Three-Dimensional Biocarbon Framework Coupled with Uniformly

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Energy, Environmental, and Catalysis Applications

Three Dimensional Biocarbon Framework Coupled with Uniform Distributed FeSe Nanoparticles Derived from Pollen as Bifunctional Electrocatalysts for Oxygen Electrode Reactions Guanghua Wang, Jing Li, Mingrui Liu, Li Du, and Shijun Liao ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b10373 • Publication Date (Web): 04 Sep 2018 Downloaded from http://pubs.acs.org on September 5, 2018

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ACS Applied Materials & Interfaces

Three Dimensional Biocarbon Framework Coupled with Uniform Distributed FeSe Nanoparticles Derived from Pollen as Bifunctional Electrocatalysts for Oxygen Electrode Reactions

Guanghua Wang, Jing Li, Mingrui Liu, Li Du, Shijun Liao* The Key Laboratory of Fuel Cell Technology of Guangdong Province, School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou, China

Abstract The development of carbon-based catalysts with satisfactory performance for oxygen reduction and evolution reactions (ORR and OER) is critical but challenging to achieve sustainable energy conversion and storage. Herein, a pollen biomass-derived carbon electrocatalyst with a three-dimensional porous framework, coupled with uniform distribution of FeSe nanoparticles has been prepared by pyrolysis of the pollen precursor, followed by selenylation. The optimal catalyst FeSe/NC-PoFeSe exhibits superb ORR activity with a half-wave potential of 0.86 V vs. reversible hydrogen electrode (RHE) and OER activity with a low overpotential (330 mV at 10 mA cm–2) in alkaline media, compared with commercial Pt/C and IrO2/C catalysts, respectively. Based on the characterization results, we ascribe the enhanced ORR performance to sufficient Fe−Nx, pyridinic N, and graphitic N, and the excellent OER performance to the presence of FeSe nanoparticles uniformly mounted on the N-doped carbon materials. In addition, we believe that the coupling effect between the FeSe nanoparticles and biocarbon led to further improvement in *

Corresponding author. Fax: +86 20 8711 3586. E-mail address: [email protected]

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electrochemical performance. Significantly, the prominent ORR and OER stability of FeSe/NC-PoFeSe shows great promise in renewable energy devices.

Keywords: biomass; transition metal selenides; heteroatom-doped carbon; coupling effect; oxygen reduction reaction; oxygen evolution reaction


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Introduction The heteroatom (e.g., N, S, P, and B) doped nanocarbon materials (HCMs) have attracted extensive attention as effective non-noble metal catalysts for the ORR and/or OER in energy conversion and storage systems, owing to their attractive electrocatalytic performance, cheap, and environmental friendliness.1-2 Incorporating transition metals (Fe and/or Co) into HCMs is a proven strategy to improve their ORR and/or OER activity.2-3 Although some progress has been made in developing HCMs for the ORR and/or OER,4-5 challenges remain: (i) Most HCMs show good ORR performance with excellent conductivity but poor OER activity and stability due to the carbon oxidation/corrosion at high potential species.4 (ii) The controllable fabrication of HCMs with a rational porosity and a uniformly distributed catalytic active sites are seldom achieved simultaneously.6 (iii) The roles of N species (pyridinic N, graphitic N, Fe−Nx or Co−Nx), and metallic nanoparticles in the formation of ORR and/or OER active centers in HCMs are still a controversial issue.5-7 Therefore, further boosting the ORR and OER electrocatalytic activity, optimizing the porous structure, and exploring the origin of catalytic activity for HCMs in ORR and/or OER is highly necessary. Recently, transition metal selenides nanoparticles (e.g., NiSe, CoSe2, and FeSe2) have been exploited for OER.8 Iron selenides, in particular, show outstanding OER activity and durability due to the metal species’ intrinsic activity toward the OER.9-10 However, transition metal-based catalysts are generally deposited or supported on conducting substrates (Ni foam, Ti plate, carbon cloth, etc.) due to their poor electrical



conductivity.11-13 Thus, combining the high OER activity of transition metal selenides with the good electrical conductivity and solid ORR performance of HCMs is quite a promising idea for bifunctional ORR/OER catalysis.14-15 However, the majority of transition metal nanoparticles are generally prone to aggregation and detachment from the carbon supports during the synthetic and reaction process, resulting in the nonuniform distribution of transition metal nanoparticles in the HCMs and a serious performance degradation.16-17 One effective solution is to encapsulate these active nanoparticles into carbon layers.18 The other is to anchor these active nanoparticles on the carbon matrix.19 More importantly, the synergistic effect between HCMs and transition metal nanoparticles can markedly improve the ORR and OER performance of the transition metal/HCMs hybrids.2 As is well known, biomasses contain rich organic compounds including C, N, S, and P, which are considered as ideal precursors for the green synthesis of HCMs.20-21 Also, biomasses possess numerous micro-nanostructure as well as unique naturally-occurring porous structures and well-defined morphologies.22-23 Natural pollen grains are a common, cheap, and widely available type of biomass waste. More importantly, most pollens have a unique porous surface structure.24 When we remove the core substance of pollen and carbonize the shell, it often displays a hollow 3D porous framework. The unique 3D porous framework of pollen can be utilized to provide pore passage and carbon skeleton for the mass transfer and the binding site for transition metal nanoparticles.25 Further, the pollen derived hollow 3D porous material provides a high surface area and rich cavities for exposing more catalytic


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sites.26 Plus, the 3D porous material contains macro, meso, and micro levels of porous structures, which potentially are a perfect solution to the low porosity of HCMs. Based on the above information and considerations, we designed and prepared a new type of OER/ORR bifunctional catalyst, in which FeSe nanoparticles were uniformly mounted on pollen derived 3D hollow porous carbon framework, through pyrolyzing and selenizing a pollen grain precursor mixed with NH4Fe(SO4)2, and selenium. As expected, the catalyst displayed preferable ORR/OER performance, compared with separate 3D hollow biocarbon or FeSe nanoparticles. We found that the N species are essential to boost the high ORR performance and the FeSe nanoparticles play a key role in enhanced OER performance. What’s more, the coupling effect between the FeSe nanoparticles and the HCMs not only induced large numbers of catalytic active sites but also generated strong interaction further improving the ORR/OER activity and stability. We believe these findings explain the simultaneously improved ORR and OER performance.

Experimental section Pre-treatment of rape pollen grains (RPGs) The pre-treatment process of RPGs was carried out as described in the literature.27 Typically, 5 g RPGs were dispersed in 100 mL of anhydrous ethanol and stirred constantly for 24 h at 50 ºC. Then, the RPGs were collected and washed successively with anhydrous ethanol and deionized water. Next, the alcohol-treated RPGs were dispersed in 100 mL alcohol−formaldehyde mixture (volume ratio = 1:1) and stirred for 15 min to fix the RPGs’ morphology. The fixed RPGs were washed with deionized



water and dried at 80 ºC; then they were placed in 100 mL 12 M H2SO4 solution under stirring at 80 ºC for 2 h. The RPGs’ color gradually deepened to brown during the dehydration process with concentrated sulfuric acid, implying that primary carbonization occurred. Finally, the brown RPGs were collected and washed to neutral with deionized water, followed by drying at 60 ºC overnight. Preparation of catalysts The fabrication process of the catalyst is illustrated in Scheme 1. First, 0.10 g pre-carbonized RPGs were dispersed in 15 mL 0.01 M NH4Fe(SO4)2 aqueous solution and ultrasonicated for 1 h. Then the suspension was stirred for 6 h to form a uniform mixture, which was freeze-dried at –45 ºC for 24 h. Next, 0.5 g RPGs containing Fe and 0.0234 g selenium powder were put in two separate location in a quartz boat, which selenium powder located in the upstream of an Ar/H2 (H2, 8 vol%) gas flow and annealed at 800 ºC for 3 h. The obtained sample was denoted as FeSe/NC-PoFeSe. For comparison, similar procedures were used to prepare another three samples from RPGs on their own (denoted as NC-Po), RPGs with NH4Fe(SO4)2 (denoted as Fe3O4/NC-PoFe), and RPGs with selenium powder (denoted as NC-PoSe). Samples with Fe/Se molar ratio of 1:0.5, 1:1, and 1:4 in the precursors were synthesized using the same procedures and conditions. Characterization of Catalysts The morphology and structure, elemental composition and chemical state, specific surface areas of catalysts were studied by Carl Zeiss Scanning electron microscopy (SEM), JEM-2100 Transmission electron microscopy (TEM), TD-3500 powder X-ray


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diffraction (XRD), LabRAM Aramis Raman spectrometer, AXIS Ultra DLD X-ray photoelectron spectroscopy (XPS), and Tristar II 3020 gas adsorption analyzer, respectively. Evaluation of Catalysts The ORR/OER performance tests of catalysts were performed on an Autolab electrochemical workstation with a rotating disk electrode (RDE) in a three-electrode configuration (a glassy carbon working electrode (GCWE, 5 mm diameter), a Hg/HgO reference electrode, and a platinum wire counter electrode). All potentials were converted into the RHE. All the GCWEs were fabricated as follows. 10 µL of 4.0 mg mL−1 catalyst inks (Nafion/isopropyl alcohol solution, 0.25 wt % Nafion) were pipetted onto the GCWE and dried in air.

Results and discussion

Scheme. 1 Schematic illustration of the preparation procedure of FeSe/NC-PoFeSe.

The morphologies of the products were first observed by SEM. As shown in Figure



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1a, the RPGs exhibits ellipsoidal particles with a lateral size of 10–20 µm (Figure 1b). The magnified SEM image in Figure 1c reveals that the RPGs possess outer walls with a lattice-like skeleton and nothing covering the surface. The FeSe/NC-PoFeSe sample completely inherited the ellipsoidal morphology of the RPGs precursor (Figure 1d), and the inset in Figure 1d shows that FeSe/NC-PoFeSe has a hollow structure.

The

individual

ellipsoidal

particle

in

Figure

1e

reveals

that

FeSe/NC-PoFeSe possesses a 3D framework with a hierarchical porous structure based on the network of extine from RPGs. The plentiful pores on the structure’s surface and interior are connected with each other, resulting in a particular porous structure that is beneficial for O2 gas diffusion and mass transference. Compared to the RPGs fairly smooth surface, the FeSe/NC-PoFeSe has a much rougher surface, and some Fe compound nanoparticles are uniformly distributed on the surface of the carbon skeleton (Figure 1f). The Fe3O4/NC-PoFe sample has a large number of Fe compound nanoparticles embedded on the surface of its ellipsoidal particles, which vary in size from tens to hundreds of nanometers (Figure S1g, h). In addition, the nanoparticles are aggregated on the surface of the carbon skeleton, forming large particles (Figure S1i). However, samples NC-Po (Figure S1a-c) and NC-PoSe (Figure S1d-f), retain a smooth, pristine surface, with almost no nanoparticles observable on the surface of their ellipsoidal particles.


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Figure 1. SEM images of pollen grains (a-c) and FeSe/NC-PoFeSe (d-f).

The structures of the samples were examined by TEM. in Figure 2 clearly show that all of them possess a laminar structure with interpenetrating macropores 200–500 nm in diameter, corresponding to what is observable in the SEM images (Figure 2a, 2c, 2e, and 2g). The 3D macropore microstructure is not only quite favorable for exposing multiple active sites but also helps to increase the diffusion velocity of O2.28 In addition, some Fe-phase nanoparticles in the carbon are also identifiable in the FeSe/NC-PoFeSe sample (Figure 2h). High-resolution TEM (HRTEM) images demonstrate that metallic nanoparticles 10–20 nm long were covered by a carbon layer. A representative HRTEM image (inset in Figure 2h) clearly shows a carbon layer that formed on the surface of a metallic nanocrystal. The resolved interplanar distance of the nanoparticle is 0.311 nm, corresponding to the (101) planes of FeSe.29 Such a structure of FeSe nanoparticles covered by N-doped carbon would experience a strong synergetic effect,30 utilizing the excellent electric conductivity of the carbon skeleton to promote electron transport in the composite catalyst, thus leading to



improved ORR and/or OER catalytic activity. Fe3O4/NC-PoFe (Figure 2f) also clearly displays much larger metallic nanoparticles in the carbon (about 50 nm across) than the FeSe nanoparticles in the FeSe/NC-PoFeSe sample. Conversely, in the NC-Po (Figure 2b) and NC-PoSe (Figure 2d), there are amorphous carbon particles but no metallic nanocrystals, further confirming that the nanoparticles originated from the doped Fe. In addition, some dark spots are observable in the NC-PoSe sample, which might be accumulations of selenide particles. Introducing Fe and Se simultaneously into the precursor not only induced the formation of FeSe nanoparticles but also caused coupling between the FeSe nanoparticles and the biocarbon skeleton during the carbonization process. As a result, FeSe/NC-PoFeSe seems a very promising ORR/OER catalyst due to its unique 3D carbon framework and the coupling of FeSe with doped carbon. Additionally, the elemental mapping images for FeSe/NC-PoFeSe in the Figure S2 indicates that the FeSe nanoparticles are uniformly distributed in biocarbon materials.

Figure 2. TEM images of NC-Po (a, b), NC-PoSe (c, d), Fe3O4/NC-PoFe (e, f) and FeSe/NC-PoFeSe (g, h).

The XRD patterns (Figure 3a) revealed the phase composition of the NC-Po,


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NC-PoSe, Fe3O4/NC-PoFe and FeSe/NC-PoFeSe. Both NC-Po and NC-PoSe show two broad signals at 23º and 44º, which can be assigned to C (002) and C (100), respectively.31 But the (002) peak intensities of Fe3O4/NC-PoFe and FeSe/NC-PoFeSe are much stronger than those of NC-Po and NC-PoSe, indicating that Fe3O4/NC-PoFe and FeSe/NC-PoFeSe had higher degrees of graphitization than NC-Po and NC-PoSe.32 This indicates that the addition of Fe have affected pyrolysis, or improved the graphitization of the catalyst. In addition, FeSe/NC-PoFeSe shows distinct peaks at 16.0º, 28.6º, 37.4º, 47.3º, 48.1º, and 57.1º, all of which can be ascribed to the (101) lattice planes of metallic FeSe (JCPDS card no. 85-0735). Other peaks at 32.0º, 41.6º, 50.0º, 55.4º, 60.9º, 62.6º, and 67.3º, all of which can be ascribed to the (101) lattice planes of metallic FeSe (JCPDS card no. 65-9127). This indicates that most of Fe species exists in FeSe/NC-PoFeSe sample as selenide, which is supported by the TEM results. The Fe3O4/NC-PoFe sample shows distinct peaks at 30.0º, 35.5º, 43.4º, 53.6º, and 62.8º, which are consistent with the standard JCPDS file 75-0033, indicating that in Fe3O4/NC-PoFe the Fe exists mainly as metallic Fe3O4.33 The Raman spectra (Figure 3b) of NC-Po, NC-PoSe, Fe3O4/NC-PoFe and FeSe/NC-PoFeSe clearly show D band (about 1350 cm–1) and G band (about 1580 cm–1), which reflects the disordered and graphitic degree of carbon,34 respectively. The ID/IG intensity ratios of NC-Po, NC-PoSe, Fe3O4/NC-PoFe and FeSe/NC-PoFeSe are 1.20, 1.18, 1.09 and 1.05, respectively. These results show that introducing of Fe can improve the graphitization of our biomass-derived HCMs,35 confirming the XRD results.



♦ ♦FeSe ♦

• ♦ •

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•FeSe

FeSe/NC-PoFeSe ♦♦ • • • PDF#85-0735 PDF#65-9127

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Figure 3. (a) XRD for NC-Po, NC-PoSe, Fe3O4/NC-PoFe and FeSe/NC-PoFeSe; (b) Raman spectra for NC-Po, NC-PoSe, Fe3O4/NC-PoFe and FeSe/NC-PoFeSe.

Figure 4a recorded the N2 adsorption–desorption analyses of the samples. The specific surface areas of NC-Po, NC-PoSe, Fe3O4/NC-PoFe and FeSe/NC-PoFeSe are 348, 317, 652, and 709 m2 g–1, respectively. Clearly, the doping of Fe in the precursor greatly enhanced the samples’ surface areas. The introduction of Fe into the precursor promoted the decomposition/dehydrogenation of the RPGs biomass during pyrolysis, and the 3D framework decorated with doped Fe and Se yielded the high large specific surface area. Furthermore, the Fe3O4/NC-PoFe and FeSe/NC-PoFeSe contains mesopores and macropores in the range of 10−250 nm (Figure 4b). In contrast, NC-Po and NC-PoSe essentially have only macropores, and almost no micro- or meso pores were observable. The Fe dopant not only improves the graphitization of the materials but also induces the formation of multilevel porous structures in the samples.


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Figure 4. (a) N2 adsorption–desorption isotherms for NC-Po, NC-PoSe, Fe3O4/NC-PoFe and FeSe/NC-PoFeSe. (b) pore-size distributions for NC-Po, NC-PoSe, Fe3O4/NC-PoFe and FeSe/NC-PoFeSe.

The surface chemical nature of NC-Po, NC-PoSe, Fe3O4/NC-PoFe, and FeSe/NC-PoFeSe was analyzed by XPS. The C, O, and N elements were confirmed in all samples by the survey spectra in Figure S3a. In addition, Fe appeared in Fe3O4/NC-PoFe and FeSe/NC-PoFeSe, and Se appeared in NC-PoSe and FeSe/NC-PoFeSe. Figure S3b shows that the FeSe/NC-PoFeSe has the highest N and Se content and the lowest O content of all the samples. And the N content has a marked impact on the ORR activity of HCMs,36 and transition metal selenides are regarded as effective OER catalysts. The C 1s XPS spectrum of FeSe/NC-PoFeSe (Figure S3c) shows five peaks at 284.5, 285.2, 286.2, 288.4, and 290.4 eV, which are consistent with C–C, C=N, C-N&C-O, O-C=O, and π-π* bonds,37 respectively, suggesting that the N atoms were doped into the carbon matrix. Moreover, doped N species are generally considered as ORR active sites of N-doped carbon.4, 7, 38 The N 1s XPS spectrum of FeSe/NC-PoFeSe (Figure 5d) shows five peaks at 398.8, 399.4, 400.6, 401.6 and 402.9 eV, corresponding to pyridinic N, Fe-N, pyrrolic N, graphitic



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N, and oxidized N, respectively.39 For comparison, the N 1s spectra of NC-Po, NC-PoSe, and Fe3O4/NC-PoFe were fitted with four or five peaks (Figure 5a-c). No peaks corresponding to Fe-N species (located at ~ 399 eV) can be identified in NC-Po or NC-PoSe because this catalyst was prepared without an iron precursor. Such different N-bonding configuration should exert a significant influence on the ORR catalytic performance. The FeSe/NC-PoFeSe had the highest ratio of pyridinic N, graphitic N, and Fe-N species among the four samples. The pyridinic N, graphitic N, and Fe-N sites are crucial for ORR activity.4 In particular, the Fe-N functionalities suggested to be the most likely active sites, play a crucial role in the ORR process. Figure S4b shows the Se 3d spectrum of the FeSe/NC-PoFeSe sample, which can be resolved into four different peaks at 52.7, 54.5, 55.8, and 57.7 eV, corresponding to Se-Fe, Se 3d5/2, Se 3d3/2, and Se-O, respectively.40 The high-resolution Se 3d spectrum of NC-PoSe (Figure S4a) can be resolved into two peaks at 55.1 and 55.9 eV, corresponding to Se 3d5/2 and Se 3d3/2. The peaks at 52.7 eV should be attributed to the formation of the FeSe phase in FeSe/NC-PoFeSe, which is consistent with the TEM

and

XRD

observations.

The

high-resolution

Fe

2p

spectrum

of

FeSe/NC-PoFeSe (Figure S4d) can be resolved into six different peaks. The small shoulder at 706.8 eV is attributable to Fe-Se, and the two peaks at binding energies of 709.8 and 724.0 eV can be assigned to Fe 2p3/2 and Fe 2p1/2, respectively. The two peaks occurring at binding energies of 719.3 and 731.6 eV correspond to shake-up satellites. According to previous reports, the peak located at around 711.8 eV can be considered evidence of Fe bound to N in the Fe and N co-doped materials.41 This


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result further confirms that Fe-N exists in FeSe/NC-PoFeSe. For comparison, the high-resolution Fe 2p spectrum of Fe3O4/NC-PoFe (Figure S4c) can be resolved into six different peaks. The two peaks at 710.5 and 712.4 eV can be assigned to Fe2+, Fe3+ (Fe 2p3/2) and the two peaks at 724.1 and 726.6 eV to Fe2+, Fe3+ (Fe 2p1/2).42 This indicates the Fe3O4 phase may exist in Fe3O4/NC-PoFe, which agrees with the XRD observations. The two peaks at binding energies of 718.2 and 732.1 eV correspond to shake-up satellites. The introduction of Fe into biocarbon resulted in a Fex–N moiety and enhanced the ORR and OER activity. In addition, the formation of FeSe during the selenylation process further dramatically improved the ORR and OER activity. These results indicate that simultaneous addition of Fe and Se to create FeSe/NC-PoFeSe not only generated new active sites but also turned single doping into multiple doping. The construction of a 3D biocarbon framework coupled with FeSe nanoparticles achieved on a single catalyst the integration of both active N species (Fex–N, pyridinic N, and graphitic N) for the ORR and transition metal selenides for the OER.



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Figure 5. (a-d) The high-resolution N 1s XPS spectrum of NC-Po, NC-PoSe, Fe3O4/NC-PoFe and FeSe/NC-PoFeSe.

The ORR performance of FeSe/NC-PoFeSe was first assessed using cyclic voltammetry (CV, Figure 6a) in 0.1 M KOH solutions saturated with O2 (solid) and N2 (dash) at a scanning rate of 10 mV s–1. The cathodic peak value of FeSe/NC-PoFeSe (0.81 V) positively shifts about 60, 90, and 140 mV compared to Fe3O4/NC-PoFe (0.75 V), NC-PoSe (0.72 V), and NC-Po (0.67 V), respectively, indicating that FeSe/NC-PoFeSe shows preferable ORR activity.43 Linear sweep voltammetry (LSV) was employed to further evaluate the catalysts’ activity in O2 saturated 0.1 M KOH solutions. Figure 6b shows the LSV curves of FeSe/NC-PoFeSe, Fe3O4/NC-PoFe, NC-PoSe, NC-Po, and commercial Pt/C (20


396

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wt.%). The half-wave potential (0.86 V) of FeSe/NC-PoFeSe not only is more positive than that of Fe3O4/NC-PoFe, NC-PoSe, and NC-Po but also precedes 30 mV compared with Pt/C (0.83 V). This indicates that FeSe/NC-PoFeSe possesses remarkable ORR activity, due to its favorable 3D framework, with a hierarchical porous structure and multiple active sites. On the one hand, the simultaneous introduction of Fe and Se not only generates Fe–Nx, pyridinic N, and graphitic N species but also forms FeSe nanoparticles protected by N-doped carbon, and the coupling effect between FeSe nanoparticles and HCMs further improved the ORR performance.4 On the other hand, the 3D framework provides a large surface area as well as numerous mesopores and macropores, which accelerates mass transport and electron transport.28 The electrochemical impedance spectroscopy (EIS, Figure S5) of NC-Po, NC-PoSe, Fe3O4/NC-PoFe, and FeSe/NC-PoFeSe also show that the charge transfer resistance of the catalysts decreased sharply with the doping of Fe and further selenizing. To investigate the ORR kinetic process on FeSe/NC-PoFeSe, LSV curves at different rotating speeds were detected in Figure 6c (inset is the corresponding K–L plots). And the calculated electron transfer number of FeSe/NC-PoFeSe for ORR is close 4.0, following a four-electron pathway. In addition, Figure 6d shows that FeSe/NC-PoFeSe has a higher current density (Ik = 4.32 mA cm−2) than that of Pt/C (4.05 mA cm−2) at 0.8 V. The catalyst durability of FeSe/NC-PoFeSe for ORR is shown in Figure 6e and 6f. After 2000 cycles tests, its potential shifts negatively 9 mV. By comparison, the potential of Pt/C decreases 33 mV. The current–time (i–t) chronoamperometric response of FeSe/NC-PoFeSe was also performed to further



evaluate its stability. The loss of current density for FeSe/NC-PoFeSe at 0.85 V after 20,000 s still keeps at 99%. However, the Pt/C attenuates up to 18%, implying the outstanding ORR stability of FeSe/NC-PoFeSe.

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FeSe/NC-PoFeSe

Fe3O4/NC-PoFe

NC-PoSe

NC-Po

1mA cm-2 0.2

0.4

0.6

0.8

1.0

0

NC-Po NC-PoSe Fe3O4/NC-PoFe FeSe/NC-PoFeSe Pt/C

-1 -2 -3 -4 -5 -6 0.2

1.2

Potential / V vs. RHE

-1

0.30

0.20 0.15

-2

0.06

0.08

0.10

0.12

0.14

400 625 900 1225 1600 2025 2500

0.16

ω-1/2 / rad-1/2s1/2

-3 -4 -5 -6 -7

3

2

0.4

0.6

0.8

o e Se /C Se NC-P NC-Po /NC-PoFNC-PoFe Pt / e O 4 Fe 3 FeS

1.0

Potential / V vs. RHE 0 -1 -2

1.0

1

f

FeSe/NC-PoFeSe initial FeSe/NC-PoFeSe after 2000 cycles Pt/C initial Pt/C after 2000 cycles

Relative currents / %

e

0.8

Ik at 0.8V vs. RHE

0

0.2

0.6

0.25

Ik / mA cm-2

0

d4

0.3V 0.4V 0.5V 0.6V

0.35

1

0.4


0.40

2 j-1 / mA-1cm2


c


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

Page 18 of 30

-3 -4 -5

100 99%

80

82%

FeSe/NC-PoFeSe Pt/C

60 40 20

-6

0 0.2

0.4

0.6

0.8

1.0

0


5000

10000

15000

Time / s

Figure 6. (a) CV curves of NC-Po, NC-PoSe, Fe3O4/NC-PoFe and FeSe/NC-PoFeSe in N2 and O2 saturated 0.1 M KOH. (b) LSV curves of NC-Po, NC-PoSe, Fe3O4/NC-PoFe, FeSe/NC-PoFeSe, and 20 wt.% commercial Pt/C at 1600 rpm. (c) LSV curves of FeSe/NC-PoFeSe at different rotation rates. The inset shows the corresponding Koutecky–Levich plots. (d) The current density


20000

Page 19 of 30 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


of the NC-Po, NC-PoSe, Fe3O4/NC-PoFe, FeSe/NC-PoFeSe and Pt/C at 0.8 V. (e) Accelerated durability measurement of FeSe/NC-PoFeSe and Pt/C. (f) Chronoamperometric curves of FeSe/NC-PoFeSe and Pt/C at 0.85 V. The data in (b-f) were recorded in O2-saturated 0.1 M KOH solution.

To expand the potential of FeSe/NC-PoFeSe as a bifunctional electrocatalyst, we further investigated its OER activity. Figure 7a shows the OER LSV curves of NC-Po, NC-PoSe, Fe3O4/NC-PoFe, FeSe/NC-PoFeSe and commercial IrO2/C in O2-saturated 0.1 M KOH solution. The onset potential of FeSe/NC-PoFeSe (1.45 V) is much lower, compared with IrO2/C (1.49 V), Fe3O4/NC-PoFe (1.50 V), NC-PoSe (1.54 V), NC-Po (1.56 V), and Pt/C (1.57 V). The introduction of Fe drastically enhanced the OER performance, and the formation of FeSe nanoparticles significantly improved it. Figure 7b shows that the FeSe/NC-PoFeSe has the lowest OER Tafel slope of 76 mV dec–1, compared to IrO2/C (97 mV dec–1), Fe3O4/NC-PoFe (102 mV dec–1), NC-PoSe (157 mV dec–1), and NC-Po (178 mV dec–1), indicating more advantageous OER reaction kinetics on FeSe/NC-PoFeSe. Moreover, FeSe/NC-PoFeSe displays quite a low overpotential (330 mV) to achieve the current density of 10 mA cm–2 (see Figure 7c), which is 40, 60, 100, 200 mV lower than that of IrO2/C (370 mV), Fe3O4/NC-PoFe (390 mV), NC-PoSe (430 mV), and NC-Po (530 mV), respectively. The excellent OER activity of FeSe/NC-PoFeSe can be attributed to the effective coupling between the FeSe and HCMs.14 Transition-metal selenides nanoparticles anchored uniformly on HCMs not only promotes the charge transfer from metal to carbon, but also makes the metal more electrophilic, resulting in the enhanced OER activity of FeSe/NC-PoFeSe.14, 2 The potential gap (∆E) between the ORR and OER is applied to estimate the bifunctional activity of oxygen electrode.18 The smaller the gap,



the more suitable the material is as a bifunctional catalyst. FeSe/NC-PoFeSe shows the lowest ∆E values of 0.72 V in Figure 7d among all the samples. This result indicates that the bifunctional ORR/OER activities of FeSe/NC-PoFeSe are superior to IrO2/C-Pt/C, Fe3O4/NC-PoFe, NC-PoSe, and NC-Po, respectively. Indeed, the FeSe/NC-PoFeSe shows more promising oxygen electrode activity, compared with other ORR/OER bifunctional catalysts reported in the literature (Table S1). FeSe/NC-PoFeSe also displays better OER stability than IrO2/C. After 2000 cycles, the potential of FeSe/NC-PoFeSe decreases by 14 mV while IrO2/C reaches 37 mV at a current density of 10 mA cm–2 (Figure 7e). Figure 7f further confirms FeSe/NC-PoFeSe has a smaller loss (2%) than that of IrO2/C (27%) after 5000 s of continuous i–t measurements.


Page 20 of 30

15

10

5

0.40

1.4

1.6

de c -1 V 7 15

dec

-1

V 102 m

0.30

97 m

dec

-1 V dec

-1 dec 76 mV

0.0

1.8

0.2

0.4

0.6

0.8

-2


Log (j / mA cm )

d 15


c 600 500 400 300 200 100

NC-Po NC-PoSe Fe3O4/NC-PoFe FeSe/NC-PoFeSe Pt/C IrO2/C

10

5

0

-5 0

e 20

e o e e NC-P NC-PoS /NC-PoFC-PoFeS IrO 2/C N O / 4 e Fe 3 FeS

15

0.4

0.6

0.8

1.0

1.2

1.4

1.6

5

1.8


f 100

FeSe/NC-PoFeSe initial FeSe/NC-PoFeSe after 2000 cycles IrO2/C initial IrO2/C after 2000 cycles

10

0 1.0

0.2

Relative currents / %

Overpotential at 10 mA cm-2 / mV

1.2

-1

mV

0.35

0.25 0 1.0

m

0.45

8

NC-Po NC-PoSe Fe3O4/NC-PoFe FeSe/NC-PoFeSe IrO2/C

17

b 0.50

NC-Po NC-PoSe Fe3O4/NC-PoFe FeSe/NC-PoFeSe IrO2/C

Overpotential / V


a 20


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


Eθ (H2O/O2) 1.23 V

Page 21 of 30

98%

80 FeSe/NC-PoFeSe IrO2/C

60

73%

40 20 0

1.2

1.4

1.6

1.8

0


1000

2000

3000

4000

Time / s

Figure 7. (a) LSV curves of NC-Po, NC-PoSe, Fe3O4/NC-PoFe, FeSe/NC-PoFeSe, and commercial IrO2/C at 1600 rpm with a scan rate of 0.2 mV s–1. (b) Tafel plots of NC-Po, NC-PoSe, Fe3O4/NC-PoFe, FeSe/NC-PoFeSe, commercial IrO2/C and Pt/C. (c) The overpotential of NC-Po, NC-PoSe, Fe3O4/NC-PoFe, FeSe/NC-PoFeSe, and commercial IrO2/C at 10 mA cm–2. (d) The potential gap (∆E) of different catalysts for oxygen electrode activities. (e) Accelerated durability measurement of FeSe/NC-PoFeSe and commercial IrO2/C. (f) Chronoamperometric curves of FeSe/NC-PoFeSe and IrO2/C at 1.60 V. All of the data were recorded in O2-saturated 0.1 M KOH solution.

Generally, Fe species are deemed to be vital to the enhancement of ORR and/or


5000


OER activity.2, prepared

4-5

Page 22 of 30

To investigate the role of FeSe in the ORR and/or OER, we

FeSe/NC-PoFeSe-AL

which

removed

a

majority

of

FeSe

in

FeSe/NC-PoFeSe by acid leaching. In addition, to explore the coupling effect between the FeSe nanoparticles and the HCMs, we also prepared NC-Po+FeSe by selenizing the physical mixtures of NC-Po and NH4Fe(SO4)2. The XRD patterns and SEM images FeSe/NC-PoFeSe-AL and NC-Po+FeSe are shown in Figure S6a, d, and e, respectively.

Compared

to

FeSe/NC-PoFeSe,

the

ORR

activity

of

FeSe/NC-PoFeSe-AL certainly has declined (Figure S6b). However, the half-wave potential of FeSe/NC-PoFeSe-AL has positively shifted by 43 mV compared with NC-Po+FeSe, and FeSe/NC-PoFeSe-AL has a higher limited current density than NC-Po+FeSe. These results indicate that FeSe nanoparticles coupled with HCMs are responsible for the enhanced ORR activity in FeSe/NC-PoFeSe. The physical mixing of FeSe nanoparticles and N doped carbon did not contribute to improving the ORR performance. Active N species, such as Fe–Nx, pyridinic N, and graphitic N may act as ORR active sites in the N-doped carbon materials. The OER activity of FeSe/NC-PoFeSe-AL has a significant degradation, compared with FeSe/NC-PoFeSe (see Figure S6c). However, the overpotential of NC-Po+FeSe is 39 mV lower than that of FeSe/NC-PoFeSe-AL at a current density of 10 mA cm–2. This indicates that the FeSe play a key role in OER activity. In addition, the coupling effect between FeSe nanoparticles and biocarbon further strengthens the OER performance of FeSe/NC-PoFeSe. According to the above results, combined with the reports of HCMs and transition


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metal selenides as ORR and/or OER electrocatalysis, a few reasons or mechanisms can be assumed to explain the prominent ORR and OER activity of FeSe/NC-PoFeSe: (1) When Fe and Se precursors are added separately to the RPGs, the Fe−Nx, pyridinic N, and graphitic N may provide main ORR active centers, and may also show particular OER activity. The formation of FeSe nanoparticles makes a major contribution to OER activity. Further, integrating multiple active N species with FeSe nanoparticles achieved the integration of ORR and OER activity on a single material. (2) The strong coupling effect between FeSe nanoparticles and biomass further improved the ORR and OER activity of FeSe/NC-PoFeSe. (3) The unique 3D carbon framework guaranteed efficient mass and electron transport during the whole ORR/OER process. As is well known, the content of transition metal directly influences ORR/OER activity. Given this, we tested a variety of Fe/Se ratios (1:0.5, 1:1, 1:2, 1:4) to determine the optimal Fe/Se ratio in this study. As shown in Figure S7a and Figure S7b, the optimal Fe/Se ratio is 1:2. Research has shown that too little or too much Fe both astrict the generation of ORR and/or OER active sites.22-23

Conclusion In summary, we successfully prepared a carbon-based ORR/OER bifunctional catalyst using a pollen biomass precursor by pyrolysis, Fe doping, and selenylation. The catalyst had rich Fe−Nx, pyridinic N, and graphitic N as major ORR active sites and FeSe nanoparticles as OER active sites. In addition, the coupling effect between FeSe nanoparticles and biocarbon significantly enhanced the ORR and OER



performance. The catalyst had a 3D, interpenetrating, the hierarchically porous framework with a large specific surface area, facilitating the mass and electron transfer. The FeSe/NC-PoFeSe catalyst exhibited superior ORR and OER activity and long-time durability, compared with commercial Pt/C and IrO2/C in alkaline electrolyte. These results demonstrate the unique advantage of using a 3D, hierarchically porous biocarbon skeleton as a bifunctional electrocatalyst for green, sustainable fuel cells and/or metal–air batteries.

ASSOCIATED CONTENT Supporting Information including: SEM, elemental mappings, XPS, EIS, XRD, LSV curves of samples.

Acknowledgments This work was supported by the National Key Research and Development Program of China (Project Nos 2017YFB0102900, 2016YFB0101201), the National Natural Science Foundation of China (NSFC Project Nos. 21476088, 21776105), the Guangdong Provincial Department of Science and Technology (Project No. 2015B010106012), and the Guangzhou Science Technology and Innovation Committee (Project Nos. 201504281614372, 2016GJ006).


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References 1.

Wang, D.-W.; Su, D., Heterogeneous Nanocarbon Materials for Oxygen Reduction Reaction.

Energy Environ. Sci. 2014, 7 (2), 576-591. 2.

Zhang, L.; Xiao, J.; Wang, H.; Shao, M., Carbon-Based Electrocatalysts for Hydrogen and

Oxygen Evolution Reactions. ACS Catal. 2017, 7 (11), 7855-7865. 3.

Peng, H.; Liu, F.; Liu, X.; Liao, S.; You, C.; Tian, X.; Nan, H.; Luo, F.; Song, H.; Fu, Z.; Huang, P.,

Effect of Transition Metals on the Structure and Performance of the Doped Carbon Catalysts Derived From Polyaniline and Melamine for ORR Application. ACS Catal. 2014, 4 (10), 3797-3805. 4.

Wu, G.; Santandreu, A.; Kellogg, W.; Gupta, S.; Ogoke, O.; Zhang, H.; Wang, H.-L.; Dai, L.,

Carbon Nanocomposite Catalysts for Oxygen Reduction and Evolution Reactions: from Nitrogen Doping to Transition-Metal Addition. Nano Energy 2016, 29, 83-110. 5.

Asefa, T., Metal-Free and Noble Metal-Free Heteroatom-Doped Nanostructured Carbons as

Prospective Sustainable Electrocatalysts. Acc. Chem. Res. 2016, 49 (9), 1873-1883. 6.

Liu, K.; Zhong, H.; Meng, F.; Zhang, X.; Yan, J.; Jiang, Q., Recent Advances in

Metal-Nitrogen-Carbon Catalysts for Electrochemical Water Splitting. Materials Chemistry Frontiers 2017, 1 (11), 2155-2173. 7.

Liu, X.; Dai, L., Carbon-based Metal-Free Catalysts. Nature Reviews Materials 2016, 1, 16064.

8.

Anantharaj, S.; Ede, S. R.; Sakthikumar, K.; Karthick, K.; Mishra, S.; Kundu, S., Recent Trends

and Perspectives in Electrochemical Water Splitting with an Emphasis on Sulfide, Selenide, and Phosphide Catalysts of Fe, Co, and Ni: A Review. ACS Catal. 2016, 6 (12), 8069-8097. 9.

Chakadola, P.; W., M. P.; Carsten, W.; Shenglai, Y.; E., M. M.; Vitaly, G.; Karsten, M.; Matthias,

D., From a Molecular 2Fe-2Se Precursor to a Highly Efficient Iron Diselenide Electrocatalyst for Overall Water Splitting. Angew. Chem. Int. Ed. 2017, 56 (35), 10506-10510. 10. Gao, R.; Zhang, H.; Yan, D., Iron Diselenide Nanoplatelets: Stable and Efficient Water-Electrolysis Catalysts. Nano Energy 2017, 31, 90-95. 11. Chun, T.; Ningyan, C.; Zonghua, P.; Wei, X.; Xuping, S., NiSe Nanowire Film Supported on Nickel Foam: An Efficient and Stable 3D Bifunctional Electrode for Full Water Splitting. Angew. Chem. Int. Ed. 2015, 54 (32), 9351-9355. 12. Pu, Z.; Luo, Y.; Asiri, A. M.; Sun, X., Efficient Electrochemical Water Splitting Catalyzed by Electrodeposited Nickel Diselenide Nanoparticles Based Film. ACS Appl. Mater. Interfaces 2016, 8 (7), 4718-4723. 13. Chuan, X.; Qiu, J.; Chao, Z.; N., H. M.; N., A. H., Selenide-Based Electrocatalysts and Scaffolds for Water Oxidation Applications. Adv. Mater. 2016, 28 (1), 77-85. 14. Meng, T.; Qin, J.; Wang, S.; Zhao, D.; Mao, B.; Cao, M., In Situ Coupling of Co0.85Se and N-Doped Carbon via One-Step Selenization of Metal-Organic Frameworks as a Trifunctional Catalyst for Overall Water Splitting and Zn-Air Batteries. J. Mater. Chem. A 2017, 5 (15), 7001-7014. 15. Li, S.; Peng, S.; Huang, L.; Cui, X.; Al-Enizi, A. M.; Zheng, G., Carbon-Coated Co3+-Rich Cobalt Selenide Derived from ZIF-67 for Efficient Electrochemical Water Oxidation. ACS Appl. Mater. Interfaces 2016, 8 (32), 20534-20539.



16. Ming, F.; Liang, H.; Shi, H.; Xu, X.; Mei, G.; Wang, Z., MOF-Derived Co-Doped Nickel Selenide/C Electrocatalysts Supported on Ni Foam for Overall Sater Splitting. J. Mater. Chem. A 2016, 4 (39), 15148-15155. 17. Dehui, D.; Liang, Y.; Xiaoqi, C.; Guoxiong, W.; Li, J.; Xiulian, P.; Jiao, D.; Gongquan, S.; Xinhe, B., Iron Encapsulated within Pod-Like Carbon Nanotubes for Oxygen Reduction Reaction. Angew. Chem. Int. Ed. 2013, 52 (1), 371-375. 18. Su, Y.; Zhu, Y.; Jiang, H.; Shen, J.; Yang, X.; Zou, W.; Chen, J.; Li, C., Cobalt Nanoparticles Embedded in N-Doped Carbon as an Efficient Bifunctional Electrocatalyst for Oxygen Reduction and Evolution Reactions. Nanoscale 2014, 6 (24), 15080-15089. 19. Sun, C.; Dong, Q.; Yang, J.; Dai, Z.; Lin, J.; Chen, P.; Huang, W.; Dong, X., Metal–Organic Framework Derived CoSe2 Nanoparticles Anchored on Carbon Fibers as Bifunctional Electrocatalysts for Efficient Overall Water Splitting. Nano Research 2016, 9 (8), 2234-2243. 20. Maryam, B.; Janika, L.; Liang, L.; J., R. O., Advanced Biomass-Derived Electrocatalysts for the Oxygen Reduction Reaction. Adv. Mater. 0 (0), 1703691. 21. Deng, J.; Li, M.; Wang, Y., Biomass-Derived Carbon: Synthesis and Applications in Energy Storage and Conversion. Green Chem. 2016, 18 (18), 4824-4854. 22. Wang, G.; Peng, H.; Qiao, X.; Du, L.; Li, X.; Shu, T.; Liao, S., Biomass-Derived Porous Heteroatom-Doped Carbon Spheres as a High-Performance Catalyst for the Oxygen Reduction Reaction. Int. J. Hydrogen Energy 2016, 41 (32), 14101-14110. 23. Wang, G.; Deng, Y.; Yu, J.; Zheng, L.; Du, L.; Song, H.; Liao, S., From Chlorella to Nestlike Framework Constructed with Doped Carbon Nanotubes: A Biomass-Derived, High-Performance, Bifunctional Oxygen Reduction/Evolution Catalyst. ACS Appl. Mater. Interfaces 2017, 9 (37), 32168-32178. 24. Fazal, H.; Ahmad, N.; Haider Abbasi, B., Identification, Characterization, and Palynology of High-Valued Medicinal Plants. The Scientific World Journal 2013, 2013, 9. 25. Wang, Y.; Liu, Z.; Han, B.; Huang, Y.; Yang, G., Carbon Microspheres with Supported Silver Nanoparticles Prepared from Pollen Grains. Langmuir 2005, 21 (23), 10846-10849. 26. Long, Z.; Fan, Z.; Xi, Y.; Kai, L.; Yi, H.; Yongsheng, C., High-Performance Supercapacitor Electrode Materials Prepared from Various Pollens. Small 2013, 9 (8), 1342-1347. 27. Xia, Y.; Zhang, W.; Xiao, Z.; Huang, H.; Zeng, H.; Chen, X.; Chen, F.; Gan, Y.; Tao, X., Biotemplated Fabrication of Hierarchically Porous NiO/C Composite from Lotus Pollen Grains for Lithium-ion Batteries. J. Mater. Chem. 2012, 22 (18), 9209-9215. 28. Zhu, C.; Li, H.; Fu, S.; Du, D.; Lin, Y., Highly Efficient Nonprecious Metal Catalysts towards Oxygen Reduction Reaction Based on Three-Dimensional Porous Carbon Nanostructures. Chem. Soc. Rev. 2016, 45 (3), 517-531. 29. Li, C.; Zhang, S.; Yu, Z.; Ma, X.; Liu, J.; Zhang, P., Room-Temperature Chemical Synthesis of PbO-Type FeSe Superconducting Nanoparticles. Journal of Superconductivity and Novel Magnetism 2015, 28 (5), 1449-1453. 30. Senchuan, H.; Yuying, M.; Shiman, H.; Anandarup, G.; Qili, W.; Junhao, L.; Shengfu, T.; Tewodros, A.; Mingmei, W., N-, O-, and S-Tridoped Carbon-Encapsulated Co9S8 Nanomaterials: Efficient Bifunctional Electrocatalysts for Overall Water Splitting. Adv. Funct. Mater. 2017, 27 (17), 1606585. 31. Xu, J.; Gao, Q.; Zhang, Y.; Tan, Y.; Tian, W.; Zhu, L.; Jiang, L., Preparing Two-Dimensional Microporous Carbon from Pistachio Nutshell with High Areal Capacitance as Supercapacitor Materials.


Page 26 of 30

Page 27 of 30 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


Sci. Rep. 2014, 4, 5545. 32. Takagi, H.; Maruyama, K.; Yoshizawa, N.; Yamada, Y.; Sato, Y., XRD Analysis of Carbon Stacking Structure in Coal during Heat Treatment. Fuel 2004, 83 (17), 2427-2433. 33. Teymourian, H.; Salimi, A.; Khezrian, S., Fe3O4 Magnetic Nanoparticles/Reduced Graphene Oxide Nanosheets as a Novel Electrochemical and Bioeletrochemical Sensing Platform. Biosens. Bioelectron. 2013, 49, 1-8. 34. Ferrari, A. C., Raman Spectroscopy of Graphene and Graphite: Disorder, Electron–Phonon Coupling, Doping and Nonadiabatic Effects. Solid State Commun. 2007, 143 (1), 47-57. 35. Antunes, E. F.; Lobo, A. O.; Corat, E. J.; Trava-Airoldi, V. J.; Martin, A. A.; Veríssimo, C., Comparative Study of First- and Second-Order Raman Spectra of MWCNT at Visible and Infrared Laser Excitation. Carbon 2006, 44 (11), 2202-2211. 36. Dominguez, C.; Perez-Alonso, F. J.; Salam, M. A.; Al-Thabaiti, S. A.; Pena, M. A.; Barrio, L.; Rojas, S., Effect of the N Content of Fe/N/Graphene Catalysts for the Oxygen Reduction Reaction in Alkaline Media. J. Mater. Chem. A 2015, 3 (48), 24487-24494. 37. Li, Y.; Zhao, Y.; Cheng, H.; Hu, Y.; Shi, G.; Dai, L.; Qu, L., Nitrogen-Doped Graphene Quantum Dots with Oxygen-Rich Functional Groups. J. Am. Chem. Soc. 2012, 134 (1), 15-18. 38. Wang, G.; Jiang, K.; Xu, M.; Min, C.; Ma, B.; Yang, X., A High Activity Nitrogen-Doped Carbon Catalyst for Oxygen Reduction Reaction Derived from Polyaniline-Iron Coordination Polymer. J. Power Sources 2014, 266, 222-225. 39. Peng, H.; Mo, Z.; Liao, S.; Liang, H.; Yang, L.; Luo, F.; Song, H.; Zhong, Y.; Zhang, B., High Performance Fe- and N- Doped Carbon Catalyst with Graphene Structure for Oxygen Reduction. Sci. Rep. 2013, 3, 1765. 40. Zheng, Q.; Cheng, X.; Li, H., Microwave Synthesis of High Activity FeSe2/C Catalyst toward Oxygen Reduction Reaction. Catalysts 2015, 5 (3), 1079. 41. Xinchen, W.; Xiufang, C.; Arne, T.; Xianzhi, F.; Markus, A., Metal-Containing Carbon Nitride Compounds: A New Functional Organic–Metal Hybrid Material. Adv. Mater. 2009, 21 (16), 1609-1612. 42. Yamashita, T.; Hayes, P., Analysis of XPS Spectra of Fe2+ and Fe3+ Ions in Oxide Materials. Appl. Surf. Sci. 2008, 254 (8), 2441-2449. 43. Shiva, G.; Shuai, Z.; Ogechi, O.; Ye, L.; Hui, X.; Gang, W., Engineering Favorable Morphology and Structure of Fe-N-C Oxygen-Reduction Catalysts through Tuning of Nitrogen/Carbon Precursors. ChemSusChem 2017, 10 (4), 774-785.



FIGUREURE CAPTIONS:

Scheme 1. Schematic illustration of the preparation procedure of FeSe/NC-PoFeSe.

Figure 1. SEM images of pollen grains (a-c) and FeSe/NC-PoFeSe (d-f).

Figure 2. TEM images of NC-Po (a, b), NC-PoSe (c, d), Fe3O4/NC-PoFe (e, f) and FeSe/NC-PoFeSe (g, h).

Figure 3. (a) XRD for NC-Po, NC-PoSe, Fe3O4/NC-PoFe and FeSe/NC-PoFeSe; (b) Raman spectra for NC-Po, NC-PoSe, Fe3O4/NC-PoFe and FeSe/NC-PoFeSe.

Figure 4. (a) N2 adsorption–desorption isotherms for NC-Po, NC-PoSe, Fe3O4/NC-PoFe and FeSe/NC-PoFeSe. (b) pore-size distributions for NC-Po, NC-PoSe, Fe3O4/NC-PoFe and FeSe/NC-PoFeSe.

Figure 5. (a-d) The high-resolution N 1s XPS spectrum of NC-Po, NC-PoSe, Fe3O4/NC-PoFe and FeSe/NC-PoFeSe.

Figure 6. (a) CV curves of NC-Po, NC-PoSe, Fe3O4/NC-PoFe and FeSe/NC-PoFeSe in N2 and O2


Page 28 of 30

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saturated 0.1 M KOH. (b) LSV curves of NC-Po, NC-PoSe, Fe3O4/NC-PoFe, FeSe/NC-PoFeSe, and 20 wt.% commercial Pt/C at 1600 rpm. (c) LSV curves of FeSe/NC-PoFeSe at different rotation rates. The inset shows the corresponding Koutecky–Levich plots. (d) The current density of the NC-Po, NC-PoSe, Fe3O4/NC-PoFe, FeSe/NC-PoFeSe and Pt/C at 0.8 V. (e) Accelerated durability measurement of FeSe/NC-PoFeSe and Pt/C. (f) Chronoamperometric curves of FeSe/NC-PoFeSe and Pt/C at 0.85 V. The data in (b-f) were recorded in O2-saturated 0.1 M KOH solution.

Figure 7. (a) LSV curves of NC-Po, NC-PoSe, Fe3O4/NC-PoFe, FeSe/NC-PoFeSe, and commercial IrO2/C at 1600 rpm with a scan rate of 0.2 mV s–1. (b) Tafel plots of NC-Po, NC-PoSe, Fe3O4/NC-PoFe, FeSe/NC-PoFeSe, commercial IrO2/C and Pt/C. (c) The overpotential of NC-Po, NC-PoSe, Fe3O4/NC-PoFe, FeSe/NC-PoFeSe, and commercial IrO2/C at 10 mA cm–2. (d) The potential gap (∆E) of different catalysts for oxygen electrode activities. (e) Accelerated durability measurement of FeSe/NC-PoFeSe and commercial IrO2/C. (f) Chronoamperometric curves of FeSe/NC-PoFeSe and IrO2/C at 1.60 V. All of the data were recorded in O2-saturated 0.1 M KOH solution.



For Table of Contents Only:

Three Dimensional Biocarbon Framework Coupled with Uniform Distributed FeSe Nanoparticles Derived from Pollen as Bifunctional Electrocatalysts for Oxygen Electrode Reactions Guanghua Wang, Jing Li, Mingrui Liu, Li Du, Shijun Liao†

A 3D hollow porous nitrogen-doped carbon framework coupled with homogenous distribution FeSe nanoparticles derived from pollen displays excellent ORR/OER activity.

†

Corresponding author. Fax: +86 20 8711 3586. E-mail address: [email protected]


Page 30 of 30

Three-Dimensional Biocarbon Framework Coupled with Uniformly

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