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PdO supported on porous graphene as electrocatalyst for methanol oxidation
Materials Letters 174 (2016) 192–196
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Plasma synthesis of Pd/PdO supported on porous graphene as electrocatalyst for methanol oxidation Fan Yang a,1, Chunxia Wang b,1, Sen Dong a, Cheng Chi a, Xilai Jia a, Liqiang Zhang a, Yongfeng Li a,n a b
State Key Laboratory of Heavy oil Processing, China University of Petroleum, Beijing 102249, China Institute of Chemistry, Chinese Academy of Science, Beijing 100190, China
art ic l e i nf o
a b s t r a c t
Article history: Received 24 November 2015 Received in revised form 29 February 2016 Accepted 19 March 2016 Available online 21 March 2016
Pd/PdO nanoparticles supported on porous graphene (PG) are synthesized by a gas-liquid interfacial plasma method using Pd(NO3)2 2H2O as precursor. The Pd/PdO ratios can be controlled by changing the amount of Pd(NO3)2 2H2O. The synthesized Pd/PdO electrocatalysts exhibit a high electrocatalytic activity for methanol oxidation. The Pd/PdO nanoparticles attached on PG support shows better activity than that on oxidation carbon nanotubes support for methanol oxidation. In addition, our findings show that the PdO present in the Pd nanoparticles can enhance the electrocatalytic activity. It is worth to mention that the Pd/PdO nanoparticles supported on porous graphene catalysts show better electrochemical stability than that of commercial Pd/C catalyst. & 2016 Elsevier B.V. All rights reserved.
Keywords: Carbon materials Nanoparticles Electrical properties
1. Introduction In recent years, as environmentally friendly power sources, direct methanol fuel cells (DMFC) as sustainable energy sources have attracted great interest for portable devices, transportation and stationary applications, owing to their high energy conversion efficiency, high energy density, and environmental benignity [1–3]. Although, platinum (Pt) is the most efficient and commonly used electrocatalyst for methanol oxidation, its high cost and low CO poisoning tolerance severely impede the commercialization of DFMC [4–6]. Therefore, considerable efforts have been made to develop non-Pt catalysts that can offer acceptable performance. Among them, palladium (Pd) based anode catalysts have received increasing attention due to their superior activity, lower cost and greater resistance to CO [7–9]. On the other hand, a suitable Supporting material could enhance the catalytic activity, such as carbon black, carbon nanofibers, carbon nanotubes and graphene [8,10–12]. Among these materials, graphene has generated a tremendous amount of research interest due to its extremely high specific surfaced area (SSA) (theoretical value of 2630 m2 g 1), high conductivity (103– 104 S m 1) and superior thermal/chemical stability properties. However, the stacking of graphene sheets can lead to their n
Corresponding author. E-mail address: yfl[email protected] (Y. Li). 1 These authors contributed equally.
http://dx.doi.org/10.1016/j.matlet.2016.03.107 0167-577X/& 2016 Elsevier B.V. All rights reserved.
agglomeration, which severely reduces the SSA to less than 700 m2 g 1 [13]. Recently, porous graphene (PG) with SSA 2038 m2 g 1 was prepared by a chemical vapour deposition (CVD) method, showing great promise as a catalyst support [14]. Moreover, our group have found that PdO presence in Pd nanoparticles catalysts can enhance the catalytic activity [15,16]. In continuation of our previous work, we report a study of Pd/PdO supported on PG as electrocatalyst for methanol oxidation. Our results indicate that the Pd/PdO nanoparticles with PG support exhibit a high electrocatalytic activity and stability for methanol oxidation.
2. Experimental The Pd/PdO nanoparticles supported on PG (Pd/PdO/PG) used in this study were prepared by a gas-liquid interfacial plasma (GLIP) method with Pd(NO3)2 2H2O [17,18]. The PG was synthesized via template growth on porous MgO layers by a CVD method [14]. Three kinds of Pd/PdO hybrid materials with different Pd weight ratios (1:19, 1:9, 2:8) were prepared, and the respective materials were called Pd-n, (n ¼1, 2 and 3). For comparison, the Pd nanoparticles and Pd/PdO nanoparticles supported on oxidation carbon nanotubes (Pd/CNT and Pd/PdO/CNT) used in this study were prepared with Pd(OAc)2 and Pd(NO3)2 2H2O, respectively. The detailed synthesis procedure is described in ESI. Electrochemical experiments are performed on a CHI842D electrochemical workstation with a conventional three-electrode
F. Yang et al. / Materials Letters 174 (2016) 192–196
system. A platinum foil and an Ag/AgCl electrode are used as the counter electrode and the reference electrode, respectively. The electrochemically active surface area is obtained with the potential ranges from 0.8 to 0.3 V with the scan rate of 50 mV s 1 and the stabilities of the catalytic performance are conducted at an operation potential of 0.1 V for 800 s in 1 M CH3OH and 1 M KOH. The fabrication of working electrode was described in ESI.
3. Results and discussion The morphology of Pd-n has been examined by TEM, as shown in Fig. 1a–c. These results demonstrate that all the synthesized Pdn electrocatalysts exhibit uniform morphologies, and the size distributions of Pd-1, Pd-2 and Pd-3 are 4.5, 5.5 and 6.8 nm, respectively (Table 1S). The interfinger distance is measured to be 0.22 nm as indicated in the high-resolution TEM image of the Pd-1 (Fig. 1d), corresponding to the (111) lattice of the face centered cubic Pd. The BET surface area and pore radius of the PG are 1561.0 m2 g 1 and 1.86 nm, and the BET results are in agreement with TEM images, which the pore sizes are about 2 nm, as shown in Fig. S1. The interlayer distance of the PG is 0.37 nm, which shows longer distance than 0.34 nm due to the porous structure. Fig. 2a shows the SAED pattern of Pd-1, and the lattice spacing measured from the diffraction rings are 0.23, 0.20, 0.14 and 0.11 nm, corresponding to reflections Pd(111), Pd(200), Pd(220)
193
and Pd(311), respectively. In addition, the crystalline phase of the Pd-n are identified by XRD, as shown in Fig. 2b. The diffraction peaks at 22.3°, 33.8°, 39.9°, 43.5°, 46.3°, 68.1° and 81.8°, corresponding to C(002), Pd(111), C(100), Pd(200), PdO(101), Pd(220) and Pd(311), respectively. These results have confirmed that the Pd-n possess a face-centered crystalline structure. XPS has been further used to get the information of different elements in the samples, as shown in Fig. 3. The main chemical components are Pd, C and O, and the peaks at 284.17 and 533.17 eV indicate that the Pd-n catalysts possess C1s and O1s chemical components. A small peak corresponding to Pd3p is observed at 562.08 eV. The Pd-n show two peaks for Pd3d5/2 and Pd3d3/2 which are split into two types of Pd electronic states (Pd0 and PdO) centered at 336.02, 337.77, 341.42 and 343.22 eV, as shown in Fig. 3b–d. The XPS results suggest that the Pd-n contains Pd and PdO, and the contents of PdO increase with the increase of the Pd loading. The corresponding ratios of PdO:Pd in Pd-n are 30:70, 60:40 and 80:20, respectively (Table 1S). We further investigate the performance of Pd-n for methanol electro-oxidation in alkaline media (Fig. 4a). The oxidation peak in the forward scan corresponds to the oxidation of freshly chemisorbed species derived from methanol adsorption, while the one in the backward scan is related to the oxidation of accumulated carbonaceous species intermediates (mainly CO) [19]. It is found that the Pd/PdO/CNT exhibits a higher current density than that of Pd/CNT, indicating that PdO nanoparticles enhance the
Fig. 1. TEM images of Pd-1 (a), Pd-2 (b), Pd-3 (c) and a high-resolution TEM image of Pd-1 (d).
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Fig. 2. XRD patterns (a) and SEAD pattern (b) of Pd-n.
Fig. 3. XPS survey of Pd-n samples (a), high resolution XPS of Pd3d image of Pd-1 (b), Pd-2 (c), Pd-3 (d).
electrocatalytic activity due to the synergistic action of the Pd/PdO nanoparticles. Although we control the same amount of Pd active species on the glassy carbon electrode, the Pd-2 with PG support gives better electrocatalytic activity than CNT support for methanol oxidation, probably due to the high SSA and electrical conductivity properties of PG support. This proposed reasons are indicated by BET (Fig. S1) and EIS measurements (Fig. S2 and Table S2). Among all the Pd-n catalysts, Pd-3 exhibits an inerter electrocatalytic activity, and the current density is reduced dramatically. These results indicate that the high PdO content in the Pd/
PdO nanoparticles exerts negative effect on methanol oxidation. The Pd-1 with small particle size and 30% PdO content in Pd/PdO nanoparticles result in the highest electrocatalytic activity. For comparison, the porous graphene support Pd nanoparticles (Pd/ PG) and PG are used as the electrocatalysts for methanol electrooxidation, respectively. Our findings indicate that without Pd active species, the PG shows no electrocatalytic activity, and the Pd/ PG shows slightly lower electrocatalytic activity (Fig. 4c), suggesting that the PdO nanoparticles can enhance the electrocatalytic activity. The catalytic stabilities of these synthesized
F. Yang et al. / Materials Letters 174 (2016) 192–196
195
Fig. 4. (a) Cyclic voltammograms of methanol oxidation on Pd-1, Pd-2, Pd/PdO/CNT, Pd/CNT, Pd-3 and Pd/C catalysts. (b) Chronoamperometry of Pd-1, Pd-2, Pd/PdO/CNT, Pd/ CNT, Pd-3 and Pd/C. (c) Cyclic voltammograms of methanol oxidation on Pd-1, Pd/PdO/CNT, Pd/PG catalysts. (d) Chronoamperometry of Pd-1 and Pd/PG.
catalysts recorded at 0.1 V for 800 s are displayed in Fig. 4b and d. The rapid decrease in the current density can be possibly attributed to the poisoning of the electrocatalysts, owing to the formation of intermediate and some poisoning species during the methanol oxidation. It is worth to mention that the current decay on the Pd-1 is slower than that of the Pd/C, suggesting that Pd-1 shows better electrochemical stability. These result demonstrates that the PG plays a critical role during promoting the methanol oxidation, which could be attributed to the good electrical conductivity of PG and well dispersion of Pd/PdO nanoparticles on the surface of PG.
4. Conclusions In summary, we have developed an efficient approach for the synthesis of Pd/PdO/PG hybrid materials by a GLIP method. The Pd/PdO nanoparticles on the surface of PG show uniform size distribution. Our results demonstrate that Pd/PdO/PG catalysts exhibit significantly enhanced electrocatalytic activity and stability than that of commercial Pd/C catalysts towards methanol electrocatalysts for DMFC. It is worth to mention that the PdO present in Pd nanoparticles can enhance the electrocatalytic activity, benefiting from the synergistic action of the Pd/PdO nanoparticles. Moreover, the Pd/PdO nanoparticles with PG support exhibits much better activity than CNT support for methanol oxidation, suggesting that the PG plays a critical role in promoting the methanol oxidation due to its good electrical conductivity and well dispersion of Pd/PdO nanoparticles on the surface of PG.
Acknowledgements This work was supported by National Natural Science Foundation of China (Nos. 21202203, 21576289 and 21322609), Science Foundation Research Funds Provided to New Recruitments of China University of Petroleum, Beijing (No. YJRC-2013-31), Science Foundation of China University of Petroleum, Beijing (Nos. 2462015YQ0306 and 2462014QZDX01) and Thousand Talents Program.
Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2016.03. 107.
References [1] E. Reddington, A. Sapienza, B. Gurau, R. Viswanathan, S. Sarangapani, E. S. Smotkin, et al., Science 280 (1998) 1735–1737. [2] H. Qian, H. Huang, X. Wang, J. Power Sources 275 (2015) 734–741. [3] Y. Li, W. Gao, L. Ci, C. Wang, P.M. Ajayan, Carbon 48 (2010) 1124–1130. [4] F. Ren, C. Zhai, M. Zhu, C. Wang, H. Wang, D. Bin, et al., Electrochim. Acta 153 (2015) 175–183. [5] R. Wang, Y. Xie, K. Shi, J. Wang, C. Tian, P. Shen, et al., Chem. Eur. J. 18 (2012) 7443–7451. [6] L.C. Nagle, J.F. Rohan, J. Power Sources 185 (2008) 411–418. [7] N. Hoshi, K. Kida, M. Nakamura, M. Nakada, K. Osada, J. Phys. Chem. B 110 (2006) 12480–12484. [8] H. Huang, X. Wang, J. Mater. Chem. 22 (2012) 22533–22541. [9] J. Cao, L. Song, J. Tang, J. Xu, W. Wang, Z. Chen, Appl. Surf. Sci. 274 (2013) 138–143.
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E. Antolini, Appl. Catal. B – Environ. 88 (2009) 1–24. X. Wang, W. Li, Z. Chen, M. Waje, Y. Yan, J. Power Sources 158 (2006) 154–159. S. Wang, A. Manthiram, Electrochim. Acta 88 (2013) 565–570. M.D. Stoller, S. Park, Y. Zhu, J. An, R.S. Ruoff, Nano Lett. 8 (2008) 3498–3502. G. Ning, Z. Fan, G. Wang, J. Gao, W. Qian, F. Wei, Chem. Commun. 47 (2011) 5976–5978. [15] F. Yang, C. Chi, S. Dong, C. Wang, X. Jia, L. Ren, et al., Catal. Today 256 (2015) 180–192. [10] [11] [12] [13] [14]
[16] C. Wang, F. Yang, W. Yang, L. Ren, Y. Zhang, X. Jia, et al., RSC Adv. 5 (2015) 27526–27532. [17] T. Kaneko, K. Baba, R. Hatakeyama, Plasma Phys. Control. Fusion 51 (2009) 124011-1241. [18] Y. Fan, Y. Li, T. Liu, K. Xu, L. Zhang, C. Xu, et al., Chem. Eng. J. 226 (2013) 52–58. [19] Q. Yong, L. Chao, J. Yuan, Y. Liu, F. Chu, Y. Kong, et al., Chem. Commun. 52 (2016) 382–385.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Plasma synthesis of Pd/PdO supported on porous graphene as electrocatalyst for methanol oxidation Fan Yang a,1, Chunxia Wang b,1, Sen Dong a, Cheng Chi a, Xilai Jia a, Liqiang Zhang a, Yongfeng Li a,n a b
State Key Laboratory of Heavy oil Processing, China University of Petroleum, Beijing 102249, China Institute of Chemistry, Chinese Academy of Science, Beijing 100190, China
art ic l e i nf o
a b s t r a c t
Article history: Received 24 November 2015 Received in revised form 29 February 2016 Accepted 19 March 2016 Available online 21 March 2016
Pd/PdO nanoparticles supported on porous graphene (PG) are synthesized by a gas-liquid interfacial plasma method using Pd(NO3)2 2H2O as precursor. The Pd/PdO ratios can be controlled by changing the amount of Pd(NO3)2 2H2O. The synthesized Pd/PdO electrocatalysts exhibit a high electrocatalytic activity for methanol oxidation. The Pd/PdO nanoparticles attached on PG support shows better activity than that on oxidation carbon nanotubes support for methanol oxidation. In addition, our findings show that the PdO present in the Pd nanoparticles can enhance the electrocatalytic activity. It is worth to mention that the Pd/PdO nanoparticles supported on porous graphene catalysts show better electrochemical stability than that of commercial Pd/C catalyst. & 2016 Elsevier B.V. All rights reserved.
Keywords: Carbon materials Nanoparticles Electrical properties
1. Introduction In recent years, as environmentally friendly power sources, direct methanol fuel cells (DMFC) as sustainable energy sources have attracted great interest for portable devices, transportation and stationary applications, owing to their high energy conversion efficiency, high energy density, and environmental benignity [1–3]. Although, platinum (Pt) is the most efficient and commonly used electrocatalyst for methanol oxidation, its high cost and low CO poisoning tolerance severely impede the commercialization of DFMC [4–6]. Therefore, considerable efforts have been made to develop non-Pt catalysts that can offer acceptable performance. Among them, palladium (Pd) based anode catalysts have received increasing attention due to their superior activity, lower cost and greater resistance to CO [7–9]. On the other hand, a suitable Supporting material could enhance the catalytic activity, such as carbon black, carbon nanofibers, carbon nanotubes and graphene [8,10–12]. Among these materials, graphene has generated a tremendous amount of research interest due to its extremely high specific surfaced area (SSA) (theoretical value of 2630 m2 g 1), high conductivity (103– 104 S m 1) and superior thermal/chemical stability properties. However, the stacking of graphene sheets can lead to their n
Corresponding author. E-mail address: yfl[email protected] (Y. Li). 1 These authors contributed equally.
http://dx.doi.org/10.1016/j.matlet.2016.03.107 0167-577X/& 2016 Elsevier B.V. All rights reserved.
agglomeration, which severely reduces the SSA to less than 700 m2 g 1 [13]. Recently, porous graphene (PG) with SSA 2038 m2 g 1 was prepared by a chemical vapour deposition (CVD) method, showing great promise as a catalyst support [14]. Moreover, our group have found that PdO presence in Pd nanoparticles catalysts can enhance the catalytic activity [15,16]. In continuation of our previous work, we report a study of Pd/PdO supported on PG as electrocatalyst for methanol oxidation. Our results indicate that the Pd/PdO nanoparticles with PG support exhibit a high electrocatalytic activity and stability for methanol oxidation.
2. Experimental The Pd/PdO nanoparticles supported on PG (Pd/PdO/PG) used in this study were prepared by a gas-liquid interfacial plasma (GLIP) method with Pd(NO3)2 2H2O [17,18]. The PG was synthesized via template growth on porous MgO layers by a CVD method [14]. Three kinds of Pd/PdO hybrid materials with different Pd weight ratios (1:19, 1:9, 2:8) were prepared, and the respective materials were called Pd-n, (n ¼1, 2 and 3). For comparison, the Pd nanoparticles and Pd/PdO nanoparticles supported on oxidation carbon nanotubes (Pd/CNT and Pd/PdO/CNT) used in this study were prepared with Pd(OAc)2 and Pd(NO3)2 2H2O, respectively. The detailed synthesis procedure is described in ESI. Electrochemical experiments are performed on a CHI842D electrochemical workstation with a conventional three-electrode
F. Yang et al. / Materials Letters 174 (2016) 192–196
system. A platinum foil and an Ag/AgCl electrode are used as the counter electrode and the reference electrode, respectively. The electrochemically active surface area is obtained with the potential ranges from 0.8 to 0.3 V with the scan rate of 50 mV s 1 and the stabilities of the catalytic performance are conducted at an operation potential of 0.1 V for 800 s in 1 M CH3OH and 1 M KOH. The fabrication of working electrode was described in ESI.
3. Results and discussion The morphology of Pd-n has been examined by TEM, as shown in Fig. 1a–c. These results demonstrate that all the synthesized Pdn electrocatalysts exhibit uniform morphologies, and the size distributions of Pd-1, Pd-2 and Pd-3 are 4.5, 5.5 and 6.8 nm, respectively (Table 1S). The interfinger distance is measured to be 0.22 nm as indicated in the high-resolution TEM image of the Pd-1 (Fig. 1d), corresponding to the (111) lattice of the face centered cubic Pd. The BET surface area and pore radius of the PG are 1561.0 m2 g 1 and 1.86 nm, and the BET results are in agreement with TEM images, which the pore sizes are about 2 nm, as shown in Fig. S1. The interlayer distance of the PG is 0.37 nm, which shows longer distance than 0.34 nm due to the porous structure. Fig. 2a shows the SAED pattern of Pd-1, and the lattice spacing measured from the diffraction rings are 0.23, 0.20, 0.14 and 0.11 nm, corresponding to reflections Pd(111), Pd(200), Pd(220)
193
and Pd(311), respectively. In addition, the crystalline phase of the Pd-n are identified by XRD, as shown in Fig. 2b. The diffraction peaks at 22.3°, 33.8°, 39.9°, 43.5°, 46.3°, 68.1° and 81.8°, corresponding to C(002), Pd(111), C(100), Pd(200), PdO(101), Pd(220) and Pd(311), respectively. These results have confirmed that the Pd-n possess a face-centered crystalline structure. XPS has been further used to get the information of different elements in the samples, as shown in Fig. 3. The main chemical components are Pd, C and O, and the peaks at 284.17 and 533.17 eV indicate that the Pd-n catalysts possess C1s and O1s chemical components. A small peak corresponding to Pd3p is observed at 562.08 eV. The Pd-n show two peaks for Pd3d5/2 and Pd3d3/2 which are split into two types of Pd electronic states (Pd0 and PdO) centered at 336.02, 337.77, 341.42 and 343.22 eV, as shown in Fig. 3b–d. The XPS results suggest that the Pd-n contains Pd and PdO, and the contents of PdO increase with the increase of the Pd loading. The corresponding ratios of PdO:Pd in Pd-n are 30:70, 60:40 and 80:20, respectively (Table 1S). We further investigate the performance of Pd-n for methanol electro-oxidation in alkaline media (Fig. 4a). The oxidation peak in the forward scan corresponds to the oxidation of freshly chemisorbed species derived from methanol adsorption, while the one in the backward scan is related to the oxidation of accumulated carbonaceous species intermediates (mainly CO) [19]. It is found that the Pd/PdO/CNT exhibits a higher current density than that of Pd/CNT, indicating that PdO nanoparticles enhance the
Fig. 1. TEM images of Pd-1 (a), Pd-2 (b), Pd-3 (c) and a high-resolution TEM image of Pd-1 (d).
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Fig. 2. XRD patterns (a) and SEAD pattern (b) of Pd-n.
Fig. 3. XPS survey of Pd-n samples (a), high resolution XPS of Pd3d image of Pd-1 (b), Pd-2 (c), Pd-3 (d).
electrocatalytic activity due to the synergistic action of the Pd/PdO nanoparticles. Although we control the same amount of Pd active species on the glassy carbon electrode, the Pd-2 with PG support gives better electrocatalytic activity than CNT support for methanol oxidation, probably due to the high SSA and electrical conductivity properties of PG support. This proposed reasons are indicated by BET (Fig. S1) and EIS measurements (Fig. S2 and Table S2). Among all the Pd-n catalysts, Pd-3 exhibits an inerter electrocatalytic activity, and the current density is reduced dramatically. These results indicate that the high PdO content in the Pd/
PdO nanoparticles exerts negative effect on methanol oxidation. The Pd-1 with small particle size and 30% PdO content in Pd/PdO nanoparticles result in the highest electrocatalytic activity. For comparison, the porous graphene support Pd nanoparticles (Pd/ PG) and PG are used as the electrocatalysts for methanol electrooxidation, respectively. Our findings indicate that without Pd active species, the PG shows no electrocatalytic activity, and the Pd/ PG shows slightly lower electrocatalytic activity (Fig. 4c), suggesting that the PdO nanoparticles can enhance the electrocatalytic activity. The catalytic stabilities of these synthesized
F. Yang et al. / Materials Letters 174 (2016) 192–196
195
Fig. 4. (a) Cyclic voltammograms of methanol oxidation on Pd-1, Pd-2, Pd/PdO/CNT, Pd/CNT, Pd-3 and Pd/C catalysts. (b) Chronoamperometry of Pd-1, Pd-2, Pd/PdO/CNT, Pd/ CNT, Pd-3 and Pd/C. (c) Cyclic voltammograms of methanol oxidation on Pd-1, Pd/PdO/CNT, Pd/PG catalysts. (d) Chronoamperometry of Pd-1 and Pd/PG.
catalysts recorded at 0.1 V for 800 s are displayed in Fig. 4b and d. The rapid decrease in the current density can be possibly attributed to the poisoning of the electrocatalysts, owing to the formation of intermediate and some poisoning species during the methanol oxidation. It is worth to mention that the current decay on the Pd-1 is slower than that of the Pd/C, suggesting that Pd-1 shows better electrochemical stability. These result demonstrates that the PG plays a critical role during promoting the methanol oxidation, which could be attributed to the good electrical conductivity of PG and well dispersion of Pd/PdO nanoparticles on the surface of PG.
4. Conclusions In summary, we have developed an efficient approach for the synthesis of Pd/PdO/PG hybrid materials by a GLIP method. The Pd/PdO nanoparticles on the surface of PG show uniform size distribution. Our results demonstrate that Pd/PdO/PG catalysts exhibit significantly enhanced electrocatalytic activity and stability than that of commercial Pd/C catalysts towards methanol electrocatalysts for DMFC. It is worth to mention that the PdO present in Pd nanoparticles can enhance the electrocatalytic activity, benefiting from the synergistic action of the Pd/PdO nanoparticles. Moreover, the Pd/PdO nanoparticles with PG support exhibits much better activity than CNT support for methanol oxidation, suggesting that the PG plays a critical role in promoting the methanol oxidation due to its good electrical conductivity and well dispersion of Pd/PdO nanoparticles on the surface of PG.
Acknowledgements This work was supported by National Natural Science Foundation of China (Nos. 21202203, 21576289 and 21322609), Science Foundation Research Funds Provided to New Recruitments of China University of Petroleum, Beijing (No. YJRC-2013-31), Science Foundation of China University of Petroleum, Beijing (Nos. 2462015YQ0306 and 2462014QZDX01) and Thousand Talents Program.
Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2016.03. 107.
References [1] E. Reddington, A. Sapienza, B. Gurau, R. Viswanathan, S. Sarangapani, E. S. Smotkin, et al., Science 280 (1998) 1735–1737. [2] H. Qian, H. Huang, X. Wang, J. Power Sources 275 (2015) 734–741. [3] Y. Li, W. Gao, L. Ci, C. Wang, P.M. Ajayan, Carbon 48 (2010) 1124–1130. [4] F. Ren, C. Zhai, M. Zhu, C. Wang, H. Wang, D. Bin, et al., Electrochim. Acta 153 (2015) 175–183. [5] R. Wang, Y. Xie, K. Shi, J. Wang, C. Tian, P. Shen, et al., Chem. Eur. J. 18 (2012) 7443–7451. [6] L.C. Nagle, J.F. Rohan, J. Power Sources 185 (2008) 411–418. [7] N. Hoshi, K. Kida, M. Nakamura, M. Nakada, K. Osada, J. Phys. Chem. B 110 (2006) 12480–12484. [8] H. Huang, X. Wang, J. Mater. Chem. 22 (2012) 22533–22541. [9] J. Cao, L. Song, J. Tang, J. Xu, W. Wang, Z. Chen, Appl. Surf. Sci. 274 (2013) 138–143.
196
F. Yang et al. / Materials Letters 174 (2016) 192–196
E. Antolini, Appl. Catal. B – Environ. 88 (2009) 1–24. X. Wang, W. Li, Z. Chen, M. Waje, Y. Yan, J. Power Sources 158 (2006) 154–159. S. Wang, A. Manthiram, Electrochim. Acta 88 (2013) 565–570. M.D. Stoller, S. Park, Y. Zhu, J. An, R.S. Ruoff, Nano Lett. 8 (2008) 3498–3502. G. Ning, Z. Fan, G. Wang, J. Gao, W. Qian, F. Wei, Chem. Commun. 47 (2011) 5976–5978. [15] F. Yang, C. Chi, S. Dong, C. Wang, X. Jia, L. Ren, et al., Catal. Today 256 (2015) 180–192. [10] [11] [12] [13] [14]
[16] C. Wang, F. Yang, W. Yang, L. Ren, Y. Zhang, X. Jia, et al., RSC Adv. 5 (2015) 27526–27532. [17] T. Kaneko, K. Baba, R. Hatakeyama, Plasma Phys. Control. Fusion 51 (2009) 124011-1241. [18] Y. Fan, Y. Li, T. Liu, K. Xu, L. Zhang, C. Xu, et al., Chem. Eng. J. 226 (2013) 52–58. [19] Q. Yong, L. Chao, J. Yuan, Y. Liu, F. Chu, Y. Kong, et al., Chem. Commun. 52 (2016) 382–385.