- Email: [email protected]
Nitrogen and sulfur dual-doped hollow mesoporous carbon spheres as efficient metal-free catalyst for oxygen reduction reaction
Journal Pre-proofs Nitrogen and Sulfur Dual-doped Hollow Mesoporous Carbon Spheres as Efficient Metal-free Catalyst for Oxygen Reduction Reaction Wanfeng Xiong, Hongfang Li, Rong Cao PII: DOI: Reference:
S1387-7003(20)30091-5 https://doi.org/10.1016/j.inoche.2020.107848 INOCHE 107848
To appear in:
Inorganic Chemistry Communications
Received Date: Revised Date: Accepted Date:
21 January 2020 13 February 2020 17 February 2020
Please cite this article as: W. Xiong, H. Li, R. Cao, Nitrogen and Sulfur Dual-doped Hollow Mesoporous Carbon Spheres as Efficient Metal-free Catalyst for Oxygen Reduction Reaction, Inorganic Chemistry Communications (2020), doi: https://doi.org/10.1016/j.inoche.2020.107848
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2020 Published by Elsevier B.V.
Nitrogen and Sulfur Dual-doped Hollow Mesoporous Carbon Spheres as Efficient Metal-free Catalyst for Oxygen Reduction Reaction Wanfeng Xiong1,2, Hongfang Li1,2*, and Rong Cao1 1 College of Chemistry and Materials Science, Fujian Normal University, Fuzhou 350007, China 2 State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, China. * Corresponding authors. E-mail: [email protected] Abstract Developing a cheap and efficient oxygen reduction reaction (ORR) catalyst is one of the emerging issues. The doped carbon materials have attracted much attention due to the controllable and cheap synthesis methods. In this work, the nitrogen and sulfur dualdoped hollow mesoporous carbon sphere (NS-HMCS) has been synthesized through a hard-template method. During the co-polymerization process of dopamine (DA) and cysteamine (CA), the nitrogen (N) and sulfur (S) sites are introduced into the carbon skeleton at the same time, which simplifies the tedious steps in the post-modification of carbon materials. The obtained NS-HMCS-32 exhibits high content of nitrogen about 4.8 % and sulfur about 1.4 %. NS-HMCS-32 has a high specific surface areas (898 m2 g-1) and a large pore volume (2.99 cm3 g-1). During the ORR measurement, the halfwave potential of NS-HMCS-32 reaches up to 0.77 V vs. RHE. Moreover, NS-HMCS32 reveals a better durability than commercial Pt/C and 79.2 % of current density remains after 9 hours chronoamperometry test. This work provides a design idea for dual-doped carbon materials and the obtained NS-HMCS is a potential candidate for metal-free catalyst in fuel cells.
Keywords: dual-doped carbon materials, oxygen reduction reaction, metal-free catalyst Energy crisis has been a rigorous problem during the rapid society development [1]. Therefore, lots of researches are dedicated to the exploitation of clean energy source [2-4], such as fuel cell and metal-air batteries [5, 6]. Oxygen reduction reaction (ORR), the crucial semi-reaction in these devices, has got in-depth study for enhancing its sluggish kinetic processes [7]. The traditional platinum-based catalyst is the effective electrocatalyst for ORR [8]. However, the expensive price and the poor catalysis durability are still the bottleneck which limits its wide application. Therefore, exploring a cheap catalyst with high activity and long-standing durability receives a huge amount of attention. Recent years, metal-free catalysts have been eye-catching due to its low price and structure stability [9, 10]. Among them, heteroatom-doped carbon materials receive the most attention in the field of ORR [11]. Heteroatom doping can not only change the electronic structure, but also create the structural defects in the carbon-based materials, which effectively solves the sluggishness of pristine carbon in catalysis [12]. With the atomic size similar to carbon, nitrogen has been widely doped in carbon matrix and built active sites for ORR. But one-type doping still has limitation in activity improvement and therefore the dual-doping or tri-doping with B, S and P in carbon skeleton have been achieved through chemical vapor deposition (CVD) [13, 14] and post-modification [15, 16]. With the synergistic effect of multiple heteroatoms, the obtained metal-free catalysts have all shown significant performance improvements comparing with one-type doping [17-19]. However, the synthetic processes are complicated and tedious. Hence, exploring a facile method to fabricate the dual-doped carbon materials with excellent catalytic activity is still a challenge for developing the efficient metal-free catalysts. Hollow mesoporous carbon sphere (HMCS) is a three-dimensional carbon material with huge cavity and porous carbon shell [20]. Comparing with the solid counterparts, HMCS exhibits higher surface area, more exposed sites and larger interior space. These
advantages make it a great potential application in the field of biotechnology, energy storage and chemical catalysis [21]. But how to create the active sites for enhancing its catalytic capability is still a problem. Liang et al. have found that the synergistic effect between nitrogen and sulfur could bring the redistribution of spin and charge densities in carbon and therefore produced active sites efficiently [22]. Therefore, we choose nitrogen and sulfur dopants for getting a high active carbon based ORR catalyst. In this work, N and S atom dual-doped HMCS has been fabricated through the simple onestep template method. The obtained NS-HMCS-32 exhibits a high catalysis activity which could catch up with commercial Pt/C and even a superior durability. The influence of N, S dual-doping on electronic structure and porosity of HMCS has also been studied intensively. All the changes on electronic and porous structure for HMCS greatly promote the improvement of ORR performance.
Scheme 1. Schematic illustration of the synthesis for N, S dual-doped HMCS
As seen in Scheme 1, the primary silica sphere was firstly assembled as the core through an in-situ stöber templating. During the polymerization of TEOS, the dopamine (DA) and cysteamine (CA) were added at the same time. The secondary silica sphere and the PDA/CA grew on the primary silica sphere core to form the core-shell structure. After the carbonizing at high temperature and etching with sodium hydroxide solution, the
N, S dual-doped hollow mesoporous carbon sphere (NS-HMCS) was obtained.
Fig. 1. (a) SEM, (b) TEM and (c) HAADF-STEM images of NS-HMCS-32, (d) EDS mapping of C, N and S distributed on the NS-HMCS-32.
The morphology of NS-HMCS could be observed directly through scanning electron microscope (SEM) and the transmission electron microscopy (TEM). Monitoring the molar ratio of DA and CA (3:1 and 3:2), the obtained NS-HMCS-31 (Fig. S1a and S1c) and NS-HMCS-32 (Fig. 1a and b) both displayed a regular hollow carbon sphere morphology. Further increasing CA content to 3:3, the obtained NS-HMCS-33 showed broken sphere morphology (Fig. S1b and S1d). This result indicated that the ratio between DA and CA played a vital role in the polymerization of PDA/CA precursor. When excess sulfur was introduced, the scale discrepancy between S and C atom made carbon skeleton collapsed and therefore leaded to the broken carbon spheres. With the high-angle annular dark-field scanning transmission electron microscopy (HAADFSTEM) and energy-dispersive X-ray spectroscope (EDS), the morphology of NSHMCS-32 was further observed. As shown in Fig. 1c, the ultra-thin carbon shell ca. 12 nm and the plentiful pore construction could be seen directly in NS-HMCS-32. The EDS-mapping of NS-HMCS-32 displayed the existence of C, N and S elements (Fig. 1d), which demonstrated that the N and S atoms were uniformly distributed in the
carbon spheres. Base on the observation above, it could be confirmed that N, S dualdoped NS-HMCS with huge cavity, ultra-thin carbon shell and highly porosity was produced successfully. The unique hollow structure of NS-HMCS not only enhanced the mass transfer ability, but also made more active sites exposed, which was benefit for the electrocatalytic performance [23].
Fig. 2. (a) PXRD pattern and (b) Raman spectrum of NS-HMCS, High-resolution (c) N 1s and (d) S 2p XPS spectra of NS-HMCS.
The chemical constitution of NS-HMCS was characterized through the spectroscopy technology. The PXRD patterns of NS-HMCS were shown in Fig. 2a. After the hightemperature carbonization, all samples displayed a wide diffraction peaks at 23o, which could be attributed to plane of graphitic carbon (002). The Raman spectroscopy was
used to characterize the structural defect of carbon skeleton (Fig. 2b). The typical D peak and G peak were corresponding to the disordered and sp2-hybrid graphitic carbon [24]. The intensity ratio (ID/IG) of the D and G peak increased slightly from 1.00 to 1.11 with the increase in CA content, which indicated the increase of the defect graphite carbon. This result showed that the introduction of sulfur atom could create large numbers of defect sites in the carbon skeleton, and these sites could play the vital roles in catalyzing ORR [25]. The element compositions of NS-HMCS were determined with the X-ray photoelectron spectroscopy (XPS) measurement. The N 1s and S 2p high-resolution XPS spectrum were displayed in Fig. 2c and d. The fitting of N 1s in HMCS exhibited three peaks assigned to graphitic-N (400.9 eV), pyrrolic-N (399.4 eV) and pyridinic-N (398.3 eV), respectively [26]. The high content of pyrrolic-N and pyridinic-N could regulate the electronic structure of carbon materials effectively and therefore enhancing the activity toward ORR. The chemical environment of S element was also analyzed by fitting the XPS spectrum and the existence of S element in HMCS were S-O (2P3/2 168.1 eV and 2P1/2 169.3 eV) and C-S-C (2P3/2 163.9 eV and 2P1/2 165.0 eV), respectively [27, 28]. Obviously, the content of C-S-C typed S element held a dominant position, which demonstrated the successful doping of S element in the HMCS. The sulfur doped would further modulate the long-range interaction between S and N sites [29]. The deconvoluted C 1s spectra (Fig. S2) also displayed the evidence of C-N and C-S connection. The content of nitrogen and sulfur was also evaluated by the element analysis (Table S1). The nitrogen and sulfur content was higher than 4.0 % and 1.0 % respectively in all NS-HMCS, which was a relatively high N and S content in the previously reported dual-doped carbon materials [25]. The XPS measurement and element analysis verified the existential form of N and S elements in HMCS, and the successful N, S dual-doping could be the advantage for the ORR performance enhancing.
Fig. 3. (a) N2 adsorption-desorption isotherms and (b) BJH pore size distributions of NS-HMCS.
The pore structure of the materials also played the vital role on the catalystic activity because it deeply affected the diffusion and mass transfer ability of the catalyst [26]. The N2 adsorption method was applied to evaluate the Brunauer-Emmett-Teller (BET) surface area and porous structure. The N2 adsorption-desorption isotherms (Fig. 3a) showed that all of the NS-HMCS displayed the type-II isotherms with H4 typed hysteresis loop. Increasing the CA content, the specific surface areas of NS-HMCS-32 increased firstly. Further increasing CA content, the specific surface areas of NSHMCS-33 reduced greatly (Table S2). Such obvious decrease in BET surface areas was probably originated from the structure collapse of the hollow mesoporous carbon sphere which have been confirmed by above SEM and TEM images. The broken carbon shell resulted in a decrease in specific surface areas as well as the porosity. The NS-HMCS32 sample had highest BET surface areas ca. 898 m2 g-1 and largest porous volume ca. 2.99 cm3 g-1. As shown in Fig. 3b, the pore distribution of NS-HMCS-32 was mainly at 2.2 nm, which indicated the abundant mesopores existed in the shell of carbon spheres. This large specific surface area and abundant pore structure would facilitate the diffusion and mass transfer ability and therefore improve the ORR catalytic performance [31].
Fig. 4. (a) LSV curves toward ORR and (b) Tafel plots of NS-HMCS and N-HMCS, (c) K-L plots of NS-HMCS-32 at different potentials, (d) RRDE linear sweep voltammogram of NS-HMCS-32, (e) Double-layer Capacitance (Cdl) obtained by a different scan rate for NS-HMCS, (f) chronoamperometric responses of NS-HMCS-32 and 20 wt % Pt/C at 0.6 V vs. RHE.
In order to verify the catalytic performance of NS-HMCS, the linear scan voltammogram (LSV) measurement were tested firstly. As displayed in Fig. 4a, the N, S dual-doped NS-HMCS-31 and NS-HMCS-32 both shown a significant improvement compared with only N-doped N-HMCS. But the catalytic activity of NS-HMCS-33 was declined dramatically, which could be ascribed to the broken carbon spheres. The NSHMCS-32 exhibited a half-wave potential of 0.77 V vs. RHE, which surpassed most dual-doped carbon materials (Table S3) and could catch up with the commercial Pt/C (0.82 V vs. RHE). The Tafel slope of samples was calculated and displayed in Fig. 4b. As can be seen, the Tafel slope of NS-HMCS-32 was only 48.8 mV dec-1, which revealed the highest catalytic efficiency. The LSV curves of NS-HMCS-32 at different rotate speed were measured (Fig. S3) and the relationship of current density and rotate speed were converted through the Koutecky-Levich (K-L) equation. As shown in Fig.
4c, the fitting lines were nearly parallel, which demonstrate the potential-independent electron transfer rate and O2 first-order reaction kinetics. The calculated electron transfer number (n) indicated a nearly four-electron transfer process. For further confirming the value of n, rotating ring-disk electrode (RRDE) measurement was applied. The RRDE linear sweep of NS-HMCS-32 in Fig. 4d showed a nearly fourelectron transfer process, which is consistent with the above calculation value from KL equation. The four-electron process verified the extremely high selectivity of NSHMCS-32 in catalyzing ORR. Among the three samples, NS-HMCS-32 displayed a higher sulfur content than NS-HMCS-31 and therefore more sulfur active sites can be used in the electrochemical catalysis. Further increasing the sulfur content in NSHMCS-33, the hollow mesoporous carbon spheres structure was collapsed and the specific surface area and pore volume decreased greatly which deteriorated its catalytic performance. Conversely, NS-HMCS-32 maintained the unique three-dimensional structure and the highest surface areas and porous volume. facilitated the diffusion and mass transfer ability and therefore improved the ORR catalytic performance. For further exploring the promotion of catalytic activity, electrochemical surface areas (ECSAs) were applied to evaluate the active site numbers. The cyclic voltammograms at different scan rates were measured (Fig. S5) and the double-layer capacitance (Cdl) were obtained through the fitting result from current density and scan rates. As shown in Fig. 4e, NS-HMCS-32 displayed the highest Cdl performance of 11.4 mF cm-2. This result indicated that larger numbers of active sites existed in the NS-HMCS-32 and there enhancing the ORR performance [5, 32]. It is well known that, the electrocatalytic durability was a key factor for assessing the property of catalysts. Therefore, chronoamperometry was applied to evaluate the durability NS-HMCS-32. After 9 hours durability measurement, the current density of NS-HMCS-32 still remained 79.2 %, but the Pt/C catalyst presented a much lower remaining about only 59.7 %. This result indicated that the as prepared NS-HMCS-32 exhibited outstanding durability compared with the commercial Pt/C. Based on the electrocatalysis measurement and the characterizations above, it could be
found that the heteroatom dual-doping of N and S effectively regulated the electronic structure in the carbon skeleton and therefore created active sites. On the other hand, the morphology of HMCS also has a great influence on the ORR performance. The destruction of carbon spheres leaded to a decrease in the mass transfer ability and therefore reduced the ORR activity. As a result, the heteroatom doping and the pore structure played an equally important status in catalyzing ORR. In summary, the N, S dual-doped hollow mesoporous carbon sphere was fabricated through a facile one-step method. The N, S dual-doped NS-HMCS-32 had a high specific surface area (898 m2 g-1) and a large pore volume (2.99 cm3 g-1). Moreover, NS-HMCS-32 displayed high ORR activity and good durability. It is believed that the unique electronic and porous structure of NS-HMCS played a decisive role on the high catalytic performance in ORR. This work provides a simple method for designing a high activity dual-doped carbon materials and lays the foundation for exploring the cheap metal-free ORR catalysts.
References [1] Barnham. K. W. J, Mazzer M, Clive B, Resolving the energy crisis: nuclear or photovoltaics? , Nature Materials, 5 (2006) 161. [2] M. Chen, Y. Xie, J.-X. Wu, H. Huang, J. Teng, D. Wang, Y. Fan, J.-J. Jiang, H.-P. Wang, C.-Y. Su, Cobalt (oxy)hydroxide nanosheet arrays with exceptional porosity and rich defects as a highly efficient oxygen evolution electrocatalyst under neutral conditions, Journal of Materials Chemistry A, 7 (2019) 10217-10224. [3] Y. Jiao, Y. Zheng, M. Jaroniec, S.Z. Qiao, Design of electrocatalysts for oxygenand hydrogen-involving energy conversion reactions, Chem Soc Rev, 44 (2015) 20602086. [4] Y Hu, D Huang, J Zhang, Y Huang, M.-S. Balogun, Y. Tong, Dual Doping Induced Interfacial Engineering of Fe2N/Fe3N Hybrids with Favorable d-band towards Efficient
Overall Water Splitting, ChemCatChem, 11 (2019) 6051-6060. [5] W.-F. Xiong, H.-F. Li, H-H. You, M.-N. Cao, R Cao, Encapsulating metal organic framework into hollow mesoporous carbon sphere as efficient oxygen bifunctional electrocatalyst, National Science Review, DOI: 10.1093/nsr/nwz166. [6] C. Santoro, A. Serov, L. Stariha, M. Kodali, J. Gordon, S. Babanova, O. Bretschger, K. Artyushkova, P. Atanassov, Iron based catalysts from novel low-cost organic precursors for enhanced oxygen reduction reaction in neutral media microbial fuel cells, Energy & Environmental Science, 9 (2016) 2346-2353. [7] Y. Li, B. Jia, Y. Fan, K. Zhu, G. Li, C.-Y. Su, Bimetallic Zeolitic Imidazolite Framework Derived Carbon Nanotubes Embedded with Co Nanoparticles for Efficient Bifunctional Oxygen Electrocatalyst, Advanced Energy Materials, 8 (2018) 1702048. [8] X. Yang, L.T. Roling, M. Vara, A.O. Elnabawy, M. Zhao, Z.D. Hood, S. Bao, M. Mavrikakis, Y. Xia, Synthesis and Characterization of Pt-Ag Alloy Nanocages with Enhanced Activity and Durability toward Oxygen Reduction, Nano Letters, 16 (2016) 6644-6649. [9] D. Liu, L. Dai, X. Lin, J.F. Chen, J. Zhang, X. Feng, K. Mullen, X. Zhu, S. Dai, Chemical Approaches to Carbon-Based Metal-Free Catalysts, Adv Mater, 31 (2019) 1804863. [10] J.-H. Zhang, Y.-J. Hou, S.-J. Wang, X. Zhu, C.-Y. Zhu, Z. Wang, C.-J. Li, J.-J. Jiang, H.-P. Wang, M. Pan, C.-Y. Su, A facile method for scalable synthesis of ultrathin g-C3N4 nanosheets for efficient hydrogen production, Journal of Materials Chemistry A, 6 (2018) 18252-18257. [11] X. Li, B.Y. Guan, S. Gao, X.W. Lou, A general dual-templating approach to biomass-derived hierarchically porous heteroatom-doped carbon materials for enhanced electrocatalytic oxygen reduction, Energy & Environmental Science, 12 (2019) 648-655. [12] L. Yang, J. Shui, L. Du, Y. Shao, J. Liu, L. Dai, Z. Hu, Carbon-Based Metal-Free
ORR Electrocatalysts for Fuel Cells: Past, Present, and Future, Adv Mater, 31 (2019) 1804799. [13] D.-C. Wei, Y.-Q. Liu, Y. Wang, H.-L. Zhang, L.-P. Huang, G Yu, Synthesis of Ndoped graphene by chemical vapor deposition and its electrical properties, Nano letters, 5 (2009) 1752-1758. [14] F. Hassani, H. Tavakol, F. Keshavarzipour, A. Javaheri, A simple synthesis of sulfur-doped graphene using sulfur powder by chemical vapor deposition, RSC Advances, 6 (2016) 27158-27163. [15] H. Lin, D. Chen, C. Lu, C. Zhang, F. Qiu, S. Han, X. Zhuang, Rational synthesis of N/S-doped porous carbons as high efficient electrocatalysts for oxygen reduction reaction and Zn-Air batteries, Electrochimica Acta, 266 (2018) 17-26. [16] H. Yang, Y. Hu, D. Huang, T. Xiong, M. Li, M.-S. Balogun, Y. Tong, Efficient hydrogen and oxygen evolution electrocatalysis by cobalt and phosphorus dual-doped vanadium nitride nanowires, Materials Today Chemistry 11 (2019) 1-7. [17] R. Li, Z.D. Wei, X.L. Gou, Nitrogen and Phosphorus Dual-doped Graphene/Carbon Nanosheets as Bifunctional Electrocatalysts for Oxygen Reduction and Evolution, ACS Catalysis 5 (2015) 4133-4142. [18] H. Wang, X. Bo, Y. Zhang, L. Guo, Sulfur-doped ordered mesoporous carbon with high electrocatalytic activity for oxygen reduction, Electrochimica Acta, 108 (2013) 404-411. [19] Z. Liu, H. Nie, Z. Yang, J. Zhang, Z. Jin, Y. Lu, Z. Xiao, S. Huang, Sulfur-nitrogen co-doped three-dimensional carbon foams with hierarchical pore structures as efficient metal-free electrocatalysts for oxygen reduction reactions, Nanoscale, 5 (2013) 32833288. [20] W. Zhu, Z. Chen, Y. Pan, R. Dai, Y. Wu, Z. Zhuang, D. Wang, Q. Peng, C. Chen, Y. Li, Functionalization of Hollow Nanomaterials for Catalytic Applications: Nanoreactor Construction, Adv Mater, 31 (2019) 1800426.
[21] L. Yu, X.Y. Yu, X.W.D. Lou, The Design and Synthesis of Hollow Micro/Nanostructures: Present and Future Trends, Adv Mater, 30 (2018) 1800939. [22] J. Liang, Y Jiao, M Jaroniec, S.Z. Qiao, Sulfur and Nitrogen Dual-Doped Mesoporous Graphene Electrocatalyst for Oxygen Reduction with Synergistically Enhanced Performance, Angew Chem Int Ed Engl, 51 (2012) 11496-11500. [23] S. Cai, Z. Meng, H. Tang, Y. Wang, P. Tsiakaras, 3D Co-N-doped hollow carbon spheres as excellent bifunctional electrocatalysts for oxygen reduction reaction and oxygen evolution reaction, Applied Catalysis B: Environmental, 217 (2017) 477-484. [24] Y. Li, J. Yang, J. Huang, Y. Zhou, K. Xu, N. Zhao, X. Cheng, Soft templateassisted method for synthesis of nitrogen and sulfur co-doped three-dimensional reduced graphene oxide as an efficient metal free catalyst for oxygen reduction reaction, Carbon, 122 (2017) 237-246. [25] K. Gao, B. Wang, L. Tao, B.V. Cunning, Z. Zhang, S. Wang, R.S. Ruoff, L. Qu, Efficient Metal-Free Electrocatalysts from N-Doped Carbon Nanomaterials: MonoDoping and Co-Doping, Adv Mater, 31 (2019) 1805121. [26] S. Wang, J. Teng, Y. Xie, Z.-W. Wei, Y. Fan, J.-J. Jiang, H.-P. Wang, H. Liu, D. Wang, C.-Y. Su, Embedding CoO nanoparticles in a yolk–shell N-doped porous carbon support for ultrahigh and stable lithium storage, Journal of Materials Chemistry A, 7 (2019) 4036-4046. [27] S.-A. Wohlgemuth, R.J. White, M.-G. Willinger, M.-M. Titirici, M. Antonietti, A one-pot hydrothermal synthesis of sulfur and nitrogen doped carbon aerogels with enhanced electrocatalytic activity in the oxygen reduction reaction, Green Chemistry, 14 (2012) 1515. [28] Z. Ma, S. Dou, A. Shen, L. Tao, L. Dai, S. Wang, Sulfur-doped graphene derived from cycled lithium-sulfur batteries as a metal-free electrocatalyst for the oxygen reduction reaction, Angew Chem Int Ed Engl, 54 (2015) 1888-1892. [29] Y. Han, Y. Wang, R. Xu, W. Chen, L. Zheng, A. Han, Y. Zhu, J. Zhang, H. Zhang,
J. Luo, C. Chen, Q. Peng, D. Wang, Y. Li, Electronic structure engineering to boost oxygen reduction activity by controlling the coordination of the central metal, Energy & Environmental Science, 11 (2018) 2348-2352. [30] Y.-F. Chen, J.-F. Huang, M.-H. Shen, J.-M. Liu, L.-B. Huang, Y.-H. Zhong, S. Qin, J. Guo, C.-Y. Su, A porous hybrid material based on calixarene dye and TiO2 demonstrating high and stable photocatalytic performance, Journal of Materials Chemistry A, 7 (2019) 19852-19861. [31] H.W. Liang, X. Zhuang, S. Bruller, X. Feng, K. Mullen, Hierarchically porous carbons with optimized nitrogen doping as highly active electrocatalysts for oxygen reduction, Nat Commun, 5 (2014) 4973. [32] T.Y. Ma, S. Dai, M. Jaroniec, S.Z. Qiao, Metal-organic framework derived hybrid Co3O4-carbon porous nanowire arrays as reversible oxygen evolution electrodes, J Am Chem Soc, 136 (2014) 13925-13931.
N, S dual-doped hollow mesoporous carbon sphere (HMCS) was fabricated through a facile one-step method. Such HMCS displayed high ORR activity and good durability
Rong Cao and Hongfang Li supervised the research. Hongfang Li and Wanfeng Xiong designed the experiment and wrote the paper. Wangfeng Xiong synthesized the materials and performed the catalyst characterizations and catalytic experiments. Rong Cao, Hongfang Li and Wanfeng Xiong contributed to scientific discussion of the article.
Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
1, Nitrogen and sulfur dual-doped hollow mesoporous carbon sphere has been synthesized through a hard-template method. 2, The dual-doped carbon material exhibits a high catalysis activity and a superior durability. 3. The unique hollow mesoporous carbon sphere structure facilitates the diffusion and mass transfer ability and therefore improve the ORR catalytic performance.
S1387-7003(20)30091-5 https://doi.org/10.1016/j.inoche.2020.107848 INOCHE 107848
To appear in:
Inorganic Chemistry Communications
Received Date: Revised Date: Accepted Date:
21 January 2020 13 February 2020 17 February 2020
Please cite this article as: W. Xiong, H. Li, R. Cao, Nitrogen and Sulfur Dual-doped Hollow Mesoporous Carbon Spheres as Efficient Metal-free Catalyst for Oxygen Reduction Reaction, Inorganic Chemistry Communications (2020), doi: https://doi.org/10.1016/j.inoche.2020.107848
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2020 Published by Elsevier B.V.
Nitrogen and Sulfur Dual-doped Hollow Mesoporous Carbon Spheres as Efficient Metal-free Catalyst for Oxygen Reduction Reaction Wanfeng Xiong1,2, Hongfang Li1,2*, and Rong Cao1 1 College of Chemistry and Materials Science, Fujian Normal University, Fuzhou 350007, China 2 State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, China. * Corresponding authors. E-mail: [email protected] Abstract Developing a cheap and efficient oxygen reduction reaction (ORR) catalyst is one of the emerging issues. The doped carbon materials have attracted much attention due to the controllable and cheap synthesis methods. In this work, the nitrogen and sulfur dualdoped hollow mesoporous carbon sphere (NS-HMCS) has been synthesized through a hard-template method. During the co-polymerization process of dopamine (DA) and cysteamine (CA), the nitrogen (N) and sulfur (S) sites are introduced into the carbon skeleton at the same time, which simplifies the tedious steps in the post-modification of carbon materials. The obtained NS-HMCS-32 exhibits high content of nitrogen about 4.8 % and sulfur about 1.4 %. NS-HMCS-32 has a high specific surface areas (898 m2 g-1) and a large pore volume (2.99 cm3 g-1). During the ORR measurement, the halfwave potential of NS-HMCS-32 reaches up to 0.77 V vs. RHE. Moreover, NS-HMCS32 reveals a better durability than commercial Pt/C and 79.2 % of current density remains after 9 hours chronoamperometry test. This work provides a design idea for dual-doped carbon materials and the obtained NS-HMCS is a potential candidate for metal-free catalyst in fuel cells.
Keywords: dual-doped carbon materials, oxygen reduction reaction, metal-free catalyst Energy crisis has been a rigorous problem during the rapid society development [1]. Therefore, lots of researches are dedicated to the exploitation of clean energy source [2-4], such as fuel cell and metal-air batteries [5, 6]. Oxygen reduction reaction (ORR), the crucial semi-reaction in these devices, has got in-depth study for enhancing its sluggish kinetic processes [7]. The traditional platinum-based catalyst is the effective electrocatalyst for ORR [8]. However, the expensive price and the poor catalysis durability are still the bottleneck which limits its wide application. Therefore, exploring a cheap catalyst with high activity and long-standing durability receives a huge amount of attention. Recent years, metal-free catalysts have been eye-catching due to its low price and structure stability [9, 10]. Among them, heteroatom-doped carbon materials receive the most attention in the field of ORR [11]. Heteroatom doping can not only change the electronic structure, but also create the structural defects in the carbon-based materials, which effectively solves the sluggishness of pristine carbon in catalysis [12]. With the atomic size similar to carbon, nitrogen has been widely doped in carbon matrix and built active sites for ORR. But one-type doping still has limitation in activity improvement and therefore the dual-doping or tri-doping with B, S and P in carbon skeleton have been achieved through chemical vapor deposition (CVD) [13, 14] and post-modification [15, 16]. With the synergistic effect of multiple heteroatoms, the obtained metal-free catalysts have all shown significant performance improvements comparing with one-type doping [17-19]. However, the synthetic processes are complicated and tedious. Hence, exploring a facile method to fabricate the dual-doped carbon materials with excellent catalytic activity is still a challenge for developing the efficient metal-free catalysts. Hollow mesoporous carbon sphere (HMCS) is a three-dimensional carbon material with huge cavity and porous carbon shell [20]. Comparing with the solid counterparts, HMCS exhibits higher surface area, more exposed sites and larger interior space. These
advantages make it a great potential application in the field of biotechnology, energy storage and chemical catalysis [21]. But how to create the active sites for enhancing its catalytic capability is still a problem. Liang et al. have found that the synergistic effect between nitrogen and sulfur could bring the redistribution of spin and charge densities in carbon and therefore produced active sites efficiently [22]. Therefore, we choose nitrogen and sulfur dopants for getting a high active carbon based ORR catalyst. In this work, N and S atom dual-doped HMCS has been fabricated through the simple onestep template method. The obtained NS-HMCS-32 exhibits a high catalysis activity which could catch up with commercial Pt/C and even a superior durability. The influence of N, S dual-doping on electronic structure and porosity of HMCS has also been studied intensively. All the changes on electronic and porous structure for HMCS greatly promote the improvement of ORR performance.
Scheme 1. Schematic illustration of the synthesis for N, S dual-doped HMCS
As seen in Scheme 1, the primary silica sphere was firstly assembled as the core through an in-situ stöber templating. During the polymerization of TEOS, the dopamine (DA) and cysteamine (CA) were added at the same time. The secondary silica sphere and the PDA/CA grew on the primary silica sphere core to form the core-shell structure. After the carbonizing at high temperature and etching with sodium hydroxide solution, the
N, S dual-doped hollow mesoporous carbon sphere (NS-HMCS) was obtained.
Fig. 1. (a) SEM, (b) TEM and (c) HAADF-STEM images of NS-HMCS-32, (d) EDS mapping of C, N and S distributed on the NS-HMCS-32.
The morphology of NS-HMCS could be observed directly through scanning electron microscope (SEM) and the transmission electron microscopy (TEM). Monitoring the molar ratio of DA and CA (3:1 and 3:2), the obtained NS-HMCS-31 (Fig. S1a and S1c) and NS-HMCS-32 (Fig. 1a and b) both displayed a regular hollow carbon sphere morphology. Further increasing CA content to 3:3, the obtained NS-HMCS-33 showed broken sphere morphology (Fig. S1b and S1d). This result indicated that the ratio between DA and CA played a vital role in the polymerization of PDA/CA precursor. When excess sulfur was introduced, the scale discrepancy between S and C atom made carbon skeleton collapsed and therefore leaded to the broken carbon spheres. With the high-angle annular dark-field scanning transmission electron microscopy (HAADFSTEM) and energy-dispersive X-ray spectroscope (EDS), the morphology of NSHMCS-32 was further observed. As shown in Fig. 1c, the ultra-thin carbon shell ca. 12 nm and the plentiful pore construction could be seen directly in NS-HMCS-32. The EDS-mapping of NS-HMCS-32 displayed the existence of C, N and S elements (Fig. 1d), which demonstrated that the N and S atoms were uniformly distributed in the
carbon spheres. Base on the observation above, it could be confirmed that N, S dualdoped NS-HMCS with huge cavity, ultra-thin carbon shell and highly porosity was produced successfully. The unique hollow structure of NS-HMCS not only enhanced the mass transfer ability, but also made more active sites exposed, which was benefit for the electrocatalytic performance [23].
Fig. 2. (a) PXRD pattern and (b) Raman spectrum of NS-HMCS, High-resolution (c) N 1s and (d) S 2p XPS spectra of NS-HMCS.
The chemical constitution of NS-HMCS was characterized through the spectroscopy technology. The PXRD patterns of NS-HMCS were shown in Fig. 2a. After the hightemperature carbonization, all samples displayed a wide diffraction peaks at 23o, which could be attributed to plane of graphitic carbon (002). The Raman spectroscopy was
used to characterize the structural defect of carbon skeleton (Fig. 2b). The typical D peak and G peak were corresponding to the disordered and sp2-hybrid graphitic carbon [24]. The intensity ratio (ID/IG) of the D and G peak increased slightly from 1.00 to 1.11 with the increase in CA content, which indicated the increase of the defect graphite carbon. This result showed that the introduction of sulfur atom could create large numbers of defect sites in the carbon skeleton, and these sites could play the vital roles in catalyzing ORR [25]. The element compositions of NS-HMCS were determined with the X-ray photoelectron spectroscopy (XPS) measurement. The N 1s and S 2p high-resolution XPS spectrum were displayed in Fig. 2c and d. The fitting of N 1s in HMCS exhibited three peaks assigned to graphitic-N (400.9 eV), pyrrolic-N (399.4 eV) and pyridinic-N (398.3 eV), respectively [26]. The high content of pyrrolic-N and pyridinic-N could regulate the electronic structure of carbon materials effectively and therefore enhancing the activity toward ORR. The chemical environment of S element was also analyzed by fitting the XPS spectrum and the existence of S element in HMCS were S-O (2P3/2 168.1 eV and 2P1/2 169.3 eV) and C-S-C (2P3/2 163.9 eV and 2P1/2 165.0 eV), respectively [27, 28]. Obviously, the content of C-S-C typed S element held a dominant position, which demonstrated the successful doping of S element in the HMCS. The sulfur doped would further modulate the long-range interaction between S and N sites [29]. The deconvoluted C 1s spectra (Fig. S2) also displayed the evidence of C-N and C-S connection. The content of nitrogen and sulfur was also evaluated by the element analysis (Table S1). The nitrogen and sulfur content was higher than 4.0 % and 1.0 % respectively in all NS-HMCS, which was a relatively high N and S content in the previously reported dual-doped carbon materials [25]. The XPS measurement and element analysis verified the existential form of N and S elements in HMCS, and the successful N, S dual-doping could be the advantage for the ORR performance enhancing.
Fig. 3. (a) N2 adsorption-desorption isotherms and (b) BJH pore size distributions of NS-HMCS.
The pore structure of the materials also played the vital role on the catalystic activity because it deeply affected the diffusion and mass transfer ability of the catalyst [26]. The N2 adsorption method was applied to evaluate the Brunauer-Emmett-Teller (BET) surface area and porous structure. The N2 adsorption-desorption isotherms (Fig. 3a) showed that all of the NS-HMCS displayed the type-II isotherms with H4 typed hysteresis loop. Increasing the CA content, the specific surface areas of NS-HMCS-32 increased firstly. Further increasing CA content, the specific surface areas of NSHMCS-33 reduced greatly (Table S2). Such obvious decrease in BET surface areas was probably originated from the structure collapse of the hollow mesoporous carbon sphere which have been confirmed by above SEM and TEM images. The broken carbon shell resulted in a decrease in specific surface areas as well as the porosity. The NS-HMCS32 sample had highest BET surface areas ca. 898 m2 g-1 and largest porous volume ca. 2.99 cm3 g-1. As shown in Fig. 3b, the pore distribution of NS-HMCS-32 was mainly at 2.2 nm, which indicated the abundant mesopores existed in the shell of carbon spheres. This large specific surface area and abundant pore structure would facilitate the diffusion and mass transfer ability and therefore improve the ORR catalytic performance [31].
Fig. 4. (a) LSV curves toward ORR and (b) Tafel plots of NS-HMCS and N-HMCS, (c) K-L plots of NS-HMCS-32 at different potentials, (d) RRDE linear sweep voltammogram of NS-HMCS-32, (e) Double-layer Capacitance (Cdl) obtained by a different scan rate for NS-HMCS, (f) chronoamperometric responses of NS-HMCS-32 and 20 wt % Pt/C at 0.6 V vs. RHE.
In order to verify the catalytic performance of NS-HMCS, the linear scan voltammogram (LSV) measurement were tested firstly. As displayed in Fig. 4a, the N, S dual-doped NS-HMCS-31 and NS-HMCS-32 both shown a significant improvement compared with only N-doped N-HMCS. But the catalytic activity of NS-HMCS-33 was declined dramatically, which could be ascribed to the broken carbon spheres. The NSHMCS-32 exhibited a half-wave potential of 0.77 V vs. RHE, which surpassed most dual-doped carbon materials (Table S3) and could catch up with the commercial Pt/C (0.82 V vs. RHE). The Tafel slope of samples was calculated and displayed in Fig. 4b. As can be seen, the Tafel slope of NS-HMCS-32 was only 48.8 mV dec-1, which revealed the highest catalytic efficiency. The LSV curves of NS-HMCS-32 at different rotate speed were measured (Fig. S3) and the relationship of current density and rotate speed were converted through the Koutecky-Levich (K-L) equation. As shown in Fig.
4c, the fitting lines were nearly parallel, which demonstrate the potential-independent electron transfer rate and O2 first-order reaction kinetics. The calculated electron transfer number (n) indicated a nearly four-electron transfer process. For further confirming the value of n, rotating ring-disk electrode (RRDE) measurement was applied. The RRDE linear sweep of NS-HMCS-32 in Fig. 4d showed a nearly fourelectron transfer process, which is consistent with the above calculation value from KL equation. The four-electron process verified the extremely high selectivity of NSHMCS-32 in catalyzing ORR. Among the three samples, NS-HMCS-32 displayed a higher sulfur content than NS-HMCS-31 and therefore more sulfur active sites can be used in the electrochemical catalysis. Further increasing the sulfur content in NSHMCS-33, the hollow mesoporous carbon spheres structure was collapsed and the specific surface area and pore volume decreased greatly which deteriorated its catalytic performance. Conversely, NS-HMCS-32 maintained the unique three-dimensional structure and the highest surface areas and porous volume. facilitated the diffusion and mass transfer ability and therefore improved the ORR catalytic performance. For further exploring the promotion of catalytic activity, electrochemical surface areas (ECSAs) were applied to evaluate the active site numbers. The cyclic voltammograms at different scan rates were measured (Fig. S5) and the double-layer capacitance (Cdl) were obtained through the fitting result from current density and scan rates. As shown in Fig. 4e, NS-HMCS-32 displayed the highest Cdl performance of 11.4 mF cm-2. This result indicated that larger numbers of active sites existed in the NS-HMCS-32 and there enhancing the ORR performance [5, 32]. It is well known that, the electrocatalytic durability was a key factor for assessing the property of catalysts. Therefore, chronoamperometry was applied to evaluate the durability NS-HMCS-32. After 9 hours durability measurement, the current density of NS-HMCS-32 still remained 79.2 %, but the Pt/C catalyst presented a much lower remaining about only 59.7 %. This result indicated that the as prepared NS-HMCS-32 exhibited outstanding durability compared with the commercial Pt/C. Based on the electrocatalysis measurement and the characterizations above, it could be
found that the heteroatom dual-doping of N and S effectively regulated the electronic structure in the carbon skeleton and therefore created active sites. On the other hand, the morphology of HMCS also has a great influence on the ORR performance. The destruction of carbon spheres leaded to a decrease in the mass transfer ability and therefore reduced the ORR activity. As a result, the heteroatom doping and the pore structure played an equally important status in catalyzing ORR. In summary, the N, S dual-doped hollow mesoporous carbon sphere was fabricated through a facile one-step method. The N, S dual-doped NS-HMCS-32 had a high specific surface area (898 m2 g-1) and a large pore volume (2.99 cm3 g-1). Moreover, NS-HMCS-32 displayed high ORR activity and good durability. It is believed that the unique electronic and porous structure of NS-HMCS played a decisive role on the high catalytic performance in ORR. This work provides a simple method for designing a high activity dual-doped carbon materials and lays the foundation for exploring the cheap metal-free ORR catalysts.
References [1] Barnham. K. W. J, Mazzer M, Clive B, Resolving the energy crisis: nuclear or photovoltaics? , Nature Materials, 5 (2006) 161. [2] M. Chen, Y. Xie, J.-X. Wu, H. Huang, J. Teng, D. Wang, Y. Fan, J.-J. Jiang, H.-P. Wang, C.-Y. Su, Cobalt (oxy)hydroxide nanosheet arrays with exceptional porosity and rich defects as a highly efficient oxygen evolution electrocatalyst under neutral conditions, Journal of Materials Chemistry A, 7 (2019) 10217-10224. [3] Y. Jiao, Y. Zheng, M. Jaroniec, S.Z. Qiao, Design of electrocatalysts for oxygenand hydrogen-involving energy conversion reactions, Chem Soc Rev, 44 (2015) 20602086. [4] Y Hu, D Huang, J Zhang, Y Huang, M.-S. Balogun, Y. Tong, Dual Doping Induced Interfacial Engineering of Fe2N/Fe3N Hybrids with Favorable d-band towards Efficient
Overall Water Splitting, ChemCatChem, 11 (2019) 6051-6060. [5] W.-F. Xiong, H.-F. Li, H-H. You, M.-N. Cao, R Cao, Encapsulating metal organic framework into hollow mesoporous carbon sphere as efficient oxygen bifunctional electrocatalyst, National Science Review, DOI: 10.1093/nsr/nwz166. [6] C. Santoro, A. Serov, L. Stariha, M. Kodali, J. Gordon, S. Babanova, O. Bretschger, K. Artyushkova, P. Atanassov, Iron based catalysts from novel low-cost organic precursors for enhanced oxygen reduction reaction in neutral media microbial fuel cells, Energy & Environmental Science, 9 (2016) 2346-2353. [7] Y. Li, B. Jia, Y. Fan, K. Zhu, G. Li, C.-Y. Su, Bimetallic Zeolitic Imidazolite Framework Derived Carbon Nanotubes Embedded with Co Nanoparticles for Efficient Bifunctional Oxygen Electrocatalyst, Advanced Energy Materials, 8 (2018) 1702048. [8] X. Yang, L.T. Roling, M. Vara, A.O. Elnabawy, M. Zhao, Z.D. Hood, S. Bao, M. Mavrikakis, Y. Xia, Synthesis and Characterization of Pt-Ag Alloy Nanocages with Enhanced Activity and Durability toward Oxygen Reduction, Nano Letters, 16 (2016) 6644-6649. [9] D. Liu, L. Dai, X. Lin, J.F. Chen, J. Zhang, X. Feng, K. Mullen, X. Zhu, S. Dai, Chemical Approaches to Carbon-Based Metal-Free Catalysts, Adv Mater, 31 (2019) 1804863. [10] J.-H. Zhang, Y.-J. Hou, S.-J. Wang, X. Zhu, C.-Y. Zhu, Z. Wang, C.-J. Li, J.-J. Jiang, H.-P. Wang, M. Pan, C.-Y. Su, A facile method for scalable synthesis of ultrathin g-C3N4 nanosheets for efficient hydrogen production, Journal of Materials Chemistry A, 6 (2018) 18252-18257. [11] X. Li, B.Y. Guan, S. Gao, X.W. Lou, A general dual-templating approach to biomass-derived hierarchically porous heteroatom-doped carbon materials for enhanced electrocatalytic oxygen reduction, Energy & Environmental Science, 12 (2019) 648-655. [12] L. Yang, J. Shui, L. Du, Y. Shao, J. Liu, L. Dai, Z. Hu, Carbon-Based Metal-Free
ORR Electrocatalysts for Fuel Cells: Past, Present, and Future, Adv Mater, 31 (2019) 1804799. [13] D.-C. Wei, Y.-Q. Liu, Y. Wang, H.-L. Zhang, L.-P. Huang, G Yu, Synthesis of Ndoped graphene by chemical vapor deposition and its electrical properties, Nano letters, 5 (2009) 1752-1758. [14] F. Hassani, H. Tavakol, F. Keshavarzipour, A. Javaheri, A simple synthesis of sulfur-doped graphene using sulfur powder by chemical vapor deposition, RSC Advances, 6 (2016) 27158-27163. [15] H. Lin, D. Chen, C. Lu, C. Zhang, F. Qiu, S. Han, X. Zhuang, Rational synthesis of N/S-doped porous carbons as high efficient electrocatalysts for oxygen reduction reaction and Zn-Air batteries, Electrochimica Acta, 266 (2018) 17-26. [16] H. Yang, Y. Hu, D. Huang, T. Xiong, M. Li, M.-S. Balogun, Y. Tong, Efficient hydrogen and oxygen evolution electrocatalysis by cobalt and phosphorus dual-doped vanadium nitride nanowires, Materials Today Chemistry 11 (2019) 1-7. [17] R. Li, Z.D. Wei, X.L. Gou, Nitrogen and Phosphorus Dual-doped Graphene/Carbon Nanosheets as Bifunctional Electrocatalysts for Oxygen Reduction and Evolution, ACS Catalysis 5 (2015) 4133-4142. [18] H. Wang, X. Bo, Y. Zhang, L. Guo, Sulfur-doped ordered mesoporous carbon with high electrocatalytic activity for oxygen reduction, Electrochimica Acta, 108 (2013) 404-411. [19] Z. Liu, H. Nie, Z. Yang, J. Zhang, Z. Jin, Y. Lu, Z. Xiao, S. Huang, Sulfur-nitrogen co-doped three-dimensional carbon foams with hierarchical pore structures as efficient metal-free electrocatalysts for oxygen reduction reactions, Nanoscale, 5 (2013) 32833288. [20] W. Zhu, Z. Chen, Y. Pan, R. Dai, Y. Wu, Z. Zhuang, D. Wang, Q. Peng, C. Chen, Y. Li, Functionalization of Hollow Nanomaterials for Catalytic Applications: Nanoreactor Construction, Adv Mater, 31 (2019) 1800426.
[21] L. Yu, X.Y. Yu, X.W.D. Lou, The Design and Synthesis of Hollow Micro/Nanostructures: Present and Future Trends, Adv Mater, 30 (2018) 1800939. [22] J. Liang, Y Jiao, M Jaroniec, S.Z. Qiao, Sulfur and Nitrogen Dual-Doped Mesoporous Graphene Electrocatalyst for Oxygen Reduction with Synergistically Enhanced Performance, Angew Chem Int Ed Engl, 51 (2012) 11496-11500. [23] S. Cai, Z. Meng, H. Tang, Y. Wang, P. Tsiakaras, 3D Co-N-doped hollow carbon spheres as excellent bifunctional electrocatalysts for oxygen reduction reaction and oxygen evolution reaction, Applied Catalysis B: Environmental, 217 (2017) 477-484. [24] Y. Li, J. Yang, J. Huang, Y. Zhou, K. Xu, N. Zhao, X. Cheng, Soft templateassisted method for synthesis of nitrogen and sulfur co-doped three-dimensional reduced graphene oxide as an efficient metal free catalyst for oxygen reduction reaction, Carbon, 122 (2017) 237-246. [25] K. Gao, B. Wang, L. Tao, B.V. Cunning, Z. Zhang, S. Wang, R.S. Ruoff, L. Qu, Efficient Metal-Free Electrocatalysts from N-Doped Carbon Nanomaterials: MonoDoping and Co-Doping, Adv Mater, 31 (2019) 1805121. [26] S. Wang, J. Teng, Y. Xie, Z.-W. Wei, Y. Fan, J.-J. Jiang, H.-P. Wang, H. Liu, D. Wang, C.-Y. Su, Embedding CoO nanoparticles in a yolk–shell N-doped porous carbon support for ultrahigh and stable lithium storage, Journal of Materials Chemistry A, 7 (2019) 4036-4046. [27] S.-A. Wohlgemuth, R.J. White, M.-G. Willinger, M.-M. Titirici, M. Antonietti, A one-pot hydrothermal synthesis of sulfur and nitrogen doped carbon aerogels with enhanced electrocatalytic activity in the oxygen reduction reaction, Green Chemistry, 14 (2012) 1515. [28] Z. Ma, S. Dou, A. Shen, L. Tao, L. Dai, S. Wang, Sulfur-doped graphene derived from cycled lithium-sulfur batteries as a metal-free electrocatalyst for the oxygen reduction reaction, Angew Chem Int Ed Engl, 54 (2015) 1888-1892. [29] Y. Han, Y. Wang, R. Xu, W. Chen, L. Zheng, A. Han, Y. Zhu, J. Zhang, H. Zhang,
J. Luo, C. Chen, Q. Peng, D. Wang, Y. Li, Electronic structure engineering to boost oxygen reduction activity by controlling the coordination of the central metal, Energy & Environmental Science, 11 (2018) 2348-2352. [30] Y.-F. Chen, J.-F. Huang, M.-H. Shen, J.-M. Liu, L.-B. Huang, Y.-H. Zhong, S. Qin, J. Guo, C.-Y. Su, A porous hybrid material based on calixarene dye and TiO2 demonstrating high and stable photocatalytic performance, Journal of Materials Chemistry A, 7 (2019) 19852-19861. [31] H.W. Liang, X. Zhuang, S. Bruller, X. Feng, K. Mullen, Hierarchically porous carbons with optimized nitrogen doping as highly active electrocatalysts for oxygen reduction, Nat Commun, 5 (2014) 4973. [32] T.Y. Ma, S. Dai, M. Jaroniec, S.Z. Qiao, Metal-organic framework derived hybrid Co3O4-carbon porous nanowire arrays as reversible oxygen evolution electrodes, J Am Chem Soc, 136 (2014) 13925-13931.
N, S dual-doped hollow mesoporous carbon sphere (HMCS) was fabricated through a facile one-step method. Such HMCS displayed high ORR activity and good durability
Rong Cao and Hongfang Li supervised the research. Hongfang Li and Wanfeng Xiong designed the experiment and wrote the paper. Wangfeng Xiong synthesized the materials and performed the catalyst characterizations and catalytic experiments. Rong Cao, Hongfang Li and Wanfeng Xiong contributed to scientific discussion of the article.
Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
1, Nitrogen and sulfur dual-doped hollow mesoporous carbon sphere has been synthesized through a hard-template method. 2, The dual-doped carbon material exhibits a high catalysis activity and a superior durability. 3. The unique hollow mesoporous carbon sphere structure facilitates the diffusion and mass transfer ability and therefore improve the ORR catalytic performance.