processes. These findings are confirmed by IR spectroscopy, acid-base titration, and data on proton conductivity of the modified membranes. Proton conductivity of the modified membranes is shown to be effectively described by a percolation model with parameters that agree with published data for commercial Nafion membranes. Based on these results, a model is proposed for the interaction of TPA cations with the sulfonate groups in Nafion membranes. According to this model, TPA cations form hydrophobic clusters in hydrophilic regions of the polymer matrix, thus preventing some of the protonated sulfonate groups from participating in transport processes.     

Microstructural and metal-support interactions of the Pt-CeO2/C catalysts for direct methanol fuel cell application

To understand the ceria promotion effect of Pt-CeO(2)/C catalysts on methanol oxidation, microstructural and metal-oxide interactions of Pt-CeO(2)/C catalysts with an atomic ratio of Pt/Ce between 0.14 and 1.4 were systematically examined using high-resolution transmission electron microscopy and electron energy loss spectroscopy (EELS). With an increasing Pt content in the catalysts, Pt particles gradually invaded into the ceria supports and decoration on Pt particles was observed. Simultaneously, the morphology of the supports was dramatically modified with nanocrystalline and amorphous ceria formed between and/or around the Pt particles. It reveals that the Pt-ceria interaction could take place in the catalysts and the influence of the interaction was enhanced with an increasing Pt/Ce ratio. The EELS study demonstrated that the strong Pt-ceria interaction was related to the redox reaction between Pt and ceria. Experimental results also suggested that the strong interaction between Pt and ceria could contribute to the promotion effect of ceria on the oxidation of methanol.     

Electronic structure and magnetic properties of the graphene/Fe/Ni111 intercalation-like system

The electronic structure and magnetic properties of the graphene/Fe/Ni(111) system were investigated via combination of the density functional theory calculations and electron-spectroscopy methods. This system was prepared via intercalation of thin Fe layers (1 ML) underneath graphene on Ni(111) and its inert properties were verified by means of photoelectron spectroscopy. Intercalation of iron in the space between graphene and Ni(111) changes drastically the magnetic response from the graphene layer that is explained by the formation of the highly spin-polarized 3d(z(2)) quantum-well state in the thin iron layer.     

Structural and electronic effects on the reactivity of carbamoylsilanes towards acrylonitrile addition

The effect of substituents on Si and N on t_1/2 values in the addition of carbamoylsilanes to acrylonitrile was explored. After examination of steric and structural parameters, the best correlation was found to be that rates increased with a decrease in the ionization potential of the carbamoylsilane.     

Cu单原子修饰对Fe(111)表面CO吸附性能及电子性质调变的第一性原理研究

采用密度泛函理论方法研究了Cu单原子修饰对Fe(111)表面CO吸附性能和电子性质的调变作用,其中,Cu单原子修饰研究了吸附和取代两种方式。结果表明,CO在Cu修饰的Fe(111)面吸附能力都会变弱,一是Cu原子自身提供的位点对CO的吸附较弱;二是Cu会使其附近的Fe对CO的吸附变弱。分析电子性质表明,Cu作用于Fe表面后,会导致Cu附近Fe原子部分电子向Cu原子转移,进而削弱了Fe与吸附分子间电子交互作用而改变Fe原子的吸附能力。故Cu原子改性Fe表面可以很好地调变CO的吸附、解离及后续反应催化活性,这为进一步探究Cu改性Fe表面的合成气催化反应机理提供了基础信息。     

Preparation and characterization of CPPO/BPPO blend membranes for potential application in alkaline direct methanol fuel cell

A series of hydroxyl-conducting anion-exchange membranes were prepared by blending chloroacetylated poly(2,6-dimethyl-1,4-phenylene oxide) (CPPO) with bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO), and their fuel cell-related performances were evaluated. The resulting membranes exhibited high hydroxyl conductivities (0.022–0.032 S cm⁻¹ at 25 °C) and low methanol permeability (1.35 × 10⁻⁷ to 1.46 × 10⁻⁷ cm² s⁻¹). All the blend membranes proved to be miscible or partially miscible under the investigations of scanning electron microscopy (SEM) and differential scanning calorimeters (DSC). By condition optimization, the blend membranes with 30–40 wt% CPPO are recommended for application in direct methanol alkaline fuel cells because they showed low methanol permeability, excellent mechanical properties and comparatively high hydroxyl conductivity.     

Hierarchical interactions and their influence upon the adsorption of organic molecules on a graphene film

The competition between intermolecular interactions and lateral variations in the molecule-substrate interactions has been studied by scanning tunneling microscopy (STM), comparing the phase formation of (sub)monolayers of the organic molecule 2,4'-BTP on buckled graphene/Ru(0001) and Ag(111) oriented thin films on Ru(0001). On the Ag films, the molecules form a densely packed 2D structure, while on graphene/Ru(0001), only the areas between the maxima are populated. The findings are rationalized by a high corrugation in the adsorption potential for 2,4'-BTP molecules on graphene/Ru(0001). These findings are supported by temperature programmed desorption (TPD) experiments and theoretical results.     

Fe/MgO催化合成碳纳米管和氮掺杂碳纳米管

以MgO负载的Fe为催化剂、正己烷为碳源、乙二胺为氮源, 用催化化学气相沉积法合成了碳纳米管(CNTs)和氮掺杂碳纳米管(CNx). 通过还原焙烧的Mg/Fe水滑石(LDH)和Mg(NO3)2/Fe(NO3)3前驱体得到具有催化活性的Fe催化剂(Fe-LDH和Fe-Mg(NO3)2/Fe(NO3)3). 由这两种催化剂催化合成的CNTs都具有中空的管状结构. Fe-LDH催化合成的CNx具有明显的“竹节”状形貌, 而Fe-Mg(NO3)2/Fe(NO3)3催化合成的部分CNx的形貌与“竹节”状不同. 该CNx具有厚的管壁且在管壁的石墨层与层之间存在大量的空隙. Fe-LDH催化合成的CNx中氮摩尔分数为6.3%, 高于Fe-Mg(NO3)2/Fe(NO3)3催化合成CNx中的5.7%; 但后者具有更多的缺陷, 石墨化程度更加无序.     

Molecular and electronic structures and magnetic properties of multilayer graphene nanoclusters and their changes under the influence of adsorbed molecules

The results of investigations of the structures and properties of multilayer graphene nano-clusters (nanographites), structural blocks of activated carbon fibers, and their changes under the influence of adsorbed molecules are presented. The presence of specific edge p-electron-ic states in the nanographites and a reversible decrease in their density at the Fermi level upon the interaction of the graphite nanoparticles with adsorbed molecules of oxygen, chlorine, and water were found. The explanation of the discovered effect was proposed in the terms of the model of spin splitting of edge p-electronic states initiated by the transfer of a small fraction of the electron density from the nanographites to adsorbed molecules. The change in the sign of the temperature coefficient of current carrier spin relaxation rate in the presence of adsorbates can be accounted for by their interaction with edge spin-split (magnetically ordered) states. The preservation of peripheral p-electronic states of the nanographites of free (dangling) s-orbitals of edge carbon atoms at saturation with chlorine was substantiated.     

Synthesis,characterization, and transport properties of Nafion-polypyrrole membrane for direct methanol fuel cell (DMFC) application

Journal of Solid State Electrochemistry - Due to their distinctive chemical, electronic, and environmental properties, polypyrrole is used as a blocking barrier for methanol leakage in direct...