DIP-COATED AND ELECTRODEPOSITED MESOPOROUS WO 3 THIN FILMS FOR ELECTROCHROMIC APPLICATIONS

Transcription

1 DIP-COATED AND ELECTRODEPOSITED MESOPOROUS WO 3 THIN FILMS FOR ELECTROCHROMIC APPLICATIONS Speaker: Chatzikyriakou Dafni Supervisors: Dr. Henrist Catherine, Prof. Cloots Rudi 16th International Conference on Thin Films October, Dubrovnik, Croatia

2 WO 3 (PROPERTIES/APPLICATIONS) n-type semiconductor ( eV) Photocatalyst Gas sensing applications Dye-Sensitized Solar Cells (DSSC) Optical properties/chromism W(VI) (transparent) W(V) (blue) Gasochromism Electrochromism Thermochromism Photochromism Li + Li + Li + e - e - e - 2

3 WO 3 (ELECTROCHROMISM/APPLICATIONS) WO 3 + xli + + xe - Li x WO 3 Bleached state Coloured state o Electrochromic displays o Auto-dimming car mirrors o Smart windows 3

4 SMART WINDOWS o Control heat, glare, fading o Reduce the need for air-conditioning o Better management of natural light o Require less than 5V (DC) Reduce energy demands PROBLEM!!! HIGH COST (3x) SMALL MARKET NEED FOR A MORE COST-EFFECTIVE BUT EFFICIENT PRODUCTION ROUTE 4

5 GOAL OF THIS WORK COST o No vacuum techniques o Cheap materials EFFICIENCY o Cyclic stability o Reversibility o Optical modulation o Color/Bleach time o Charge density o Coloration efficiency o Increased surface area increase of active material o Reduces the diffusion length of cations 5

6 POROUS FILMS THROUGH TEMPLATING Hydrophilic part metal precursor template Hydrophobic part hydrolysis condensation Removal of the template 6 Acc. Chem. Res. 2007, 40, Chem. Soc. Rev., 2013, 42,

7 TECHNIQUES 7 Chem. Mater. 2008, 20,

8 EXPERIMENTAL PROCEDURE OF THE DIP-COATING TECHNIQUE Controlled RH% Brij-56 in EtOH/H 2 O W x (H 2 O 2 ) y (acetic acid) z in EtOH/H 2 O Controlled speed Evaporation Induced Self-Assembly (EISA) Crystalline films Calcination at elevated temperatures o o Robust and rigid materials Less absorption of visible light Porous amorphous films Superior electrochromic properties 8 D. Chatzikyriakou et al., Electrochimica Acta 137 (2014), 75-82

9 STRUCTURAL CHARACTERIZATION OF THE DIP- COATED FILMS Without template With template dense film Compact and smooth surface porous film o Regular porosity o Pores diameter: 2-3nm o Pore-pore distance: 6nm o Wall thickness: 3-4nm 9

10 I (A.cm -2 ) I (A.cm -2 ) ELECTROCHROMIC CHARACTERIZATION OF THE DIP-COATED FILMS: CYCLIC VOLTAMMETRY oxidation E (V) vs. Li/Li + E (V) vs. Li/Li + reduction porous film dense film Reversibility % 1 st cycle 20 th cycle Dense film 54% 94% Porous film 93% 98% Permanent coloration 10

11 COATED FILMS: CHRONOAMPEROMETRIC MEASUREMENTS I (ma.cm -2 ) 0,6 0,4 0,2 0,0 dense film mesoporous film 4.225V vs. Li/Li + bleaching Sample Time for attaining the 10% of total current capacity (20 th cycle) Coloration time (s) Bleaching time (s) Dense film , V vs. Li/Li + coloration Porous film , time (s) Charge capacity (mc.cm -2 ) ELECTROCHROMIC CHARACTERIZATION FOR THE DIP- Deintercalation Intercalation (20 th cycle) (20 th cycle) Dense film faster inter-/de-intercalation Charge capacity (mc.cm -2 ) Deintercalation Intercalation Sample (20 th cycle) (20 th cycle) Dense film Porous film

12 ELECTROCHROMIC CHARACTERIZATION OF THE DIP-COATED FILMS Virgin state Bleached state Virgin state T% virgin film colored film bleached film wavelength (nm) Coloured state porous film T (%) dense film Bleached state Coloured state wavelength (nm) virgin film colored film bleached film ΔT% (550/750nm) Optical Efficiency (cm -2 /C) Sample 20 th cycle (550/750nm) log (Tb/Tc) η = C Dense film 4.6/5.6 12/17 Porous film 27.2/ /60 12

13 SUMMARIZING FOR THE DIP-COATED FILMS Mesoporous film Dense film Switching kinetics Worse Better Charge capacity (mc.cm -2 ) Better Worse Reversibility Better Worse ΔΤ% Better Worse Coloration efficiency Better Worse 13 Porous film has better properties than the dense film

14 EXPERIMENTAL PROCEDURE FOR THE ELECTRODEPOSITION o Reduction of H 2 O 2 (W(H 2 O 2 ) x (CH 3 COO) y ) to OH - o Precipitation of MO x (OH) y on the surface of the electrode o Framework s built-up around the template o Calcination (350 o C/2h or 400 o C/1h) Reference electrode (Calomel) PSS-Na Counter electrode (Pt) Working electrode (glass/fto) 350mC.cm -2 14

15 Balance between condensation and co-assembly formation STRUCTURAL CHARACTERIZATION OF THE ELECTRODEPOSITED FILMS CALCINED AT 350 O C -0.6V dense -0.5V dense porous -0.4V Uncalcined films -0.4V Less PSS-Na Not homogeneous coating!! 15

16 STRUCTURAL CHARACTERIZATION OF THE ELECTRODEPOSITED FILMS 400 o C/1h 400 o C/1h CRYSTALLINE FILMS 16

17 STRUCTURAL CHARACTERIZATION OF THE ELECTRODEPOSITED FILMS -0.6V -0.5V dense films porous -0.4V -0.4V Less PSS-Na Porous films Not adequate coating!! 17

18 ELECTROCHROMIC CHARACTERIZATION OF THE ELECTRODEPOSITED FILMS: CYCLIC VOLTAMMETRY Partial deterioration Porous film Dense film Dense Porous Reversibility % 1 st cycle 20 th cycle Dense film 83% (54%) 18 Porous film 91% (77%)

19 ELECTROCHROMIC CHARACTERIZATION FOR THE ELECTRODEPOSITED FILMS: CHRONOAMPEROMETRIC MEASUREMENTS Sample Time for attaining the 10% of total current capacity (20 th cycle) Coloration time (s) Bleaching time (s) Dense film Porous film 20 9 Charge capacity (mc.cm -2 ) Intercalation De-intercalation Sample (20 th cycle) (20 th cycle) Dense film Porous film Thickness and relative amount of W have not been adjusted yet

20 SUMMARIZING FOR THE ELECTRODEPOSITED FILMS Porous films at -0.4V but not at -0.5V/-0.6V Calcination at 400 o C gives porous but crystalline films Deterioration of the porous film upon cycling (porous are still filled with polymer) Film at -0.5V (dense film) similar behavior with the dense film of the dip-coating technique Higher charge capacity for the films at -0.4V (porous films) Thank you for your attention! 20