Fe-N Co-doped Porous Carbon Derived from Ionic Liquids as Efficient

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Kinetics, Catalysis, and Reaction Engineering

Fe-N Co-doped Porous Carbon Derived from Ionic Liquids as Efficient Electrocatalyst for Oxygen Reduction Reaction Yong Liu, Shenshen Li, Xiying Li, Liqun Mao, and Fujian Liu Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b03375 • Publication Date (Web): 29 Oct 2018 Downloaded from http://pubs.acs.org on November 3, 2018

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Industrial & Engineering Chemistry Research

Fe-N Co-doped Porous Carbon Derived from Ionic Liquids as Efficient Electrocatalyst for Oxygen Reduction Reaction

Yong Liu,*,† Shenshen Li,† Xiying Li,† Liqun Mao, † Fujian Liu*,‡

†

Henan Key Laboratory of Polyoxometalate Chemistry, College of Chemistry and

Chemical Engineering, Henan University, Kaifeng, 475004, PR China ‡

National Engineering Research Center of Chemical Fertilizer Catalyst (NERC-CFC), School of Chemical Engineering, Fuzhou University, Fuzhou, 350002, PR China.

Abstract

Development of efficient catalysts with low cost for the oxygen reduction reaction (ORR) plays an important role in the commercialization of fuel cells. Herein, we reported a facile method to synthesize Fe-N co-doped porous carbon (Fe-N/C) by using green media ionic liquids 1-butyl-3-methylimidazolium tetrachloridoferrate ([Bmim][FeCl4]) as precursor of C, N and Fe, and spherical silica as template through one step pyrolysis. Electrochemical measurements show that Fe-N/C800 possesses excellent ORR catalytic activity. The onset potential and half-wave potential are 0.964 V and 0.821 V, respectively, which is close to those on the commercial Pt/C catalyst. Moreover, it exhibits better methanol tolerance and durability in comparison with the Pt/C catalyst. Good performance of Fe-N/C800 in ORR is attributed to its abundant porous structure, large BET surface area, and the synergism of Fe and N dopants.

Keywords: Fe-N co-doped porous carbon, Oxygen reduction reaction, Ionic liquids,

ACS Paragon Plus Environment

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Pyrolysis synthesis.

1. Introduction Fuel cells are recognized as one of the most promising energy transformation and storages device, which have received more and more attention in mobile, aerospace, and vehicle applications during these years.1-4 However, the sluggish cathode oxygen reduction reaction (ORR) significantly hinders the wide applications of fuel cells.5-7 Pt-based catalysts are highly effective catalysts for the ORR, but it has several drawbacks such as high cost, limited reserves, and poor durability.8-10 Therefore, the development of new type of ORR catalysts with low-cost and high catalytic performances to substitute of Pt-based catalysts, has received considerable attention.11 Heteroatoms (e.g. B,12 N,13 S14and P15) doping carbon materials have been considered as an effective way to tune the surface wettability and electronic conductivity of carbon materials. This is one of the ways to and thus can improve the electrocatalytic activity for ORR. Among them, nitrogen-doped carbon materials including carbon nanotubes,16 graphene,17 carbon nanospheres,18 and porous carbon19 have been used as the metal-free catalysts for the ORR, which exhibits reasonable electro-catalytic activity, and excellent long-term stability. The doping of nitrogen is provided the numbers of structural defects and adjust the charge distribution of carbon.20,

21

However, N-doped

carbon materials usually possess relatively limited electro-catalytic activity for ORR. Therefore, to solve the above problem, non-precious metal (Fe, Co, Ni, etc.) doped carbon materials have been widely studied because of their low-cost, high catalytic activity, and excellent electrical conductivity properties.22-24 Especially, Fe-N co-doped carbon materials have been used for ORR electrocatalysts with high catalytic performances.25 Li et al

26

reported a synthesis of Fe-N co-doped carbon nanolayers

wrapped around graphdiyne core-shell electrocatalyst (Fe-PANI@GD-900) for ORR by


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one-step pyrolysis of iron and polyaniline loaded onto graphdiyne nanocomposite at 900 °C, they studied that the electrochemical results exhibit high ORR activity and it has onset and half-wave potentials are 1.05 V and 0.82 V (vs. RHE) respectively. Wu et al 27 reported a series of high-performing oxygen reduction reaction (ORR) catalysts based on N/S-Me-doped (Me=Fe, Co, Ni) hierarchical porous carbons (N/S-Fe-HPC, N/S-Co-HPC and N/S-Ni-HPC), compared to N/S-Co-HPC and N/S-Ni-HPC the obtained N/S-Fe-HPC catalyst exhibit excellent ORR performance in both alkaline and acidic media. In recent years, ionic liquids (ILs) have attracted much attention due to their unique physical and chemical properties.28-31 ILs could be used as suitable precursors for carbon materials 32 because of their intrinsic negligible vapor pressure, which enables them to be applied for the carbonization process without evaporation. In especial, the structure of ILs can be designed. Different heteroatoms doped carbon materials have been successfully achieved via employing functionalized ILs, which have been used in many different fields.33, carbon

34

For example, Dai and co-workers

materials

using

cross-linkable

1-butyl-3-methaylimidazolium

35

have successfully prepared N-doped ILs

as

tricyanomethanide

precursors,

such

([BMIM][C(CN)3]

as and

1-ethyl-3-methyl-imidazolium tetracyanoborate ([EMIM][B(CN)4]). These N-doped materials show high adsorption capacity for CO2 adsorption and selectivity for CO2/N2 separation. Sun et al36 have synthesized Fe-N-doped ordered mesoporous carbon materials using the “task-specific” Fe-IL ([FcN][NTf2]) as metal-containing precursor, which exhibit outstanding ORR performance under alkaline media. In our previous work, honeycomb-like nitrogen-doped porous carbon materials have been prepared using the ionic liquid 1-butyl-3-methylimidazolium dicyanamide (BMIMdca) as a carbon precursor and silica spheres as a template, which was used as a carrier for Pt nanoparticles for methanol oxidation in an alkaline media.37 In this paper, we report the synthesis of novel Fe-N co-doped porous carbon materials

(Fe-N/C)

using

ILs

1-butyl-3-methylimidazolium

tetrachloridoferrate

([Bmim]FeCl4) as the sources of carbon, nitrogen and iron, and silica nanospheres as the hard template by one-step pyrolysis at different temperatures (from 600 to 900 °C). The



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synthesized Fe-N co-doped porous carbons show large BET surface areas, abundant nanoporosity, where Fe and N were homogeneously dispersed into the samples. In addition, the prepared porous Fe-N/C was used in ORR in alkaline media, which show excellent catalytic activities, good reusability and enhanced methanol tolerance in the ORR in comparison with Pt/C. This work develops a new way for preparation of multiple functional porous carbon materials, which show great important applications in the area of ORR.

2. Experimental 2.1. Chemicals and materials N-methylimidazole was purchased from Aladdin Chemical Co. Ltd. (Shanghai, China), chlorobutane and tetraethyl orthosilicate (TEOS) were purchased from Tianjin Kermel Chemical Co. Ltd. (Tianjin, China), ferric chloride was purchased from Sinopharm Chemical Co. Ltd, Nafion solution (5 wt.%) was purchased from DuPont (Wilmington, DE, USA), hydrofluoric acid, ammonium hydroxide, ethanol, and KOH were analytical grade and directly applied without any treatment. 2.2. Preparation of ILs [Bmim]FeCl4 The [Bmim]FeCl4 synthesis method is improved as follows:

38,

39

Firstly,

1-butyl-3-methylimidazolium chloride ([Bmim]Cl) was prepared by stirring of equimolar N-methylimidazole and chlorobutane at 70 °C in oil bath for 24 h. Water was removed in a vacuum oven at 60 °C. Then, an equimolar of FeCl3·6H2O was added to the above prepared

ILs

[Bmim]Cl.

After

stirring

the

mixtures

for

24

h,

1-butyl-3-methylimidazolium tetrachloridoferrate ([Bmim]FeCl4) were obtained. 2.3. Preparation of Fe-N doped porous carbon Fe-N co-doped porous carbons (Fe-N/C) were synthesized using ILs [Bmim]FeCl4 as the precursors and SiO2 spheres as the hard template. SiO2 spheres with a diameter of 300 nm were synthesized using the Stöber method.40 After that, 4.0 g of ILs


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[Bmim]FeCl4 and 1.5 g of SiO2 spheres were mixed with 50 mL of water by ultrasonic treatment for 30 min, and then stirred at room temperature for 12 h. After drying at 60 °C in the oven for 24 h, the products were carbonized by heating to 600, 700, 800, and 900 °C with a rate of 2 °C min-1 under nitrogen atmosphere for 4 h, respectively. The obtained black powders were treated with 10 wt.% HF solution to remove the silica template, and washed by deionized water for several times until the pH of the filtrate approached 7. After dried in vacuum at 80 °C for 12 h, the final products were obtained and denoted as Fe-N/CT with T being the pyrolysis temperature (Scheme 1).

Scheme 1. Schematics of the synthesis process of Fe-N/C catalysts. 2.4. Characterizations The scanning electron microcopy (SEM, JSM-7610F) and transmission electron microscopy (TEM, FEITecnaiG20) were used to observe the morphology of the electrocatalysts. N2 sorption analysis was conducted on a Quadrasorb SI (Quantachrome), equipped with an automated surface areas using the Brunauer–Emmett–Teller (BET) method. X-ray photoelectron spectroscopy (XPS) was performed on ThermoFisher Scientific Escalab 250Xi (UK) to elemental analysis. Raman spectra were collected on a Princeton MSL 532-50 spectrometer with λ=532 nm laser excitation. 2.5. Electrochemical measurement Electrochemical measurements were carried out using a CHI760D electrochemical workstation (CH Instruments, China) with a standard three-electrode cell. A rotating disk



electrode (RDE) modified with catalysts were used as a working electrode. A platinum wire was used as a counter electrode and saturated calomel electrode (SCE) as reference electrode. All potentials of electrodes were referenced to a reversible hydrogen electrode (RHE), ERHE=ESCE + 0.0591pH + 0.241 V. The working electrode was prepared as follows: 3.5 mg of Fe-N/C catalyst were ultrasonically mixed with 120 μL of isopropanol, 370 μL of deionized water and 10 μL of Nafion solution (5 wt.%, DuPont) for 30 min to obtain catalyst ink. Then, 6.5 μL of the catalyst ink was dropped onto the clear RDE (3 mm in diameter), and dried at room temperature. The catalyst loading was 0.64 mg cm-2 for as-prepared catalyst Fe-N/C. For comparison, the catalyst loading of commercial Pt/C (20 %, JM) has the same catalyst loading as Fe-N/C. SEM of Fe-N/C800 coated on the electrode seen in Figure S2. The cyclic voltammetry (CV) measurements were performed in O2 or N2-sarurated 0.1 M KOH solution with a scan rate of 50 mV s-1. Linear sweep voltammetry (LSV) were obtained in O2-sarurated 0.1 M KOH solution at the different electrode rotated with a scan rate of 10 mV s-1. The tolerance of Fe-N/C catalysts to methanol was tested by LSV in O2-sarurated 0.1 M KOH solution containing 1.0 M CH3OH. Durability testing were conducted by chronoamperometric technique at 0.66 V (vs. RHE) in O2-saturated 0.1 M KOH electrolyte with a rotation rate of 1600 rpm. The number of electron (n) transferred was estimated using the Koutecky–Levich (K-L) equation41: 1 1 1 = + 𝑗 𝑗𝑘 𝐵𝜔0.5 where j represents the measured current density, jk represents kinetic current densities, ω represents the angular velocity of the disk, and B could be determined from the slope of K-L plots based on the Levich equation as follows: B = 0.2nF(𝐷𝑂2)2/3𝑣 ―1/6𝐶𝑂2 where n is the number of electrons transferred per oxygen molecule, F is the Faraday constant (96500 C mol-1), 𝐷𝑂2is the diffusion coefficient of O2 in 0.1 M KOH, υ is the


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kinetic viscosity (0.01 cm2 s-1), and 𝐶𝑂2is the bulk concentration of O2 (1.2×10-6 mol cm-3). All the electrochemical experiments were carried out at room temperature.

3. Results and discussion 3.1. Physical properties of the Fe-N/C catalysts



Figure 1. SEM images of SiO2 spheres (a), Fe-N/C800 (b). TEM images of Fe-N/C800 (c). HRTEM image of Fe-N/C800 (d). Elemental mapping images of Fe-N/C800 (e) and corresponding elements of C, N, O and Fe (f). XRD patterns (g) and Raman spectra (h) of different Fe-N/CT samples.

Figure 1 (a-b) shows SEM of SiO2 spheres and series of Fe-N/C catalyst. The SEM images of Fe-N/C catalysts (Figure 1b and Figure S1) indicates that the Fe-N/C catalysts show honeycomb-like monolith morphology after removal of the silica template. As shown in Figure 1c, it can be seen that some black spots (marked by red circles) spread on the surface of the porous of Fe-N/C800, which maybe Fe nanoparticles. It can be seen from Figure 1d that significant lattice fringes are present, wherein the measured lattice spacing is 0.204 nm, which may be correspond to the (110) or (220) plane of Fe3C. The combination of iron and carbon provides an active site for the oxygen reduction reaction.42 Figure 1(e) shows the TEM image of Fe-N/C800 catalyst and Figure 1(f) shows the corresponding elemental mapping images of C, N, O and Fe elements on the surface of


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the Fe-N/C800 catalysts. It can be seen that the N and Fe elements are distributed in the hybrids uniformly, which indicates that N and Fe atoms are successfully introduced into the porous carbon material. Figure 1(g) shows the XRD patterns of different Fe-N/CT samples. From the XRD patterns, a distinct peak appeared at 26°, corresponding to the C(002). And as the temperature increases, the peak becomes more pronounced, which means that as the temperature increases, the crystallinity C may been increased. No obvious iron-corresponding signal was found in the XRD pattern,43, 44 which may be due to a low iron content or low crystallinity.45 However, the presence of iron in the sample can be seen from the elemental mapping (Figure 1f), the EDS spectra (Figure S3) and the HRTEM image (Figure 1d). Raman spectroscopy analysis was used to determine the degree of graphitization of various Fe-N/C catalysts prepared at 600, 700, 800 and 900 °C. The Raman spectra of Fe-N/C catalyst are shown in Figure 1 (h). As can be seen, the samples have two significant characteristic peaks. The D peak approximately at 1339 cm-1 corresponds the amorphous carbon, and G peak at 1589 cm-1 represents the graphitized carbon[46]. The ratio of D peak to G peak intensity is used as an important index for the degree of graphitization of carbon materials.47 The value of ID/IG decreased gradually with the increase of calcination temperature, indicating that the increase of calcination temperature favored the formation of graphitization.



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Figure 2. Nitrogen adsorption-desorption isotherms of the synthesized catalysts (a), XPS spectra for the Fe-N/CT (b), the N 1s spectra of Fe-N/C800(c), the Fe 2p spectra of Fe-N/C800(d). Table 1 Characterization results of the different Fe-N/C catalysts samples

N/wt.% b

O/wt.% b

Fe/wt.% b

Fe/wt.% c

67.36

17.32

11.56

3.76

3.45

4.2

63.14

12.26

7.11

11.11

5.39

0.75

5.5

71.66

7.11

12.86

8.37

5.26

0.75

7.1

78.44

3.67

9.48

8.41

4.77

surface areas

pore volume

pore size

C/wt.%

(cm2 g-1) a

(cm3 g-1) a

(nm) a

b

Fe-N/C600

568

0.17

5.0

Fe-N/C700

790

0.22

Fe-N/C800

930

Fe-N/C900

494

a

from N2 adsorption-desorption isotherms; b from XPS results; c from ICP results.

BET analysis was conducted by using nitrogen adsorption-desorption isotherms at 77 K, as shown in Figure 2a. The adsorption isotherm of Fe-N/C catalysts have obvious hysteresis loops exhibit a behavior of hole structure caused by stacking of flake particles. The corresponding BET surface areas, pore volume, and pore size of the Fe-N/C catalysts were illustrated in the Table 1. The results indicate that Fe-N/C800 catalyst has a high BET surface area of 930 m2 g−1 with pore volume of 1.2 cm3 g−1 and pore size of 5.5 nm. The pore size distribution, calculated using the Barrett-Joyner-Halenda (BJH) method, was shown in Figure S4. Two distinct peaks are at about 4 nm and 30 nm, indicating the existence of mesopores. The corresponding BET surface areas, pore volume, and pore size of the Fe-N/C catalysts were illustrated in the Table 1. The results indicate that


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Fe-N/C800 catalyst has a high BET surface area of 930 m2 g−1 with pore volume of 1.2 cm3 g−1 and pore size of 5.5 nm. The largest specific surface area of Fe-N/C800 may be attributed to the increase of the escaped component in the material with increasing temperature (600~800 °C). However, when the temperature was further increased to 900 °C, the BET specific surface area is reduced dramatically because of the collapse of pores and the enhanced orientation in the graphitizing process.45, 48, 49 Large BET surface area and abundant porosity strongly promote the accessibility of Fe-N active sites to various guest molecules. Inductively coupled plasma spectrometer (ICP) was used to detect the metal content in the samples. The iron content of the samples calcined under different temperature were shown in Table 1. From the Table 1, the iron content of was 3.45% (Fe-N/C600), 5.39% (Fe-N/C700), 5.26% (Fe-N/C800), and 4.77% (Fe-N/C900), respectively. X-ray photoelectron spectroscopy (XPS) measurement was used to illustrate the chemical state of the elements and content in the samples. The element compositions of catalysts are identified from the full survey scan XPS spectra. From Figure 3b, all the samples show dominant narrow C1s peaks at 284.6 eV, O1s peaks at 531.4 eV, N1s peaks at 399.7 eV, and Fe 2p peaks at 711.3 eV. It indicates that C, O, N, and Fe elements are presents on the surface of the films. The element compositions of samples are shown in Table 1. It can be seen that as the temperature increases, the nitrogen content in the sample becomes lower gradually, which is due to that the increase of temperature makes the surface of the material unbonded nitrogen elements to escape. At higher pyrolysis temperature (e.g. 900 °C), the N content is only 3.67 wt.%. The N 1s spectra of Fe-N/C800 reveal the presence of four peaks at 398.4, 399.2, 400.8, and 402.9 eV, corresponding pyridinic-N, pyrrolic-N, graphitic-N, and oxidized nitrogen,50 respectively (Figure 2c). In addition, it is possible to contain a peak of Fe-N at around 398.4 eV because the binding energy of pyridinic-N and Fe-N is extremely similar.51, 52 Some researchers believe that in addition to oxidized nitrogen, other types of N1s can play an important role in promoting the catalytic performance of ORR.53 The Fe 2p



spectrum of Fe-N/C800 (Figure 2d) shows five peaks at 711.5, 713.5, 717.3, 724.7, and 733.7 eV. Among them, the peak at 717.3 eV is a satellite peak, the peaks at 711.5 and 713.5 eV can be ascribed to the binding energies of the 2p3/2 orbits of Fe2+ and Fe3+, the peaks at 724.7 and 733.7 eV can be ascribed to the binding energies of the 2p1/2 orbits of Fe2+ and Fe3+, respectively.54 According to the literature, 2P3/2 of Fe at 711.5 eV belongs to the binding energy of nitrogen and iron.42,

55

The N1s and Fe 2p peaks of others

Fe-N/C catalyst shown in Figure S5. From the above analysis pattern, nitrogen and iron successfully combined and providing active sites for the catalytic ORR process.56 3.2. Electrochemical property of the synthesized Fe-N/C catalysts


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Figure 3. CV curves of Fe-N/CT in O2-saturated (solid line) and N2-saturated (dash line) 0.1 M KOH solution (a), LSV curves of Fe-N/CT and Pt/C in O2-saturated 0.1 M KOH solution at 1600 rpm (b), LSV curves of Fe-N/C800 in O2 saturated 0.1 M KOH solution at various rotation speeds (c), K-L plots derived from the RDE measurement for Fe-N/C800 with different rotation rates at different potential and transferred electron number (insert) (d), Tafel plots for Fe-N/CT and Pt/C (e).

Table 2 Electrochemical parameters of the ORR on different catalysts Samples

Eonset (V vs.RHE)

E1/2 (V vs.RHE)

Reference

Fe-N/C600

0.805

0.630

this work

Fe-N/C700

0.912

0.799

this work

Fe-N/C800

0.964

0.821

this work

Fe-N/C900

0.905

0.815

this work

Pt/C

0.986

0.824

JM

Fe-N-PPC

0.966

---

[50]

Fe-N/C

0.910

---

45

N-P-Fe/C

0.957

---

57

FexP/NPCS

0.918

---

58

The electrocatalytic ORR activity of Fe-N/C were firstly examined by CV in N2saturated and O2-saturated 0.1 M KOH solutions at a scan rate of 50 mV s-1. As shown in



Figure 3a, in the N2-saturated electrolyte, the CV curves of Fe-N/C are quasi-rectangular without an obvious cathodic peak. When the electrolyte was saturated with O2, the obvious oxygen reduction peak appeared at 0.558 V (Fe-N/C600), 0.757 V (Fe-N/C700), 0.764 V (Fe-N/C800), and 0.677 V (Fe-N/C900), respectively. The results suggest that Fe-N/C catalysts have excellent catalytic activities for the ORR. Further to compare the activities of these catalysts and commercial Pt/C for ORR, linear sweep voltammetry (LSV) measurements were conducted at 1600 rpm (Figure 3b) and the electrochemical parameters associated with the ORR were all presented in Table 2. It can be observed that among this series of Fe-N/CT catalysts, the ORR activity of the Fe-N/C800 catalyst is preferable, the onset (Eonset) and the half-wave (E1/2) potentials reach about 0.964 and 0.821 V, respectively, more positive than those on the other Fe-N/C catalysts. The Eonset and E1/2 potentials of the Fe-N/C800 catalyst shifts negatively about 22 mV and 3 mV than that of the Pt/C, respectively, and the maximum limiting current density of Fe-N/C800 (7.18 mA/cm2) is higher than that of Pt/C (5.8 mA/cm2). The catalyst has a high oxygen reduction catalytic property which may be caused by Fe3C in the material. It has been proved that Fe3C is an effective component for catalyzing the oxygen reduction reaction.42 In addition, the LSV curves were also normalized to the BET specific surface area, as shown in Figure S6. It can be seen that the Eonset of all catalysts is consistent with the calculated results based on the geometrical area (Figure 3b). However, Fe-N/C900 exhibits the highest limiting current density normalized to the BET specific surface area due to its BET specific surface area is much smaller than Fe-N/C800. The ORR performance of the Fe-N/C800 catalyst, and LSV measurements were conducted at different rotating speeds from 400 to 2500 rpm (Figure 3c). With the increase in rotating speed, the limiting current density of the Fe-N/C800 catalyst increases owing to the fast diffusion rate. Koutecky-Levich (K-L) equation was used to calculate the electron-transfer numbers of the catalysts. As shown in Figure 3d, the linear K-L plots of the Fe-N/C800 catalyst shows the first-order reaction kinetics toward O2 from 0.40 to


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0.70 V. The number of electrons transferred (n) was calculated by the slopes of their linear fit lines (insert). The number of electrons transferred (n) was calculated to be 3.78-3.89 at a potential range from 0.4 to 0.7 V, suggesting that the Fe-N/C800 catalyst shows a mainly four-electron transfer pathway for the ORR. The electron transfer kinetics of the catalyst can be further studied by the Tafel plots. As can be seen from Figure 3e, the Tafel slope values for ORR were calculated to be 58 mV dec−1 (Fe-N/C900), 47 mV dec−1(Fe-N/C800), 71 mV dec−1(Fe-N/C700), 107 mV dec−1(Fe-N/C700), and 56 mV dec−1 (Pt/C), respectively, indicating the most favorable kinetics of Fe-N/C800 catalyst during ORR in alkaline media.49 3.3. Stability and methanol resistance of the Fe-N/C Besides catalytic activity, the methanol tolerance and long-term stability of catalysts are also important factors for practical applications in fuel cell, especially for direct methanol fuel cells. The tolerance to methanol poisoning effects of Fe-N/C800 and Pt/C catalysts were investigated by using the LSV measurements in O2-saturated 0.1 M KOH solution with 1 M methanol at the rotation speed of 1600 rpm. As shown in Figure 4a, it can be clearly seen that the influence of methanol addition into the electrolyte on the LSV curves of Fe-N/C800 and Pt/C catalysts under identical experimental conditions. When the methanol was added into the electrolyte, there is no activity specific to methanol on the Fe-N/C800 catalyst. In contrast, for Pt/C catalyst, the methanol oxidation peak was observed obviously.59 All these phenomena indicate that Fe-N/C800 catalyst possesses fairly better tolerance to methanol crossover than Pt/C. The stability of catalyst was tested by using the current-time chronoamperometric measurement at 0.66 V in O2-saturated 0.1M KOH solution for 7000 s. As shown in Figure 4b, about 90.19 % of the original current density was remained for Fe-N/C800 catalyst, while the commercial Pt/C catalyst exhibited a much higher current loss of 24.36 %. The results suggest that the Fe-N/C800 has significantly better stability than commercial 20 wt.% Pt/C catalyst. After the chronoamperometric measurement for 7000 s, the Fe-N/C800 was collected and conducted the XPS test again. The results were shown in Figure 4(c, d), it can be observed that the chemical state of the catalyst did not obvious change after the reaction compared with before (Figure 2c and 2d), indicating that the Fe-N/C catalysts not only have high electrochemical stability but also high chemical stability. The preparation of Fe-N/C



opens a new way for transformation of green ionic liquids into functional porous carbons, which shows excellent catalytic activities in the ORR.

Figure 4. LSV curves of Fe-N/C800 and Pt/C catalysts in O2-saturated 0.1 M KOH solution with or without 1 M methanol (a), Chronoamperometric curves of the Fe-N/C800 and Pt/C catalysts at 0.66 V in O2 saturated 0.1 M KOH solution with the rotation speed of 1600 rpm, insert is the local magnification of the curves (b), the N 1s spectra (c) and Fe 2p spectra (d) of Fe-N/C800 after 7000s.

4. Conclusions In summary, novel hierarchical porous Fe-N co-doped carbon (Fe-N/C) with honeycomb-like structures has been successfully prepared by one-step pyrolysis. The electrochemical measurements reveal that the alkaline media used in an RDE system to prove the efficiency, stability and tolerance of the Fe-N/C catalysts as compared to commercial Pt/C catalyst. The as-prepared Fe-N/C800 possesses excellent ORR catalytic


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activity. Its onset potential and half-wave potential are 0.964 V and 0.821 V, respectively, which is close to the commercial Pt/C catalyst. The porous Fe-N/C800 shows a four-electron transfer pathway and its electron transfer number is 3.78-3.89 from 0.40 to 0.70 V. Moreover, the Fe-N/C800 catalyst exhibits remarkable methanol tolerance and enhanced catalytic stability for ORR than that of Pt/C. The improvement in ORR performance of Fe-N/C800 catalyst is attributed to its porous structure, large BET surface area, and successful doping of Fe, N atoms. The results indicate that the Fe-N/C800 catalyst is a promising electro-catalytic candidate for the ORR with much enhanced catalytic performance. ASSOCIATED CONTENT Supporting Information SEM of Fe-N/C; SEM images of Fe-N/C800 coated on the electrode; EDS spectra of Fe-N/C800; Pore size distribution curve of Fe-N/C600 (a), Fe-N/C600 (b), Fe-N/C600 (c), Fe-N/C600 (d); the N 1s spectra of Fe-N/C600, Fe-N/C700, and Fe-N/C900; the Fe 2p spectra of Fe-N/C600, Fe-N/C700, and Fe-N/C900 ; LSV curves of Fe-N/CT.

AUTHOR INFORMATION Corresponding Authors. *Y.

Liu. E-mail: [email protected].

*F.

Liu. E-mail: [email protected]

Notes The authors declare no competing financial interest.

Acknowlegements This work was supported by the National Natural Science Foundations of China (No. 21676072,

21573150),

the

Natural

Science

Foundation

of

Henan

Province

(182300410244), and Foundation for University Youth Key Teachers from Henan



Province (No. 2017GGJS018). References

(1) Zeng, D. G.; Huang, J. L.; Lin, Z. P.; Yu, X.; Zhan, Y. F.; Xie, F. Y.; Zhang, W. H.; Chen, J.; Meng, H. Non-noble metal catalyst on carbon ribbon for fuel cell cathode. J. Solid State Electr. 2017, 22, 761-771. (2) Majlan, E.H.; Rohendi, D.; Daud, W. R. W.; Husaini, T.; Haque, M. A. Electrode for proton exchange membrane fuel cells: A review. Renew. Sust. Energ. Rev. 2018, 89, 117-134. (3) Liu, Y.; Li, S. S.; Zhang, Y. M.; Liu, W.H.; Wang, J. H.; Zhai, C. P. Electrocatalytic oxidation of methanol on Pt-Pd nanoparticles supported on honeycomb-like porous carbons in alkaline media. J. Solid State Electrochem. 2017, 22, 817-824. (4) Katsounaros, I.; Cherevko, S.; Zeradjanin, A. R.; Mayrhofer, K. J. Oxygen electrochemistry as a cornerstone for sustainable energy conversion. Angew. Chem. Int. Ed. 2014, 53, 102-121. (5) Song, A.; Cao, L.; Yang, W.; Li, Y.; Qin, X.; Shao, G. Uniform Multilayer Graphene-Coated Iron and Iron-Carbide as Oxygen Reduction Catalyst. ACS Sustainable Chem. Eng. 2018, 6, 4890-4898. (6) Tang, F.; Lei, H.; Wang, S.; Wang, H.; Jin, Z. A novel Fe-N-C catalyst for efficient oxygen reduction reaction based on polydopamine nanotubes. Nanoscale 2017, 9, 17364-17370. (7) Zhang, X.; Huang, Y.; Chen, X.; Gao, Q.; Zhang, W. Nitrogen-doped carbon nanotubes based on melamine-formaldehyde resin as highly efficient catalyst for oxygen reduction reaction. J. Colloid Interface Sci. 2018, 509, 1-9. (8) Niu, Q. J.; Guo, J. X.; Tang, Y. H.; Guo, X. D.; Nie, J.; Ma, G. P. Sandwich-type Bimetal-Organic Frameworks/Graphene Oxide Derived Porous Nanosheets doped Fe/Co-N Active Sites for Oxygen Reduction Reaction. Electrochim. Acta 2017, 255,


Page 18 of 26

Page 19 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


72-82. (9) An, L.; Jiang, N.; Li, B.; Hua, S. X.; Fu, Y. T.; Liu, J. X.; Hao, W.; Xia, D. G.; Sun, Z. C. A highly active and durable iron/cobalt alloy catalyst encapsulated in N-doped graphitic carbon nanotubes for oxygen reduction reaction by a nanofibrous dicyandiamide template. J. Mater. Chem. A 2018, 6, 5962-5970. (10)Xuan, C. J.; Wu, Z. X.; Lei, W.; Wang, J.; Guo, J. P.; Wang, D. L. Nitrogen-Doped Hierarchical Porous Carbons Derived from Sodium Alginate as Efficient Oxygen Reduction Reaction Electrocatalysts. ChemCatChem 2017, 9, 809-815. (11)Shao, M. H.; Chang, Q. W.; Dodelet, J. P.; Chenitz, R. Recent Advances in Electrocatalysts for Oxygen Reduction Reaction. Chem. Rev. 2016, 116, 3594-657. (12)Lei, Z. L.; Chen, H.; Yang, M.; Yang, D. G.; Li, H. M. Boron and oxygen-codoped porous carbon as efficient oxygen reduction catalysts. Appl. Surf. Sci. 2017, 426, 294-300. (13)Zhao, Q. P.; Ma, Q.; Pan, F. P.; Wang, Z. M.; Yang, B. P.; Zhang, J. Q.; Zhang, J. Y. Facile synthesis of nitrogen-doped carbon nanosheets as metal-free catalyst with excellent oxygen reduction performance in alkaline and acidic media. J. Solid State Electrochem. 2016, 20, 1469-1479. (14)Zhang, C.; An, B.; Yang, L.; Wu, B. B.; Shi, W.; Wang, Y. C.; Long, L. S.; Wang, C.; Lin, W. B. Sulfur-doping achieves efficient oxygen reduction in pyrolyzed zeolitic imidazolate frameworks. J. Mater. Chem. A 2016, 4, 4457-4463. (15)Yu, Y. N.; Wang, M. Q.; Bao, S. J. Biomass-derived synthesis of nitrogen and phosphorus Co-doped mesoporous carbon spheres as catalysts for oxygen reduction reaction. J. Solid State Electrochem. 2016, 21, 103-110. (16)Zhang, C.; Wang, Y. C.; An, B.; Huang, R. Y.; Wang, C.; Zhou, Z. Y.; Lin, W. B. Networking Pyrolyzed Zeolitic Imidazolate Frameworks by Carbon Nanotubes Improves

Conductivity

and

Enhances

Oxygen-Reduction

Performance

Polymer-Electrolyte-Membrane Fuel Cells. Adv. Mater. 2017, 29, 1604556.


in


(17)Kong, D.; Yuan, W. J.; Li, C.; Song, J. M.; Xie, A. J.; Shen, Y. H. Synergistic effect of Nitrogen-doped hierarchical porous carbon/graphene with enhanced catalytic performance for oxygen reduction reaction. Appl. Surf. Sci. 2017, 393, 144-150. (18)Zhou, T. S.; Zhou, Y.; Ma, R. G.; Zhou, Z. Z.; Liu, G. H.; Liu, Q.; Zhu, Y.; Wang, J. C. In situ formation of nitrogen-doped carbon nanoparticles on hollow carbon spheres as efficient oxygen reduction electrocatalysts. Nanoscale 2016, 8, 18134-18142. (19)Song, L.; Wang, T.; Ma, Y.; Xue, H. R.; Guo, H.; Fan, X. L.; Xia, W.; Gong, H.; He, J. Functional Species Encapsulated in Nitrogen-Doped Porous Carbon as a Highly Efficient Catalyst for the Oxygen Reduction Reaction. Chem.-Eur. J. 2017, 23, 3398-3405. (20)Jiao, Y.; Zheng, Y.; Jaroniec, M.; Qiao, S. Z. Origin of the electrocatalytic oxygen reduction activity of graphene-based catalysts: a roadmap to achieve the best performance. J. Am. Chem. Soc 2014, 136, 4394-403. (21)Zhang, P.; Zhao, Y.; Zhang, X. B. Functional and stability orientation synthesis of materials and structures in aprotic Li–O2 batteries. Chem. Soc. Rev. 2018, 47, 2921-3004. (22)Li, Q. R.; Wan, G.; Zhao, H.; Pan, L.Y.; Wang, N. ; Zhao, W. P.; Zhou, X. X.; Cui, X. Z.; Chen, H. Nitrogen-Doped Carbon Vesicles with Dual Iron-Based Sites for Efficient Oxygen Reduction. ChemSusChem 2017, 10, 499-505. (23)Zhang, X. L.; Lin, J. J.; Chen, S. M.; Yang, J.; Song, L.; Wu, X. J.; Xu, H. X. Co Nanoparticles Encapsulated in N-Doped Carbon Nanosheets: Enhancing Oxygen Reduction Catalysis without Metal–Nitrogen Bonding. ACS Appl. Mat. Interfaces 2017, 9, 38499-38506. (24)N.S. S.; Goubert-Renaudin; Wieckowski, A. Ni and / or Co nanoparticles as catalysts for oxygen reduction reaction (ORR) at room temperature. J. Electroanal. Chem. 2011, 652, 44-51.


Page 20 of 26

Page 21 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(25)Shi, X. X.; Zhang, J. N.; Huang, T. L. The key roles of trace iron for nitrogen, sulfur dual-doped carbon nanospheres as high efficient oxygen reduction catalyst. J. Mater. Sci. 2017, 53, 1404-1413. (26)Li, Y. R. Guo, C. Z.; Li, J. Q. Liao, W. L.; Li, Z. B.; Zhang, J.; Chen, C. G. Pyrolysis-induced synthesis of iron and nitrogen-containing carbon nanolayers modified graphdiyne nanostructure as a promising core-shell electrocatalyst for oxygen reduction reaction. Carbon 2017, 119, 201-210. (27)Wu, M. J.; Zhang, E. G.; Guo, Q. P.; Wang, Y. Z.; Qiao, J. L.; Li, K. X.; Pei, P. C. N/S-Me (Fe, Co, Ni) doped hierarchical porous carbons for fuel cell oxygen reduction reaction with high catalytic activity and long-term stability. Appl. Energy 2016, 175, 468-478. (28)M. Watanabe; Thomas, M. L.; Zhang, S. G.; Ueno, K.; Yasuda, T.; Dokko, K. Application of Ionic Liquids to Energy Storage and Conversion Materials and Devices. Chem. Rev. 2017, 117, 7190-7239. (29)Amarasekara, A. S. Acidic Ionic Liquids. Chem. Rev. 2016, 116, 6133-6183. (30)Su, H. ; Zhang, H. T.; Liu, F. Y.; Chun, F. J.; Zhang, B. B.; Chu, X.; Huang, H. C.; Deng, W. L.; Gu, B. N.; Zhang, H. P.; Zheng, X. T.; Zhu, M. H.; Yang, W. Q. High power supercapacitors based on hierarchically porous sheet-like nanocarbons with ionic liquid electrolytes. Chem. Eng. J. 2017, 322, 73-81. (31)Zhang, Z. R.; Song, J. L.; Han, B. X. Catalytic Transformation of Lignocellulose into Chemicals and Fuel Products in Ionic Liquids. Chem. Rev. 2017, 117, 6834-6880. (32)Paraknowitsch, J. P.; Zhang, J.; Su, D. S.; Thomas, A.; Antonietti, M. Ionic liquids as precursors for nitrogen-doped graphitic carbon. Adv. Mater. 2010, 22, 87-92. (33)Gao, J.; Ma, N.; Zheng, Y. M.; Zhang, J. F.; Gui, J. Z.; Guo, C. K.; An, H. Q.; Tan, X. Y.; Yin, Z.; Ma, D. Cobalt/Nitrogen-Doped Porous Carbon Nanosheets Derived from Polymerizable Ionic Liquids as Bifunctional Electrocatalyst for Oxygen Evolution and Oxygen Reduction Reaction. ChemCatChem 2017, 9, 1601-1609.



Page 22 of 26

(34)Gao, J.; Ma, N.; Zhai, J. F.; Li, T. Y.; Qin, W.; Zhang, T. T.; Yin, Z. Polymerizable Ionic Liquid as Nitrogen-Doping Precursor for Co–N–C Catalyst with Enhanced Oxygen Reduction Activity. Ind. Eng. Chem. Res. 2015, 54, 7984-7989. (35)Fulvio, P. F.; Lee, J. S.; Mayes, R. T.; Wang, X. Q.; Mahurin, S. M.; Dai, S. Boron and nitrogen-rich carbons from ionic liquid precursors with tailorable surface properties. Phys. Chem. Chem. Phys. 2011, 13, 13486-13491. (36)Li, Z. L.; Li, G. L.; Jiang, L. H.; Li, J. L.; Sun, G. Q.; Xia, C. G.; Li,

F. W. Ionic

liquids as precursors for efficient mesoporous iron-nitrogen-doped oxygen reduction electrocatalysts. Angew Chem. Int. Ed. Engl. 2015, 54, 1494-1498. (37)Liu, Y.; Zhang, Y. M.; Zhai, C. P.; Li, X. Y.; Mao, L. Q. Nitrogen-doped porous carbons supported Pt nanoparticles for methanol oxidation in alkaline medium. Mater. Lett. 2016, 166, 16-18. (38)Hayashi, S.; Hamaguchi, H.-o. Discovery of a Magnetic Ionic Liquid [bmim]FeCl4. Chem. Lett. 2004, 33, 1590-1591. (39)Xie, Z. L.; Taubert, A. Thermomorphic Behavior of the Ionic Liquids [C4mim][FeCl4] and [C12mim][FeCl4]. Chemphyschem 2011, 12, 364-368. (40)Stöber, W.; Fink, A.; Bohn, E. Controlled growth of monodisperse silica spheres in the micron size range. J. Colloid Interf. Sci. 1968, 26, 62-69. (41)Wang, S. Y.; Yu, D. S.; Dai, L. M. Polyelectrolyte functionalized carbon nanotubes as efficient metal-free electrocatalysts for oxygen reduction. J. Am. Chem. Soc. 2011, 133, 5182-5185. (42)Wang, C. X.; Yang, F.; Qiu, T.; Cao, Y.; Zhong, H. L.; Yu,C. C.; Li, R. J.; Mao, L. Q.; Li, Y. F. Preparation of an efficient Fe/N/C electrocatalyst and its application for oxygen reduction reaction in alkaline media. J. Electroanal. Chem. 2018, 810, 62-68. (43)Zhang, X. L.; Lin, J. J.; Chen, S. M.; Yang, J. ; Song, L.; Wu, X. J.; Xu, H. X. Co Nanoparticles Encapsulated in N-Doped Carbon Nanosheets: Enhancing Oxygen Reduction Catalysis without Metal-Nitrogen Bonding. ACS Appl. Mater. Interfaces


Page 23 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2017, 9, 38499-38506. (44)Wang, Y. Y.; Xie, C.; Liu, D. D.; Huang, X. B.; Huo, J.; Wang, S. Y. Nanoparticle-Stacked Porous Nickel-Iron Nitride Nanosheet: A Highly Efficient Bifunctional Electrocatalyst for Overall Water Splitting. ACS Appl. Mater. Interfaces 2017, 8, 18652-7. (45)Liu, Y. Y.; Ruan, J. M.; Sang, S. B.; Zhou, Z. C.; Wu, Q. M.; Iron and nitrogen co-doped carbon derived from soybeans as efficient electro-catalysts for the oxygen reduction reaction. Electrochim. Acta 2016, 215, 388-397. (46)Ferrari, A. C. Raman spectroscopy of graphene and graphite: Disorder, electron–phonon coupling, doping and nonadiabatic effects. Solid State Commun. 2007, 143, 47-57. (47)Huang, H.; Wei, X. J.; Gao, S. Y. Nitrogen-Doped Porous Carbon Derived from Malachium Aquaticum Biomass as a Highly Efficient Electrocatalyst for Oxygen Reduction Reaction. Electrochim. Acta 2016, 220, 427-435. (48)Zhu, H.; Wang, X. L.; Liu, X. X.; Yang, X. R. Integrated Synthesis of Poly(o-phenylenediamine)-Derived

Carbon

Materials

for

High

Performance

Supercapacitors. Adv. Mater. 2012, 24, 6524-6529. (49)Liu, X. J.; Zhou, Y. C.; Zhou, W. J.; Li, L. G.; Huang, S. B.; Chen, S. W. Biomass-derived nitrogen self-doped porous carbon as effective metal-free catalysts for oxygen reduction reaction. Nanoscale 2015, 7, 6136-6142. (50)Wang, Y. Q.; Zhu, M. Y.; Wang, G.; Dai, B.; Yu, F.; Tian, Z.; Guo, X. H. Enhanced Oxygen Reduction Reaction by In Situ Anchoring Fe(2)N Nanoparticles on Nitrogen-Doped Pomelo Peel-Derived Carbon. Nanomaterials-Basel 2017, 7, 404. (51)Zang, Y. P.; Zhang, H. M.; Zhang, X.; Liu, R. R.; Liu, S. W.; Wang, G. W.; Zhang, Y. X.; Zhao, H. J. Fe/Fe2O3 nanoparticles anchored on Fe-N-doped carbon nanosheets as bifunctional oxygen electrocatalysts for rechargeable zinc-air batteries. Nano Research 2016, 9, 2123-2137.



(52)Li, J. C.; Hou, P. X.; Shi, C.; Zhao, S. Y.; Tang, D. M.; Cheng, M.; Liu, C.; Cheng, H. M. Hierarchically porous Fe-N-doped carbon nanotubes as efficient electrocatalyst for oxygen reduction. Carbon 2016, 109,

632-639.

(53)Wu, Z. Y.; Xu, X. X.; Hu, B. C.; Liang, H. W.; Lin, Y.; Chen, L. F.; Yu, S. H. Iron Carbide Nanoparticles Encapsulated in Mesoporous Fe-N-Doped Carbon Nanofibers for Efficient Electrocatalysis. Angew. Chem. Int. Edit. 2015, 54, 8179-8183. (54)Zhang, X.; Liu, R. R.; Zang, Y. P.; Liu, G. Q.; Liu, S. W.; Wang, G. Z.; Zhang, Y. X.; Zhang, H. M.; Zhao, H. J. Shrimp-shell derived carbon nanodots as precursors to fabricate Fe,N-doped porous graphitic carbon electrocatalysts for efficient oxygen reduction in zinc–air batteries. Inorg. Chem. Front. 2016, 3, 910-918. (55)Jiao, L.; Wan, G.; Zhang, R.; Zhou, H.; Yu, S. H.; Jiang, H. L. From Metal-Organic Frameworks to Single-Atom Fe Implanted N-doped Porous Carbons: Efficient Oxygen Reduction in Both Alkaline and Acidic Media. Angew. Chem. Int. Edit. Ed. Engl. 2018, 57, 8525-8529. (56)Chung, H. T.; Cullen, D. A.; Higgins, D.; Sneed, B. T.; Holby, E. F.; More, K. L.; Zelenay, P. Direct atomic-level insight into the active sites of a high-performance PGM-free ORR catalyst. Science 2017, 357, 479-484. (57)Wan, W.; Wang, Q.; Zhang, L.; Liang, H. W.; Chen, P.; Yu, S. H. N-, P- and Fe-tridoped nanoporous carbon derived from plant biomass: an excellent oxygen reduction electrocatalyst for zinc–air batteries. J. Mater. Chem. A 2016, 4, 8602-8609. (58)Hu, K.; Xiao, Z. H.; Cheng, Y.; Yan, D. F.; Chen, R.; Huo, J.; Wang, S. Y. Iron phosphide/N, P-doped carbon nanosheets as highly efficient electrocatalysts for oxygen reduction reaction over the whole pH range. Electrochim. Acta 2017, 254, 280-286. (59)Qu, K. G.; Zheng, Y.; Dai, S.; Qiao, S. Z. Graphene oxide-polydopamine derived N, S-codoped carbon nanosheets as superior bifunctional electrocatalysts for oxygen


Page 24 of 26

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reduction and evolution. Nano Energy 2016, 19, 373-381.



TABLE OF CONTENTS


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Fe-N Co-doped Porous Carbon Derived from Ionic Liquids as Efficient

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