Carboxylic Acid Group-Induced Oxygen Vacancy Migration on an

Subscriber access provided by University of Groningen

Article

Carboxylic acid group induced oxygen vacancy migration on anatase (101) surface Yadong Li, and Yi Gao Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.7b02977 • Publication Date (Web): 17 Dec 2017 Downloaded from http://pubs.acs.org on December 18, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Langmuir is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 18 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Carboxylic acid group induced oxygen vacancy migration on anatase (101) surface Yadong Li ,a, b Yi Gao a * a

Division of Interfacial Water and Key Laboratory of Interfacial Physics and Technology,

Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China b

University of Chinese Academy of Sciences, Beijing 100049, China

ACS Paragon Plus Environment

1

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 18

ABSTRACT Dye-sensitized solar cells have aroused intensive interest for the replacement of conventional crystalline silicon solar cells. Through carboxylic acid groups, the dyes attach to the TiO2 anatase (101) surface, on which the subsurface oxygen vacancies are predominant. The performance of dye-sensitized solar cells can be affected by the presence and positions of oxygen vacancies. By applying density functional theory calculations, we found the adsorption of carboxylic acid group decorated dye molecule reverses the relative stability between the surface and subsurface oxygen vacancy on anatase (101) surface, which facilitates the migration of oxygen vacancy from subsurface to surface by overcoming an energy barrier of less than 0.16 eV, significantly lower than the 1.01 eV energy barrier on clean surface. Further ab initio molecular dynamics simulations indicate the subsurface oxygen vacancy can easily migrate to the surface at room temperature. This dynamic interplay between the oxygen vacancy of anatase (101) surface and the carboxylic acid group would be important for future studies concerning the stability and photovoltaic efficiency of the solar cells. INTRODUCTION To slow down the greenhouse gas emission related global warming, a disruptive shift from fossil energy to renewable energy is undergoing. The prospect of converting solar energy into electricity or chemical energy is promising as the photovoltaic industry has already seen a rapid growth in the past few years. In this context, dye-sensitized solar cells (DSSC) and recently developed perovskite sensitized solar cells emerges as the promising low-cost replacements of conventional crystalline silicon solar cells that can be installed for both grid-scale power generation and household for daily usage.1-4 In DSSC, dye molecules attaches to the TiO2


2

Page 3 of 18 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

nanoparticles by decorating anchor groups, to which carboxylic acid group is a common choice. The bindings between the dye molecules and TiO2 surfaces play the important role in determining the overall performance of solar cells, as the binding energies affects solar cells’ long-term stabilities and the binding geometries affect the excited electron injection rates.5-7 On perfect anatase (101) surface, the monodentate adsorption is the most stable adsorption geometry for carboxylic acid group decorated dye molecule while bidentate adsorption is slightly unfavorable.5, 8-10 Point defects, especially oxygen vacancies (Vo’s), play the important role in the surface chemistry of TiO2.11-12 Unlike rutile (110) surface, on which the surface Vo’s (Vosurf’s) are abundant, Vosurf’s have rarely been observed experimentally on anatase (101) surface.13-14 In fact, subsurface Vo’s (Vosub’s) are more stable than their surface counterparts on anatase (101) surface and Vosurf’s could migrate to subsurface or bulk sites at temperature as low as 200 K.15-17 The Vo’s presence and positions could affect the photovoltaic efficiency of DSSC. With the introduction of Vosurf’s, the dye molecules bind more strongly to the surface, enhancing the stabilities and long-term endurance of the solar cells. Stronger adsorption of dye molecules on the surface also give higher dye density over surface, which results in higher short circuit current density.18 Theoretical study also shows charge injection is promoted by the Vosurf’s.5 On the other hand, the Vo’s serve as recombination centers for photo excited electrons and holes, thus reducing the photovoltaic efficiency.5, 19-20 Currently, most theoretical studies are focused on dye adsorption on perfect surface or surface with Vosurf. As the predominance of Vosub on anatase (101) surface, a systematic study on the Vosub’s effect on the dye’s adsorption is critical to the understanding and improving of the DSSC’s efficiency. Previous studies have shown that adsorbed O2, water and methanol molecule


3

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 18

can induce Vo migration from subsurface to surface.12, 21-23 The carboxylic acid group’s effect on the relative stability between surface and subsurface Vo has not been studied yet. By using density functional theory (DFT) and ab initio molecular dynamic (AIMD) calculations, we studied the interplay between carboxylic acid group and Vo on the anatase (101) surface. Formic acid and benzoic acid are used as model molecules to study the dye-anatase interface (Figure 1). For the two molecules considered, the relative stabilities between Vosub and Vosurf are reversed upon adsorption. Moreover, the energy barriers for Vo migration from subsurface to surface are greatly lowered to less than 0.16 eV. The subsurface to surface migration of Vo could readily happen in the time scale of picoseconds according to the AIMD simulation. This finding reveals the dynamic interplay between the dye molecules and anatase (101) surface and could deepen the understanding of the dye-TiO2 interfaces.

Figure 1. Molecular geometry of (a) formic acid and (b) benzoic acid COMPUTATIONAL DETAILS Geometry optimizations and transition state calculations are carried out using generalized gradient approximations (GGA) method with Perdew-Burke-Ernzerhof (PBE) exchangecorrelation functional as implemented in the VASP code.24-26 The projector augmented wave


4

Page 5 of 18 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

(PAW) method is used for description of the interaction between core and valence electrons with energy cutoff of 400 eV. 27-28 The slab model, composed by 288 atoms, is built by (1*4) supercell with six anatase TiO2 (101) layers separated by vacuum layer of 20 Å. The bottom TiO2 layer is fixed during calculation to mimic the bulk structure. Only Gamma point is used for k-point sampling due to the large cell size. The climbing-image nudged band method is used for transition state calculations.29 All AIMD simulations are carried out at temperature of 298 K using implementations in CP2K/QUICKSTEP package with PBE functional.30 The molecularly optimized double-ζ Gaussian basis is chosen to minimize basis set superposition errors. The auxiliary plane wave is expanded to 280 Ry to calculate the electrostatic energy. A (1*4) supercell with three TiO2 layers are used in AIMD simulations for computational efficiency. Canonical ensemble employing Nose-Hoover thermostats is used in the AIMD simulations with time step of 1fs. The pure DFT rather than DFT+U is used in this study because pure DFT calculations give results that better agree with experimental observed relative stability of surface/subsurface Vo on anatase (101) surface.31-32 RESULTS AND DISCUSSION The formation energies and relative stabilities of multiple surface and subsurface Vo sites on anatase (101) surface have been extensively studied using different theoretical methods.16, 21, 31-32

At the DFT level of theory, the most stable Vosub site (shown in Figure 2 IS) is 0.46 eV

lower in energy than the most stable Vosurf site (shown in Figure 2 FS). The energy barrier for Vo migration from subsurface to surface is 1.01 eV, in consistent with results from Cheng et. al.16


5

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 18

Figure 2. Calculated Vo subsurface to surface migration pathway on clean anatase (101) surface. Enclosed in the parentheses is corresponding energy for each state The adsorption of formic acid on perfect anatase (101) surface is studied (Figure S1). The most stable geometry is formic acid adsorbing associatively on surface Ti-5c (surface five coordinated Ti) site to form the hydrogen bond with surface O-2c (surface two coordinated O). The adsorption energy is -0.95 eV (Figure S1(a)). The dissociative monodentate adsorption geometry is 0.03 eV higher in energy than the associative one (Figure S1(b)). This small energy difference indicates that the adsorption of formic acid could be either dissociative or associative on surface. The dissociative bidentate geometry is energetically unfavorable with the adsorption energy of -0.82 eV (Figure S1(c)). The adsorption energies and geometries of formic acid are changed with the introduction of Vosub. Dissociative monodentate adsorption is the most energetically favorable geometry with adsorption energy of -1.16 eV (Figure 3 Msub). The associative monodentate geometry is no longer stable as it spontaneously dissociates after geometry optimization. The adsorption energy of dissociative bidentate geometry is -1.00 eV (Figure 3 Bsub).


6

Page 7 of 18 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Figure 3. Optimized geometries of formic acid adsorbed on anatase (101) surface with Vosub. The adsorptions are further enhanced by Vosurf. The most stable geometries are characterized by the formate group filling Vosurf site while the formate O pointing to surface Ti4c (four coordinated surface Ti atom) atom (Figure 4 M1surf and M2surf). The positions of adsorption sites for H atoms have minor effects on the adsorption energies as the adsorption energies of M1surf and M2surf are -1.95 eV and -1.90 eV, respectively. Another low-lying geometry with adsorption energy of -1.83 eV is similar to the dissociative monodentate geometry on perfect surface (Figure 4 M3surf). The bidentate geometry is the least favorable geometry with the adsorption energy of -1.57 eV (Figure 4 Bsurf). The introduction of Vo changes the electronic structure of surface Ti atom. Figure S2 shows the projected density of states (PDOS) of clean surface’s low coordinated Ti atom on which the formic acid molecule adsorbs. Ti’s 3d orbitals mainly contribute to the conduction band. Comparing to perfect surface, the surfaces with Vo have stronger peaks near the conduction band minimum (CBM), indicating higher reactivity of the reduced surfaces. Indeed, the adsorption


7

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 18

energy is enhanced on surface with Vo and the Ti-O bond length between formic acid and surface is reduced from 2.14 Å for the perfect surface (Figure S1a) to 1.93 Å for the surface with Vo (Msub and M3surf).

Figure 4. Optimized geometries of formic acid adsorbed on anatase (101) surface with Vosurf. Based on the above geometric and energetic information, the mono- and bi-dentate adsorbed formic acid are both considered in the Vo migration barrier calculations. For the monodentate adsorption, the Vosub migrates to surface site by overcoming an overall energy barrier of 0.12 eV as shown in Figure 5. The intermediate state is stabilized by the hydrogen bond between formate group and surface hydroxyl group. This barrier is significantly lower


8

Page 9 of 18 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

comparing with 1.01 eV on clean surface (Figure 2). Furthermore, with the introduction of formic acid, the Vosurf is 0.29 eV lower in energy than Vosub. This is due to the stronger adsorption of formic acid on surface with Vosurf than that on surface with Vosub. AIMD simulation is carried out to further confirm the transition state calculations. Starting from optimized Vosub structure, the Vo readily migrates to the surface site after 1 ps simulation at temperature of 298 K. By further investigating the bond length between the formate O and surface Ti (Figure 6), we find the Ti-O bond length is reduced at the Vo migration phase, indicating a stronger Ti-O bond. It is noteworthy that a bidentate geometry over Vosurf (Figure 6(c)), similar to what previous study proposed, is observed during the simulation.33 However, by taking this structure as initial structure, further geometry optimization gives final structure similar to the M2surf, indicating this is not a local minimum structure.

Figure 5. Calculated Vo subsurface to surface migration pathway with formic acid monodentate adsorbed on surface. Enclosed in the parentheses is corresponding energy for each state.


9

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 18

Figure 6. AIMD simulation of Vo subsurface to surface migration induced by monodentate adsorbed formic acid. (a) The evolution of Ti-O length and O displacement from its initial position along the AIMD trajectory. (b) – (d) Selected geometries from the AIMD simulation. The dentate adsorbed formic acid induced Vo migration is also studied (Figure 7). Similar to monodentate adsorption, the overall Vo migration barrier is relatively low (~0.16 eV). There are two pathways for the bidentate adsorbed formic acid to fill the Vosurf. In the first pathway, the bidentate adsorbed formate group directly fills the Vosurf with energy barrier of 0.13 eV. In the second pathway, the formate group first reaches an intermediate state by crossing an energy barrier of 0.19 eV, then reaches the final state by overcoming a 0.27 eV energy barrier. The


10

Page 11 of 18 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

intermediate state M4surf is characterized by the formate group filling the Vosurf while the formate O atom pointing to the adjacent Ti-5c atom.

Figure 7. Calculated Vo subsurface to surface migration pathway with formic acid bidentate adsorbed on surface. Enclosed in the parentheses is corresponding energy for each state. Starting from the same bidentate adsorption geometry, two pathways have been reproduced by room temperature AIMD simulation (Figure 8 and Figure S3). In the first pathway, the Vosub migrates to the surface site after ~0.5 ps simulation. The Ti-O bond between formate group and surface away from Vo site breaks and the formate group rotates around the Ti-O bond near the Vo. This Ti-O bond length is reduced after Vo migration from subsurface to surface similar to


11

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 18

the monodentate adsorption case. After ~2.0 ps simulation, the formate group fills Vosurf and the Ti-O bond length shows larger fluctuation. The spike of Ti-O bond length at 2.6 ps of Figure 8 corresponds to a geometry similar to the monodentate case as discussed previously. The second pathway shows the similar trajectory as the first pathway at first. But after rotating around the TiO bond near Vosurf, the formate group fills the Vosurf while its oxygen atom pointing to the surface Ti-5c and is stabilized at this position for the rest of simulation. The reason that this simulation does not transit to the most stable state is the energy barrier from this intermediate state to the most stable geometry is relatively high (~0.27 eV according to the transition state calculation), indicating that it will take longer time to overcome this barrier. Also the structural stability of this intermediate state is evidenced by the less fluctuating Ti-O bond length as shown in Figure S3.


12

Page 13 of 18 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Figure 8. AIMD simulation of Vo subsurface to surface migration induced by bidentate adsorbed formic acid. (a) The evolution of Ti-O length and O displacement from its initial position along the AIMD trajectory. (b) – (d) Selected geometries from the AIMD simulation. The dramatic decrease of Vo migration barrier on formic acid adsorbed surface comparing to clean surface could be explained by the longer lattice O-Ti bond length upon formic acid adsorption (Figure 2 IS, Figure 5 IS, Figure 7 IS). As the O-Ti bond breaking is the transition state of Vo migration step, the longer O-Ti bond length indicates weaker O-Ti interaction, thus a lower barrier for Vo migration. Indeed the O-Ti bond distance is 1.85 Å for clean surface with Vosub. While the O-Ti bond length is 2.13 Å and 2.06 Å for surface with monodentate and bidentate adsorbed formic acid, respectively.

Figure 9. Calculated Vo subsurface to surface migration pathway with benzoic acid monodentate adsorbed on surface. Enclosed in the parentheses is corresponding energy for each state.


13

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 18

It also should be noted that as the energy barriers of the Vo migration for the monodenate and bidentate adsorptions are very close (0.12 eV vs 0.16 eV), the periods of time for Vo migration are also very close (1.2 ps vs. 0.5 ps). The slight difference of migration time during the MD simulation is mainly coming from the different initial velocity and temperature fluctuation. Besides the formic acid, the benzoic acid is also studied. The adsorption and Vo migration energy of anatase-benzoic acid system is very similar to that of anatase-formic acid system (Figure 9 and Figure S4). On surface with Vosub, the adsorption energy for monodentate and bidentate geometry is -1.16 eV and -1.06 eV, respectively. The adsorption energy for the most stable geometry on surface with Vosurf is -2.03 eV. The overall Vo migration barriers for surface with monodentate and bidentate adsorbed benzoic acid are 0.11 eV and 0.14 eV, respectively. The similar energetic and geometric data between formic acid system and benzoic acid system indicate the adsorption and Vo migration energies are mainly determined by the carboxylic acid group rather than the dye molecule, thus the proposed Vo migration mechanism could be applied to other carboxylic acid group decorated dyes. CONCLUSIONS In summary, we systematically studied the interplay between carboxylic acid group and Vo on anatase (101) surface. Formic acid and benzoic acid are selected as model molecules to study the effect of carboxylic acid group on the Vo’s stability and migration energy. By applying transition state calculations and AIMD simulations, we found the relative stability of surface and subsurface Vo is reversed upon molecule adsorption and the Vo can migrate from subsurface to surface with a relatively low energy barrier (less than 0.16 eV) for both monodentate and


14

Page 15 of 18 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

bidentate adsorption configurations. This study reveals the dynamic interplay between carboxylic acid decorated dye molecules and Vo on anatase (101) surface. As the Vosurf density is an important factor in determining the DSSC performance, this study could shield light on the understanding and improving the DSSC stability and photovoltaic efficiency. Further study using industry used dye molecules should be carried out to investigate the Vosub and Vosurf’s effect on the electronic property of the dye-anatase system. SUPPORTING INFORMATIONS Optimized geometries of formic acid adsorbed on perfect anatase (101) surface, projected density of states of surface Ti atoms of perfect surface and surface with Vo, AIMD simulation of Vo subsurface to surface migration induced by bidentate adsorbed formic acid, calculated Vo subsurface to surface migration pathway with benzoic acid bidentate adsorbed on surface. CORRESPONDING AUTHOR *E-mail: [email protected]. ACKNOWLEDGEMENTS Y.G. thanks for the funding support from National Natural Science Foundation of China (11574340). The work is supported by grants from CAS-Shanghai Science Research Center, Grant CAS-SSRC-YJ-2015-01. The authors also thank Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund (the second phase) under Grant No.U1501501. The computational resources utilized in this research were provided by Shanghai Supercomputer Center, National Supercomputer Centers in Tianjin, Shenzhen.


15

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 18

REFERENCES 1. O'Regan, B.; Gratzel, M., A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films. Nature 1991, 353 (6346), 737-740. 2. Mathew, S.; Yella, A.; Gao, P.; Humphry-Baker, R.; CurchodBasile, F. E.; Ashari-Astani, N.; Tavernelli, I.; Rothlisberger, U.; NazeeruddinMd, K.; Grätzel, M., Dye-sensitized solar cells with 13% efficiency achieved through the molecular engineering of porphyrin sensitizers. Nat. Chem. 2014, 6 (3), 242-247. 3. Kojima, A.; Teshima, K.; Shirai, Y.; Miyasaka, T., Organometal Halide Perovskites as VisibleLight Sensitizers for Photovoltaic Cells. J. Am. Chem. Soc. 2009, 131 (17), 6050-6051. 4. Green, M. A.; Ho-Baillie, A.; Snaith, H. J., The emergence of perovskite solar cells. Nat. Photon 2014, 8 (7), 506-514. 5. Meng, S.; Kaxiras, E., Electron and Hole Dynamics in Dye-Sensitized Solar Cells: Influencing Factors and Systematic Trends. Nano Lett. 2010, 10 (4), 1238-1247. 6. Li, S.-C.; Wang, J.-g.; Jacobson, P.; Gong, X.-Q.; Selloni, A.; Diebold, U., Correlation between Bonding Geometry and Band Gap States at Organic− Inorganic Interfaces: Catechol on Rutile TiO2 (110). J. Am. Chem. Soc. 2009, 131 (3), 980-984. 7. Ambrosio, F.; Martsinovich, N.; Troisi, A., What Is the Best Anchoring Group for a Dye in a Dye-Sensitized Solar Cell? J. Phys. Chem. Lett 2012, 3 (11), 1531-1535. 8. Miller, K. L.; Musgrave, C. B.; Falconer, J. L.; Medlin, J. W., Effects of Water and Formic Acid Adsorption on the Electronic Structure of Anatase TiO2(101). J. Phys. Chem. C 2011, 115 (6), 2738-2749. 9. Vittadini, A.; Selloni, A.; Rotzinger, F. P.; Grätzel, M., Formic Acid Adsorption on Dry and Hydrated TiO2 Anatase (101) Surfaces by DFT Calculations. J. Phys. Chem. B 2000, 104 (6), 1300-1306. 10. Ikalainen, S.; Laasonen, K., A DFT study of adsorption of perylene on clean and altered anatase (101) TiO2. Phys. Chem. Chem. Phys. 2013, 15 (28), 11673-11678. 11. Kong, M.; Li, Y.; Chen, X.; Tian, T.; Fang, P.; Zheng, F.; Zhao, X., Tuning the Relative Concentration Ratio of Bulk Defects to Surface Defects in TiO2 Nanocrystals Leads to High Photocatalytic Efficiency. J. Am. Chem. Soc. 2011, 133 (41), 16414-16417. 12. Setvín, M.; Aschauer, U.; Scheiber, P.; Li, Y.-F.; Hou, W.; Schmid, M.; Selloni, A.; Diebold, U., Reaction of O2 with Subsurface Oxygen Vacancies on TiO2 Anatase (101). Science 2013, 341 (6149), 988-991. 13. Diebold, U., The surface science of titanium dioxide. Surf. Sci. Rep. 2003, 48 (5–8), 53-229. 14. Thomas, A.; Flavell, W.; Mallick, A.; Kumarasinghe, A.; Tsoutsou, D.; Khan, N.; Chatwin, C.; Rayner, S.; Smith, G.; Stockbauer, R., Comparison of the electronic structure of anatase and rutile TiO2 single-crystal surfaces using resonant photoemission and X-ray absorption spectroscopy. Phys. Rev. B 2007, 75 (3), 035105. 15. He, Y.; Dulub, O.; Cheng, H.; Selloni, A.; Diebold, U., Evidence for the Predominance of Subsurface Defects on Reduced Anatase TiO2(101). Phys. Rev. Lett. 2009, 102 (10), 106105. 16. Cheng, H.; Selloni, A., Surface and subsurface oxygen vacancies in anatase TiO2 and differences with rutile. Phys. Rev. B 2009, 79 (9), 092101. 17. Scheiber, P.; Fidler, M.; Dulub, O.; Schmid, M.; Diebold, U.; Hou, W.; Aschauer, U.; Selloni, A., (Sub)Surface Mobility of Oxygen Vacancies at the TiO2 Anatase (101) Surface. Phys. Rev. Lett. 2012, 109 (13), 136103. 18. Zhang, J.; Zhao, Z.; Wang, X.; Yu, T.; Guan, J.; Yu, Z.; Li, Z.; Zou, Z., Increasing the Oxygen


16

Page 17 of 18 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Vacancy Density on the TiO2 Surface by La-Doping for Dye-Sensitized Solar Cells. J. Phys. Chem. C 2010, 114 (43), 18396-18400. 19. Stefik, M.; Heiligtag, F. J.; Niederberger, M.; Grätzel, M., Improved Nonaqueous Synthesis of TiO2 for Dye-Sensitized Solar Cells. ACS Nano 2013, 7 (10), 8981-8989. 20. Das, P. P.; Agarkar, S. A.; Mukhopadhyay, S.; Manju, U.; Ogale, S. B.; Devi, P. S., Defects in Chemically Synthesized and Thermally Processed ZnO Nanorods: Implications for Active Layer Properties in Dye-Sensitized Solar Cells. Inorg. Chem. 2014, 53 (8), 3961-3972. 21. Li, Y.; Gao, Y., Interplay between Water and TiO2 Anatase (101) Surface with Subsurface Oxygen Vacancy. Phys. Rev. Lett. 2014, 112 (20), 206101. 22. Lang, X.; Liang, Y.; Sun, L.; Zhou, S.; Lau, W.-M., Interplay between Methanol and Anatase TiO2(101) Surface: The Effect of Subsurface Oxygen Vacancy. J. Phys. Chem. C 2017, 121 (11), 6072-6080. 23. Cao, Y.; Chen, S.; Li, Y.; Gao, Y.; Yang, D.; Shen, Y. R.; Liu, W.-T., Evolution of anatase surface active sites probed by in situ sum-frequency phonon spectroscopy. Science Advances 2016, 2 (9), e1601162. 24. Perdew, J. P.; Burke, K.; Ernzerhof, M., Generalized gradient approximation made simple. Phys. Rev. Lett. 1996, 77 (18), 3865. 25. Kresse, G.; Furthmüller, J., Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B 1996, 54 (16), 11169-11186. 26. Kresse, G.; Furthmüller, J., Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Comput. Mater. Sci. 1996, 6 (1), 15-50. 27. Kresse, G.; Joubert, D., From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B 1999, 59 (3), 1758-1775. 28. Blöchl, P. E., Projector augmented-wave method. Phys. Rev. B 1994, 50 (24), 17953. 29. Henkelman, G.; Uberuaga, B. P.; Jonsson, H., A climbing image nudged elastic band method for finding saddle points and minimum energy paths. J. Chem. Phys. 2000, 113 (22), 9901-9904. 30. VandeVondele, J.; Krack, M.; Mohamed, F.; Parrinello, M.; Chassaing, T.; Hutter, J., Quickstep: Fast and accurate density functional calculations using a mixed Gaussian and plane waves approach. Comput. Phys. Commun. 2005, 167 (2), 103-128. 31. Haa, M.-A.; Alexandrova, A. N., Oxygen Vacancies of Anatase(101): Extreme Sensitivity to the Density Functional Theory Method. J. Chem. Theory Comput. 2016, 12 (6), 2889-2895. 32. Li, H.; Guo, Y.; Robertson, J., Calculation of TiO2 Surface and Subsurface Oxygen Vacancy by the Screened Exchange Functional. J. Phys. Chem. C 2015, 119 (32), 18160-18166. 33. Xu, M.; Noei, H.; Buchholz, M.; Muhler, M.; Wöll, C.; Wang, Y., Dissociation of formic acid on anatase TiO2(101) probed by vibrational spectroscopy. Catal. Today 2012, 182 (1), 12-15.


17

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 18

Table of Contents


18

Carboxylic Acid Group-Induced Oxygen Vacancy Migration on an

Recommend Documents