ARTICLE pubs.acs.org/JPCC
First-Principles Study of Zigzag MoS2 Nanoribbon As a Promising Cathode Material for Rechargeable Mg Batteries Siqi Yang, Daixin Li, Tianran Zhang, Zhanliang Tao, and Jun Chen* Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), College of Chemistry, Nankai University, 94 Weijin Road, Tianjin 300071, P. R. China
bS Supporting Information ABSTRACT: Zigzag MoS2 nanoribbon is a promising cathode of rechargeable magnesium batteries. A first-principles study based on density functional theory (DFT) has been carried out on this material concentrating on key issues relating to magnesium adsorption sites, theoretical capacity, and diffusion kinetics. It is found that the Mo top site at the edge of the nanoribbon is favorable for Mg locations. On zigzag MoS2 nanoribbon, a maximum theoretical capacity of 223.2 mAh g 1 could be achieved by double-side Mg adsorptions. Electronic calculations suggest that partial charge transfers occur between the adsorbed Mg atoms and zigzag MoS2 nanoribbon, but meanwhile, the covalent hybridizations are still observable. A Mg diffusion pathway on the zigzag MoS2 nanoribbon is identified as passing two adjacent T sites mediated by the nearest neighboring H site in between. The activation barrier of this process is only 0.48 eV, much reduced from the 2.61 eV of the bulk interlayer migration. The present results give expectation of excellent battery performance by the zigzag MoS2 nanoribbons.
1. INTRODUCTION Molybdenum disulfide (MoS2) has attracted a considerable attention due to its typical layered structure and has been investigated extensively as a solid lubricant,1 3 industrial hydrosulfurization catalyst,4 6 and as a hydrogen and electrochemical energy storage and conversion material.7,8 In MoS2, Mo and S atoms first bond covalently forming two-dimensional S Mo S trilayers, which then are held together through weak van der Waals interactions forming a sandwich structure.9 This special layered structure leads MoS2 nanoparticles to be classified as inorganic nanocarbon analogues of which structures like onionlike fullerenes, pipe-like nanotubes, and plate-like graphene are already well-known and have shown properties distinct from the bulk materials.10 12 MoS2 is regarded as a desirable intercalation host material since the guest atoms or molecules could reversibly intercalate and diffuse through its weak stacked layers.13,14 The intercalation process brings about two main effects: expansion of the interlayer spacing and charge transfer from the guests to the host.15 Featuring outstanding reversibility during the ions intercalation/deintercalation, MoS2 thus meets the basic demands needed for electrodes of secondary batteries,16,17 and different morphologies or composite forms have been tested.18,19 Recently, the exfoliated and restacked graphene-like MoS2 with enlarged c-axis spacing outperformed and exhibited high reversible lithium storage capacity, cyclic stability, and superior rate capacity.20 22 Resembling the Li system in basic operation mechanism and physical properties, rechargeable Mg batteries are now gaining increasing interest especially after work pioneered by Aurbach’s r 2011 American Chemical Society
group.23,24 Besides, the high theoretical specific capacity (2205 mA h g 1), great raw material abundance, and good operational safety of the Mg anode stimulate efforts to search for reasonable and novel cathode materials for the development of efficient Mg secondary batteries.25 Our group lately has reported a competitive secondary Mg battery system, which successively combined the above-mentioned highly exfoliated, graphene-like MoS2 with ultrasmall Mg nanoparticles and showed a perfect performance in operating voltage, and capacity retention.26 It is suggested that due to the adequately separated single layers, the inorganic graphene-like MoS2 can facilitate Mg2+ intercalation and migration, which opens up a new ground for the investigation of cathode materials in Mg rechargeable batteries. Furthermore, on the basis of previous understanding of carbon nanomaterials, nanoribbons are elongated stripes of single layered nanosheets with finite width possessing higher flexibility in spatial distribution.27 There have been some theoretic studies of single-layer MoS2 and zigzag MoS2 nanoribbons based on density functional theory recently. Li et al. revealed that zigzag MoS2 nanoribbons are all metallic independent of the ribbon width, while armchair ones are semiconducting with lower stability.28 Ataca and co-workers later reported twodimensional single-layer MoS2 to be a material that is suitable for functionalization and confirmed the stability and stiffness of the MoS2 nanoribbons.29,30 This special electronic property of Received: October 9, 2011 Revised: December 7, 2011 Published: December 09, 2011 1307
dx.doi.org/10.1021/jp2097026 | J. Phys. Chem. C 2012, 116, 1307–1312
The Journal of Physical Chemistry C
ARTICLE
the zigzag MoS2 nanoribbons will benefit the migration of ions on their surfaces and render them to be a more promising cathode material than the corresponding bulk matrix. Experimentally, using electrochemical methods, MoS2 nanoribbons were synthesized from crystalline 2H-MoS2,31 and the width has been distinctively reduced to 1 4 nm when encapsulated in the carbon nanotubes.32 All the research progress stated above encourages us to impose sufficient regard to the zigzag MoS2 nanoribbons as a promising functional material for Mg-ion batteries. Before the successful realization of this idea, several questions could be addressed in advance so as to well predict and understand its feasibility and advantage: at what specific sites will the guest Mg atoms locate on the nanoribbon? How will Mg atoms interact with MoS2 nanoribbon substrate? To what extent could the MoS2 nanoribbons improve the diffusion kinetics? In this work, we employed first-principles density functional theory (DFT)33 computation to unravel the questions listed above and illustrate the MoS2 nanoribbons to be a promising cathode of Mg secondary batteries.
2. COMPUTATIONAL DETAILS 2.1. Methodology. Calculations were carried out using density functional theory with the projector-augmented wave method34 as implemented in the Vienna ab initio simulation package (VASP).35 The generalized gradient approximation (GGA) functional of Perdew and Wang (PW91) was adopted to treat the exchange and correlation potential in all calculations.36 Interactions between ion and electron were described by the projector augmented wave (PAW) approach. The electron wave functions were expanded by a plane wave cutoff of 360 eV, and the total energy was converged to 10 6 eV. The following electronic states are treated as valence electrons: Mo, 4p65s14d5; S, 3s23p4; and Mg, 3s23p0. The infinite one-dimensional nanoribbon system was modeled by periodic boundary condition along the stretching direction of the ribbon (x direction). Meanwhile, vacuum layers of more than 15 Å along the y and z directions were, respectively, constructed to avoid periodical repetitiveness and interaction in these two directions. The positions of all the atoms in the supercell were fully relaxed using three special Monkhorst Pack k points until the residual Hellmann Feynman force on each atom was less than 10 2 eV/Å. To study the Mg diffusion kinetics, activation barriers were calculated using the climbing image nudged elastic band (CINEB) method.37 The CI-NEB is an efficient method to determine the minimum energy path and saddle points between a given initial and final positions.38 40 Before the CI-NEB calculation, structures of start and end points were first fully optimized. Then, nine intermediate images were linearly interpolated between them. Each image searched for its potential lowest energy configuration along the reaction path while maintaining equal distance to nearby images. To contrast the activation barriers of Mg motion on the surface of nanoribbon and in the interlayer of bulk, we also constructed an orthorhombic MoS2 bulk supercell that contains 24 molybdenum and 48 sulfur atoms. Bulk calculations were performed on 5 5 5 Monkhorst Pack k point meshes to a convergence criterion of 10 2 eV/Å in force. CINEB calculation of the bulk MoS2 was performed based on similar details and conditions described above. 2.2. Models. Three crystal polytypes of bulk MoS2 have been reported so far. Among them, the 2H type, which has trigonal prismatic coordination around Mo and two S Mo S units per
Figure 1. Top and side views of two possible Mg adsorption sites: (1) hollow site above the center of a hexagon (denoted as H site) and (2) ontop site directly above a molybdenum atom (denoted as T site).
elemental cell, is the most stable modification at normal conditions.9 However, according to previous nomenclature of graphene nanoribbons (GNRs),41 the width of zigzag nanoribbons is defined by parameter Nz, meaning the number of zigzag lines across the ribbon. In our present calculation, the initial structure model of the zigzag MoS2 nanoribbon (ZMoS2NR) was extracted from a separated molecular monolayer of the 2HMoS2 bulk crystal and had 20 formula units named 5-ZMoS2NR (Figure S1 in the Supporting Information). Structural relaxations of the 2H-MoS2 bulk crystal and 5-ZMoS2NR were first carried out. Results showed that the optimized bulk MoS2 structure was in good agreement with previous experimental reports.42 As to 5-ZMoS2NR, although the distances between Mo and S atoms (dMo S) at both edges decreased ca. 1.24%, the sandwich-like geometry was well kept, and the atom distances and bond angles inside the ribbon were almost unchanged. Detailed data are listed in Table S1 of the Supporting Information. Since Mg tends to coordinate to three S atoms other than Mo atoms, two possible Mg adsorption sites on the 5-ZMoS2NR are totally considered: (1) hollow (H) sites above the center of hexagon; (2) top of Mo atom (T) sites. The H and T sites, as illustrated in Figure 1, correspond to the bulk’s octahedral site and tetrahedral sites. Besides the H and T sites, the edge and center of the nanoribbon also exert varying influences to Mg adsorption.
3. RESULTS AND DISCUSSION 3.1. Mg Adsorption on Zigzag MoS2 Nanoribbon. In the present study, different Mg adsorption positions and amounts 1308
dx.doi.org/10.1021/jp2097026 |J. Phys. Chem. C 2012, 116, 1307–1312
The Journal of Physical Chemistry C
ARTICLE
Figure 2. Equilibrium configurations of the Mg adsorbed 5-ZMoS2NR. Panels a d represent single-side adsorptions of one, two, four, and six Mg atoms, while panels e h correspond to double-side adsorptions of two, four, eight, and twelve Mg atoms, respectively. The binding energy (Eb) of each case is listed right below.
are given a comprehensive consideration. Situations of adsorptions on only one single side and both sides are also included. The equilibrium Mg positions are determined by first placing Mg atom at a certain distance (ca. 1.50 Å) above the surface of different sites and subsequently optimizing the whole structures. Here, we employ binding energy (Eb) to represent the stability of Mg adsorbed system, which is defined as Eb = (aEMo + bES + cEMg EMgc @MoaSb)/(a + b + c) . EMo, ES, EMg, and EMgc @MoaSb indicate the energies of Mo, S, Mg atoms and Mg adsorbed MoS2 nanoribbon (represented by Mgc@MoaSb), while a, b, and c are the numbers of Mo, S, and Mg atoms. As to only one Mg atom adsorption on one side of the 5-ZMoS2NR, four initial potential positions are fully investigated (Figure S2 in the Supporting Information). Comparison reveals that the T site at the edge of the nanoribbon is the most stable for Mg location as shown in Figure 2a. The distance from Mg to the surface of nanoribbon is 1.39 Å, while the bond length of Mg to its neighboring three S atoms is 2.38 Å. Moreover, with respect to Mg adsorption, we can infer that the edges of MoS2 nanoribbon are more active relative to the center, and the T sites are energetically more favorable compared to the H sites. To investigate the Mg adsorption amount, two Mg atoms at a time are successively added to the previous most stable configuration. At each step, different potential positions are attempted (Figure S3 in the Supporting Information), and geometries with the maximum binding energy are displayed in Figure 2b d. About the adsorption process, three points need to be illustrated: (1) Mg atoms first prefer to occupy the top sites at the edge of MoS2 nanoribbon and then hold the hollow sites in the center of the 5-ZMoS2NR; (2) neither Mg atoms could share the S atoms to form continuous T or H occupation; (3) as the number of Mg atoms increases, the corresponding binding energy gradually decreases, indicating a descending thermodynamic stability. However, when the total Mg coverage reaches seven or eight, the distance of middle H-site Mg atoms to its nearest S atom gets 18.8% longer than the average Mg S bond length (ca. 2.38 Å), meaning the bonds between Mg atoms and the 5-ZMoS2NR break (Figure S4 in the Supporting Information). Thus, we can
say that on one side of the 5-ZMoS2NR, the maximum Mg adsorption number is six. As to the double-side adsorption, similar investigation strategy is conducted. Two Mg atoms are first separately adsorbed to this 5-ZMoS2NR from both sides, and the magnitude grows stepwise to four, eight, and twelve. A series of initial geometries with two Mg atom double-side adsorptions are optimized (Figure S5 in the Supporting Information). It is interesting to find that Mg atoms prefer to coordinate upward and downward to the same site of the 5-ZMoS2NR, unlike the common case in graphene nanoribbon that atoms occupy staggered locations above and below it.43 Moreover, in this case, the specific Mg sites and amount at each side are similar to that of the single-side adsorption discussed above, which are presented in Figure 2e h. Both sides together could accommodate up to twelve Mg atoms, thus bringing about a stoichiometric ratio Mg12Mo20S40 and a specific Mg storage capacity of 200.9 mA h g 1 as calculated by the Faraday equation. For a more general case, a MoS2 nanoribbon with a random width, a formula unit of Mg4Mo6S12 could be derived, reaching the largest theoretical capacity of 223.2 mA h g 1.26 It should be noted that there is ca. 24% difference between the calculated capacity and the observed experimental capacity (ca. 170 mA h g 1).26 Different crystal structures of MoS2 host are responsible for the discrepancy of electrode capacity. The highly exfoliated, graphene-like MoS2 cathode synthesized in experiment is not ideally single-layered. However, Mg atoms could adsorb on both sides of the monolayer MoS2 nanoribbon, which fully exposes additional active sites for accommodation of Mg atoms. 3.2. Electronic Properties. The electronic properties of the Mg adsorbed MoS2 nanoribbon systems are illustrated by density of states (DOS). Pristine 5-ZMoS2NR is studied to be metallic without a band gap around the Fermi level, in agreement with previous reports.28,44,45 Besides, the states near the Fermi levels are mainly dominated by the 4d electrons of edge Mo atoms and 3p electrons of edge S atoms. (Figure S6 in the Supporting Information) Figure 3 displays the calculated DOS of single-side one, four, and six, as well as double-side two, eight, and twelve Mg adsorbed 1309
dx.doi.org/10.1021/jp2097026 |J. Phys. Chem. C 2012, 116, 1307–1312
The Journal of Physical Chemistry C
ARTICLE
Figure 3. Density of states (DOS) of one (a), four (b), and six (c) Mg atom adsorptions on one single side of the 5-ZMoS2NR and two (d), eight (e), and twelve (f) Mg atom symmetrical adsorptions on double sides of the 5-ZMoS2NR. The red, blue, and green lines represent PDOS of the pure 5-ZMoS2NR host and Mg s and p states.
Table 1. Calculated Mean Bader Charges in |e| and Optimized Mean Mg S Bond Distance (Å) for Mg/MoS2NR Systems Bader charge |e|
a
system
qMg
qMo
Mg1@MoS2NRa
+0.505
+4.955
6.560
2.386
Mg2@MoS2NRa
+0.605
+4.962
6.589
2.411
Mg4@MoS2NRa
+0.693
+4.983
6.639
2.419
Mg6@MoS2NRa
+0.894
+4.994
6.669
2.526
Mg2@MoS2NRb
+0.482
+4.970
6.591
2.375
Mg4@MoS2NRb Mg8@MoS2NRb
+0.656 +0.865
+4.982 +5.008
6.643 6.723
2.426 2.490
Mg12@MoS2NRb
+1.045
+5.020
6.776
2.602
Single-side Mg adsorption systems. systems.
qS
b
dMg
S
(Å)
Double-side Mg adsorption
systems. In common, a single Mg atom has a fully filled 3s shell with two electrons. However, after adsorption, Mg 3s states (blue) become highly delocalized and split into mainly two peaks. The energy level of one peak is higher than Fermi energy indicating partial charge transfer to the 5-ZMoS2NR. Meanwhile, it can be seen from the plots that from the energy of 2 eV to 2 eV, the projected DOS of Mg-s and Mg-p overlap that of MoS2NR, which feature covalent hybridization interactions. Therefore, the cohesion between Mg and the 5-ZMoS2NR is dominated by ionic interactions but some covalent components are still not negligible. As stated above, edge Mo and S atoms contributed mainly to the vicinity of nanoribbon’s Fermi level and hence will foremost react with guest Mg atoms, which explains the site preference of Mg atoms to the edge of the nanoribbon from the point of electrostatic interaction. It also can be observed from Figure 3 that as the progressive addition of Mg atoms, the conduction band proportions of Mg-3s states reduce, indicating a decreasing charge transfer from Mg atoms to 5-ZMoS2NR substrates. This
observation exactly interprets the weakening of system’s stability upon gradual Mg adsorptions. After contrast of Figure 3c and 3f, we can find that their MoS2NR projected DOS plots are similar and analogous situations can also be obtained by comparison of Figure 3a and 3d, Figure 3b and 3e. So, relative to the single-side counterpart, double-side adsorption will not affect the structural stability of the 5-ZMoS2NR host in a large extent. In order to quantify the chemical bonding and charge transfer between Mg atoms and substrate, we have also performed Bader charge analysis.46 The Bader charges of Mg, Mo, and S atoms and the Mg S distance are summarized in Table 1. For single-side Mg adsorption, the Bader charges of Mg atoms monotonically increase from +0.505|e| (Mg1@MoS2NR) to +0.894|e| (Mg6@MoS2NR), and yet those of S atoms vary over the range from 6.560|e| to 6.669|e|. These changes reveal that more than one valence electron of each adsorbed Mg atom is transferred to the MoS2 nanoribbon. Furthermore, less valence electrons transfer to the ribbons with an increased Mg-adsorbed case. We found that the alteration of the dMg S is in conformity with the charge transfer between Mg atoms and S atoms in Table 1. The Mg6@MoS2NR system has the longest ), which corresponds to the least charges transferdMg S (2.526 Å ring between Mg atoms and S atoms. As to double-side adsorption systems, the situation is analogous to the single-side one. In all Mg adsorption systems, the Bader charges of Mg atoms range from +0.482|e| to +1.045|e|, while those of S atoms are in the scope from 6.776|e| to 6.560|e|. The data suggest that at least half of the valence electrons of the adsorbed Mg atom are transferred to the MoS2 nanoribbon corresponding well to the DOS analyzed above. 3.3. Mg Diffusion Process. Examination of the intrinsic Mg mobility on the MoS2 nanoribbon is significant and meaningful in terms of its actual application as a cathode material of Mg secondary batteries. The diffusion path is investigated between two adjacent T-sites, due to the energetic favorability to the H-sites, by assuming dilute Mg concentrations and no constraints from electronic mobility. Using the CI-NEB method, we find that the specific path by which Mg migrates between two adjacent T sites is through a nearest-neighbor H site in a zigzag way as presented in Figure 4a. The Mg diffusion path on MoS2 1310
dx.doi.org/10.1021/jp2097026 |J. Phys. Chem. C 2012, 116, 1307–1312
The Journal of Physical Chemistry C
ARTICLE
Figure 4. (a) Mg diffusion path on the surface of MoS2 nanoribbon. (b) Energy curve along the Mg diffusion path. ΔENR represents the activation barrier of this process.
Figure 5. (a) Mg migration path in the interlayer of MoS2 bulk. (b) Energy curve along the Mg diffusion path. ΔEbulk represents the activation barrier of this process.
nanoribbon is much distinct from our previous understanding of the graphene nanoribbon in which a hop happens between the intralayer hollow sites across the C C bridge.47 The corresponding energy along this path is plotted in Figure 4b, and the activation energy is identified to be only 0.48 eV. To better understand the enhancement of Mg diffusion by the nanoribbon, Mg migration in the interlayer of bulk MoS2 is also considered. In this case, Mg migrates between two octahedral (H) sites through a neighboring tetrahedral (T) site as an intermediate (Figure 5a). The energy barrier of this process is 2.61 eV, more than 5-fold higher than that of the nanoribbon (Figure 5b). It would result in a notable retard in Mg diffusion by a factor of 106 at room temperature since the diffusion constant is proportional to exp( Ebarrier/kBT). Therefore, we can expect a great improvement of Mg diffusion with the application of a MoS2 nanoribbon as a cathode.
4. CONCLUSIONS In this work, we employ the DFT method to systematically investigate the zigzag MoS2 nanoribbon as a promising cathode of Mg secondary batteries. When adsorbing onto the MoS2 nanoribbon surface, Mg atoms tend to occupy the Mo top site at the edge of the nanoribbon both energetically and electronically. Our MoS2 nanoribbon model with a width of 5 could accommodate at most six Mg atoms on the single side. Double-side adsorption is achieved through upward and downward to the same site of the host, after which a maximum theoretical capacity of 223.2 mA h g 1 could be attained. Electronic analysis reveals that the interactions between the guest Mg atoms and the MoS2 nanoribbon substrate are predominated by ionic bonds, while to some extent, covalent hybridizations still exist simultaneously. With the CI-NEB approach, Mg diffusion path on the MoS2 nanoribbon is identified to pass two adjoining T sites mediated by the closest
neighboring H site in between. The activation barrier of this process is only 0.48 eV, a great decrease compared to that in the bulk interlayer (2.61 eV). Above all, our first-principles study suggests that as a hopeful cathode of Mg secondary batteries, the MoS2 nanoribbon could achieve a great improvement in terms of Mg storage capacity and diffusion kinetics.
’ ASSOCIATED CONTENT
bS
Supporting Information. The optimized average neighbor atom distances and bond angles of 5-ZMoS2NR; structure models of the 5-ZMoS2NR; possible sites considered for one Mg atom adsorption on one single side of 5-ZMoS2NR; different potential positions investigated for single-side adsorptions of two and four Mg atoms on the 5-ZMoS2NR; starting and optimized structures of single-side six, seven, and eight Mg adsorbed 5-ZMoS2NR; different potential positions investigated for doubleside adsorptions of two Mg atoms on the 5-ZMoS2NR; total DOS of the pristine 5-ZMoS2NR and partial DOS of edge S atoms and edge Mo atoms. This material is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION Corresponding Author
*Tel: 86-22-23506808. Fax: 86-22-23509571. E-mail: chenabc@ nankai.edu.cn.
’ ACKNOWLEDGMENT This work was supported by the Research Programs of NSFC (20873071), 973 (2011CB935902), MOE (IRT0927), Tianjin 1311
dx.doi.org/10.1021/jp2097026 |J. Phys. Chem. C 2012, 116, 1307–1312
The Journal of Physical Chemistry C High-Tech (10SYSYJC27600), and the Fundamental Research Funds for the Central universities.
’ REFERENCES (1) Chhowalla, M.; Amaratunga, G. A. J. Nature 2000, 407, 164. (2) Stefanov, M.; Enyashin, A. N.; Heine, T.; Seifer, G. J. Phys. Chem. C 2008, 112, 46. (3) Tenne, R. Chem. Soc. Rev. 2010, 39, 1423. (4) Cheng, F. Y.; Chen, J.; Gou, X. L. Adv. Mater. 2006, 18, 2561. (5) Huang, M.; Cho, K. J. Phys. Chem. C 2009, 113, 5238. (6) Andersen, A.; Kathmann, S. M.; Lilga, M. A.; Albrecht, K. O.; Hallen, R. T.; Mei, D. J. Phys. Chem. C 2011, 115, 9025. (7) Chen, J.; Kuriyama, N.; Yuan, H.; Takeshita, H. T.; Sakai, T. J. Am. Chem. Soc. 2001, 123, 11813. (8) Tenne, R. Nat. Nanotechnol. 2006, 1, 103. (9) Benavente, E.; Santa Ana, M. A.; Mendizabal, F.; Gonzalez, G. Coord. Chem. Rev. 2002, 224, 87. (10) Remskar, M.; Mrzel, A.; Skraba, Z.; Jesih, A.; Ceh, M.; Demsar, J.; Stadelmann, P.; Levy, F.; Mihailovic, D. Science 2001, 292, 479. (11) Tenne, R. Angew. Chem., Int. Ed. 2003, 42, 5124. (12) Ataca, C.; Topsakal, M.; Akt€urk, E.; Ciraci, S. J. Phys. Chem. C 2011, 115, 16354. (13) Remskar, M.; Skraba, Z.; Stadelmann, P.; Levy, F. Adv. Mater. 2000, 12, 814. (14) Remskar, M.; Mrzel, A.; Virsek, M.; Jesih, A. Adv. Mater. 2007, 19, 4276. (15) Zak, A.; Feldman, Y.; Lyakhovitskaya, V.; Leitus, G.; PopovitzBiro, R.; Wachtel, E.; Cohen, H.; Reich, S.; Tenne, R. J. Am. Chem. Soc. 2002, 124, 4747. (16) Li, X. L.; Li, Y. D. J. Phys. Chem. B 2004, 108, 13893. (17) Cheng, F.; Liang, J.; Tao, Z.; Chen, J. Adv. Mater. 2011, 23, 1695. (18) Dominko, R.; Arcon, D.; Mrzel, A.; Zorko, A.; Cevc, P.; Venturini, P.; Gaberscek, M.; Remskar, M.; Mihailovic, D. Adv. Mater. 2002, 14, 1531. (19) Wang, Q.; Li, J. J. Phys. Chem. C 2007, 111, 1675. (20) Du, G.; Guo, Z.; Wang, S.; Zeng, R.; Chen, Z.; Liu, H. Chem. Commun. 2010, 46, 1106. (21) Xiao, J.; Choi, D.; Cosimbescu, L.; Koech, P.; Liu, J.; Lemmon, J. P. Chem. Mater. 2010, 22, 4522. (22) Chang, K.; Chen, W.; Ma, L.; Li, H.; Li, H.; Huang, F.; Xu, Z.; Zhang, Q.; Lee, J.-Y. J. Mater. Chem. 2011, 21, 6251. (23) Aurbach, D.; Lu, Z.; Schechter, A.; Gofer, Y.; Gizbar, H.; Turgeman, R.; Cohen, Y.; Moshkovich, M.; Levi, E. Nature 2000, 407, 724. (24) Chen, J.; Cheng, F. Acc. Chem. Res. 2009, 42, 713. (25) Peng, B.; Chen, J. Coord. Chem. Rev. 2009, 253, 2805. (26) Liang, Y.; Feng, R.; Yang, S.; Ma, H.; Liang, J.; Chen, J. Adv. Mater. 2011, 23, 640. (27) Barone, V.; Hod, O.; Scuseria, G. E. Nano Lett. 2006, 6, 2748. (28) Li, Y.; Zhou, Z.; Zhang, S.; Chen, Z. J. Am. Chem. Soc. 2008, 130, 16739. (29) Ataca, C.; Ciraci, S. J. Phys. Chem. C 2011, 115, 13303. (30) Ataca, C.; Sahin, H.; Akt€urk, E.; Ciraci, S. J. Phys. Chem. C 2011, 115, 3934. (31) Li, Q.; Newberg, J. T.; Walter, E. C.; Hemminger, J. C.; Penner, R. M. Nano Lett. 2004, 4, 277. (32) Wang, Z.; Li, H.; Liu, Z.; Shi, Z.; Lu, J.; Suenaga, K.; Joung, S.-K.; Okazaki, T.; Gu, Z.; Zhou, J.; Gao, Z.; Li, G.; Sanvito, S.; Wang, E.; Iijima, S. J. Am. Chem. Soc. 2010, 132, 13840. (33) Kohn, W.; Sham, L. J. Phys. Rev. 1965, 140, A1133. (34) Bl€ochl, P. E. Phys. Rev. B 1994, 50, 17953. (35) Kresse, G.; Hafner, J. Phys. Rev. B 1993, 47, 558. (36) Wang, Y.; Perdew, J. P. Phys. Rev. B 1991, 44, 13298. (37) Henkelman, G.; Uberuaga, B. P.; Jonsson, H. J. Chem. Phys. 2000, 113, 9901.
ARTICLE
(38) Tibbetts, K.; Miranda, C. R.; Meng, Y. S.; Ceder, G. Chem. Mater. 2007, 19, 5302. (39) Wen, S. H.; Hou, Z. F.; Han, K. L. J. Phys. Chem. C 2009, 113, 18436. (40) Peng, B.; Cheng, F. Y.; Tao, Z. L.; Chen, J. J. Chem. Phys. 2010, 133, 034701. (41) Son, Y.-W.; Cohen, M. L.; Louie, S. G. Phys. Rev. Lett. 2006, 97, 216803. (42) Petkov, V.; Billinge, S. J. L.; Larson, P.; Mahanti, S. D.; Vogt, T.; Rangan, K. K.; Kanatzidis, M. G. Phys. Rev. B 2002, 65, 092105. (43) Sevinc-li, H.; Topsakal, M.; Durgun, E.; Ciraci, S. Phys. Rev. B 2008, 77, 195434. (44) Raybaud, P.; Hafner, J.; Kresse., G.; Toulhoat, H. Surf. Sci. 1998, 407, 237. (45) Bollinger, M. V.; Lauritsen, J. V.; Jacohsen, K. W.; Norskov, J. K.; Helveg, S.; Besenbacher, F. Phys. Rev. Lett. 2001, 87, 196803. (46) Henkelman, G.; Arnaldsson, A.; Jonsson, H. Comput. Mater. Sci. 2006, 36, 354. (47) Uthaisar, C.; Barone, V. Nano Lett. 2010, 10, 2838.
1312
dx.doi.org/10.1021/jp2097026 |J. Phys. Chem. C 2012, 116, 1307–1312
