Electrolytic membranes : Ion conduction in nanometric channels

Transcription

1 Electrolytic membranes : Ion conduction in nanometric channels Philippe Knauth Aix Marseille Université - CNRS Marseille, France Philippe Knauth 1

2 utline of the Presentation 1. Introduction 2. Synthesis 3. Properties 4. Conclusion/Questions

3 utline of the Presentation 1. Introduction 2. Synthesis 3. Properties 4. Conclusion/Questions

4 Electrochemical energy technologies Polymer Electrolyte Membrane Fuel Cells (PEMFC) Small-scale energy conversion Transportation, small stationary, portable microelectronics Redox flow batteries Large-scale energy storage «Smart grid» Hydrated Polymer Electrolytes hierarchical porous structure Interconnected nanometric channels (percolation and tortuosity) Challenges High cost (Nafion, Pt) Insufficient durability Difficult water management Limited ionic conductivity Examples: Nafion, SPEEK H. Hou, M. L. Di Vona, P. Knauth, ChemSusChem, 4, 1526 (2011) 4 H S n G. Gebel Science 2008

5 Nafion: relations between membrane stiffness, hydration, morphology and conductivity G. Gebel, Polymer,

6 Microstructure: aqueous nanometric channels 6

7 Schematic microstructure of hydrated proton-conducting polymers Hydrophilic domain with sulfonic acid groups and absorbed water: proton conductivity Hydrophobic polymer backbone: thermal and mechanical stability Dead-end Pocket (Tortuosity) K. D. Kreuer, J. Membr. Sci Percolating nanodomains Y. D. Premchand, M. L. Di Vona, P. Knauth in Nanocomposites: Ionic Conducting Materials and Structural Spectroscopies, Springer, New York (2008). 7

8 PLYMER ELECTRLYTES Space charge regions Sulfonated Poly-Ether-Ether-Ketone (SPEEK) S 3 H FP C X Pr. Philippe Knauth 8

9 Aromatic polymers PolyPhenylSulfone PolyEtherSulfone PolySulfone PolyEtherEtherKetone Easy to functionalize Less environmental problems than perfluorinated polymers Stable in oxidative and reductive media Thermally stable Low gas permeability Low cost (inexpensive monomers) Philippe Knauth April/May 2015 Erasmus Univ. Roma Tor Vergata 9

10 Comparison of SAP with Nafion Nafion Example: Sulfonated Poly-Ether-Ether-Ketone (SPEEK) Properties of SAP Inexpensive synthesis and environmentally friendly Non-fluorinated monomers Very high thermal stability (>450ºC) Strong aromatic bonds, rigid chains with little mobility Good mechanical properties Low molar mass: chains free of entanglements High glass transition (>150ºC): high elastic strength and elastic modulus, low fracture elongation Proton conductivity Less connected hydrated domains (percolation!) More tortuous channels 10

11 utline of the Presentation 1. Introduction 2. Synthesis 3. Properties 4. Conclusion/Questions

12 Protonic membranes DS = Groups S3H Repeat Unit 12

13 SPEEK Membrane Synthesis Sulfonation of PEEK in H 2 S 4 98% SPEEK DMS Precipitation of SPEEK in Ice Water Purification in Dialysis Membranes Film Casting: Solvent DMS Philippe Knauth April/May 2015 Erasmus Univ. Roma Tor Vergata 13

14 Protonic membranes DS = Groups S3H Repeat Unit Crosslinking! As cast membrane instable in water! Crosslinking by thermal treatment at 180 C 14

15 Dependence on thermal treatment time Wwet Wdry WU (%) = 100 W dry Water uptake Mechanical stability increases dramatically!!! Young modulus 15

16 Anion Exchange Membranes CH H 3 C 3 S N + CH 3 CH 3 + N H 3 C CH 3 CH3 CH 3 cationic groups e H 2 + 2H - 2H 2 + 2e ½ 2 + H 2 + 2e 2H - H 2 +1/2 2 H 2 Ea = V Ec = 0.39 V (ph = 14) H 2 -H 2 2H - + H 2 2H 2 + 2e H - 1/2 2 + H 2 + 2e 2H H 2 16

17 C:\Users\Luca\Desktop\dettagli.tif Anionic conducting membranes Sulfaminated PolyEtherEtherKetone (PEEK) Chlorosulfonation reaction Amination reaction DSA = Groups S 2 - NR 2 Repeat Unit Activation of the secondary amine Reaction with different acids by immersion in 2M solutions 24 h at RT: HCl, HBr, H 2 S 4, HN 3, and H 3 P 4 Secondary amine! R-S 2 -NR 2 + HX R-S 2 -NHR 2+ + X - 17

18 utline of the Presentation 1. Introduction 2. Synthesis 3. Properties 4. Conclusion/Questions

19 Conductivity measurements by impedance spectroscopy (fully humidified) Pt Counter Electrode 3-Electrode Configuration Reference Electrode (Ag/AgCl) Working electrode 2-Electrode Configuration in Swagelok Cells (stainless steel or Li electrodes) Reference Counter Electrode Working Electrode 19

20 IMPEDANCE SPECTRSCPY Investigate the membrane conductivity σ ionic Membrane (thickness d) + membrane-electrode interface (area A) Resistance R in series with a parallel RC, R(CR) model σ AC amplitude: 20 mv ionic 1 d = = ρ R A Frequency: 100 khz 1 Hz 20

21 Study of Thermal Stability: Thermogravimetry Main Chain Sulfonamide Group Main Chain PEEK sulfaminated (dimethylamine and HCl) Trimethylammonium Group PSU (fonctionnalised with trimethylamine)

22 Mechanical Tests (tensile stress-strain) Adamel-Lhomargy Testometric M CT T=25 C, ambient RH Crosshead speed: 5 mm/min 22

23 Mechanical properties (tensile stress-strain tests) PEEK sulfaminated (dimethylamine and HCl) E>1,4 GPa, σ MAX =53 MPa, ε=6% Addition of acid: slight plasticizer effect

24 Reactant permeability: Vanadium ions in redox flow batteries 1,5 M VS 4 + H 2 S 4 3 M Permeation cell 1,5 M MgS 4 + H 2 S 4 3 M Stirrer NAFIN 1.4*10-6 cm2 min-1 SPEEK 1.5*10-7 cm2 min-1 PEEK functionalized with diethylammonium groups 5*10-10 cm2 min-1 Donnan effect! 24

25 Solid Ion Conductors Solid-State Ionics 2002 Volume 756 Editors: P. Knauth, J.-M. Tarascon, E. Traversa, H. L. Tuller Solid State Ionics 2004 Volume 835 Editors: P. Knauth, C. Masquelier, E. Traversa, E. D. Wachsman

26 Questions? Post-docs and PhD students: Dr. H. Hou Dr. D. Marani Dr. E. Sgreccia Dr. R. Narducci L. Pasquini M. Braglia I. V. Ferrari EU FP7 (JU-FCH 2008) LLIPEM project MESC Erasmus Mundus Master 26