Hybrid of g-C3N4 Assisted MetalâOrganic Frameworks and Their

Subscriber access provided by Macquarie University

Article

Hybrid of g-C3N4 Assistanted Metal–Organic Frameworks and Their Derived High-Efficiency Oxygen Reduction Electrocatalyst In the whole pH range Wenling Gu, Liuyong Hu, Jing Li, and Erkang Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b12031 • Publication Date (Web): 01 Dec 2016 Downloaded from http://pubs.acs.org on December 2, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 27

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

ACS Applied Materials & Interfaces

Hybrid of g-C3N4 Assistanted Metal–Organic Frameworks and Their Derived High-Efficiency Oxygen Reduction Electrocatalyst In the whole pH range

Wenling Gu,Ɨ§ Liuyong Hu,£§ Jing Li*Ɨ and Erkang Wang*Ɨ

Ɨ

State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied

Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, PR China; £

State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of

Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, PR China; §

University of the Chinese Academy of Sciences, Beijing, 100049, PR China

Corresponding author: Associate Prof. Jing Li, Prof. Erkang Wang, Tel: +86-431-85262003, Email: [email protected] and [email protected]

1

ACS Paragon Plus Environment


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 2 of 27

ABSTRACT A highly active electrocatalyst in the whole pH range for oxygen reduction reaction (ORR) is produced by employing the g-C3N4 assistanted metal–organic frameworks (MOF) of C3N4@NH2-MIL-101 as the precursor. By pyrolyzing the hybrid at 700 °C, the C3N4@NH2-MIL-101 could be easily transformed into an abundant iron and nitrogen co-doped porous carbon skeleton. The selective use of g-C3N4 as a support template plays a critical role in facilitating the formation of the architecture with high surface area and rich N content. The obtained catalyst of C3N4@NH2-MIL-101-700 manifested remarkable oxygen reduction activity over the pH 0-14. Noteworthy, the catalyst displayed outstanding ORR activity with more positive half-wave potential than that of the commercial Pt/C catalyst both in alkaline and neutral conditions. Additionally, the optimal C3N4@NH2-MIL-101-700 also exhibited prominent ORR activity which is almost equal to that of commercial Pt/C in acidic electrolyte with high selectivity and very low H2O2 yield. Most importantly, the better methanol tolerance

and

much

higher

stability

than

the

commercial

Pt/C

of

C3N4@NH2-MIL-101-700 no matter under alkaline, neutral or acid conditions, further demonstrate the catalyst to be a promising candidates for practical electrocatalytic applications.

KEYWORDS: electrocatalysts, g-C3N4, metal–organic frameworks, oxygen reduction reaction, porous materials

2


Page 3 of 27

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


1. INTRODUCTION Electrochemical oxygen reduction reaction (ORR) is the heart reaction in many high energy-conversion devices, such as metal-air batteries and fuel cells.1-3 Noble metal and noble metal based alloy catalysts (e.g., Pt, Pd, and PtAu) are the state of the art for the ORR with high activity and current density,4,5 but the prohibitive cost, limited availability and easy corrosion of the noble metal catalysts have restricted their wide-spread use.6,7 Consequently, much attention has been paid to develop non-precious metal electrocatalyst (NPMCs), such as heteroatom (N, S, P, Fe, Co etc.) doped carbon materials, transition metal-nitrogen doped carbon (M-N-C), transition metal oxides and metal-Nx macrocycles, etc, as the alternatives to Pt.8-12 In particular, the M-N-C catalysts have been regarded as one of the most promising alternatives for costly Pt-based catalysts owing to their specially structural features of surface nitrogen coordinate with metal.13,14 By pyrolyzing the mixture of precursors containing Fe or Co, carbon and nitrogen precursors, M-N-C catalysts will effectively produce.15-18 Despite of these numerous efforts, the ORR activities of M-N-C catalysts in neutral and acidic conditions was still barely satisfied. Therefore, an outstanding M-N-C catalyst with largely enhanced ORR behaviors especially in neutral and acidic electrolyte remains a challenge and significantly demanded. Additionally, the issues of the available part of the active sites and the transport ability of the ORR relevant substance also strongly affect the performance of the M-N-C catalysts, which are always depended on the specific surface area (SSA) and porous

3



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

network.19-21 To afford catalysts with higher SSA and favorable active site, various strategies have been performed to synthesize porous M-N-C catalysts.22,23 Among them, the rigid template method and the soft-template method are the common routes, but the complicated subsequent processing engineering and the lack of effectiveness limit the scale-up production. On the other hand, the simple self-template method using porous precursors such as metal-organic frameworks (MOFs) which with significantly high surface areas via a direct pyrolysis process to easily convert into various functional carbon materials have been drawing much attention.24,25 Nonetheless, the surface area derived from the self-template method is not large enough, which is presumably due to agglomeration and collapse of pores at the succedent pyrolysis process. Thus we designed a sustainable support template as scaffold to prevent the MOF aggregating at elevated temperatures to produce the carbon-based catalyst, which should be expected with large surface area and enhanced catalytic performance. In this work, inspired by this, we designed and fabricated a hybrid of g-C3N4 sustained metal–organic frameworks of C3N4@NH2-MIL-101, following by a subsequent heat treating process at 700 °C to obatin an excellent ORR catalyst. Herein, the g-C3N4 is applied as the support template, which plays a vital part in facilitating the formation of the architecture with high surface area and rich N content. The obtained catalyst exhibited largely enhanced electrocatalytic ORR activity in the whole pH and satisfied features with highly available active sites (eg. N-C, Fe-N-C), high surface area of 232.9 m2g-1 and suitable mesoporous structure (mainly centered at

4


Page 4 of 27

Page 5 of 27

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


3 nm and 10.3 nm). Moreover, the remarkable catalytic activity together with the excellent durability and methanol tolerance for ORR, which is superior to the commercial Pt/C, sufficiently demonstrate the promising applications for practical devices of C3N4@NH2-MIL-101-700 catalyst.

2. EXPERIMENTAL SECTION The g-C3N4 was first obtained as follows: 8 g urea was added in a tube furnace and heated at 550 °C with the protection of highly pure argon gas (99.999%) for 4 h. And in the typical process of preparation the g-C3N4 assisted NH2-MIL-101 metal–organic frameworks (C3N4@NH2-MIL-101), 0.35 g C3N4 powder were first dissolved in 30 mL DMF to from a uniform solution. Then, 0.7464 g FeCl3·6H2O and 0.25 g 2-aminoterephthalate were successively put into the above system with the assistance of ultrasonication and vigorous stirring. After stirring at least for 30 minutes, the mixture was poured into a 50 mL poly-tetrafluoroethylene reaction kettle and kept at 110 °C for 24 h. Subsequently, the resulting hybrid was separated and washed using DMF and deionized H2O for several times, then baked in a vacuum drying oven at 60 °C. Afterwards, the obtained hybrid as the precursor were heated at 180 °C, 800 °C (or 600 °C, 700 °C, 900 °C) in tube furnace for 1 h and 2 h , respectively under flowing highly pure argon gas. Moreover, the obtained black catalysts of X-T (where T refers to the calcination temperature) were treated in 0.5 M H2SO4 for 10 h in order to remove the inactive metal species. Additional, in order to better investigate the catalytic properties, the contrastive NH2-MIL-101-700 and NPGC were also prepared. And the NH2-MIL-101 was

5



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

obtained using the same hydrothermal method like C3N4@NH2-MIL-101 except no addition of C3N4. Electrocatalytic Activity Measurements The catalyst ink was prepared as follows: the 4 mg/mL homogeneous catalyst ink in 0.79 mL absolute ethanol, 0.2 mL H2O and 0.01 mL (5%) Nafion was prepared under sonication for 10 min and then used for modification. Before each experiment, 0.021 mL catalyst ink was dropped on the RRDE electrode surface (D=5.6 mm). For comparison, the Pt catalyst with an amount of 20 µg Pt/cm2 was prepared.

3. RESULTS AND DISCUSSION The synthesis process is displayed in Figure 1A, which includes the directed growth of the NH2-MIL-101 metal–organic frameworks on the surface or around of g-C3N4 by a solvothermal reaction (denoted as C3N4@NH2-MIL-101), and followed with heat treating process to achieve the porous carbon-based architecture (the details was illustrated in Supporting Information). Firstly, the TEM image and XRD of the g-C3N4 were collected in Figure 1B & Figure S1, which possessed a sheet-like morphology with various pores. Additionally, the typical TEM image of C3N4@NH2-MIL-101 (Figure 1C) clearly indicated that the spindly NH2-MIL-101 was successfully grown on the surface or around of g-C3N4, which further proved by XRD patterns of NH2-MIL-101 and C3N4@NH2-MIL-101 (Figure S2). Then the as-obtained precursor of C3N4@NH2-MIL-101 was pyrolyzed in a tube furnace under Ar atmosphere at 700 °C for 2 h (the resulting product was labeled as C3N4@NH2-MIL-101-700). Figure 1D & E exhibited that the obtained product was 6


Page 6 of 27

Page 7 of 27

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


the porous matrix with homogeneous spindly carbon based materials and some nanoparticles encapsulated in them. Moreover, the HRTEM manifested that the nanoparticle was packaged in a graphite-like carbon shell with an interlayer distance of 0.348 nm corresponding to the (002) crystal planes of graphitic carbon (Figure 1F). For the typical nanoparticle, the lattice spacing of 0.403 nm should be assigned to the (110) crystal planes of the Fe3C phase, which matched with the SAED pattern (Figure 1G). In order to give a comparison study, the TEM images of control materials of NH2-MIL-101 and NH2-MIL-101-700 were provided in Figure S3. Figure 1H-L showed

the

HAADF-STEM

and

its

elemental

mapping

images

of

the

C3N4@NH2-MIL-101-700. It could be confirmed that the elements of C, O, Fe, N were all homogeneously distributed over the selected area, implying that the iron and nitrogen elements were co-doped in the porous carbon architecture in the form of Fe-Nx. The crystal structures of C3N4@NH2-MIL-101-700 were then characterized by powder XRD pattern. As displayed in Figure 2A, after pyrolysis, the generated sharp reflection at 26.4 should be ascribed to the (002) crystal of graphitic carbon. And a series of new peaks at 37.7, 42.9, 43.6, 44.6, 46.06, 49.1, 50.9, 54.8, 65.1, 77.9, 82.4, which can be assigned to Fe3C (JCPDS No.72-1110) and cubic Fe (CPDS No.87-0722), respectively. According to the reference, the existent Fe/Fe3C NPs could assist oxygen adsorption on the active sites, which would promote the ORR activity of the Fe-Nx site.27 The XPS analysis provided the chemical compositions and element bonding information of the afforded C3N4@NH2-MIL-101-700 catalyst. The full

7



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

survey spectrum of Figure 2B revealed signals of C (84.14 At.%), N (6.28 At.%), O (9.44 At.%) and trace Fe (0.14 At. %) element. Among them, the high resolution C 1s spectra (Figure S4) with the peaks were located at 284.2 eV, 284.7 eV, 285.8 eV and 289.2 eV, which should be ascribed to the sp2 C, C=N, C-N and O-C=O bonds, respectively. In addition, the N 1s was convoluted into three types of N species, including pyridine N (N1, 398.2 eV), pyrrolic N (N2, 399.3 eV) and graphitic N (N3 401.0 eV) (Figure 2C). Both the pyridine N and graphitic N reported were electroactive nitrogen species, while the pyrrolic N was uncertain.27 Indeed, due to the larger atomic radius of than C, the doped N can provide more defects and surface polarity for efficient ORR activity.28 Moreover, since the pyridine N owned lone pair electrons, which can easily coordinate metal Fe iron to form the desirable ORR active sites of Fe-Nx.29 The Fe 2p spectrum shown in Figure 2D exhibited two spin-orbit doublets. The first at 710.2 and 722.5 eV, and the second doublet at 712.9 and 725.2 eV, were corresponding to Fe2+ and Fe3+, respectively. Moreover, the XPS survey spectra of NH2-MIL-101-700 also provided in Figure S5, and it’s worth mentioning that the content of N is only 1.32 At.%. SEM images of C3N4@NH2-MIL-101-700 displayed a typical porous structure with many holes at the surface (Figure 3A & B). The surface area and porous property of the catalyst were further confirmed by N2 adsorption-desorption tests. The BET analysis showed that the surface area of C3N4@NH2-MIL-101-700 catalyst were about 232.1 m2 g-1, significantly higher than that of NH2-MIL-101-700 (108.14 m2 g-1). Moreover, a type-IV isotherm with pronounced hysteresis loop was observed for

8


Page 8 of 27

Page 9 of 27

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


the sample of C3N4@NH2-MIL-101-700, indicating the porous structure of the catalyst (Figure 3C) with pore-size distributions centered at 3 nm and 10.3 nm which will provide more accessible active sites.30 In addition, according to the BJH analysis, the pore volume of the C3N4@NH2-MIL-101-700 catalyst was about 0.578 cm3 g-1, while the NH2-MIL-101-700 showed much limited pore volume of 0.122 cm3 g-1. Based on the above results, it can be summarized that the selective use of g-C3N4 as a support template played a pivotal role in the construction of the architecture with rich N content, high surface area and pore volume. In order to study the structural formation of C3N4@NH2-MIL-101-700 during pyrolysis process, thermogravimetric analysis (TGA) was conducted with C3N4@NH2-MIL-101 precursor in N2 atmosphere (Figure 3D). As shown, the initial weight loss (10%) before 180 °C should be ascribed to the constitution water and absorbed water. Then the organic framework and C3N4 existed in the precursors start to decompose from 180 to 500 °C (Figure S6). During this stage, some produced gases (e.g., N2, CO2) were released, along with the formation of pores structure in the catalyst. The continuous sharp weight loss was observed from 500 to 700 °C, corresponding to the decomposition of the precursor to construct the graphitized carbon. The ORR activity of C3N4@NH2-MIL-101-700 and corresponding reference materials were firstly studied in alkaline electrolyte (0.1M KOH). As shown in Figure 4A, the obviously paramount cathodic ORR peak for C3N4@NH2-MIL-101-700 in an O2 saturated electrolyte implied an outstanding ORR performance of this catalyst. The ORR activity of the as-obtained catalysts were further examined by RRDE technique.

9



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

As presented in Figure 4B, C3N4@NH2-MIL-101-700 demonstrated a more positive onset-potential (0.99 V vs. RHE), half-wave potential (0.84 V vs. RHE) and larger diffusion limited current density (6.44 mA/cm2), which were superior to the activity of NH2-MIL-101-700 and NPC-700 (Table S1). Notably, the catalyst of C3N4@NH2-MIL-101-700 also exhibited enhanced ORR performance compared to the commercial Pt/C catalyst. In general, a four electrode (4e-) ORR process is considered as the favorable reaction process, due to the low H2O2 yields. Herein, the electron transferred number (n) and H2O2 yield were calculated by the id (the current from disk electrode) and ir (the current from ring electrode). Figure 4C & D show that the H2O2 yield of C3N4@NH2-MIL-101-700 is below 4% and n ranges in 3.94-3.98, proving the almost complete four electrode (4e-) reaction pathway like Pt/C in alkaline solution. In contrast, the catalyst of NPC-700 showed an inferior electrocatalytic activity with lower electron transferred number of 3.4-3.7 and higher H2O2 yield, which was consistent with the embedded metal nanoparticles to effectively promote the ORR activity.26 To deeply learn the ORR mechanism of the C3N4@NH2-MIL-101-700, RDE technique was also conducted. The Koutecky-Levich equation was applied to obtain the kinetic parameters (Figure S7). The lines of J-1 to ω-1/2 at different electrode potentials indicated a first-order reaction kinetics and the calculated electrode transfer number were close to 4.0, which was in accordance with the RRDE measurement. As far as we know, transition metal element (eg. Fe) was a good mediator for promoting the electron transfer in acidic electrolyte,31 so the C3N4@NH2-MIL-101-700 catalyst was also tested in 0.5 M H2SO4 electrolyte. As

10


Page 10 of 27

Page 11 of 27

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


shown in Figure 5A & B, an onset potential of 0.92 V was observed using C3N4@NH2-MIL-101-700 catalyst with half-wave potential of 0.67 V and diffusion limited current density of 5.83 mA/cm2, which were almost equal to that of Pt/C. Noteworthily, H2O2 yield of C3N4@NH2-MIL-101-700 was below 2% (Figure 5D) and n ranged in 3.97-3.98 (Figure 5C), proving the excellent ORR activity of C3N4@NH2-MIL-101-700 in acidic solution. For commercialization, the tolerance and electrochemical durability are another key evaluation parameters for the catalyst. In this work, amperometric i-t measurements were applied to test the inference of methanol and long-time stability of C3N4@NH2-MIL-101-700 in both 0.1 M KOH and 0.5 M H2SO4 electrolytes. As presented in Figure 4E & 5E, there is almost no change of the i-t curves compared to the commercial Pt/C, were observed when injected 0.3 M methanol in the alkaline and acidic solution, convincingly implying favorable tolerance toward the small organic molecules. Moreover, the relative slow attenuation trend compared to Pt/C of the C3N4@NH2-MIL-101-700 after a long-time tests (Figure 4F & 5F), further indicating the superb stability of the catalyst. These results convincingly exemplified the afforded C3N4@NH2-MIL-101-700 catalyst held a great potential for practical applications. To our knowledge, the ORR in neutral condition have attracted much attention in recent years for their extensive application in bioelectrochemical systems, such as microbial and enzymatic fuel cells.32 However, nowadays, the expensive Pt and poor stability of metallo-enzymes are still the main catalysts. Hence, the use of an efficient NPMCs catalyst operated in these neutral system is urgently demanded. In this work,

11



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 12 of 27

we also investigated the ORR performance of C3N4@NH2-MIL-101-700 in neutral conditions.

To

our

surprise,

as

presented

in

Figure

6A

&

B,

the

C3N4@NH2-MIL-101-700 catalyst exhibited a remarkable ORR activity with onset potential of 0.90 V, half-wave potential of 0.65 V and diffusion limited current density of 5.9 mA/cm2 in the neutral condition, which were obviously superior to the activity of NH2-MIL-101-700 and comparable to Pt/C. In addition, the low H2O2 yield (Figure 6D) combining with the almost 4e- reaction process (Figure 6C) also strongly proved the excellent ORR activity of C3N4@NH2-MIL-101-700 catalyst in neutral condition. Figure 6E provided RDE measurements of the catalyst, according to the Koutecky-Levich equation, it could be further confirmed that the catalyst occupied a 4e- reaction process in neutral solution. Moreover, after 16000s long-time tests (Figure 6F), the C3N4@NH2-MIL-101-700 catalyst showed a relative slow attenuation trend compared to Pt/C as well as demonstrating the prominent ORR catalytic activity in neutral solution. Therefore, based on the above tests, it can be concluded that the C3N4@NH2-MIL-101-700 catalyst manifested superb ORR activity in the whole pH range. Additionally, it’s worth to mention that the obtained catalyst exhibited clear advantages compared with other reported non-precious metal catalysts (Table S3).6,33-39 Previous studies had indicated that N species played a significant role in the activity of the pyrolytic carbon-based ORR activity.24 Herein, in order to demonstrate the effect of N species, the contrastive samples of C3N4@NH2-MIL-101-T were prepared (T = 600, 700, 800 and 900 °C, respectively). Figure S8 & S9 show the TEM images

12


Page 13 of 27

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


and XRD patterns of the catalysts acquired at various pyrolysis temperatures. Moreover, the XPS measurements were further employed to analyze the doped N at different temperatures (Figure S10). With the increase of calcination temperature, the relative composition of N1 (pyridine N) reduced gradually, while the N3 (graphitic N) was raised significantly. Among them, the electroactive nitrogen species of N1and N3 reached the maximum of 82 % at 700 °C, which was consistent with the trend of ORR performance of C3N4@NH2-MIL-101-T catalysts (Figure S11-S13). This indicated that the pyridine N and graphitic N are more beneficial to the enhanced ORR activity. Additionally, the C3N4@NH2-MIL-101-900 exhibited an obvious decreased catalytic activity, which may be due to the decrease of pyridine N. Overall, based on the all characterization, both the corresponding chemical components and the existent porous architectures endowed the C3N4@NH2-MIL-101-700 catalyst with the remarkable electrocatalytic activity and durability for ORR.

4. CONCLUSION In summary, a highly efficient and durable non-precious metal electrocatalyst of C3N4@NH2-MIL-101-700 was successfully prepared. The afforded catalyst exhibited remarkable catalytic performance with high selectivity and very low H2O2 yield, excellent stability and durability in the whole pH range. The catalytic activity of C3N4@NH2-MIL-101-700 is superior to the commercial Pt/C catalyst and most of the highest reported non-precious metal electrocatalyst. Additionally, the whole preparation process of the catalyst is cost-effective and easy to mass production. All these excellent features make its promising practical applications in technological 13



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

devices. The facile synthetic strategy of C3N4@NH2-MIL-101-700 presented here is expected to develop new opportunities for the rational design and construction of other C3N4@MOF based catalysts for energy storage and renewable energy applications yet. ASSOCIATED CONTENT Supporting Information. Additional information about the SEM image, XPS spectra and supporting CVs, LSV analysis. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *Tel: +86-431-85262003. Fax: +86-431-85689711. E-mail: [email protected]. *Tel: +86-431-85262003. Fax: +86-431-85689711. E-mail: [email protected]. Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS Support from the National Natural Science Foundation of China (Grant No. 21190040 and 21427811), Most China 2016 YFA 0203200 and Youth innovation promotion Association CAS (No.2016208).

REFERENCES (1) Nie, Y.; Wei, Z. Recent Advancements in Pt and Pt-Free Catalysts for Oxygen Reduction Reaction. Chem. Soc. Rev. 2015, 44, 2168-2201. 14


Page 14 of 27

Page 15 of 27

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


(2) Steele, B. C. H.; Heinzel, A. Review Article Materials for Fuel-Cell Technologies. Nature 2001, 414, 345-352. (3) Dai, L. M.; Xue, Y. H.; Qu, L. T.; Choi, H. J.; Baek, J. B. Metal-Free Catalysts for Oxygen Reduction Reaction. Chem. Rev. 2015, 115, 4823-4892. (4) Greeley, J.; Stephens, E. L.; Bondarenko, A. S.; Johansson, T. P.; Hansen, H. A.; Jaramillo, T. F.; Rossmeis, J.; Chorkendorff, I.; Nørskov, J. K. Alloys of Platinum and Early Transition Metals as Oxygen Reduction Electrocatalysts. Nat. Chem. 2009, 1, 552-556. (5) Liang, H.; Cao, X.; Zhou, F.; Cui, C.; Zhang, W.; Yu, S. A Free-Standing Pt-Nanowire Membrane as a Highly Stable Electrocatalyst for the Oxygen Reduction Reaction. Adv. Mater. 2011, 23, 1467-1471. (6) Li, Z. H.; Shao, M. F.; Zhou, L.; Zhang, R. K.; Zhang, C.; Wei, M.; Evans, D. G.; Duan, X. Directed Growth of Metal-Organic Frameworks and Their Derived Carbon-Based Network for Efficient Electrocatalytic Oxygen Reduction. Adv. Mater. 2016, 28, 2337-2344. (7) Gu, W. L.; Hu, L. Y.; Hong, W.; Jia, X. F.; Li, J.; Wang, E. K. Noble-Metal-Free Co3S4-S/G Porous Hybrids As an Efficient Electrocatalyst for Oxygen Reduction Reaction. Chem. Sci. 2016, 7, 4167-4173. (8) Liang, E. K.; Du, X.; Gibson, C.; Du, X.; Qiao, S. N-Doped Graphene Natively Grown on Hierarchical Ordered Porous Carbon for Enhanced Oxygen Reduction. Adv. Mater. 2013, 25, 6226-6231. (9) Masa, J.; Xia, W.; Muhler, M.; Schuhmann, W. On the Role of Metals in

15



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

Nitrogen-Doped Carbon Electrocatalysts for Oxygen Reduction. Angew. Chem. Int. Ed. 2015, 54, 10102-10120. (10) Xiang, Z.; Cao, D.; Huang, L.; Shui, J.; Wang, M.; Dai, L. Nitrogen-Doped Holey Graphitic Carbon from 2D Covalent Organic Polymers for Oxygen Reduction. Adv. Mater. 2014, 26, 3315-3320. (11) Zhu, Y. S.; Zhang, B. S.; Liu, X.; Wang, D. W.; Su, D. S. Unravelling the Structure of Electrocatalytically Active Fe–N Complexes in Carbon for the Oxygen Reduction Reaction. Angew. Chem. Int. Ed. 2014, 53, 10673-10677. (12) Zhang, J.; Qu, L.; Shi, G.; Liu, J.; Chen, J.; Dai, L. N,P-Codoped Carbon Networks as Efficient Metal-free Bifunctional Catalysts for Oxygen Reduction and Hydrogen Evolution Reactions. Angew. Chem. Int. Ed. 2016, 55, 2230-2234. (13) Wei, P. J.; Yu, G. Q.; Naruta, Y.; Liu, J. G. Covalent Grafting of Carbon Nanotubes with a Biomimetic Heme Model Compound To Enhance Oxygen Reduction Reactions. Angew. Chem. Int. Ed. 2014, 53, 6659-6663. (14) Hijazi, I.; Bourgeteau, T.; Cornut, R.; Morozan, A.; Filoramo, A.; Leroy, J.; Derycke, V.; Jousselme, B.; Campidelli, S. Carbon Nanotube-Templated Synthesis of Covalent Porphyrin Network for Oxygen Reduction Reaction. J. Am. Chem. Soc. 2014, 136, 6348-6354. (15) Yasuda, S. S.; Furuya, A.; Uchibori, Y. K.; Kim, J.; Murakoshi, K. Iron–Nitrogen-Doped Vertically Aligned Carbon Nanotube Electrocatalyst for the Oxygen Reduction Reaction. Adv. Funct. Mater. 2016, 26, 738-744. (16) Nabae, Y.; Kuang, Y.; Chokai, M.; Ichihara, T.; Isoda, A.; Hayakawa, T.; Aoki, T.

16


Page 16 of 27

Page 17 of 27

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


High Performance Pt-Free Cathode Catalysts for Polymer Electrolyte Membrane Fuel Cells Prepared from Widely Available Chemicals. J. Mater. Chem. A 2014, 2, 11561-11564. (17) Gu, W. L.; Hu, L. Y.; Li, J.; Wang, E. K. Iron and Nitrogen Co-doped Hierarchical Porous Graphitic Carbon for a High-Efficiency Oxygen Reduction Reaction in a Wide Range of pH. J. Mater. Chem. A 2016, 4, 14364-14370. (18) Zhao, Y.; Watanabe, K.; Hashimoto, K. Self-Supporting Oxygen Reduction Electrocatalysts Made from a Nitrogen-Rich Network Polymer. J. Am. Chem. Soc. 2012, 134, 19528-19531. (19) Jaouen, F.; Proietti, E.; Lefevre, M.; Chenitz, R.; Dodelet, J. P.; Wu, G.; Chung, H. T.; Johnston, C. M.; Zelenay, P. Recent Advances in Non-Precious Metal Catalysis for Oxygen-Reduction Reaction in Polymerelectrolyte Fuel Cells. Energy Environ. Sci. 2011, 4, 114-130. (20) 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. Ed. 2015, 54, 8179-8183. (21) Liang, H. W.; Wei, W.; Wu, Z. S.; Feng, X.; Mülen, K. Mesoporous Metal–Nitrogen-Doped Carbon Electrocatalysts for Highly Efficient Oxygen Reduction Reaction. J. Am. Chem. Soc. 2013, 135, 16002-16005. (22) Liang, H. W.; Zhuang, X.; Brüller, S.; Feng, X.; Müllen, K. Hierarchically Porous Carbons with Optimized Nitrogen Doping as Highly Active Electrocatalysts for Oxygen Reduction. Nat. Commun. 2014, 5, 4973-4979.

17



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

(23) Silva, R.; Voiry, D.; Chhowalla, M.; Asefa, T. Efficient Metal-Free Electrocatalysts for Oxygen Reduction: Polyaniline-Derived N- and O-Doped Mesoporous Carbons. J. Am. Chem. Soc. 2013, 135, 7823-7826. (24) Chen, Y.; Wang, C.; Wu, Z.; Xiong, Y.; Xu, Q.; Yu, S.; Jiang, H. From Bimetallic Metal-Organic Framework to Porous Carbon: High Surface Area and Multicomponent Active Dopants for Excellent Electrocatalysis. Adv. Mater. 2015, 27, 5010-5016. (25) Xia, W.; Zou, R.; An, L.; Xia, D.; Guo, S. A Metal–Organic Framework Route to in Situ Encapsulation of Co@Co3O4@C Core@Bishell Nanoparticles into a Highly Ordered Porous Carbon Matrix for Oxygen Reduction. Energy Environ. Sci. 2015, 8, 568-576. (26) Jiang, W. J.; Gu, L.; Li, L.; Zhang, Y.; Zhang, X.; Zhang, L. J.; Wang, J. Q.; Hu, J. S.; Wei, Z. D.; Wan, L. J. Understanding the High Activity of Fe–N–C Electrocatalysts in Oxygen Reduction: Fe/Fe3C Nanoparticles Boost the Activity of Fe–Nx. J. Am. Chem. Soc. 2016, 138, 3570-3578. (27) Xia, W.; Mahmood, A.; Zou, R.; Xu, Q. Metal–Organic Frameworks and Their Derived Nanostructures for Electrochemical Energy Storage and Conversion. Energy Environ. Sci. 2015, 8, 1837-1866. (28) Wu, G.; Zelenay, P. Nanostructured Nonprecious Metal Catalysts for Oxygen Reduction Reaction. Acc. Chem. Res. 2013, 46, 1878-1889. (29) Schulenburg, H.; Stankov, S.; Schünemann, V.; Radnik, J.; Dorbandt, I.; Fiechter, S.; Bogdanoff, P.; Tributsch, H. Catalysts for the Oxygen Reduction from Heat-Treated Iron(III) Tetramethoxyphenylporphyrin Chloride: Structure and

18


Page 18 of 27

Page 19 of 27

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


Stability of Active Sites. J. Phys. Chem. B 2003, 107, 9034-9041. (30) 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. Ed. 2015, 54, 8179-8183. (31) Jiang, R.; Chu, D. Comparative Study of CoFeNx/C Catalyst Obtained by Pyrolysis of Hemin and Cobalt Porphyrin for Catalytic Oxygen Reduction in Alkaline and Acidic Electrolytes. J. Power Sources 2014, 245, 352-361. (32) Zhao, F.; Slade, R. C. T.; Varcoe, J. R. Techniques for the Study and Development of Microbial Fuel Cells: an Electrochemical Perspective. Chem. Soc. Rev. 2009, 38, 1926-1939. (33) Lin, L.; Zhu, Q.; Xu, A. W. Noble-Metal-Free Fe–N/C Catalyst for Highly Efficient Oxygen Reduction Reaction under Both Alkaline and Acidic Conditions. J. Am. Chem. Soc. 2014, 136, 11027-11033. (34) Hou, Y.; Huang, T.; Wen, Z.; Mao, S.; Cui, S.; Chen, J. Metal−Organic Framework-Derived Nitrogen-Doped Core-Shell-Structured Porous Fe/Fe3C@C Nanoboxes Supported on Graphene Sheets for Efficient Oxygen Reduction Reactions. Adv. Energy Mater. 2014, 4, 1400337. (35) Iwase, K.; Yoshioka, T.; Nakanishi, S. J.; Hashimoto, K.; Kamiya, K. Copper-Modified

Covalent

Triazine

Frameworks

as

Non-Noble-Metal

Electrocatalysts for Oxygen Reduction. Angew. Chem. Int. Ed. 2015, 54, 11068-11072. (36) Singh, K. P.; Bae, E. J.; Yu, J. S. Fe–P: A New Class of Electroactive Catalyst for

19



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

Oxygen Reduction Reaction. J. Am. Chem. Soc. 2015, 137, 3165-3168. (37) Zhao, D.; Shui, J.; Chen, C.; Chen, X.; Reprogle, B. M.; Wang, D.; Liu, D. Iron Imidazolate Framework as Precursor for Electrocatalysts in Polymer Electrolyte Membranefuel Cells. Chem. Sci. 2012, 3, 3200-3205. (38) Zhang, W.; Wu, Z.; Jiang, H.; Yu, S. Nanowire-Directed Templating Synthesis of Metal–Organic Framework Nanofibers and Their Derived Porous Doped Carbon Nanofibers for Enhanced Electrocatalysis J. Am. Chem. Soc. 2014, 136, 14385-14388. (39) Aijaz, A.; Fujiwara, N.; Xu, Q. From Metal–Organic Framework to Nitrogen-Decorated Nanoporous Carbons: High CO2 Uptake and Efficient Catalytic Oxygen Reduction. J. Am. Chem. Soc. 2014, 136, 6790-6793.

20


Page 20 of 27

Page 21 of 27

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


Figure 1 Schematic illustration (A) for the fabrication of C3N4@NH2-MIL-101-700 catalyst and their electrocatalytic activity for ORR; TEM images of C3N4 (B), C3N4@NH2-MIL-101 (C), and C3N4@NH2-MIL-101-700 (D, E); HRTEM image (F), SAED pattern (G), HAADF-STEM (H) and its elemental mapping images (I–L) of the C3N4@NH2-MIL-101-700 catalyst.

21



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

Figure 2 XRD patterns (A) of the C3N4@NH2-MIL-101-700 catalyst; XPS survey spectra (B) of C3N4@NH2-MIL-101-700; High resolution N 1s spectra (C) and Fe 2p spectra (D) of the fabricated C3N4@NH2-MIL-101-700 catalyst.

22


Page 22 of 27

Page 23 of 27

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


Figure 3 SEM images (A, B) of the obtained C3N4@NH2-MIL-101-700 catalyst; N2 adsorption-desorption isotherm (C) of NH2-MIL-101-700 and C3N4@NH2-MIL-101-700 (inset shows the BJH pore distributions); TGA analysis (D) of C3N4@NH2-MIL-101 precursors in N2 atmosphere.

23



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

Figure 4 CVs (A) of the C3N4@NH2-MIL-101-700 catalyst and Pt/C in N2 or O2 saturated 0.1 M KOH electrolyte; LSV (B), electron transfer number (C), H2O2 yield (D) of the NPC-700, NH2-MIL-101-700, C3N4@NH2-MIL-101-700 and commercial 20% Pt/C catalysts in O2 saturated 0.1 M KOH electrolyte. The scan rate and rotation rate were 5 mVs-1 and 1600 rpm, respectively; Methanol tolerance test (E) of C3N4@NH2-MIL-101-700 and Pt/C in O2-saturated 0.1 M KOH; The amperometric i-t response (F) to the C3N4@NH2-MIL-101-700 and Pt/C in O2 saturated 0.1 M KOH electrolyte.

24


Page 24 of 27

Page 25 of 27

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


Figure 5 CVs (A) of the C3N4@NH2-MIL-101-700 catalyst and Pt/C in N2 or O2 saturated 0.5 M H2SO4 electrolyte; LSV (B), electron transfer number (C), H2O2 yield (D) of the NH2-MIL-101-700, C3N4@NH2-MIL-101-700 and commercial 20% Pt/C catalysts in O2 saturated 0.5 M H2SO4 electrolyte. The scan rate and rotation rate were 5 mVs-1 and 1600 rpm, respectively; Methanol tolerance test (E) of C3N4@NH2-MIL-101-700 and Pt/C in O2-saturated 0.5 M H2SO4; The amperometric i-t response (F) to the C3N4@NH2-MIL-101-700 and Pt/C in O2 saturated 0.5 M H2SO4 electrolyte.

25



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

Figure 6 CVs (A) of the C3N4@NH2-MIL-101-700 catalyst and Pt/C in N2 or O2 saturated 0.1 M PBS (pH = 7.4) electrolyte; LSV (B), electron transfer number (C), H2O2 yield (D) of the NH2-MIL-101-700, C3N4@NH2-MIL-101-700 and commercial 20% Pt/C catalysts in O2 saturated 0.1 M PBS electrolyte. The scan rate and rotation rate were 5 mVs-1 and 1600 rpm, respectively; RDE voltammograms (E) of the obtained C3N4@NH2-MIL-101-700 at different rotation rates in 0.1 M PBS electrolyte; The inset is the corresponding koutecky–levich plots. The amperometric i-t response (F) to the C3N4@NH2-MIL-101-700 and Pt/C in O2 saturated 0.1 M PBS electrolyte.

26


Page 26 of 27

Page 27 of 27

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


Table of contents entry

A highly actived electrocatalyst for oxygen reduction reaction (ORR) over the pH 0-14 was produced by employing the g-C3N4 assistanted metal–organic frameworks (MOF) of C3N4@NH2-MIL-101 as the precursor.

27


Hybrid of g-C3N4 Assisted MetalâOrganic Frameworks and Their

Recommend Documents

Hybrid of g-C3N4 Assisted MetalâOrganic Frameworks and Their