• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    基于金屬有機(jī)框架衍生的Fe-N-C納米復(fù)合材料作為高效的氧還原催化劑

    2019-07-26 09:13:26王倩倩劉大軍何興權(quán)
    物理化學(xué)學(xué)報 2019年7期
    關(guān)鍵詞:理工大學(xué)長春框架

    王倩倩,劉大軍,何興權(quán)

    長春理工大學(xué)化學(xué)化工系,長春 130022

    1 Introduction

    The oxygen reduction reaction (ORR) is regarded as one of the most important cathode reactions in clean energy conversion devices such as fuel cells and metal-air batteries1-6. Although platinum is considered as the best electrocatalyst for the ORR,its high cost and scarcity hinder its large-scale practical applications7,8. Furthermore, Pt-based catalysts usually suffer from multiple drawbacks such as low stability and methanol crossover9,10. Therefore, it is highly necessary to develop inexpensive alternatives that possess high efficiency, durability and resistance to methanol. Consequently, much research effort has been devoted to the design and preparation of non-precious metal catalysts (NPMCs) with excellent catalytic activity for the ORR, such as heteroatom (N, S, P, etc.) doped carbon materials10-15,transition metal-nitrogen doped carbon (M-N-C)16-19, transition metal oxides7,20, non-precious metal carbides21-26, metal-Nxmacrocycles27,28, etc. Among them, transition metal-nitrogencarbon (M-N-C) materials, especially for Fe-N-C or Co-N-C,have been a major focus of research and development because of their low cost, excellent electrocatalytic activity and good

    stability. It has been demonstrated that heteroatom doping can greatly affect the charge distribution of carbon atoms and their spin density, which can induce active sites in carbon materials3,12,29. In particular, nitrogen atoms can cause adjacent carbon atoms to produce Lewis base sites for greater O2 reduction ability, thus effectively improving ORR activity30.Heteroatom-doped carbon also contributes to mitigating the leaching of metal particles in the catalysts by forming M-N-C bonds and enhances catalytic activity and durability29. Since the first discovery of ORR activity of the Co phthalocyanine complex in 196431, the heat-treated M-N-C (M = Fe or Co) ORR catalysts have been extensively studied32,33. Such catalysts are typically prepared via pyrolyzing a composite precursor containing iron or cobalt, nitrogen, and carbon at temperatures above 700 °C to achieve high activity and a robust structure16-19,32,33.

    To design high-performance Fe-N-C catalysts, it is of prime importance to understand their active sites. While multiple active sites have been suggested for these catalysts, including Fe-Nxsites, pyridinic-N and/or graphitic-N, and defect sites of graphitic carbon, and there has been a growing consensus that the Fe-Nxsites are the dominant active centers17,34,35. Recently,metal/metal carbide nanoparticles encased within carbon layers have also been suggested as active sites for Fe-N-C catalysts,whose active sites are believed to be the graphitic carbon shells activated by the encased nanoparticles23,25,26,36,37.

    Metal-organic frameworks (MOFs) are a class of porous materials, assembled from metal ions or ion clusters bridged by organic ligands. Owing to their high surface area, controlled crystalline structure, various composition, well-organized framework and tunable porous structure, MOFs have been considered as ideal precursor materials to fabricate high performance carbon-based electrocatalysts31,38-43. For example,Dodelet et al.31developed a new Fe-N-C catalyst through physical mixing of ZIF-8, a zeolitic imidazolate framework(ZIF) composed of Zn and 2-methylimidazole, together with N-chelating Fe compounds using ball milling followed by two annealing treatments using Ar and NH3, respectively. The resulting catalyst generated a high volumetric activity and facilitated mass transport in the porous catalyst layers.

    Herein, we report a facile and easily scalable method to prepare a highly active Fe-N-C catalyst, involving physical mixing of MIL-100(Fe) with glucose and urea, and subsequent pyrolysis under inert atmosphere. We demonstrate that the annealing temperature is an important parameter that can be used to tune the composition and structure of the Fe-N-C materials,thus optimizing their electrocatalytic performances. It also shows excellent operational stability and methanol tolerance better than the state-of-the-art Pt/C catalyst.

    2 Experimental and computational section

    2.1 Materials

    1,3,5-Benzenetricarboxylic acid, iron(III) nitrate nonahydrate,glucose, urea and KOH were provided by Beijing Chemical Corp. 5% Nafionperfluorinated resin solution (in ethanol) was obtained from Aladdin. 20% (mass fraction) Pt on Vulcan XC-72 (Pt/C catalyst) was purchased from Alfa Aesar. All the reagents were of analytical grade and used without further purification. Aqueous solutions were prepared using ultrapure water (18.2 MΩ·cm) from a Milli-Q Plus system (Millipore).

    2.2 Preparation of the samples

    2.2.1 Preparation of MIL-100(Fe)

    The synthesis of MIL-100(Fe) was carried out using a previous procedure with slight modifications44. Typically,iron(III) nitrate nonahydrate (484 mg, 1.2 mmol) and 1,3,5-benzenetricarboxylic acid (210 mg, 1.0 mmol) were dissolved in deionized water (5 mL). Then, the resulting solution was stirred for 0.5 h, transferred into a Teflon lined stainless autoclave, and heated at 180 °C for 12 h. The autoclave was let to cool to room temperature in air on its own. The obtained yellow solid was recovered by centrifugation and washed several times with deionized water and ethanol. The material was finally dried overnight at 60 °C in an oven, producing MIL-100(Fe).

    2.2.2 Preparation of Fe-N-C

    Glucose (40 mg), urea (240 mg) and MIL-100(Fe) (20 mg)were dissolved in the mixed solution of distilled water (5 mL)and ethanol (5 mL), followed by sonication for half an hour. The solvent was slowly removed by rotary evaporation. During this process, glucose and urea molecules self-assembled onto MIL-100(Fe) due to the physical interactions such as van der Waals force and hydrogen bonding. Subsequently, the obtained mixture was heated to 800-1000 °C for 2 h in argon atmosphere at a rate of 5 °C·min-1. The obtained materials were labeled as Fe-N-C-800, Fe-N-C-900 and Fe-N-C-1000.

    The Fe-C-900 and Fe-N-900 were also synthesized by a similar procedure as Fe-N-C-900, except that urea and glucose were not added to the synthesis mixture, respectively. MIL-100(Fe) was directly pyrolyzed at 900 °C by using the same procedure as the one used to make Fe-N-C-900 above. The resulting material was named as MIL-900.

    2.3 Structure characterization of the samples

    The morphologies and structures of the fabricated samples were acquired using scanning electron microscopy (SEM, a JEOL JSM-6701F electron microscope operating at 5 kV),transmission electron microscopy (TEM, a tecnai G220 S-Twin transmission electron microscope operating at 200 kV) and X-ray diffractometer (RIGAK, D/MAX2550 VB/PC, Japan).Raman spectra were obtained using a TriVista?555CRS Raman spectrometer. The laser frequency used was the 532 nm line. X-ray photoelectron spectroscopy (XPS) measurements were performed using an ESCLAB 250 spectrometer with a monochromatized Al KαX-ray source (1486.6 eV) to determine surface chemical compositions and bonding states. Fitting was done using a nonlinear least-squares curve-fitting program(XPSPEAK41 software). XPS deconvolution conditions showed that the background type was Shirley and the FWHM value, as well as the percentage Lorentzian-Gaussian value of these peaks split by the same peak should be close. The Brunauer-Emmett-Teller (BET) surface areas and pore volumes were evaluated using nitrogen adsorption-desorption isotherms measured on a V-SORB2802 volumetric adsorption analyzer at 77 K.

    2.4 Electrochemical studies of the prepared samples

    In the present work, all electrochemical tests were conducted on an electrochemical workstation (CHI760E, Shanghai Chenhua Co. Ltd., China) with a conventional three-electrode cell system, where a modified electrode was used as the working electrode, a platinum plate as the counter electrode, a saturated calomel electrode (SCE) as the reference electrode, and 0.1 mol·L-1KOH was used as the electrolyte. The working electrode was prepared by the following procedures: the catalyst ink was first prepared by distributing 1 mg of as-synthesizedFe-N-C-900 catalyst or 20% (mass fraction) Pt/C in 1 mL of ethanol under sonication for 3 h. Subsequently, a certain amount of the uniform ink was carefully deposited on the glassy carbon electrode(rotating disk electrode (RDE), d = 5 mm; rotating ring disk electrode (RRDE), d = 5.61 mm), resulting in a catalyst loading of 0.28 mg cm-2. Other counterparts were also kept at the same loading. All potentials in this work were reported vs the reversible hydrogen electrode (RHE) in the working pH, which can be calibrated from the Nernst equation.

    The ORR kinetic parameters of the catalysts can be obtained using the following Koutecky-Levich (K-L) equation, Eqs. (1)and (2):

    where J is the measured current density; JL and JK are the diffusion limiting and kinetic limiting current densities,respectively; ω is the angular velocity of the disk (ω = 2πN,where N is the electrode rotating speed); B is the Levich slope; n is the transferred electron number; F is the Faraday constant(96485 C·mol-1); C0is the bulk concentration of O2(1.2 × 10-3mol mL-1in 0.1 mol·L-1KOH solution). D0 is the diffusion coefficient of O2 in electrolyte (1.9 × 10-5cm2·s-1in 0.1 mol·L-1KOH solution), and v is the kinetic viscosity (0.01 cm2·s-1in 0.1 mol·L-1KOH solution). Moreover, the diffusion-limiting current density (JL) is obtained from the corresponding current divided by the geometric area of the glassy carbon electrode. The transferred electron number (n) and the yield of H2O2 (Y) during ORR can be calculated using the following equations:

    where Iris the ring current, Idis the disk current, and N is the current collection efficiency of the Pt ring.

    3 Results and discussion

    Fig. 1 XRD patterns of Fe-N-C-900, Fe -C-900,Fe-N-900 and MIL-900.

    To study the composition of as-obtained samples, XRD measurement was carried out. In Fig. 1, a broad diffraction peak at 2θ ~ 25° appears for Fe-N-C-900, Fe-C-900, Fe-N-900 and MIL-900 samples, implying the formation of the graphitic structure in the hybrid. It is worth noting that the peak intensity of Fe-C-900 and Fe-N-900 at 2θ ~ 25° are distinctly stronger than that of MIL-900, demonstrating that the introduction of glucose or urea is beneficial for the formation of the graphitic structure. It is obvious that the Fe-N-C-900 has the strongest peak at 2θ ~ 25°, which suggests the synergistic effect of glucose and urea. Other diffraction peaks at 37.7°, 39.8°, 40.6°, 43.7°,44.5°, 45.8°, and 49.1° in Fig. 1 can be indexed to the diffraction from (210), (002), (201), (102), (220), (112) and (221) planes of Fe3C (PDF #65-2411) for Fe-N-C-900, Fe-C-900, Fe-N-900 and MIL-900 samples. The XRD results prove the formation of active Fe3C nanocrystals derived from MIL-100(Fe) during the carbonization process.

    The morphological and structural properties of Fe-N-C-900 were examined by scanning electron microscope (SEM) and transmission electron microscopy (TEM) techniques. Typical SEM images of the Fe-N-C-900 catalyst are shown in Fig. 2a, b.The Fe-N-C-900 exhibits a folded sheet-like morphology with numerous edges, and the Fe3C nanoparticles seem to be embedded in the matrix of carbon sheets. Fig. S1a-e (Supporting Information) corresponds to SEM images of Fe-N-C-800, Fe-NC-1000, Fe-C-900, Fe-N-900 and MIL-900, respectively. For all of the as-obtained contrast materials, the Fe3C nanoparticles anchored on carbon nanosheets can also be clearly observed. It is worth noting that the mean size of particles loaded on the Fe-N-900 (Fig. S1d) is apparently smaller than that supported on the MIL-900 (Fig. S1e). This result indicates that the addition of urea is beneficial for forming small size of Fe3C nanoparticles,enabling the exposure of more defective sites. After introducing glucose into MIL-100(Fe), the mean size of Fe3C nanoparticles on the Fe-C-900 (Fig. S1c) is similar to that on the MIL-900,while those nanoparticles seem to be covered by carbon layers.This result suggests that the addition of glucose is conducive for producing carbon-encapsulated Fe3C nanoparticles. Metal-based nanoparticles embedded in a few graphitic carbon layers can efficiently optimize the electronic structure of the outer carbon layers, enhancing the activity of the catalysts toward ORR25,26.Above observations distinctly demonstrate that the introduction of both urea and glucose is quite essential to produce Fe-N-C hybrid materials with small and carbon-enclosed Fe3C nanoparticles. Fig. 2c shows a typical TEM image of Fe-N-C-900. The Fe3C nanoparticles encapsulated with graphitic carbon layers can be clearly seen. The inner nanocrystal cores display the lattice fringes with a d-spacing of 0.21 nm in high-resolution TEM (HRTEM, Fig. 2d), which are ascribed to (211) plane in Fe3C (PDF #65-2411)21. The clear lattice fringes with an interlayer distance of 0.348 nm in the shell part correspond to the(002) plane in graphitic carbon19. The TEM image and corresponding elemental mapping results (Fig. 3) confirm the existence of C, N, O and Fe elements in Fe-N-C-900. Notably,except for Fe, all the elements are homogeneously distributed.Fe is obviously concentrated mainly in some sections of the nanoparticles.

    Fig. 2 (a, b) SEM images of Fe-N-C-900 under differentmagnifications; (c) TEM and (d) HRTEM images of Fe-N-C-900.

    The high degree of graphitization of the resultant catalysts was further confirmed by Raman spectroscopy, a sensitive tool for characterization of graphitic carbon. As shown in Fig.4a, the Raman spectroscopy of Fe-N-C-T (where T represents the pyrolysis temperature) show two prominent peaks at 1350 and 1582 cm-1, belonging to the D band arising from the disordered carbon atoms and the G band related to sp2-hybridized graphitic carbon atoms, respectively45. Obviously, the ID/IGratios of Fe-N-C catalysts decrease with the elevated pyrolysis temperature,indicating a higher pyrolysis temperature tends to obtain a Fe-NC sample with higher degree of graphitization. Raman spectra of Fe-C-900, Fe-N-900 and MIL-900 samples are shown in Fig. S2(Supporting Information). Both the Fe-N-900 (0.966) and Fe-C-900 (1.162) have smaller ID/IGvalues than MIL-900 (1.293),suggesting the introduction of urea or glucose can obviously increase the degree of graphitization of the obtained samples.Fe-N-C-900 shows an ID/IGvalue of 1.00, which is slightly higher than that of Fe-N-900 but lower than those of Fe-C-900 and MIL-900, ascribing to the balance between the disorder structure caused by heteroatoms doping and the graphitic structure. The changes in the crystallite size of Fe-N-C-T, Fe-C-900, Fe-N-900 and MIL-900 further prove above results, as shown in Table S1(Supporting Information). The low ID/IGvalue indicates the good electrical conductivity of the as-prepared catalysts46,47.

    Fig. 3 TEM image with the corresponding C, N, O and Fe element mapping images of the Fe-N-C-900.

    Fig. 4 (a) Raman spectra of Fe-N-C-800, -900 and -1000. (b) N2 adsorption and desorption isotherms of Fe-N-C-800, -900, -1000, Fe-C-900,Fe-N-900 and MIL-900 samples. (c) XPS survey of Fe-N-C-800, -900 and -1000. High-resolution N 1s XPS spectra of Fe-N-C-800 (d),Fe-N-C-900 (e) andFe-N-C-1000 (f).

    The surface area and porous texture of the resultant catalysts were characterized on the basis of N2adsorption/desorption analysis. N2 sorption isotherms of the as-obtained Fe-N-C-800,Fe-N-C-900, Fe-N-C-1000, Fe-C-900, Fe-N-900 and MIL-900 samples (Fig.4b) can be identified as typed-IV isotherms with a pronounced hysteresis loop, suggesting the existence of mesoporous structure48,49. The BET surface areas and total pore volumes are summarized in Table S1. Obviously the Fe-N-C-900 possesses the highest BET surface area and largest pore volume, which are beneficial for the exposure of more active sites and faster mass transfer50. Notably, without adding urea or glucose, the BET surface areas of the obtained Fe-C-900 (435 m2·g-1) or Fe-N-900 (428 m2·g-1) are distinctly larger than that of MIL-900 (112 m2·g-1) but smaller than that of Fe-N-C-900(502 m2·g-1). These results prove that urea and glucose may have double functions in the pore formation processes: as extra poregenerating agents and dopant precursors.

    To study the surface composition and chemical states of these materials, X-ray photoelectron spectroscopic (XPS) analyses were performed. As shown in Fig.4c, the XPS survey spectra of Fe-N-C obtained at different pyrolysis temperatures show the presence of C 1s, N 1s, O 1s and Fe 2p peaks in the materials.The nitrogen contents of Fe-N-C-800, -900 and -1000 catalysts are 5.69%, 4.2% and 3.0% (atom percent), as shown in Table S2(Supporting Information). Obviously the overall nitrogen content of the samples decreases with the elevated pyrolysis temperatures, which is possibly ascribed to the decomposition of nitrogen-containing species at higher temperatures. The highresolution N 1s XPS spectra are shown in Fig.4d-f. The N 1s spectra for Fe-N-C can be fitted into five peaks corresponding to pyridinic-N (~398.2 eV), Fe-Nx(~399.3 eV), pyrrolic-N (~400.2 eV), graphitic-N (~401.0 eV), and oxidized-N (402.0 eV)species (Table S3, Supporting Information)51. It is generally believed that pyridinic-N and pyrrolic-N may coordinate with Fe to form Fe-Nxmoieties17,35. It is clear from Table S3, an increase in pyrolysis temperature leads to lower content of pyridinic-N,while the graphitic-N content becomes dominant in the materials. The increase of graphitic-N content is attributed to the conversion of the unstable pyridinic-N and pyrrolic-N to graphitic-N under higher temperature51-53. It is evident that the Fe-N-C-900 possesses the highest total content of pyridinic-N and graphitic-N functionalities (Table S3). Generally, pyridinic-N and graphitic-N species are often regarded as the active sites in N-doped carbon materials that participate in ORR54,55. In addition, the as-obtained Fe-N-C-900 also shows dominant Fe-N content. It is widely accepted that Fe-Nxspecies are the electrocatalytically active sites for ORR17. Fig. S3 (Supporting Information) shows the high-resolution Fe 2p XPS spectra of the Fe-N-C-900. The deconvoluted spectra show the existence of five different peaks. The peak centered at 707.4 eV suggests the presence of Fe3C. The Fe 2p peaks at 710.4 and 712.3 eV are assigned to 2p3/2of Fe2+and Fe3+species. The peaks at 723.4 and 725.8 eV are fitted to 2p1/2of Fe2+or Fe3+species53,56.

    To investigate the ORR activities of various catalysts, the samples were deposited onto GCE to form the working electrodes. The ORR catalytic activity of the catalysts was first characterized by cyclic voltammetry (CV) and rotating disk electrode (RDE) tests in 0.1 mol·L-1KOH. As depicted in Fig.5a, in contrast to the featureless CV curve in a N2saturated electrolyte, Fe-N-C-900 presents a well-defined oxygen reduction peak in an O2-saturated electrolyte. Remarkably, the Fe-N-C-900 exhibits an ORR peak potential at 0.79 V vs RHE with the peak current density of -2.6 mA·cm-2, suggesting the prominent ORR activity of the Fe-N-C-900. To further evaluate the electrocatalytic activity of the Fe-N-C-900, Pt/C, Fe-C-900,Fe-N-900 and MIL-900, linear scan voltammetry (LSV)measurements of catalysts for ORR were performed in an O2saturated 0.1 mol·L-1KOH solution at a rotation rate of 1600 r·min-1. As shown in Fig. 5b, the Fe-C-900 displays worse activity than MIL-900 in terms of onset potential and half-wave potential, suggesting that the introduction of exotic inert carbon(glucose) is not beneficial for the improvement of ORR activity.In contrast, the ORR activity of Fe-N-900 is superior to MIL-900, which demonstrates that the nitrogen doping is conducive for the enhancement of the ORR activity. Compared to other control catalysts, the Fe-N-C-900 shows a superior onset potential (0.96 V vs RHE), more positive half-wave potential(0.830 V) and lager ORR current density. Although its half-wave potential is slightly worse than Pt/C (0.85 V), the onset potential of Fe-N-C-900 is the same with the benchmark Pt/C catalyst(0.96 V vs RHE). These results indicate that the Fe-N-C-900 possesses superior ORR activity, demonstrating the cooperativity of glucose and urea contributes a lot to enhancing ORR activity of the fabricated Fe-N-C-900. To further evaluate the electrocatalytic activity of the Fe-N-C-900 and Pt/C with the different catalyst loadings, linear scan voltammetry (LSV)measurements of catalysts for ORR were performed in an O2 saturated 0.1 mol·L-1KOH solution at a rotation rate of 1600 r·min-1in Fig. S4 (Supporting Information). The electrocatalytic activities of the Fe-N-C catalysts obtained at different pyrolysis temperatures were measured by RDE in Fig. 5c. It is found that all the Fe-N-C samples show prominent ORR catalytic activities,and the optimum carbonization temperature appears to be 900 °C. The enhanced performance of the Fe-N-C-900 toward ORR is attributed to an optimal balance of the specific surface area, active site density and electronic conductivity. We also compare the ORR activity of our as-obtained Fe-N-C-900 with those of some state-of-the-art M-N-C catalysts reported in literature (Table S4, Supporting Information). As seen from Table S4, the electrocatalytic activity of the as-preparedFe-N-C-900 catalyst is comparable or superior to those M-N-C catalysts in terms of the onset potential, half-wave potential and limiting current density.

    Fig. 5 (a) CV curves of Fe-N-C-900 in O2- and N2-saturated 0.1 mol·L-1 KOH solutions with a scan rate of 100 mV·s-1.(b) LSV curves of Fe-N-C-900, Fe-C-900, Fe-N-900, MIL-900 and Pt/C. (c) LSV curves of Fe-N-C-T catalysts at a rotation speed of 1600 r·min-1 with a scan rate of 10 mV s-1. (d) LSV curves of Fe-N-C-900 at different rotation speeds in O2-saturated 0.1 mol·L-1 KOH.(e) The corresponding Koutecky-Levich plots of ORR for Fe-N-C-900. (f) Tafel plots obtained from the RDE measurements on Fe-N-C-900 and Pt/C catalysts in O2-saturated 0.1 mol·L-1 KOH at 1600 r·min-1.

    The LSVs of Fe-N-C-900 with various rotation speeds in an O2saturated 0.1 mol·L-1KOH solution were implemented to thoroughly explore the ORR kinetics of the Fe-N-C-900 catalyst.In Fig. 5d, the current densities are increased with the increase of rotating speed from 200 to 2500 r·min-1owing to the faster oxygen diffusion to the electrode surface. The Koutecky-Levich(K-L) plots shown in Fig.5e suggest that these plots exhibit good linearity with a rather consistent slope over the potential range of 0.55-0.25 V, demonstrating that the ORR process on the Fe-N-C-900 follows the first-order reaction kinetics to oxygen concentration57. Fig. 5f displays the Tafel slopes of Fe-N-C-900 and Pt/C. It is noticed that the Tafel slope of Fe-N-C-900 (72 mV·dec-1) is the same with that of Pt/C (72 mV·dec-1), further demonstrating they possess a very similar reaction mechanism of ORR, where the rate-determining step is likely the first electron reduction of oxygen58.

    To further examine the ORR activity on the samples, RRDE measurements were employed to evaluate the ORR mechanism in depth. Fig. 6a shows the disk and ring current density on Fe-N-C-900 and Pt/C. The electron transfer number (n, Eq. (3))calculated from a RRDE technique suggests that the Fe-N-C-900 catalyst favors a 4e ORR process, similar to ORR catalyzed by the commercial Pt/C catalyst (n ≈ 4, Fig. 6b), producing water as the main product. RRDE measurement was conducted to monitor the formation of H2O2during the ORR process. As shown in Fig. 6c, the H2O2yield of Fe-N-C-900 in 0.1 mol·L-1KOH is below 4% in the measured potential range from 0.4 to 0.55 V, which is even smaller than that of the benchmark Pt/C catalyst, manifesting higher catalytic efficiency of the Fe-N-C-900 toward ORR.

    For practical applications, the methanol crossover effect and stability toward ORR are also important parameters in the quantification and comparison of catalytic performance. The methanol crossover effect was evaluated on both Fe-N-C-900 and Pt/C (Fig. 6d). The Fe-N-C-900 catalyst suffers from a little change in current density upon the introduction of 3 mol·L-1methanol into 0.1 mol·L-1KOH saturated with O2; however, for the case of Pt/C the current density undergoes a sharp decrease under the same conditions. Above results suggest that our Fe-NC-900 catalyst has good tolerance to methanol crossover. For investigating the electrode stability, an operational stability test was performed using the chronoamperometric current-time (i-t)method in an O2-saturated 0.1 mol·L-1KOH aqueous solution at 0.79 V and a rotation rate of 1600 r·min-1. As shown in Fig. 6e,the current density of Fe-N-C-900 remains 94.9% of its initial value after 10000 s, and the value for Pt/C catalyst is 82%. To further evaluate the electrocatalytic activity of the Fe-N-C-900 after the stability test, LSV measurements of Fe-N-C-900 for ORR were performed in an O2-saturated 0.1 mol·L-1KOH solution at a rotation speed of 1600 r·min-1. Fig. S5 (Supporting Information) shows LSV curves of Fe-N-C-900 before and after stability tests. It is clear from Fig. S5 that the onset potential of the ORR over Fe-N-C-900 remains unchanged and the halfwave potential is decreased only by 5 mV after stability test.Above results demonstrate that our fabricated Fe-N-C-900 catalyst possesses high ORR activity. The high stability of Fe-N-C-900 can be attributed to the uniformly distributed iron carbide nanoparticles with graphitized carbon outlayer, avoiding the aggregation or dissolution of iron carbide nanoparticles.

    Fig. 6 (a) Rotating ring disk electrode (RRDE) measurements of Fe-N-C-900 and Pt/C in O2-saturated 0.1 mol·L-1 KOH at a rotation speed of 1600 r·min-1 with a scan rate of 10 mV s-1. (b) Electron transfer number of Fe-N-C-900 and Pt/C. (c) Peroxide percentage of Fe-N-C-900 and Pt/C.(d) Chronoamperometric response of Fe-N-C-900 and Pt/C to addition of methanol at 300 s. (e) Chronoamperometric response of Fe-N-C-900 and Pt/C in O2-saturated 0.1 mol·L-1 KOH.

    The remarkable electrocatalytic activity of Fe-N-C-900 for ORR in alkaline media may have resulted from the combination of the following factors: (1) the outer protective graphitic layers stabilize the Fe3C nanoparticles of the materials in alkaline media, although the inner Fe3C nanoparticles are not in direct contact with the electrolyte, they play a crucial role in catalyzing ORR by activating the outer surface of the graphitic layers; (2)the Fe-N-C-900 possesses dominant electrocatalytically active species such as pyridinic-N (25.3%)and graphitic-N (27%); (3)the high surface area of the Fe-N-C-900 can help creating more surface-exposed reactive sites that promote ORR over the material; and (4) more importantly, the synergistic effect among the catalytic active species in the materials contributes to the substantial enhancement in the catalytic activity of the material toward ORR.

    4 Conclusions

    In summary, a highly active Fe-N-C catalyst was obtained by pyrolyzing the mixture of MIL-100, glucose and urea under inert atmosphere. Among the materials obtained, the one made at 900 °C, Fe-N-C-900, was found to exhibit superior ORR activity, high durability and good methanol tolerance under alkaline media, comparable to the benchmark Pt/C (20% Pt)catalyst. The large BET area and total pore volume, high contents of nitrogen doping species, excellent electrical conductivity and cooperative effects between reactive functionalities are proposed to be responsible for excellent ORR activity and stability of the material. The Fe-N-C catalyst reported here is, therefore, highly promising to be part of highlyefficient and cost-effective future energy devices.

    Supporting Information:available free of charge via the internet at http://www.whxb.pku.edu.cn.

    猜你喜歡
    理工大學(xué)長春框架
    昆明理工大學(xué)
    框架
    初夏
    廣義框架的不相交性
    昆明理工大學(xué)
    昆明理工大學(xué)
    浙江理工大學(xué)
    印語長春
    WTO框架下
    法大研究生(2017年1期)2017-04-10 08:55:06
    一種基于OpenStack的云應(yīng)用開發(fā)框架
    国产色爽女视频免费观看| 午夜视频国产福利| 男人添女人高潮全过程视频| 亚洲精品乱码久久久v下载方式| 国产人妻一区二区三区在| 视频中文字幕在线观看| 精品久久久久久久久av| 精品久久久久久久久av| 亚洲欧洲日产国产| 黄色怎么调成土黄色| 麻豆成人午夜福利视频| 老女人水多毛片| 91狼人影院| 高清黄色对白视频在线免费看 | 日本色播在线视频| 18禁在线播放成人免费| a 毛片基地| 中文在线观看免费www的网站| 伦精品一区二区三区| 日韩人妻高清精品专区| 麻豆国产97在线/欧美| 夜夜骑夜夜射夜夜干| 亚洲人成网站在线播| 国产成人一区二区在线| 日本av免费视频播放| 激情 狠狠 欧美| 亚洲欧美中文字幕日韩二区| 一本一本综合久久| 国产毛片在线视频| kizo精华| 99热这里只有是精品50| 热re99久久精品国产66热6| 18禁动态无遮挡网站| 成人午夜精彩视频在线观看| 婷婷色麻豆天堂久久| 国产男女内射视频| 一本久久精品| 亚洲av不卡在线观看| 伦精品一区二区三区| 黄片无遮挡物在线观看| 天堂8中文在线网| 99热全是精品| 高清视频免费观看一区二区| 日韩精品有码人妻一区| 美女内射精品一级片tv| 国产亚洲av片在线观看秒播厂| 大香蕉久久网| 我的女老师完整版在线观看| av不卡在线播放| 中文字幕人妻熟人妻熟丝袜美| 伦理电影大哥的女人| 亚洲成人中文字幕在线播放| 欧美成人a在线观看| 久久久久久久大尺度免费视频| 国产精品99久久久久久久久| 精品人妻视频免费看| 偷拍熟女少妇极品色| 国产乱来视频区| a级一级毛片免费在线观看| 岛国毛片在线播放| 亚洲欧美精品自产自拍| 日韩人妻高清精品专区| av播播在线观看一区| 亚洲成人中文字幕在线播放| 成人国产麻豆网| 国产国拍精品亚洲av在线观看| 高清欧美精品videossex| 中文在线观看免费www的网站| 国产有黄有色有爽视频| 国产精品欧美亚洲77777| 欧美日韩视频高清一区二区三区二| 国产黄色视频一区二区在线观看| 赤兔流量卡办理| 国产乱人视频| av在线播放精品| 亚洲精品国产av蜜桃| 国产成人一区二区在线| 1000部很黄的大片| 亚洲欧洲国产日韩| 国产精品女同一区二区软件| 国产黄色免费在线视频| 日韩欧美 国产精品| 哪个播放器可以免费观看大片| 国产精品秋霞免费鲁丝片| 一本色道久久久久久精品综合| 国产国拍精品亚洲av在线观看| a 毛片基地| 赤兔流量卡办理| 日产精品乱码卡一卡2卡三| 99九九线精品视频在线观看视频| 成年av动漫网址| 国产高清不卡午夜福利| 又粗又硬又长又爽又黄的视频| 亚洲精品日本国产第一区| 99久久精品一区二区三区| 午夜福利高清视频| 日韩强制内射视频| 晚上一个人看的免费电影| 免费大片黄手机在线观看| 日韩精品有码人妻一区| 美女cb高潮喷水在线观看| 久久久久久久亚洲中文字幕| 亚洲精品自拍成人| 亚洲色图综合在线观看| 国产精品麻豆人妻色哟哟久久| 精品熟女少妇av免费看| 久久ye,这里只有精品| 国产乱来视频区| 伊人久久精品亚洲午夜| 爱豆传媒免费全集在线观看| 久久99热6这里只有精品| 精品少妇黑人巨大在线播放| 精品国产三级普通话版| 日韩亚洲欧美综合| 久久久久久久久久成人| 亚洲综合色惰| 99热全是精品| 大陆偷拍与自拍| 啦啦啦在线观看免费高清www| 国产人妻一区二区三区在| 91精品一卡2卡3卡4卡| 亚洲精品视频女| 大码成人一级视频| 国精品久久久久久国模美| 高清欧美精品videossex| 国产精品嫩草影院av在线观看| 下体分泌物呈黄色| 精品亚洲乱码少妇综合久久| 久久av网站| 交换朋友夫妻互换小说| 久久久久久伊人网av| 日日摸夜夜添夜夜爱| 久久精品国产a三级三级三级| 国产有黄有色有爽视频| 偷拍熟女少妇极品色| 女的被弄到高潮叫床怎么办| 国产男女超爽视频在线观看| 麻豆国产97在线/欧美| 99热全是精品| 国产av精品麻豆| 一级a做视频免费观看| 麻豆精品久久久久久蜜桃| 伦理电影大哥的女人| 各种免费的搞黄视频| 国产美女午夜福利| 网址你懂的国产日韩在线| 99久久中文字幕三级久久日本| 女性被躁到高潮视频| kizo精华| 一本—道久久a久久精品蜜桃钙片| 简卡轻食公司| 女性生殖器流出的白浆| 男女国产视频网站| 国产大屁股一区二区在线视频| 边亲边吃奶的免费视频| 91精品国产国语对白视频| 中文在线观看免费www的网站| 22中文网久久字幕| 少妇裸体淫交视频免费看高清| 99热这里只有精品一区| 日韩人妻高清精品专区| 毛片一级片免费看久久久久| 亚洲av中文字字幕乱码综合| 日韩欧美 国产精品| 亚洲av福利一区| 青青草视频在线视频观看| 亚洲人与动物交配视频| 国产人妻一区二区三区在| 亚洲国产毛片av蜜桃av| 久久久久久久久久人人人人人人| 99热国产这里只有精品6| 超碰av人人做人人爽久久| 日韩免费高清中文字幕av| 久久人人爽人人片av| 国产日韩欧美在线精品| 大陆偷拍与自拍| 美女国产视频在线观看| 大片免费播放器 马上看| 纯流量卡能插随身wifi吗| 国产伦理片在线播放av一区| 国产精品秋霞免费鲁丝片| 下体分泌物呈黄色| av福利片在线观看| 偷拍熟女少妇极品色| av在线app专区| 国产永久视频网站| 亚洲国产最新在线播放| 97超碰精品成人国产| 视频区图区小说| 王馨瑶露胸无遮挡在线观看| 久久久久久久久久久丰满| 蜜桃在线观看..| 岛国毛片在线播放| 亚洲激情五月婷婷啪啪| 视频区图区小说| 亚洲aⅴ乱码一区二区在线播放| 一级爰片在线观看| 久久久久精品久久久久真实原创| 最近的中文字幕免费完整| 亚洲欧美日韩东京热| 国产欧美另类精品又又久久亚洲欧美| 纯流量卡能插随身wifi吗| 成人毛片60女人毛片免费| 亚洲国产精品一区三区| 成人综合一区亚洲| 视频区图区小说| 男人爽女人下面视频在线观看| 亚洲美女黄色视频免费看| 美女cb高潮喷水在线观看| 欧美老熟妇乱子伦牲交| 日日撸夜夜添| 欧美 日韩 精品 国产| 你懂的网址亚洲精品在线观看| 国产精品一区二区在线不卡| 99热这里只有是精品50| 搡女人真爽免费视频火全软件| 亚洲国产精品成人久久小说| 亚洲色图av天堂| 欧美另类一区| 欧美一级a爱片免费观看看| 街头女战士在线观看网站| 国语对白做爰xxxⅹ性视频网站| 日韩成人伦理影院| 啦啦啦在线观看免费高清www| 国产一级毛片在线| 亚洲一区二区三区欧美精品| 一本一本综合久久| 少妇高潮的动态图| 欧美一区二区亚洲| 国产av一区二区精品久久 | 王馨瑶露胸无遮挡在线观看| 不卡视频在线观看欧美| 亚洲国产欧美在线一区| 国产精品伦人一区二区| 亚洲精品日韩在线中文字幕| 亚洲四区av| 日韩,欧美,国产一区二区三区| 自拍欧美九色日韩亚洲蝌蚪91 | 黄色一级大片看看| 一级二级三级毛片免费看| 观看免费一级毛片| 久久精品国产自在天天线| 熟女人妻精品中文字幕| 精品熟女少妇av免费看| 精品久久久久久久末码| 免费大片黄手机在线观看| 黑人猛操日本美女一级片| 亚洲国产精品国产精品| 日韩中字成人| 国产精品国产三级国产专区5o| 黄色日韩在线| 校园人妻丝袜中文字幕| h视频一区二区三区| 精品国产三级普通话版| 如何舔出高潮| 国产亚洲5aaaaa淫片| 最近手机中文字幕大全| 国产白丝娇喘喷水9色精品| a级毛片免费高清观看在线播放| 亚洲国产精品国产精品| 又大又黄又爽视频免费| 国产乱来视频区| 制服丝袜香蕉在线| 亚洲精品国产av成人精品| 亚洲国产日韩一区二区| 免费不卡的大黄色大毛片视频在线观看| 最近手机中文字幕大全| 亚洲国产精品成人久久小说| tube8黄色片| 欧美97在线视频| 亚洲av二区三区四区| 久久久久久久久大av| 国产在视频线精品| 一级毛片aaaaaa免费看小| 自拍偷自拍亚洲精品老妇| 国精品久久久久久国模美| 日日啪夜夜爽| 我的老师免费观看完整版| 国产精品女同一区二区软件| 日韩电影二区| 啦啦啦在线观看免费高清www| 直男gayav资源| av播播在线观看一区| 丝袜脚勾引网站| 久久国产精品大桥未久av | 青春草国产在线视频| 1000部很黄的大片| 国产精品嫩草影院av在线观看| av福利片在线观看| 欧美成人a在线观看| 内射极品少妇av片p| 麻豆国产97在线/欧美| 国产色爽女视频免费观看| 日韩精品有码人妻一区| 免费看日本二区| 午夜福利在线在线| 久久人人爽人人片av| 1000部很黄的大片| 99久久精品国产国产毛片| 亚洲经典国产精华液单| 亚洲aⅴ乱码一区二区在线播放| 国产伦理片在线播放av一区| 成人18禁高潮啪啪吃奶动态图 | 国产中年淑女户外野战色| 国产免费一级a男人的天堂| 最后的刺客免费高清国语| 精品酒店卫生间| 我要看日韩黄色一级片| 欧美老熟妇乱子伦牲交| 青春草亚洲视频在线观看| 国产伦精品一区二区三区四那| 十分钟在线观看高清视频www | 在线观看免费视频网站a站| 免费不卡的大黄色大毛片视频在线观看| 亚洲精品乱码久久久v下载方式| 一区在线观看完整版| 免费在线观看成人毛片| 日韩av不卡免费在线播放| 久久久色成人| 两个人的视频大全免费| 男人和女人高潮做爰伦理| 99国产精品免费福利视频| 中国国产av一级| 国产av一区二区精品久久 | 老师上课跳d突然被开到最大视频| 日本午夜av视频| 久久精品久久久久久久性| 亚洲av国产av综合av卡| 久久久久国产精品人妻一区二区| 天堂中文最新版在线下载| 卡戴珊不雅视频在线播放| 国产在线视频一区二区| 精品少妇久久久久久888优播| 欧美老熟妇乱子伦牲交| 一级毛片久久久久久久久女| 亚洲在久久综合| 一级a做视频免费观看| 精品一区二区三卡| 色哟哟·www| 黄色欧美视频在线观看| av又黄又爽大尺度在线免费看| 精品亚洲成a人片在线观看 | 久久久欧美国产精品| 国产精品欧美亚洲77777| 一级毛片aaaaaa免费看小| 777米奇影视久久| 免费黄网站久久成人精品| 日本黄大片高清| av一本久久久久| 如何舔出高潮| 波野结衣二区三区在线| 26uuu在线亚洲综合色| av女优亚洲男人天堂| 熟女av电影| 少妇被粗大猛烈的视频| 视频中文字幕在线观看| 亚洲国产精品国产精品| 国产女主播在线喷水免费视频网站| 亚洲,一卡二卡三卡| 日韩视频在线欧美| 中文欧美无线码| 春色校园在线视频观看| 中国美白少妇内射xxxbb| 国产一区二区三区av在线| 亚洲国产最新在线播放| 国产精品人妻久久久久久| 最近最新中文字幕大全电影3| 亚洲av日韩在线播放| 欧美一区二区亚洲| 精品一品国产午夜福利视频| 多毛熟女@视频| 日韩电影二区| a级毛片免费高清观看在线播放| 午夜视频国产福利| 18禁在线播放成人免费| 久久鲁丝午夜福利片| 国精品久久久久久国模美| 欧美激情极品国产一区二区三区 | 亚洲色图av天堂| 亚洲高清免费不卡视频| 国产成人精品福利久久| 大片免费播放器 马上看| 亚洲,欧美,日韩| 黄色怎么调成土黄色| 亚洲国产日韩一区二区| 久久午夜福利片| 人体艺术视频欧美日本| 五月天丁香电影| 欧美精品一区二区大全| 97精品久久久久久久久久精品| 精品人妻偷拍中文字幕| 美女高潮的动态| 欧美精品一区二区免费开放| 国产精品蜜桃在线观看| 亚洲美女视频黄频| 又黄又爽又刺激的免费视频.| 国产精品人妻久久久影院| 中文字幕久久专区| 狂野欧美激情性xxxx在线观看| 久久久欧美国产精品| 一级二级三级毛片免费看| 99re6热这里在线精品视频| 天堂8中文在线网| 人妻制服诱惑在线中文字幕| 97热精品久久久久久| 亚洲经典国产精华液单| 亚洲四区av| 三级国产精品欧美在线观看| 国产精品99久久99久久久不卡 | 波野结衣二区三区在线| 99久国产av精品国产电影| 高清黄色对白视频在线免费看 | 精品一品国产午夜福利视频| 国产精品欧美亚洲77777| 日韩在线高清观看一区二区三区| 一级毛片久久久久久久久女| 性高湖久久久久久久久免费观看| 能在线免费看毛片的网站| 黑丝袜美女国产一区| 日韩免费高清中文字幕av| 三级国产精品欧美在线观看| 日韩一区二区三区影片| 少妇人妻一区二区三区视频| 狠狠精品人妻久久久久久综合| 少妇人妻 视频| 尤物成人国产欧美一区二区三区| 亚洲精品色激情综合| 中文字幕久久专区| 亚洲国产精品专区欧美| 成人二区视频| 男女啪啪激烈高潮av片| 91精品国产国语对白视频| 国产在线男女| 精品国产三级普通话版| 99热全是精品| 成年美女黄网站色视频大全免费 | 伦理电影大哥的女人| 观看美女的网站| 免费看不卡的av| 久久久精品94久久精品| 亚洲久久久国产精品| 高清不卡的av网站| 成年美女黄网站色视频大全免费 | 美女cb高潮喷水在线观看| 91久久精品电影网| 成人二区视频| 久久久久久久久大av| 联通29元200g的流量卡| 深爱激情五月婷婷| 女性生殖器流出的白浆| 在现免费观看毛片| 亚洲精品日韩在线中文字幕| 国产欧美日韩一区二区三区在线 | 欧美bdsm另类| 97在线人人人人妻| 大香蕉久久网| 啦啦啦中文免费视频观看日本| 久久国产精品大桥未久av | av专区在线播放| 搡老乐熟女国产| www.av在线官网国产| 午夜福利影视在线免费观看| 日韩av不卡免费在线播放| 一级av片app| 色婷婷av一区二区三区视频| 国产欧美日韩精品一区二区| 嫩草影院新地址| 亚洲av二区三区四区| 日韩亚洲欧美综合| 欧美精品一区二区免费开放| 亚洲图色成人| 精品久久久久久久久av| 亚洲欧美日韩东京热| 最近手机中文字幕大全| 亚洲精品久久久久久婷婷小说| 中文字幕制服av| 成人国产av品久久久| 久久久久国产精品人妻一区二区| 美女主播在线视频| 最近最新中文字幕大全电影3| 国产精品欧美亚洲77777| 免费看光身美女| 亚洲精品国产av成人精品| 日韩av在线免费看完整版不卡| 美女视频免费永久观看网站| 色吧在线观看| 美女中出高潮动态图| 偷拍熟女少妇极品色| 欧美最新免费一区二区三区| 2021少妇久久久久久久久久久| 国产精品国产三级专区第一集| 九九爱精品视频在线观看| 国产成人精品婷婷| 日本黄色日本黄色录像| 国内精品宾馆在线| 国产一区二区三区av在线| 中文在线观看免费www的网站| 欧美另类一区| 亚洲经典国产精华液单| 国产成人aa在线观看| 少妇被粗大猛烈的视频| 欧美一级a爱片免费观看看| 国产精品女同一区二区软件| 国产av码专区亚洲av| 少妇熟女欧美另类| 亚洲国产av新网站| 另类亚洲欧美激情| 少妇猛男粗大的猛烈进出视频| 大香蕉久久网| 亚洲成人手机| 波野结衣二区三区在线| 美女福利国产在线 | 黄片wwwwww| 在线亚洲精品国产二区图片欧美 | 亚洲丝袜综合中文字幕| 国产亚洲91精品色在线| 国产色婷婷99| 777米奇影视久久| 精品视频人人做人人爽| 一级片'在线观看视频| 男女无遮挡免费网站观看| 免费久久久久久久精品成人欧美视频 | 国产精品爽爽va在线观看网站| 99久久精品一区二区三区| a级毛片免费高清观看在线播放| 赤兔流量卡办理| 亚洲精品国产成人久久av| 伦精品一区二区三区| 亚洲精品国产av成人精品| 国产亚洲5aaaaa淫片| 涩涩av久久男人的天堂| 18禁在线播放成人免费| 亚洲电影在线观看av| 青春草国产在线视频| 色吧在线观看| 国产伦理片在线播放av一区| 午夜老司机福利剧场| 亚洲精品视频女| 亚洲国产精品国产精品| 我要看日韩黄色一级片| 人体艺术视频欧美日本| 性色av一级| 一级毛片 在线播放| 人人妻人人看人人澡| 国模一区二区三区四区视频| 日产精品乱码卡一卡2卡三| 97在线人人人人妻| 国产精品精品国产色婷婷| 高清午夜精品一区二区三区| 亚洲成人一二三区av| 国产男人的电影天堂91| 黄色一级大片看看| 国产精品99久久99久久久不卡 | 91午夜精品亚洲一区二区三区| 九九爱精品视频在线观看| 精品一区在线观看国产| 久久女婷五月综合色啪小说| 久久久久性生活片| 黑人高潮一二区| 亚洲欧美日韩东京热| 亚洲欧美中文字幕日韩二区| 一区二区av电影网| 精品一品国产午夜福利视频| 毛片一级片免费看久久久久| 男人舔奶头视频| 精品亚洲成国产av| 国产精品精品国产色婷婷| 久久人妻熟女aⅴ| 亚洲av综合色区一区| 亚洲一级一片aⅴ在线观看| 内射极品少妇av片p| 国产淫片久久久久久久久| 日韩精品有码人妻一区| 亚洲精华国产精华液的使用体验| 日本一二三区视频观看| 精华霜和精华液先用哪个| 久久这里有精品视频免费| 国产免费一区二区三区四区乱码| 免费人妻精品一区二区三区视频| 国产成人a区在线观看| 女人十人毛片免费观看3o分钟| 久久精品人妻少妇| 老女人水多毛片| 久久青草综合色| 日韩一本色道免费dvd| 精品亚洲成a人片在线观看 | 免费观看在线日韩| 亚洲av综合色区一区| 精品久久久久久久久av| 欧美日韩综合久久久久久| 成年免费大片在线观看| 精品午夜福利在线看| 成人免费观看视频高清| 人妻系列 视频| 又粗又硬又长又爽又黄的视频| 伦理电影大哥的女人| 三级国产精品片| 精品午夜福利在线看| 看十八女毛片水多多多| 狂野欧美白嫩少妇大欣赏| 国产精品国产三级国产av玫瑰| 国产一区二区三区综合在线观看 | 26uuu在线亚洲综合色| 国产精品人妻久久久久久| 国内精品宾馆在线| 亚洲欧洲国产日韩| 日韩在线高清观看一区二区三区| 男人和女人高潮做爰伦理| 亚洲怡红院男人天堂| 欧美激情国产日韩精品一区| 欧美精品亚洲一区二区| 色婷婷av一区二区三区视频| 国产伦理片在线播放av一区| 大片免费播放器 马上看| 成人毛片a级毛片在线播放|