Coverage-Dependent Water Agglomerates on Fe 3 O 4 (001):

Transcription

1 Coverage-Dependent Water Agglomerates on Fe 3 O 4 (001): From Partially-Dissociated Dimers and Trimers to a Hydrogen-Bonded Network Matthias Meier 1,2, Jan Hulva 2, Zdeněk Jakub 2, Jiří Pavelec 2, Martin Setvin 2, Michael Schmid 2, Ulrike Diebold 2, Cesare Franchini 1 and Gareth S. Parkinson 2 1 Institute of Applied Physics, Technische Universität Wien, Vienna, Austria 2 University of Vienna, Faculty of Physics and Center for Computational Materials Science, Vienna, Austria January 22, 2018 Computational Materials Physics H 2 O/Fe 3 O 4 (001) 1 / 15

2 Computational Materials Physics H2 O/Fe3 O4 (001) 2 / 15

3 Context Water is important (corrosion, oxidation, catalysis,...) 1,2. Water might be present: part of the reaction itself or in the environment (under reaction condition). Its interaction with the catalyst s surface is therefore of interest. Most metals oxidize under reaction condition. Therefore we study water on oxides. H 2 O on the reference oxide TiO 2 : 20 year long controversy solved last year 3. This work aims to understand how H 2 O interacts with Fe 3 O 4 (001) 4, another commonly found and used oxide. 1 O. Björneholm et al., Chem. Rev. 116, 7698 (2016) 2 A. Hodgson and S. Haq, Surf. Sci. Rep. 64, 381 (2009) 3 U. Diebold, J. Chem. Phys. 147, (2017) 4 G. S. Parkinson, Surf. Sci. Rep. (2016) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 3 / 15

4 Temperature Programmed Desorption Water adsorbed at 100 K, with different coverages: H 2 O mass spec. signal as a function of T. Amount of water molecules adsorbed on surface known: Calibrated molecular beam 1 quantitative. D 2 O or H 2 O doesn t matter. Jan Hulva 1 J. Pavelec et al., J. Chem. Phys. 146, (2017) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 4 / 15

5 Temperature Programmed Desorption Water adsorbed at 100 K, with different coverages: H 2 O mass spec. signal as a function of T. Amount of water molecules adsorbed on surface known: Calibrated molecular beam 1 quantitative. D 2 O or H 2 O doesn t matter. Jan Hulva 1 J. Pavelec et al., J. Chem. Phys. 146, (2017) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 4 / 15

6 Temperature Programmed Desorption Water adsorbed at 100 K, with different coverages: H 2 O mass spec. signal as a function of T. Amount of water molecules adsorbed on surface known: Calibrated molecular beam 1 quantitative. D 2 O or H 2 O doesn t matter. Jan Hulva 1 J. Pavelec et al., J. Chem. Phys. 146, (2017) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 4 / 15

7 Temperature Programmed Desorption Water adsorbed at 100 K, with different coverages: H 2 O mass spec. signal as a function of T. Amount of water molecules adsorbed on surface known: Calibrated molecular beam 1 quantitative. D 2 O or H 2 O doesn t matter. Jan Hulva 1 J. Pavelec et al., J. Chem. Phys. 146, (2017) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 4 / 15

8 Temperature Programmed Desorption Water adsorbed at 100 K, with different coverages: H 2 O mass spec. signal as a function of T. Amount of water molecules adsorbed on surface known: Calibrated molecular beam 1 quantitative. D 2 O or H 2 O doesn t matter. Jan Hulva 1 J. Pavelec et al., J. Chem. Phys. 146, (2017) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 4 / 15

9 Temperature Programmed Desorption Water adsorbed at 100 K, with different coverages: H 2 O mass spec. signal as a function of T. Amount of water molecules adsorbed on surface known: Calibrated molecular beam 1 quantitative. D 2 O or H 2 O doesn t matter. Jan Hulva 1 J. Pavelec et al., J. Chem. Phys. 146, (2017) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 4 / 15

10 Temperature Programmed Desorption Water adsorbed at 100 K, with different coverages: H 2 O mass spec. signal as a function of T. Amount of water molecules adsorbed on surface known: Calibrated molecular beam 1 quantitative. D 2 O or H 2 O doesn t matter. Jan Hulva 1 J. Pavelec et al., J. Chem. Phys. 146, (2017) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 4 / 15

11 Temperature Programmed Desorption Water adsorbed at 100 K, with different coverages: H 2 O mass spec. signal as a function of T. Amount of water molecules adsorbed on surface known: Calibrated molecular beam 1 quantitative. D 2 O or H 2 O doesn t matter. Jan Hulva 1 J. Pavelec et al., J. Chem. Phys. 146, (2017) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 4 / 15

12 Temperature Programmed Desorption Water adsorbed at 100 K, with different coverages: H 2 O mass spec. signal as a function of T. Amount of water molecules adsorbed on surface known: Calibrated molecular beam 1 quantitative. D 2 O or H 2 O doesn t matter. Jan Hulva 1 J. Pavelec et al., J. Chem. Phys. 146, (2017) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 4 / 15

13 Temperature Programmed Desorption Water adsorbed at 100 K, with different coverages: H 2 O mass spec. signal as a function of T. Amount of water molecules adsorbed on surface known: Calibrated molecular beam 1 quantitative. D 2 O or H 2 O doesn t matter. Jan Hulva 1 J. Pavelec et al., J. Chem. Phys. 146, (2017) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 4 / 15

14 Temperature Programmed Desorption Water adsorbed at 100 K, with different coverages: H 2 O mass spec. signal as a function of T. Amount of water molecules adsorbed on surface known: Calibrated molecular beam 1 quantitative. D 2 O or H 2 O doesn t matter. Jan Hulva 1 J. Pavelec et al., J. Chem. Phys. 146, (2017) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 4 / 15

15 Temperature Programmed Desorption Water adsorbed at 100 K, with different coverages: H 2 O mass spec. signal as a function of T. Amount of water molecules adsorbed on surface known: Calibrated molecular beam 1 quantitative. D 2 O or H 2 O doesn t matter. Jan Hulva 1 J. Pavelec et al., J. Chem. Phys. 146, (2017) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 4 / 15

16 Temperature Programmed Desorption Water adsorbed at 100 K, with different coverages: H 2 O mass spec. signal as a function of T. Amount of water molecules adsorbed on surface known: Calibrated molecular beam 1 quantitative. D 2 O or H 2 O doesn t matter. Jan Hulva 1 J. Pavelec et al., J. Chem. Phys. 146, (2017) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 4 / 15

17 Temperature Programmed Desorption Water adsorbed at 100 K, with different coverages: H 2 O mass spec. signal as a function of T. Amount of water molecules adsorbed on surface known: Calibrated molecular beam 1 quantitative. D 2 O or H 2 O doesn t matter. Jan Hulva 1 J. Pavelec et al., J. Chem. Phys. 146, (2017) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 4 / 15

18 Temperature Programmed Desorption Water adsorbed at 100 K, with different coverages: H 2 O mass spec. signal as a function of T. Amount of water molecules adsorbed on surface known: Calibrated molecular beam 1 quantitative. D 2 O or H 2 O doesn t matter. Jan Hulva 1 J. Pavelec et al., J. Chem. Phys. 146, (2017) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 4 / 15

19 Temperature Programmed Desorption Water adsorbed at 100 K, with different coverages: H 2 O mass spec. signal as a function of T. Amount of water molecules adsorbed on surface known: Calibrated molecular beam 1 quantitative. D 2 O or H 2 O doesn t matter. Jan Hulva 1 J. Pavelec et al., J. Chem. Phys. 146, (2017) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 4 / 15

20 Temperature Programmed Desorption Water adsorbed at 100 K, with different coverages: H 2 O mass spec. signal as a function of T. Amount of water molecules adsorbed on surface known: Calibrated molecular beam 1 quantitative. D 2 O or H 2 O doesn t matter. Jan Hulva 1 J. Pavelec et al., J. Chem. Phys. 146, (2017) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 4 / 15

21 : short summary 4 distinct peaks K (inv. analysis 1 E ad = 0.8 ev). Peak areas used to determine amount of molecules desorbing for each peak: molecules desorbing with increasing T. Suggests that stable surface phases are completed at the coverages of 3, 6, 8 and 9 mol./u.c.. 1 S. L. Tait, Z. Dohnálek, C. T. Campbell, and B. D. Kay, J. Chem. Phys. 122, (2005) Jan Hulva Computational Materials Physics H 2 O/Fe 3 O 4 (001) 5 / 15

22 Subsurface cation vacancy (SCV) surface reconstruction 1 with isolated active sites 2. Some defects (ɛ and Φ). Low T: monomers, 2 dimers... Higher coverage difficult to interpret... 1 R. Bliem et al., Science 346, 1215 (2014) 2 M. Meier et al., Nanoscale (2018) Zdeněk Jakub Computational Materials Physics H 2 O/Fe 3 O 4 (001) 6 / 15

23 Subsurface cation vacancy (SCV) surface reconstruction 1 with isolated active sites 2. Some defects (ɛ and Φ). Low T: monomers, 2 dimers... Higher coverage difficult to interpret... 1 R. Bliem et al., Science 346, 1215 (2014) 2 M. Meier et al., Nanoscale (2018) Zdeněk Jakub Computational Materials Physics H 2 O/Fe 3 O 4 (001) 6 / 15

24 Subsurface cation vacancy (SCV) surface reconstruction 1 with isolated active sites 2. Some defects (ɛ and Φ). Low T: monomers, 2 dimers... Higher coverage difficult to interpret... 1 R. Bliem et al., Science 346, 1215 (2014) 2 M. Meier et al., Nanoscale (2018) Zdeněk Jakub Computational Materials Physics H 2 O/Fe 3 O 4 (001) 6 / 15

25 Non-contact atomic force microscopy with a CO functionalised tip 1. A mixture of water dimers/trimers (δ peak 3 mol./u.c.). A ring like network (γ peak 6 mol./u.c.). Zdeněk Jakub 1 L. Gross et al., Science 325, 1110 (2009) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 7 / 15

26 Non-contact atomic force microscopy with a CO functionalised tip 1. A mixture of water dimers/trimers (δ peak 3 mol./u.c.). A ring like network (γ peak 6 mol./u.c.). Zdeněk Jakub 1 L. Gross et al., Science 325, 1110 (2009) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 7 / 15

27 Water dimers and trimers are partially dissociated. Intensity 1:1, suggests 1 molecule in 3 is dissociated. Higher coverage: mostly water signal increases. Jan Hulva Computational Materials Physics H 2 O/Fe 3 O 4 (001) 8 / 15

28 Models Substrate DFT VASP 1,2 optpbe-df 3,4,5. DFT independent from experiments. Energetically most favorable configurations are systematically determined for each coverage (1 n 9): Trial calculations. Identify factors leading to lower total energies. New configurations (repeat...) 1 G. Kresse and J. Hafner, Phys. Rev. B 48, (1993) 2 G. Kresse and J. Furthmüller, Comput. Mater. Sci. 6, 15 (1996) 3 M. Dion et al., Phys. Rev. Lett. 92, (2004) 4 J. Klimeš, D. R. Bowler, and A. Michaelides, J. Phys. Condens. Matter 22, (2010) 5 M. J. Gillan, D. Alfè, and A. Michaelides, J. Chem. Phys. 144, (2016) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 9 / 15

29 Models Substrate DFT VASP 1,2 optpbe-df 3,4,5. DFT independent from experiments. Energetically most favorable configurations are systematically determined for each coverage (1 n 9): Trial calculations. Identify factors leading to lower total energies. New configurations (repeat...) 1 G. Kresse and J. Hafner, Phys. Rev. B 48, (1993) 2 G. Kresse and J. Furthmüller, Comput. Mater. Sci. 6, 15 (1996) 3 M. Dion et al., Phys. Rev. Lett. 92, (2004) 4 J. Klimeš, D. R. Bowler, and A. Michaelides, J. Phys. Condens. Matter 22, (2010) 5 M. J. Gillan, D. Alfè, and A. Michaelides, J. Chem. Phys. 144, (2016) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 9 / 15

30 DFT: short summary Water located on isolated sites. Importance substrate. Models Substrate 6 mol./u.c.: bridge mol., 2 H2 O-OH-H2 O (fav. angles1 ). DFT gives 2 trimers, H-bond length under-estimated, energy over-estimated: 2 trimers from DFT: Combination of exp./calc.. 1 T. Schiros et al., J. Phys. Chem. C 111, (2007) Computational Materials Physics H2 O/Fe3 O4 (001) 9 / 15

31 Models Substrate Importance of the substrate Mulakuluri et al. 1,2 on bulk-truncated surface (1, 2, 4 mol./u.c.). One major difference: Isolated water monomer adsorbs molecularly in our case (0.05 ev). Originates in the structural model used. (Fe 2+ in subsurface layer promote dissociation 1, not present in the SCV reconstructed surface). 1 N. Mulakaluri et al., Phys. Rev. Lett. 103, (2009) 2 N. Mulakaluri, R. Pentcheva, and M. Scheffler, J. Phys. Chem. C 114, (2010) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 10 / 15

32 Bonds Cooperativity Why is it behaving like this? Why are these agglomerates forming? And why are they partially dissociated? (despite a molecular monomer) Molecular dimer The dimerization energy is small ( 0.02 ev, gas phase 0.11 ev): Despite shorter H-bond, energy is lost. The H-bond acceptor H 2 O has a worse Surf-bond. The same orbital is used for H-bond and Surf-bond 1. 1 T. Schiros et al., J. Phys. Chem. C 114, (2010) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 11 / 15

33 Bonds Cooperativity Why is it behaving like this? Why are these agglomerates forming? And why are they partially dissociated? (despite a molecular monomer) Dissociated dimer If the dimer is dissociated ( 0.92 ev per mol. vs ev per mol.). The initial cost of dissociation (in the monomer, 0.05 ev) can easily be compensated. All bonds are shorter / stronger, except the OH Surf-bond. In short: the OH Surf-bond is sacrificed to enhance the rest. 1 T. Schiros et al., J. Phys. Chem. C 114, (2010) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 11 / 15

34 Bonds Cooperativity Why is it behaving like this? Why are these agglomerates forming? And why are they partially dissociated? (despite a molecular monomer) Dissociated trimer Trimer slightly worse ( 0.88 ev per mol.), as the OH is shared on both sides, the Fe-Fe distance hinders adsorbates to be perfectly atop positions. Angle bent, slight loss in energy. 1 T. Schiros et al., J. Phys. Chem. C 114, (2010) Computational Materials Physics H 2 O/Fe 3 O 4 (001) 11 / 15

35 Bonds Cooperativity Answer: Cooperativity All the previous observations are consistent with the cooperativity effect 1. Observed in gas phase 2, metal surfaces 3 and recently on Fe 3 O 4 (111) 4. In short: Water molecules seek a balance (donor/acceptor) in their H-bonds (and Surf-bonds). to reduce repulsive effects. by charge rearrangements and internal charge transfers 3. 1 H. S. Frank and W.-Y. Wen, Discuss. Faraday Soc. 24, 133 (1957) 2 S. S. Xantheas, Chem. Phys. 258, 225 (2000) 3 T. Schiros et al., J. Phys. Chem. C 114, (2010) 4 F. Mirabella et al., Angew. Chemie Int. Ed. 56, 1 (2017) Taken from 3 Computational Materials Physics H 2 O/Fe 3 O 4 (001) 12 / 15

36 H 2 O on Fe 3 O 4 (001) suggests stable phases with specific water coverages. These have been imaged by nc-afm and identified with DFT: Agreement DFT - AFM/. Additionally : partially dissociated. Water dimers are the most stable configuration, isolated due to the substrate reconstruction, quickly growing into trimers then into ring like network linking isolated agglomerates. Water behavior governed by a cooperativity effect. Computational Materials Physics H 2 O/Fe 3 O 4 (001) 13 / 15

37 Soon... there is more... : why 4 peaks? Idea 1: The phases observed in are the most stable energetically. True? not really. Idea 2: Minimal energy path. 4 limiting rate steps. Ultimately using G, transition state theory, simulate the.... in progress. Computational Materials Physics H 2 O/Fe 3 O 4 (001) 14 / 15

38 Acknowledgement Thank you for your attention Computational Materials Physics H2 O/Fe3 O4 (001) 15 / 15