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Cite this: Chem. Commun., 2014, 50, 11683 Received 30th July 2014, Accepted 11th August 2014
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Molybdenum phosphide: a new highly efficient catalyst for the electrochemical hydrogen evolution reaction† Xiaobo Chen,a Dezhi Wang,ab Zhiping Wang,a Pan Zhou,a Zhuangzhi Wu*ab and Feng Jiang*ab
DOI: 10.1039/c4cc05936k www.rsc.org/chemcomm
Molybdenum phosphide was adopted as a new electrocatalyst for the hydrogen evolution reaction for the first time, exhibiting an excellent electrocatalytic activity with a small Tafel slope of 60 mV dec 1, which is amongst the most active, acid-stable, earth abundant HER electrocatalysts reported to date.
As the depletion of natural resources and environmental impacts of fossil fuel attract worldwide concerns, the development of renewable and sustainable energy sources becomes a top priority of many nations.1,2 Hydrogen has been proposed as a major energy carrier that could be used in power electronic devices, vehicles, and homes.3,4 In contrast to the traditional methods of hydrogen production, electrocatalytic hydrogen production by water splitting has attracted a great deal of attention due to its lower environmental pollution and sufficient supply. Achieving a high energetic efficiency for water splitting requires the use of a catalyst to minimize the overpotential necessary to drive the hydrogen evolution reaction (HER).5 It is well known that platinum has a high efficient catalytic performance in the HER, but its scarcity and high cost inhibit large scale applications.6 Thus, it is highly required to find an alternative new highly efficient, non-precious and abundant HER catalyst. Recently, a large amount of Mo(W)-based compounds have been reported as efficient HER catalysts, such as MoS2,7–9 WS2,10 MoC,11–13 MoN,12 MoB13 and so on. Generally, these catalysts are commonly used in the hydrodesulfurization (HDS) reaction with excellent catalytic activity. It also becomes feasible that other known catalysts for HDS are also good candidates for the HER due to the similarities and commonalities between their mechanisms and putative active sites.14
Transition metal phosphides have been widely explored as HDS catalysts due to their high catalytic ability,15,16 and can also be considered as HER catalysts. Popczun et al. reported Ni2P and CoP nanoparticles (10–20 nm) for the first time as highly efficient HER catalysts with small Tafel slopes of 46 and 50 mV dec 1, respectively.17,18 Similarly, as a well-known HDS catalyst, molybdenum phosphide (MoP), adopting a simple hexagonal structure, can also be considered as a potential catalyst for the HER. Moreover, it was proved that the turnover frequency (TOF) of MoP is much higher than that of MoS2, which is a common HER catalyst, indicating better catalytic activity.16 Therefore, in the present work, we report MoP as an active HER electrocatalyst exhibiting excellent activity and stability for the first time, which is comprised entirely of cheap and earthabundant elements. Moreover, we also give a direct comparison between MoP and Ni2P as promising HER catalysts. The XRD patterns of the MoP and Ni2P particles are demonstrated in Fig. 1. One can see that the patterns of MoP (Fig. 1a) and Ni2P (Fig. 1b) show sharp peaks and match well with the standard positions, confirming the formation of simple hexagonal MoP and Fe2P-type Ni2P in high yield. By Scherrer analysis of the peak widths, we figured out the comparably accurate crystallite size value, which was 19 nm and 31 nm for the MoP and Ni2P particles, respectively. SEM and TEM images revealed the morphology and size of MoP and Ni2P, respectively, as shown in Fig. 2. Due to the high reaction temperature, the small grain grew in size and even
a
School of Materials Science and Engineering, Central South University, Changsha 410083, PR China b Key Laboratory of Ministry of Education for Non-ferrous Materials Science and Engineering, Central South University, Changsha 410083, PR China. E-mail: [email protected]; Tel: +86 0731-88877221 † Electronic supplementary information (ESI) available: Experimental details. See DOI: 10.1039/c4cc05936k
This journal is © The Royal Society of Chemistry 2014
Fig. 1
XRD patterns of MoP (a) and Ni2P (b) catalysts.
Chem. Commun., 2014, 50, 11683--11685 | 11683
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Fig. 2
SEM and TEM images of MoP (a, c) and Ni2P (b, d) catalysts.
Fig. 3
Polarization curves (a) and Tafel slopes (b) of various catalysts.
gathered into clusters. It can be observed that the MoP particles are significantly agglomerated to form huge clusters (Fig. 2a). In contrast, the Ni2P (Fig. 2b) crystallites are dispersed as irregular spheres. Consistent with the SEM analysis, TEM images further confirmed the morphology and size. Obviously, the Ni2P particles show a much larger size than MoP. Moreover, the BET surface area of Ni2P catalyst (6.3 m2 g 1) is also slightly smaller than that of MoP (8.4 m2 g 1) because of the larger particle size. The electrochemical HER properties of the catalysts were tested using a three-electrode setup in a 0.5 M H2SO4 solution. As a reference, we demonstrated the HER activity of the commercial Pt/C catalyst (Johnson Matthey, 20 wt%) exhibiting high HER catalytic performance with an extraordinarily low overpotential and a high current density. The polarization curves recorded
Table 1
using MoP and Ni2P (as shown in Fig. 3a) on glassy carbon electrodes showed a low onset potential of approximately 100 mV and 170 mV for the HER, respectively. In addition, the overpotential required for the MoP and Ni2P catalysts to achieve 10 mA cm 2 current density were Z = 246 mV and Z = 346 mV, which means that the excellent HER catalytic activity in relation to a smaller loading of 71 mg cm 2 were comparable with other non-Pt HER electrocatalysts without conductive supports in acidic aqueous solutions. It must be noted that the MoP catalyst exhibits the best activity compared with the Ni2P and C-MoS2 catalysts. The Tafel plots of the phosphides and Pt/C catalysts are displayed in Fig. 3b, which were fitted to the Tafel equation (Z = b log j + a, where j is the current density and b is the Tafel slope), yielding Tafel slopes of 30, 60, 70 mV dec 1 for the Pt, MoP and Ni2P catalysts, respectively. The Tafel slope regarded as an inherent property of the catalyst is a significant standard for the HER performance. A smaller Tafel slope means a faster increase of HER rate with increasing potential. Therefore, the MoP catalyst exhibits a better catalytic activity than the Ni2P catalyst with a lower Tafel slope. Although the commercial Pt/C catalyst shows better activity than MoP with a much smaller Tafel slope, the activity of MoP catalyst can also be greatly improved by adding the highly conductive support of porous C with a large surface area and reducing the particle size. The exchange current density determined by fitting the j–E data to the Tafel equation has been considered as an efficient measure of activity for the HER attributed to the correlation between the hydrogen chemisorption energies and the exchange currents.19,20 The values of the MoP and Ni2P samples are listed in Table 1, where the former is larger than the latter, indicating that the MoP catalyst possesses a superior catalytic performance. In order to get a further comparison, the turnover frequencies following Eric J. Popczun’s method17 were estimated for Z = 100 mV using experimental surface areas, in which each individual atom on the outermost surface layer was treated as a potentially active site for the reaction.20 Due to the vagueness of the specific active sites of MoP and Ni2P, the calculation values represent only an estimate of the actual TOFs. The active sites of MoP exhibited a better catalytic activity resulting from their TOF value of 0.048 s 1, which was larger than that of Ni2P (0.025 s 1). To get a direct comparison, a summary of the Tafel slope and exchange current density of various non-Pt HER electrocatalysts is shown in Table 1. One can see that among these catalysts the
Summary of representative non-noble HER catalysts
Catalyst
Loading (mg cm 2)
Tafel slope (mV dec 1)
Exchange current density (10
Mo2C MoB MoN/C MoS2 MoSe2 MoP Ni2P Nano-Ni2P/Ti Nano-CoP/Ti
1.4 2.5 0.25 0.285 0.16 0.071 0.071 1.0 2.0
56 55 54.5 120 101 60 70 46 50
1.3 1.4 36 0.17 2.0 4.15 3.84 33 140
11684 | Chem. Commun., 2014, 50, 11683--11685
6
A cm 2)
Electrolyte
Ref.
1.0 1.0 0.1 0.5 0.5 0.5 0.5 0.5 0.5
13 13 21 10 22 This work This work 17 18
M M M M M M M M M
H2SO4 H2SO4 HClO4 H2SO4 H2SO4 H2SO4 H2SO4 H2SO4 H2SO4
This journal is © The Royal Society of Chemistry 2014
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Communication
activity, as well as the introduction of highly conductive supporters to minimize electronic transmission limitations.
Published on 11 August 2014. Downloaded by University of Michigan Library on 27/10/2014 16:21:53.
Notes and references
Fig. 4 Stability test of the MoP catalyst.
MoP catalyst possesses a relatively small Tafel slope, along with a large exchange current density in relation to its small mass loading. It must be noted that Ni2P and CoP nanoparticles show much smaller Tafel slopes than the MoP and Ni2P microparticles in the present case due to the exposure of more active sites resulting from the small particle size, demonstrating that the nanostructuring efforts can greatly enhance the final HER activity. Therefore, more studies can be conducted to further improve the activity, including not only exposing more active sites, but also increasing the conductive ability and enhancing the intrinsic catalytic activity of each active site. Stability is another important criterion for a good electrocatalyst. To assess this, cyclic potential sweeps were also performed over the MoP catalyst from 0.3 to +0.1 V with a scan rate of 100 mV s 1 (Fig. 4). It can be seen that there is only a slight loss of current density after 1000 cycles, indicating a moderate short-term durability in an acid solution. The MoP catalyst has been successfully synthesized using a simple TPR route, and adopted as a new HER electrocatalyst for the first time, demonstrating an excellent activity with a small Tafel slope, which is one of the best candidates among all the non-Pt electrocatalysts for the HER to date. Additionally, more research can be conducted to further improve the activity of MoP, such as nanostructuring efforts to expose more active sites and addition of promoters to enhance the inherent
This journal is © The Royal Society of Chemistry 2014
1 B. Hinnemann, P. G. Moses, J. Bonde, K. P. Jorgensen, J. H. Nielsen, S. Horch, Ib. Chorkendorff and J. K. Norskov, J. Am. Chem. Soc., 2005, 127, 5308–5309. 2 N. S. Lewis, Science, 2007, 315, 798–801. 3 J. A. Turner, Science, 2004, 305, 972–974. 4 J. Nowotny, C. C. Sorrell, L. R. Sheppard and T. Bak, Int. J. Hydrogen Energy, 2005, 30, 521–544. 5 J. D. Benck, Z. Chen, L. Y. Kuritzky, A. J. Forman and T. F. Jaramillo, ACS Catal., 2012, 2, 1916–1923. 6 Y. Hara, N. Minami, H. Matsumoto and H. Itagaki, Appl. Catal., A, 2007, 332, 289–296. 7 Z. Lu, H. Zhang, W. Zhu, X. Yu, Y. Kuang, Z. Chang, X. Lei and X. Sun, Chem. Commun., 2013, 49, 7516–7518. 8 D. Z. Wang, Z. P. Wang, C. L. Wang, P. Zhou, Z. Z. Wu and Z. H. Liu, Electrochem. Commun., 2013, 34, 219–222. 9 Z. Z. Wu, B. Z. Fang, Z. P. Wang, C. L. Wang, Z. H. Liu, F. Y. Liu, W. Wang, A. Alfantazi, D. Z. Wang and D. P. Wilinson, ACS Catal., 2013, 3, 2101–2107. 10 Z. Z. Wu, B. Z. Fang, A. Bonakdarpour, A. K. Sun, D. P. Wilkinson and D. Z. Wang, Appl. Catal., B, 2012, 125, 59–66. 11 L. Liao, S. Wang, J. Xiao, X. Bian, Y. Zhang, M. D. Scanlon, X. Hu, Y. Tang, B. Liu and H. H. Girault, Energy Environ. Sci., 2014, 7, 387–392. 12 W. F. Chen, J. T. Muckerman and E. Fujita, Chem. Commun., 2013, 49, 8896–8909. 13 H. Vrubel and X. Hu, Angew. Chem., Int. Ed., 2012, 51, 12703–12706. 14 C. G. Morales-Guio, L. A. Stern and X. Hu, Chem. Soc. Rev., 2014, DOI: 10.1039/C3CS60468C. 15 R. Wang and K. J. Smith, Appl. Catal., A, 2009, 361, 18–25. 16 V. M. L. Whiffen and K. J. Smith, Energy Fuels, 2010, 24, 4728–4737. 17 E. J. Popczun, J. R. McKone, C. G. Read, A. J. Biacchi, A. M. Wiltrout, N. S. Lewis and R. E. Schaak, J. Am. Chem. Soc., 2013, 135, 9267–9270. 18 E. J. Popczun, C. G. Read, C. W. Roske, N. S. Lewis and R. E. Schaak, Angew. Chem., Int. Ed., 2014, 126, 5531–5534. 19 T. F. Jaramillo, K. P. Jorgensen, J. Bonde, J. H. Nielsen, S. Horch and I. Chorkendorff, Science, 2007, 317, 100–102. 20 J. K. Nørskov, T. Bligaard, A. Logadottir, J. R. Kitchin, J. G. Chen, S. Pandelov and U. Stimming, J. Electrochem. Soc., 2005, 152, J23–J26. 21 W. F. Chen, K. Sasaki, C. Ma, A. I. Frenkel, N. Marinkovic, J. T. Muckerman, Y. Zhu and R. R. Adzic, Angew. Chem., Int. Ed., 2012, 51, 6131–6135. 22 H. Tang, K. Dou, C. Kaun, Q. Kuang and S. Yang, J. Mater. Chem. A, 2014, 2, 360–364.
Chem. Commun., 2014, 50, 11683--11685 | 11685
Published on 11 August 2014. Downloaded by University of Michigan Library on 27/10/2014 16:21:53.
COMMUNICATION
Cite this: Chem. Commun., 2014, 50, 11683 Received 30th July 2014, Accepted 11th August 2014
View Journal | View Issue
Molybdenum phosphide: a new highly efficient catalyst for the electrochemical hydrogen evolution reaction† Xiaobo Chen,a Dezhi Wang,ab Zhiping Wang,a Pan Zhou,a Zhuangzhi Wu*ab and Feng Jiang*ab
DOI: 10.1039/c4cc05936k www.rsc.org/chemcomm
Molybdenum phosphide was adopted as a new electrocatalyst for the hydrogen evolution reaction for the first time, exhibiting an excellent electrocatalytic activity with a small Tafel slope of 60 mV dec 1, which is amongst the most active, acid-stable, earth abundant HER electrocatalysts reported to date.
As the depletion of natural resources and environmental impacts of fossil fuel attract worldwide concerns, the development of renewable and sustainable energy sources becomes a top priority of many nations.1,2 Hydrogen has been proposed as a major energy carrier that could be used in power electronic devices, vehicles, and homes.3,4 In contrast to the traditional methods of hydrogen production, electrocatalytic hydrogen production by water splitting has attracted a great deal of attention due to its lower environmental pollution and sufficient supply. Achieving a high energetic efficiency for water splitting requires the use of a catalyst to minimize the overpotential necessary to drive the hydrogen evolution reaction (HER).5 It is well known that platinum has a high efficient catalytic performance in the HER, but its scarcity and high cost inhibit large scale applications.6 Thus, it is highly required to find an alternative new highly efficient, non-precious and abundant HER catalyst. Recently, a large amount of Mo(W)-based compounds have been reported as efficient HER catalysts, such as MoS2,7–9 WS2,10 MoC,11–13 MoN,12 MoB13 and so on. Generally, these catalysts are commonly used in the hydrodesulfurization (HDS) reaction with excellent catalytic activity. It also becomes feasible that other known catalysts for HDS are also good candidates for the HER due to the similarities and commonalities between their mechanisms and putative active sites.14
Transition metal phosphides have been widely explored as HDS catalysts due to their high catalytic ability,15,16 and can also be considered as HER catalysts. Popczun et al. reported Ni2P and CoP nanoparticles (10–20 nm) for the first time as highly efficient HER catalysts with small Tafel slopes of 46 and 50 mV dec 1, respectively.17,18 Similarly, as a well-known HDS catalyst, molybdenum phosphide (MoP), adopting a simple hexagonal structure, can also be considered as a potential catalyst for the HER. Moreover, it was proved that the turnover frequency (TOF) of MoP is much higher than that of MoS2, which is a common HER catalyst, indicating better catalytic activity.16 Therefore, in the present work, we report MoP as an active HER electrocatalyst exhibiting excellent activity and stability for the first time, which is comprised entirely of cheap and earthabundant elements. Moreover, we also give a direct comparison between MoP and Ni2P as promising HER catalysts. The XRD patterns of the MoP and Ni2P particles are demonstrated in Fig. 1. One can see that the patterns of MoP (Fig. 1a) and Ni2P (Fig. 1b) show sharp peaks and match well with the standard positions, confirming the formation of simple hexagonal MoP and Fe2P-type Ni2P in high yield. By Scherrer analysis of the peak widths, we figured out the comparably accurate crystallite size value, which was 19 nm and 31 nm for the MoP and Ni2P particles, respectively. SEM and TEM images revealed the morphology and size of MoP and Ni2P, respectively, as shown in Fig. 2. Due to the high reaction temperature, the small grain grew in size and even
a
School of Materials Science and Engineering, Central South University, Changsha 410083, PR China b Key Laboratory of Ministry of Education for Non-ferrous Materials Science and Engineering, Central South University, Changsha 410083, PR China. E-mail: [email protected]; Tel: +86 0731-88877221 † Electronic supplementary information (ESI) available: Experimental details. See DOI: 10.1039/c4cc05936k
This journal is © The Royal Society of Chemistry 2014
Fig. 1
XRD patterns of MoP (a) and Ni2P (b) catalysts.
Chem. Commun., 2014, 50, 11683--11685 | 11683
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Fig. 2
SEM and TEM images of MoP (a, c) and Ni2P (b, d) catalysts.
Fig. 3
Polarization curves (a) and Tafel slopes (b) of various catalysts.
gathered into clusters. It can be observed that the MoP particles are significantly agglomerated to form huge clusters (Fig. 2a). In contrast, the Ni2P (Fig. 2b) crystallites are dispersed as irregular spheres. Consistent with the SEM analysis, TEM images further confirmed the morphology and size. Obviously, the Ni2P particles show a much larger size than MoP. Moreover, the BET surface area of Ni2P catalyst (6.3 m2 g 1) is also slightly smaller than that of MoP (8.4 m2 g 1) because of the larger particle size. The electrochemical HER properties of the catalysts were tested using a three-electrode setup in a 0.5 M H2SO4 solution. As a reference, we demonstrated the HER activity of the commercial Pt/C catalyst (Johnson Matthey, 20 wt%) exhibiting high HER catalytic performance with an extraordinarily low overpotential and a high current density. The polarization curves recorded
Table 1
using MoP and Ni2P (as shown in Fig. 3a) on glassy carbon electrodes showed a low onset potential of approximately 100 mV and 170 mV for the HER, respectively. In addition, the overpotential required for the MoP and Ni2P catalysts to achieve 10 mA cm 2 current density were Z = 246 mV and Z = 346 mV, which means that the excellent HER catalytic activity in relation to a smaller loading of 71 mg cm 2 were comparable with other non-Pt HER electrocatalysts without conductive supports in acidic aqueous solutions. It must be noted that the MoP catalyst exhibits the best activity compared with the Ni2P and C-MoS2 catalysts. The Tafel plots of the phosphides and Pt/C catalysts are displayed in Fig. 3b, which were fitted to the Tafel equation (Z = b log j + a, where j is the current density and b is the Tafel slope), yielding Tafel slopes of 30, 60, 70 mV dec 1 for the Pt, MoP and Ni2P catalysts, respectively. The Tafel slope regarded as an inherent property of the catalyst is a significant standard for the HER performance. A smaller Tafel slope means a faster increase of HER rate with increasing potential. Therefore, the MoP catalyst exhibits a better catalytic activity than the Ni2P catalyst with a lower Tafel slope. Although the commercial Pt/C catalyst shows better activity than MoP with a much smaller Tafel slope, the activity of MoP catalyst can also be greatly improved by adding the highly conductive support of porous C with a large surface area and reducing the particle size. The exchange current density determined by fitting the j–E data to the Tafel equation has been considered as an efficient measure of activity for the HER attributed to the correlation between the hydrogen chemisorption energies and the exchange currents.19,20 The values of the MoP and Ni2P samples are listed in Table 1, where the former is larger than the latter, indicating that the MoP catalyst possesses a superior catalytic performance. In order to get a further comparison, the turnover frequencies following Eric J. Popczun’s method17 were estimated for Z = 100 mV using experimental surface areas, in which each individual atom on the outermost surface layer was treated as a potentially active site for the reaction.20 Due to the vagueness of the specific active sites of MoP and Ni2P, the calculation values represent only an estimate of the actual TOFs. The active sites of MoP exhibited a better catalytic activity resulting from their TOF value of 0.048 s 1, which was larger than that of Ni2P (0.025 s 1). To get a direct comparison, a summary of the Tafel slope and exchange current density of various non-Pt HER electrocatalysts is shown in Table 1. One can see that among these catalysts the
Summary of representative non-noble HER catalysts
Catalyst
Loading (mg cm 2)
Tafel slope (mV dec 1)
Exchange current density (10
Mo2C MoB MoN/C MoS2 MoSe2 MoP Ni2P Nano-Ni2P/Ti Nano-CoP/Ti
1.4 2.5 0.25 0.285 0.16 0.071 0.071 1.0 2.0
56 55 54.5 120 101 60 70 46 50
1.3 1.4 36 0.17 2.0 4.15 3.84 33 140
11684 | Chem. Commun., 2014, 50, 11683--11685
6
A cm 2)
Electrolyte
Ref.
1.0 1.0 0.1 0.5 0.5 0.5 0.5 0.5 0.5
13 13 21 10 22 This work This work 17 18
M M M M M M M M M
H2SO4 H2SO4 HClO4 H2SO4 H2SO4 H2SO4 H2SO4 H2SO4 H2SO4
This journal is © The Royal Society of Chemistry 2014
View Article Online
ChemComm
Communication
activity, as well as the introduction of highly conductive supporters to minimize electronic transmission limitations.
Published on 11 August 2014. Downloaded by University of Michigan Library on 27/10/2014 16:21:53.
Notes and references
Fig. 4 Stability test of the MoP catalyst.
MoP catalyst possesses a relatively small Tafel slope, along with a large exchange current density in relation to its small mass loading. It must be noted that Ni2P and CoP nanoparticles show much smaller Tafel slopes than the MoP and Ni2P microparticles in the present case due to the exposure of more active sites resulting from the small particle size, demonstrating that the nanostructuring efforts can greatly enhance the final HER activity. Therefore, more studies can be conducted to further improve the activity, including not only exposing more active sites, but also increasing the conductive ability and enhancing the intrinsic catalytic activity of each active site. Stability is another important criterion for a good electrocatalyst. To assess this, cyclic potential sweeps were also performed over the MoP catalyst from 0.3 to +0.1 V with a scan rate of 100 mV s 1 (Fig. 4). It can be seen that there is only a slight loss of current density after 1000 cycles, indicating a moderate short-term durability in an acid solution. The MoP catalyst has been successfully synthesized using a simple TPR route, and adopted as a new HER electrocatalyst for the first time, demonstrating an excellent activity with a small Tafel slope, which is one of the best candidates among all the non-Pt electrocatalysts for the HER to date. Additionally, more research can be conducted to further improve the activity of MoP, such as nanostructuring efforts to expose more active sites and addition of promoters to enhance the inherent
This journal is © The Royal Society of Chemistry 2014
1 B. Hinnemann, P. G. Moses, J. Bonde, K. P. Jorgensen, J. H. Nielsen, S. Horch, Ib. Chorkendorff and J. K. Norskov, J. Am. Chem. Soc., 2005, 127, 5308–5309. 2 N. S. Lewis, Science, 2007, 315, 798–801. 3 J. A. Turner, Science, 2004, 305, 972–974. 4 J. Nowotny, C. C. Sorrell, L. R. Sheppard and T. Bak, Int. J. Hydrogen Energy, 2005, 30, 521–544. 5 J. D. Benck, Z. Chen, L. Y. Kuritzky, A. J. Forman and T. F. Jaramillo, ACS Catal., 2012, 2, 1916–1923. 6 Y. Hara, N. Minami, H. Matsumoto and H. Itagaki, Appl. Catal., A, 2007, 332, 289–296. 7 Z. Lu, H. Zhang, W. Zhu, X. Yu, Y. Kuang, Z. Chang, X. Lei and X. Sun, Chem. Commun., 2013, 49, 7516–7518. 8 D. Z. Wang, Z. P. Wang, C. L. Wang, P. Zhou, Z. Z. Wu and Z. H. Liu, Electrochem. Commun., 2013, 34, 219–222. 9 Z. Z. Wu, B. Z. Fang, Z. P. Wang, C. L. Wang, Z. H. Liu, F. Y. Liu, W. Wang, A. Alfantazi, D. Z. Wang and D. P. Wilinson, ACS Catal., 2013, 3, 2101–2107. 10 Z. Z. Wu, B. Z. Fang, A. Bonakdarpour, A. K. Sun, D. P. Wilkinson and D. Z. Wang, Appl. Catal., B, 2012, 125, 59–66. 11 L. Liao, S. Wang, J. Xiao, X. Bian, Y. Zhang, M. D. Scanlon, X. Hu, Y. Tang, B. Liu and H. H. Girault, Energy Environ. Sci., 2014, 7, 387–392. 12 W. F. Chen, J. T. Muckerman and E. Fujita, Chem. Commun., 2013, 49, 8896–8909. 13 H. Vrubel and X. Hu, Angew. Chem., Int. Ed., 2012, 51, 12703–12706. 14 C. G. Morales-Guio, L. A. Stern and X. Hu, Chem. Soc. Rev., 2014, DOI: 10.1039/C3CS60468C. 15 R. Wang and K. J. Smith, Appl. Catal., A, 2009, 361, 18–25. 16 V. M. L. Whiffen and K. J. Smith, Energy Fuels, 2010, 24, 4728–4737. 17 E. J. Popczun, J. R. McKone, C. G. Read, A. J. Biacchi, A. M. Wiltrout, N. S. Lewis and R. E. Schaak, J. Am. Chem. Soc., 2013, 135, 9267–9270. 18 E. J. Popczun, C. G. Read, C. W. Roske, N. S. Lewis and R. E. Schaak, Angew. Chem., Int. Ed., 2014, 126, 5531–5534. 19 T. F. Jaramillo, K. P. Jorgensen, J. Bonde, J. H. Nielsen, S. Horch and I. Chorkendorff, Science, 2007, 317, 100–102. 20 J. K. Nørskov, T. Bligaard, A. Logadottir, J. R. Kitchin, J. G. Chen, S. Pandelov and U. Stimming, J. Electrochem. Soc., 2005, 152, J23–J26. 21 W. F. Chen, K. Sasaki, C. Ma, A. I. Frenkel, N. Marinkovic, J. T. Muckerman, Y. Zhu and R. R. Adzic, Angew. Chem., Int. Ed., 2012, 51, 6131–6135. 22 H. Tang, K. Dou, C. Kaun, Q. Kuang and S. Yang, J. Mater. Chem. A, 2014, 2, 360–364.
Chem. Commun., 2014, 50, 11683--11685 | 11685
