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Molten salt synthesis of Co-entrapped, N-doped porous carbon as efficient hydrogen evolving electrocatalysts
Materials Letters 209 (2017) 256–259
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Featured Letter
Molten salt synthesis of Co-entrapped, N-doped porous carbon as efficient hydrogen evolving electrocatalysts Kuo Li a, Duihai Tang a,⇑, Wenting Zhang a, Zhenan Qiao b, Yunling Liu b, Qisheng Huo b, Daxin Liang c, Junjiang Zhu a, Zhen Zhao a,⇑ a b c
Institute of Catalysis for Energy and Environment, College of Chemistry and Chemical Engineering, Shenyang Normal University, Shenyang 110034, China State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012, China Key Laboratory of Bio-based Material Science & Technology (Northeast Forestry University), Ministry of Education, Harbin 150040, China
a r t i c l e
i n f o
Article history: Received 4 June 2017 Received in revised form 30 July 2017 Accepted 6 August 2017 Available online 6 August 2017 Keywords: Composite materials Molten salt Hydrogen evolving reaction Porous materials Co nanoparticles
a b s t r a c t Co-entrapped, N-doped porous carbon (CoNPC) was synthesized via combination of hand milling and carbonation. Glucose and melamine were used as the carbon precursor and nitrogen precursor, respectively. ZnCl2 was utilized as the template, which could be removed totally with water. CoNPC possess a high BET surface area of 728.4 m2 g 1. The obtained catalyst exhibits excellent performance for hydrogen evolution reaction in both acidic and basic media, achieving a current density of 10 mA cm 2 at 171 and 202 mV in acid and base, respectively. Ó 2017 Published by Elsevier B.V.
1. Introduction Due to the sustainability and renewability, hydrogen has been considered as the promising alternatives to fossil fuels [1]. Electrochemical water splitting is one of the most investigated reactions to produce hydrogen [2]. To attain economical and active electrocatalysts, tremendous efforts have been devoted to develop noble metal-free hydrogen evolution reaction (HER) catalysts [3]. Among these materials, transition metals nanoparticles encapsulated in porous carbon show excellent electrocatalytic activity and stability. The carbon layers can prevent the transition metals nanoparticles from aggregating and corrosion under harsh conditions [4]. For instance, Zou’s group reported the preparation of cobaltembedded, nitrogen-doped carbon materials, which could show remarkable catalytic activity at all pH values [5]. The templating method is an important approach to synthesize porous materials [6]. However, the utilization of soft templates and/or hard templates has hindered the large-scale application, due to the high cost of the templates and the harsh process to remove the porogen (calcination or HF-etching) [7]. The molten salt activation process, also called salt templating, is a facile
⇑ Corresponding authors. E-mail addresses: [email protected] (D. Tang), [email protected] (Z. Zhao). http://dx.doi.org/10.1016/j.matlet.2017.08.021 0167-577X/Ó 2017 Published by Elsevier B.V.
method to prepare porous carbon without using sacrificial porogen, which is a simple and cost effective approach [8]. Various types of molten salts could be adopted, such as ZnCl2 [9], NaNO3 [10], NaCl/KCl [11], LiCl/KCl [12], Na2CO3/K2CO3 [13], LiNO3/NaNO3 [14], etc. Among these salts, ZnCl2 could act as high temperature solvent and catalyst for the polymerization reactions [9]. Herein, we synthesized Co-entrapped, N-doped porous carbon (CoNPC) by using ZnCl2 as the porogen. Glucose and melamine were utilized as carbon precursor and nitrogen precursor, respectively. Moreover, Co(NO3)2 was used as the cobalt precursor. The BET surface area of the obtained electrocatalysts is 724 m2 g 1. Compared to Co-entrapped porous carbons (CoPC), CoNPC exhibits better performance for hydrogen evolution reaction in both acidic and basic media, achieving a current density of 10 mA cm 2 at 171 and 202 mV in acid and base, respectively. This process opens up new ways to make Co-entrapped, N-doped porous carbon as efficient hydrogen evolving electrocatalysts. 2. Experimental In a typical synthesis of Co-entrapped, N-doped porous carbon (as shown in Scheme 1), Glucose (0.5 g) and melamine (0.25 g) were mixed with ZnCl2 (1.5 g) and Co(NO3)2 (0.25 g), then the mixture was ground in a mortar for 5 min. The milled pink mixture was carbonated at 800 °C for 2 h under Ar atmosphere. The as-
K. Li et al. / Materials Letters 209 (2017) 256–259
257
Scheme 1. Synthetic route of CoNPC.
prepared sample was washed with water to remove ZnCl2, which could be reused. After water washing, the black powder was further treated with 0.5 M H2SO4 for 24 h. The final product was dried at 50 °C under vacuum for 12 h. The control sample was synthesized under the same condition without adding melamine. The Co-entrapped, N-doped porous carbon was named as CoNPC, while the control sample was denoted as CoPC. Details of the characterization and catalytic testing are shown in the Supplementary Materials. 3. Results and discussion As shown in Fig. 1a, the XRD patterns of CoPC and CoNPC show that the peaks could be corresponded to metallic Co. The peaks at 44.3°, 51.4°, and 75.7° are indexed to the (1 1 1), (2 0 0), and (2 2 0) diffraction peaks of metallic Co (JCPDS Card No. 41-1476), indicating that the metallic Co could be protected by the carbon layers during the acid treatments [4]. The Raman spectra of CoPC and CoNPC are shown in Fig. 1b. The D band at 1352 cm 1 and the G band at 1593 cm 1 are both observed which are assigned to disordered and ordered structures, respectively. Calculated according to the peak intensities, the IG/ID ratios for CoPC and CoNPC are 1.12 and 1.46, respectively, which indicates that these two catalysts both have disordered and graphitic structures [4]. The surface composition of CoNPC was characterized by XPS. As shown in Fig. 1c, the high-resolution N 1s spectrum could be fitted to two individual peaks, which are pyrrolic N (400.7) and pyridinic N (398.5), respectively. The high-resolution Co 2p spectrum (Fig. 1d) shows two peaks at 792.6 and 777.2 eV, which can be assigned to Co 2p1/2 and Co 2p3/2, respectively [4]. The porous characteristics of CoPC and CoNPC were determined by the nitrogen physisorption isotherms, and their N2 adsorption
results are shown in Fig. 2a and b, respectively. Both of the nitrogen physisorption isotherms show a combined Type I/IV, indicating that they have the hierarchical porous structure. CoPC has a high BET surface area of 1691.0 m2 g 1, and the pore volume of CoPC is 1.00 cm3 g 1. However, CoNPC has a BET surface area of 728.3 m2 g 1, and the pore volume of CoNPC is only 0.42 cm3 g 1. The decrease of the BET surface area and the pore volume can be due to the introduction of nitrogen [15]. As shown in the Insets of 2a and 2b, the pore size distributions of CoPC and CoNPC further confirm the hierarchical porous structure composed of micropores and mesopores. The sample of CoNPC was further investigated by transmission electron microscopy (TEM). As shown in Fig. 2c, the Co nanoparticles are uniformly dispersed in the porous carbon matrix. The HRTEM image of CoNPC further confirms that the Co nanoparticles are encapsulated by carbon layers (Fig. 2d). Moreover, (2 0 0) planes of Co could be observed with an interplanar spacing of 0.204 nm. These carbon layers could protect the Co nanoparticles from acid leaching, which is consistent with the XRD results. According to the results above, it could be concluded that the obtained catalyst is Co-entrapped, N-doped porous carbon. The electrocatalytic activity of CoPC and CoNPC toward HER was evaluated in both 0.5 M H2SO4 (pH = 0) and 1 M KOH (pH = 14), with a three-electrode system. The working electrode was glassy carbon with an active material mass loading of 0.28 mg cm 2. For comparison, commercially available 20 wt% Pt on activated carbon under the same condition was also measured. The HER activity of CoNPC was first measured in 0.5 M H2SO4. As shown in the polarization curves of samples in acid (Fig. 3a), the blank GCE produces a weak current when the potential is 0.6 V, indicating the bare GCE shows no catalyst activity for HER. CoNPC shows a small onset overpotential of 98 mV, which is much smaller than that of CoPC (182 mV). Moreover, CoNPC deliver a current
Fig. 1. (a) XRD patterns of CoPC and CoNPC, (b) Raman spectra of CoPC and CoNPC, high-resolution (c) N1s and (d) Co2p XPS spectra for CoNPC.
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Fig. 2. (a) Nitrogen physisorption isotherms of CoPC. Inset of a, pore size distributions of CoPC, (b) Nitrogen physisorption isotherms of CoNPC. Inset of b, pore size distributions of CoNPC. (c) TEM and (d) HRTEM of CoNPC.
Fig. 3. Polarization curves of CoNPC, CoPC, Pt/C, and blank GCE in (a) 0.5 M H2SO4 and (d) 1 M KOH. Tafel plots for CoNPC, CoPC, and Pt/C in (b) 0.5 M H2SO4 and (e) 1 M KOH. Polarization curves of CoNPC before and after 1000 cycles in (c) 0.5 M H2SO4 and (f) 1 M KOH.
density of 10 mA cm 2 at a small overpotential (g) of 171 mV, whereas CoPC gets the same current density at g = 340 mV. The Tafel plots of the electrocatalysts in acidic media are shown in Fig. 3b. Pt/C reveals the smallest Tafel slope of 31.6 mV dec 1. Furthermore, the Tafel slopes of CoNPC and CoPC are 75.9 and 204.0 mV dec 1, respectively. The HER activities of CoPC and CoNPC were further examined in alkaline media. CoNPC affords a current density of 10 mA cm 2 at a small overpotential of 202 mV as well as a Tafel slope of 105.7 mV dec 1. However, without nitrogen doping, CoPC could only present overpotential of 367 mV to afford same current density, and the Tafel slope of CoPC is 241.5 mV dec 1. Long-term stability of the catalyst is another important issue. As shown in Fig. 3c and e, no obvious decay of the activity could be observed before and after 1000 cycles under both acidic and basic conditions, indicating that CoNPC has good long-term stability for HER.
Acknowledgements We thank the funding support from Key Laboratory of Biobased Material Science & Technology (Northeast Forestry University) Ministry of Education (No. SWZCL2016-15), the National Natural Science Foundation of China (No. 21601128), State Key Laboratory of Inorganic Synthesis and Preparative Chemistry (No. 2017-14), the Program for Excellent Talents in Shenyang Normal University (No. 054-51600210), Major Platform for Science and Technology of the Universities in Liaoning Province, Liaoning Province Key Laboratory for Highly Efficient Conversion and Clean Utilization of Oil and Gas Resources, Engineering Technology Research Center of Catalysis for Energy and Environment, and the Engineering Research Center for Highly Efficient Conversion and Clean Use of Oil and Gas Resources of Liaoning Province. Appendix A. Supplementary data
4. Conclusions We developed a facile approach to prepare Co-entrapped, Ndoped porous carbon via the molten salts method. ZnCl2 could be used as the porogen, which could be removed and recovered. The characterization results suggest formation of the Co-entrapped, N-doped carbon with porous structure. The obtained CoNPC exhibits excellent performance for hydrogen evolution reaction in both acidic and basic media. This process provides a novel way of developing Co-entrapped, N-doped porous carbon.
Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.matlet.2017.08. 021. References [1] [2] [3] [4]
J.A. Turner, Science 285 (1999) 687–689. J.A. Turner, Science 305 (97) (2004) 2–974. Y. Yan, B.Y. Xia, B. Zhao, X. Wang, J. Mater. Chem. A 4 (2016) 17587–17603. J. Wang, W. Cui, Q. Liu, Z. Xing, A.M. Asiri, X. Sun, Adv. Mater. 28 (2016) 215– 230. [5] S. Gao, G.D. Li, Y. Liu, H. Chen, L.L. Feng, Y. Wang, M. Yang, D. Wang, S. Wang, X. Zou, Nanoscale 7 (2015) 2306–2316. [6] Y. Wan, D. Zhao, Chem. Rev. 107 (2007) 2821–2860.
K. Li et al. / Materials Letters 209 (2017) 256–259 [7] R. Zhang, A.A. Elzatahry, S.S. Al-Deyab, D. Zhao, Nano. Today 7 (2012) 344–366. [8] P. Kuhn, A. Forget, D. Su, A. Thomas, M. Antonietti, J. Am. Chem. Soc. 130 (2008) 13333–13337. [9] X. Deng, B. Zhao, L. Zhu, Z. Shao, Carbon 93 (2015) 48–58. [10] G. Hu, W. Li, J. Xu, G. He, Y. Ge, Y. Pan, J. Wang, B. Yao, Mater. Lett. 170 (2016) 179–182. [11] J. Fu, Y. Hou, M. Zheng, Q. Wei, M. Zhu, H. Yan, ACS Appl. Mater. Interfaces 7 (2015) 24480–24491.
259
[12] Z. Yu, X. Wang, X. Song, Y. Liu, J. Qiu, Carbon 95 (2015) 852–860. [13] H. Yin, B. Lu, Y. Xu, D. Tang, X. Mao, W. Xiao, D. Wang, A.N. Alshawabkeh, Environ. Sci. Technol. 48 (2014) 8101–8108. [14] L. Zhou, C. Jin, Y. Yu, F. Chi, S. Ran, Y. Lv, J. Alloys Compd. 680 (2016) 301–308. [15] J. Lu, L. Yang, B. Xu, Q. Wu, D. Zhang, S. Yuan, Y. Zhai, X. Wang, Y. Fan, Z. Hu, ACS Catal. 4 (2014) 613–621.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Featured Letter
Molten salt synthesis of Co-entrapped, N-doped porous carbon as efficient hydrogen evolving electrocatalysts Kuo Li a, Duihai Tang a,⇑, Wenting Zhang a, Zhenan Qiao b, Yunling Liu b, Qisheng Huo b, Daxin Liang c, Junjiang Zhu a, Zhen Zhao a,⇑ a b c
Institute of Catalysis for Energy and Environment, College of Chemistry and Chemical Engineering, Shenyang Normal University, Shenyang 110034, China State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012, China Key Laboratory of Bio-based Material Science & Technology (Northeast Forestry University), Ministry of Education, Harbin 150040, China
a r t i c l e
i n f o
Article history: Received 4 June 2017 Received in revised form 30 July 2017 Accepted 6 August 2017 Available online 6 August 2017 Keywords: Composite materials Molten salt Hydrogen evolving reaction Porous materials Co nanoparticles
a b s t r a c t Co-entrapped, N-doped porous carbon (CoNPC) was synthesized via combination of hand milling and carbonation. Glucose and melamine were used as the carbon precursor and nitrogen precursor, respectively. ZnCl2 was utilized as the template, which could be removed totally with water. CoNPC possess a high BET surface area of 728.4 m2 g 1. The obtained catalyst exhibits excellent performance for hydrogen evolution reaction in both acidic and basic media, achieving a current density of 10 mA cm 2 at 171 and 202 mV in acid and base, respectively. Ó 2017 Published by Elsevier B.V.
1. Introduction Due to the sustainability and renewability, hydrogen has been considered as the promising alternatives to fossil fuels [1]. Electrochemical water splitting is one of the most investigated reactions to produce hydrogen [2]. To attain economical and active electrocatalysts, tremendous efforts have been devoted to develop noble metal-free hydrogen evolution reaction (HER) catalysts [3]. Among these materials, transition metals nanoparticles encapsulated in porous carbon show excellent electrocatalytic activity and stability. The carbon layers can prevent the transition metals nanoparticles from aggregating and corrosion under harsh conditions [4]. For instance, Zou’s group reported the preparation of cobaltembedded, nitrogen-doped carbon materials, which could show remarkable catalytic activity at all pH values [5]. The templating method is an important approach to synthesize porous materials [6]. However, the utilization of soft templates and/or hard templates has hindered the large-scale application, due to the high cost of the templates and the harsh process to remove the porogen (calcination or HF-etching) [7]. The molten salt activation process, also called salt templating, is a facile
⇑ Corresponding authors. E-mail addresses: [email protected] (D. Tang), [email protected] (Z. Zhao). http://dx.doi.org/10.1016/j.matlet.2017.08.021 0167-577X/Ó 2017 Published by Elsevier B.V.
method to prepare porous carbon without using sacrificial porogen, which is a simple and cost effective approach [8]. Various types of molten salts could be adopted, such as ZnCl2 [9], NaNO3 [10], NaCl/KCl [11], LiCl/KCl [12], Na2CO3/K2CO3 [13], LiNO3/NaNO3 [14], etc. Among these salts, ZnCl2 could act as high temperature solvent and catalyst for the polymerization reactions [9]. Herein, we synthesized Co-entrapped, N-doped porous carbon (CoNPC) by using ZnCl2 as the porogen. Glucose and melamine were utilized as carbon precursor and nitrogen precursor, respectively. Moreover, Co(NO3)2 was used as the cobalt precursor. The BET surface area of the obtained electrocatalysts is 724 m2 g 1. Compared to Co-entrapped porous carbons (CoPC), CoNPC exhibits better performance for hydrogen evolution reaction in both acidic and basic media, achieving a current density of 10 mA cm 2 at 171 and 202 mV in acid and base, respectively. This process opens up new ways to make Co-entrapped, N-doped porous carbon as efficient hydrogen evolving electrocatalysts. 2. Experimental In a typical synthesis of Co-entrapped, N-doped porous carbon (as shown in Scheme 1), Glucose (0.5 g) and melamine (0.25 g) were mixed with ZnCl2 (1.5 g) and Co(NO3)2 (0.25 g), then the mixture was ground in a mortar for 5 min. The milled pink mixture was carbonated at 800 °C for 2 h under Ar atmosphere. The as-
K. Li et al. / Materials Letters 209 (2017) 256–259
257
Scheme 1. Synthetic route of CoNPC.
prepared sample was washed with water to remove ZnCl2, which could be reused. After water washing, the black powder was further treated with 0.5 M H2SO4 for 24 h. The final product was dried at 50 °C under vacuum for 12 h. The control sample was synthesized under the same condition without adding melamine. The Co-entrapped, N-doped porous carbon was named as CoNPC, while the control sample was denoted as CoPC. Details of the characterization and catalytic testing are shown in the Supplementary Materials. 3. Results and discussion As shown in Fig. 1a, the XRD patterns of CoPC and CoNPC show that the peaks could be corresponded to metallic Co. The peaks at 44.3°, 51.4°, and 75.7° are indexed to the (1 1 1), (2 0 0), and (2 2 0) diffraction peaks of metallic Co (JCPDS Card No. 41-1476), indicating that the metallic Co could be protected by the carbon layers during the acid treatments [4]. The Raman spectra of CoPC and CoNPC are shown in Fig. 1b. The D band at 1352 cm 1 and the G band at 1593 cm 1 are both observed which are assigned to disordered and ordered structures, respectively. Calculated according to the peak intensities, the IG/ID ratios for CoPC and CoNPC are 1.12 and 1.46, respectively, which indicates that these two catalysts both have disordered and graphitic structures [4]. The surface composition of CoNPC was characterized by XPS. As shown in Fig. 1c, the high-resolution N 1s spectrum could be fitted to two individual peaks, which are pyrrolic N (400.7) and pyridinic N (398.5), respectively. The high-resolution Co 2p spectrum (Fig. 1d) shows two peaks at 792.6 and 777.2 eV, which can be assigned to Co 2p1/2 and Co 2p3/2, respectively [4]. The porous characteristics of CoPC and CoNPC were determined by the nitrogen physisorption isotherms, and their N2 adsorption
results are shown in Fig. 2a and b, respectively. Both of the nitrogen physisorption isotherms show a combined Type I/IV, indicating that they have the hierarchical porous structure. CoPC has a high BET surface area of 1691.0 m2 g 1, and the pore volume of CoPC is 1.00 cm3 g 1. However, CoNPC has a BET surface area of 728.3 m2 g 1, and the pore volume of CoNPC is only 0.42 cm3 g 1. The decrease of the BET surface area and the pore volume can be due to the introduction of nitrogen [15]. As shown in the Insets of 2a and 2b, the pore size distributions of CoPC and CoNPC further confirm the hierarchical porous structure composed of micropores and mesopores. The sample of CoNPC was further investigated by transmission electron microscopy (TEM). As shown in Fig. 2c, the Co nanoparticles are uniformly dispersed in the porous carbon matrix. The HRTEM image of CoNPC further confirms that the Co nanoparticles are encapsulated by carbon layers (Fig. 2d). Moreover, (2 0 0) planes of Co could be observed with an interplanar spacing of 0.204 nm. These carbon layers could protect the Co nanoparticles from acid leaching, which is consistent with the XRD results. According to the results above, it could be concluded that the obtained catalyst is Co-entrapped, N-doped porous carbon. The electrocatalytic activity of CoPC and CoNPC toward HER was evaluated in both 0.5 M H2SO4 (pH = 0) and 1 M KOH (pH = 14), with a three-electrode system. The working electrode was glassy carbon with an active material mass loading of 0.28 mg cm 2. For comparison, commercially available 20 wt% Pt on activated carbon under the same condition was also measured. The HER activity of CoNPC was first measured in 0.5 M H2SO4. As shown in the polarization curves of samples in acid (Fig. 3a), the blank GCE produces a weak current when the potential is 0.6 V, indicating the bare GCE shows no catalyst activity for HER. CoNPC shows a small onset overpotential of 98 mV, which is much smaller than that of CoPC (182 mV). Moreover, CoNPC deliver a current
Fig. 1. (a) XRD patterns of CoPC and CoNPC, (b) Raman spectra of CoPC and CoNPC, high-resolution (c) N1s and (d) Co2p XPS spectra for CoNPC.
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Fig. 2. (a) Nitrogen physisorption isotherms of CoPC. Inset of a, pore size distributions of CoPC, (b) Nitrogen physisorption isotherms of CoNPC. Inset of b, pore size distributions of CoNPC. (c) TEM and (d) HRTEM of CoNPC.
Fig. 3. Polarization curves of CoNPC, CoPC, Pt/C, and blank GCE in (a) 0.5 M H2SO4 and (d) 1 M KOH. Tafel plots for CoNPC, CoPC, and Pt/C in (b) 0.5 M H2SO4 and (e) 1 M KOH. Polarization curves of CoNPC before and after 1000 cycles in (c) 0.5 M H2SO4 and (f) 1 M KOH.
density of 10 mA cm 2 at a small overpotential (g) of 171 mV, whereas CoPC gets the same current density at g = 340 mV. The Tafel plots of the electrocatalysts in acidic media are shown in Fig. 3b. Pt/C reveals the smallest Tafel slope of 31.6 mV dec 1. Furthermore, the Tafel slopes of CoNPC and CoPC are 75.9 and 204.0 mV dec 1, respectively. The HER activities of CoPC and CoNPC were further examined in alkaline media. CoNPC affords a current density of 10 mA cm 2 at a small overpotential of 202 mV as well as a Tafel slope of 105.7 mV dec 1. However, without nitrogen doping, CoPC could only present overpotential of 367 mV to afford same current density, and the Tafel slope of CoPC is 241.5 mV dec 1. Long-term stability of the catalyst is another important issue. As shown in Fig. 3c and e, no obvious decay of the activity could be observed before and after 1000 cycles under both acidic and basic conditions, indicating that CoNPC has good long-term stability for HER.
Acknowledgements We thank the funding support from Key Laboratory of Biobased Material Science & Technology (Northeast Forestry University) Ministry of Education (No. SWZCL2016-15), the National Natural Science Foundation of China (No. 21601128), State Key Laboratory of Inorganic Synthesis and Preparative Chemistry (No. 2017-14), the Program for Excellent Talents in Shenyang Normal University (No. 054-51600210), Major Platform for Science and Technology of the Universities in Liaoning Province, Liaoning Province Key Laboratory for Highly Efficient Conversion and Clean Utilization of Oil and Gas Resources, Engineering Technology Research Center of Catalysis for Energy and Environment, and the Engineering Research Center for Highly Efficient Conversion and Clean Use of Oil and Gas Resources of Liaoning Province. Appendix A. Supplementary data
4. Conclusions We developed a facile approach to prepare Co-entrapped, Ndoped porous carbon via the molten salts method. ZnCl2 could be used as the porogen, which could be removed and recovered. The characterization results suggest formation of the Co-entrapped, N-doped carbon with porous structure. The obtained CoNPC exhibits excellent performance for hydrogen evolution reaction in both acidic and basic media. This process provides a novel way of developing Co-entrapped, N-doped porous carbon.
Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.matlet.2017.08. 021. References [1] [2] [3] [4]
J.A. Turner, Science 285 (1999) 687–689. J.A. Turner, Science 305 (97) (2004) 2–974. Y. Yan, B.Y. Xia, B. Zhao, X. Wang, J. Mater. Chem. A 4 (2016) 17587–17603. J. Wang, W. Cui, Q. Liu, Z. Xing, A.M. Asiri, X. Sun, Adv. Mater. 28 (2016) 215– 230. [5] S. Gao, G.D. Li, Y. Liu, H. Chen, L.L. Feng, Y. Wang, M. Yang, D. Wang, S. Wang, X. Zou, Nanoscale 7 (2015) 2306–2316. [6] Y. Wan, D. Zhao, Chem. Rev. 107 (2007) 2821–2860.
K. Li et al. / Materials Letters 209 (2017) 256–259 [7] R. Zhang, A.A. Elzatahry, S.S. Al-Deyab, D. Zhao, Nano. Today 7 (2012) 344–366. [8] P. Kuhn, A. Forget, D. Su, A. Thomas, M. Antonietti, J. Am. Chem. Soc. 130 (2008) 13333–13337. [9] X. Deng, B. Zhao, L. Zhu, Z. Shao, Carbon 93 (2015) 48–58. [10] G. Hu, W. Li, J. Xu, G. He, Y. Ge, Y. Pan, J. Wang, B. Yao, Mater. Lett. 170 (2016) 179–182. [11] J. Fu, Y. Hou, M. Zheng, Q. Wei, M. Zhu, H. Yan, ACS Appl. Mater. Interfaces 7 (2015) 24480–24491.
259
[12] Z. Yu, X. Wang, X. Song, Y. Liu, J. Qiu, Carbon 95 (2015) 852–860. [13] H. Yin, B. Lu, Y. Xu, D. Tang, X. Mao, W. Xiao, D. Wang, A.N. Alshawabkeh, Environ. Sci. Technol. 48 (2014) 8101–8108. [14] L. Zhou, C. Jin, Y. Yu, F. Chi, S. Ran, Y. Lv, J. Alloys Compd. 680 (2016) 301–308. [15] J. Lu, L. Yang, B. Xu, Q. Wu, D. Zhang, S. Yuan, Y. Zhai, X. Wang, Y. Fan, Z. Hu, ACS Catal. 4 (2014) 613–621.