Séminaire: À quoi sert la Scanning ElectroChemical Microscopy La SECM pour structurer et analyser des matériaux de water splitting Dodzi Zigah dodzi.zigah@u bordeaux.fr Team: Analytical Nanosystem (NSYSA) Institut of Molecular Science ISM UMR N 5255 Universityof Bordeaux 1
Context 02 mai 1800: 1 st electrolysis water splitting 2H 2 O + electrical energy 2H 2 + O 2 William Nicholson (1753 1815) Anthony Carlisle (1768 1840)
Context Sources of energy Non renewable Renewable Energy Carrier H H
Context Photoelectrochemical cells Light energy electricity Water splitting cell Dye sensitized solar cell
Principle Scanning ElectroChemical Microscopy (SECM) Position controller z x y WE RE CE Bi potentiostat WE2 Electrochemical cell substrate Solution with redox mediator Local information about the electrochemical activity Local surface modification 5
Principle Scanning PhotoElectroChemicalMicroscopy (SPECM) Position controller z x y WE: Optoelectrode CE RE WE2 Bi potentiostat Electrochemical cell substrate Solution with redox mediator Local information about the photoelectrochemical activity 6
macroelectrode 3mm 5 µm UME 200 100 cv 40 I / µa 0 I / na 20-100 cv -200-0.4-0.2 0.0 0.2 0.4 E / V 0-0.4-0.2 0.0 0.2 0.4 E / V Linear diffusion Radial diffusion Diffusion layer increases with time Diffusion layer constant.
Perturbation of the diffusion layer: feedback mode I T Tip far away from the surface Ox Ox Red Ox 0 Negative feedback I T, d Insulating substrat Insulating substrat hindered the diffusion layer 8
Perturbation of the diffusion layer: feedback mode I T Positive feedback Tip far away from the surface I T, Ox Ox Red Red d Conductive substrate Conductive substrate : Regeneration of Ox 9
Perturbation of the diffusion layer: feedback mode Initial state: Tip is far from any surface I T =I T, =4nFDCa : steady state current n: number of electron e- F: Faraday constant D: diffusion coefficient of Ox Ox Red C: concentration of Ox a : radius of the UME I T positive feedback X negative feedback 10 Tip far away Ox Red Ox Red insulating 0 I T, conductive d
Perturbation of diffusion layer: imaging in feedback mode Scan at constant high Tip current Tip current insulating substrate Topographical image Flat substrate electrochemical image topographical and electrochemical image
optical fiber The tips optoelectrode optoelectrode optoelectrode UME OF Anal. Chem. 2008, 80, 7445 7450, J. Lee, H. Ye, S. Pan, and A. J. Bard Conzuelo, F.; Sliozberg, K.; Gutkowski, R.; Grützke, S.; Nebel, M.; Schuhmann, W. Anal. Chem. 2017, 89 (2), 1222 1228. Badets, V.; Loget, G.; Garrigue, P.; Sojic, N.; Zigah, D. Electrochimica Acta 2016, 222, 84 91.
Rapid screening of photocatalyst optoelectrode array of photocatalysts Scheme of a basic cell setup DOI: 10.1039/C4CS00031E Chem. Soc. Rev., 2014, 43, 6485 6497
Rapid screening of photocatalyst microdispenser SPECM Schematic diagram of prepared array pattern with three components (Bi, V, and W). applied potential of 0.2 V under UV visible Published in: Heechang Ye; Joowook Lee; Jum Suk Jang; Allen J. Bard; J. Phys. Chem. C 2010, 114, 13322 13328. DOI: 10.1021/jp104343b Copyright 2010 American Chemical Society 14
High Resolution Analysis of Photoanodes Substrate : BiVO 4 on FTO E sub = +200 mv vs Ag/AgCl/3 M KCl UME(Pt) d = 25 μme tip = 600 mv Electrolyte: 0.1 M phosphate buffer, ph 8.5. Published in: Felipe Conzuelo; Kirill Sliozberg; Ramona Gutkowski; Stefanie Grützke; Michaela Nebel; Wolfgang Schuhmann; Anal. Chem. 2017, 89, 1222-1228. DOI: 10.1021/acs.analchem.6b03706 Copyright 2016 American Chemical Society 15
Context Titanium anodization Ti Ti 4+ + 4e Ti 4+ + H 2 O TiO 2 + 4H + Ti 4+ + 6F [TiF 6 ] 2 TiO 2 + 6F + 4H + [TiF 6 ] 2 + 2H 2 O Porous structure: enhancement of specific surface area enhancement of photocatalytic current G. K. Mor, O. K. Varghese, M. Paulose, K. Shankar, C. A. Grimes, Solar Energy Materials and Solar Cells 2006, 90, 2011-2075. Ghicov A, Schmuki P. Self-ordering electrochemistry: a review on growth and functionality of TiO2 nanotubes and other self-aligned MOx structures. Chem Commun (Camb). 2009;(20):2791 2808 16
Capillary microelectrode Local anodiza on Rapid genera on of TiO 2 Au Cap. Au Cap. Au Cap. Electrochemical reaction in the drop Ti + Ethylene glycol 0.1 M ammonium fluoride 5% water Potential applied Badets, V.; Loget, G.; Garrigue, P.; Sojic, N.; Zigah, D. Electrochimica Acta 2016, 222, 84 91. 17
Capillary microelectrode Local anodiza on Rapid genera on of TiO 2 Au Cap. Au Cap. Au Cap. Ti Ethylene glycol 0.1 M ammonium fluoride 5% water Badets, V.; Loget, G.; Garrigue, P.; Sojic, N.; Zigah, D. Electrochimica Acta 2016, 222, 84 91. 18
Capillary microelectrode Local anodiza on Rapid genera on of TiO 2 Au Cap. Au Cap. Au Cap. Ti + Ethylene glycol 0.1 M ammonium fluoride 5% water Badets, V.; Loget, G.; Garrigue, P.; Sojic, N.; Zigah, D. Electrochimica Acta 2016, 222, 84 91. 19
Capillary microelectrode Local anodiza on Rapid genera on of TiO 2 Au Cap. Au Cap. Au Cap. Ti Ethylene glycol 0.1 M ammonium fluoride 5% water Badets, V.; Loget, G.; Garrigue, P.; Sojic, N.; Zigah, D. Electrochimica Acta 2016, 222, 84 91. 20
Capillary microelectrode Local anodiza on Rapid genera on of TiO 2 Au Cap. Au Cap. Au Cap. Ti + Ethylene glycol 0.1 M ammonium fluoride 5% water Badets, V.; Loget, G.; Garrigue, P.; Sojic, N.; Zigah, D. Electrochimica Acta 2016, 222, 84 91. 21
SPECM Rapid screening current on TiO 2 50 V 75 V 125 V 100 V Ti E app = 0.6 V vs Ag/AgCl Photocurrent Water oxida on above TiO 2 22
SPECM SECM Approach curve above TiO 2 In the dark E tip E TiO2 = 0.6 V vs. Ag/AgCl E tip = 0.4 V vs. Ag/AgCl H 2 O O 2 Ti E TiO2 TiO 2 23
SPECM SECM Approach curve above TiO 2 Under illumination E tip E TiO2 = 0.5V vs. Ag/AgCl E tip = 0.4V vs. Ag/AgCl H 2 O O 2 H 2 O O 2 Ti E TiO2 TiO 2 24
SPECM in mode surface interrogation : SI SPECM Overall efficiency : Materials properties Efficient light illumination Interfacial charge transfer and surface reactions TiO 2 : water photoelectrolysis degradation organic pollutants Adsorbate hydroxyl radicals ( OH) ads plays a key role in these mechanisms. TiO 2 H 2 O OH TiO 2 OH hν (h + ) OH TiO 2 OH SECM for detection and quantification of ( OH) ads k OH 2 OH( ads) H2O2 OH CH OH products ( ads) 3 k MeOH 25
SPECM in mode surface interrogation : SI SPECM Light OFF E tip Light ON In situ study of adsorbed reaction intermediates Light OFF OC E tip 1 2 3 Ti TiO 2 E sub OH ads E sub OH ads E sub 2.4x10-8 Tip current / A 1.6x10-8 8.0x10-9 1 2 3 0.0 0 10 time / s 20 30 26
SPECM in mode surface interrogation : SI SPECM Microtitration K 3 Ir (IV) Cl 6 = 0.5 mm with HClO 4 = 0.1 M in H 2 O A) I-t-curve (Interrogation) B) 2.0x10-8 8.0x10-8 Tip current / A 1.0x10-8 0.0 0 20 40 t / s Q app / C 4.0x10-8 0.0 0 20 40 t / s Theoretical treatment k SI = 10 m 2 s 1 k OH = 4 10 3 mol 1 m 2 s 1 Charge OH(ads) = 3.06 10 5 mol m 2 koh 2 OH H O 2 2 k OH CH OH MeOH products ( ads) 3 OH(ads) = 0.7 10 5 mol m 2 k MeOH = 1 s 1 Zigah, D.; Rodríguez-López, J.; Bard, A. J. Microscopy. Phys. Chem. Chem. Phys. 2012, 14 (37), 12764. 27
Conclusion SPECM can be used : Rapid screening of photocatalyst Verify the photocatalyst homogeneity SI SPECM: Understanding reactions 28
Acknowledgment Vasilica Badet Post doc Patrick Garrigue Engineer INP Bordeaux Professor Neso Sojic INP Bordeaux Gabriel Loget CNRS Researcher University of Rennes Pr. Allen J. Bard University of Texas As. Pr. Joaquin Rodriguez Lopez University of Illinois Thank you for your attention 29