Effect of water and ethanol on the size distribution

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Presentation transcript:

Effect of water and ethanol on the size distribution of free-volume holes in Nafion membrane J. Čížek, Z. Barnovská, M. Šourek, I. Procházka Faculty of Mathematics and Physics, Charles University Prague, Czech Republic

Introduction Nafion Nafion – perfluorinated polymeric sulfonic acid developed by du Pont Nemours

Introduction Nafion Nafion – perfluorinated polymeric sulfonic acids developed by du Pont Nemours proton conductivity, no electron conductivity membrane for fuel cells excellent temperature and mechanical stability resistent to chemical decomposition

Introduction Nafion Nafion – perfluorinated polymeric sulfonic acids developed by du Pont Nemours hydrophobic PTFE backbone hydrophilic ionic clusters 30-50 nm P.J. Brookman, J.W. Nicholsonin: Developments in Ionic Polymers, vol. 2, eds. A. D. Wilson and H. J. Prosser (Elsevier Applied Science Publishers: London, 1986)

Experimental influence of water and ethanol on free volumes in Nafion membrane Nafion membrane N-1110 (Du Pont), surface density 500 g m-2, EW = 1100 g thickness 0.254 mm samples for positron annihilation: multi-stack consisting of 4 membranes 22Na spot 1.5 MBq mylar foil 2 mm Nafion N1110

LT spectroscopy Digital LT spectrometer: F. Bečvář et al., Nucl. Instr. Meth. A 539, 372 (2005)  BaF2 scintilators truncated cone ( 18-36 mm, thickness 12 mm)  Two photomultipliers Hamamatsu H3378 input detector 2 AS BUS External trigger data transfer to PC detector 1  two 8-bit digitizers Acqiris DC211, sampling rate 4 GHz  time resolution 145 ps (FWHM 22Na)  measurement at RT + in-situ investigations at elevated temperatures

Decompositon of LT spectra LT code version 9 (J. Kansy, University of Silesia, Katowice ) e+ annihilation  discrete exponential components Ps annihilation  complex component log-normal distribution of annihilation rates due to varying size of free volume holes Tao - Eldrup model  radius R of free volume holes

As received Nafion N1110 – positron lifetime results Nafion N1110 – as received state e+ annihilation: t1 = 205(9) ps, I1 = 5.2(8) % t2 = 430(3) ps, I2 = 80(1) % free e+ trapped e+ Ps annihilation: tp-Ps = 130(5) ps, Ip-Ps = 3.7(4) % to-Ps = 3.10(3) ns, Io-Ps = 11.1(4) %, so-Ps = 1.06(6) ns para – Positronium (p-Ps) ortho – Positronium (o-Ps) dispersion mean value of distribution

Water content in as-received Nafion N1110 as-received Nafion N1110 – drying at 130oC drying kinetics – two processes: relative weight loss: – fast: t1 = 1.0 ± 0.4 min – slow: t2 = 8 ± 2 min water content in as-received Nafion: (6.7 ± 0.8) wt.% t (min) 20 40 60 80 100 relative weight loss (%) 2 4 6 8

Dried Nafion N1110 – positron lifetime results Nafion N1110 – as received state dried state (130oC, 2h) e+ annihilation: t1 = 205(9) ps, I1 = 5.2(8) % t1 = 204(8) ps, I1 = 6.0(5) % t2 = 430(3) ps, I2 = 80(1) % t2 = 442(5) ps, I2 = 80.1(4) % Ps annihilation: p-Ps tp-Ps = 130(5) ps, Ip-Ps = 3.7(4) % tp-Ps = 130(6) ps, Ip-Ps = 3.5(4) % to-Ps = 3.10(3) ns, Io-Ps = 11.1(4) %, so-Ps = 1.06(6) ns to-Ps = 3.09(2) ns, Io-Ps = 10.5(4) %, so-Ps = 1.00(3) ns o-Ps No significant change of positron parameters

Water uptake into Nafion N1110 T = 25oC t (min) 20 40 60 weight increase (%) 10 30

Water uptake into Nafion N1110 T = 25oC T = 30oC t (min) 20 40 60 10 30 weight increase (%)

Water uptake into Nafion N1110 T = 25oC T = 30oC T = 40oC 40 30 weight increase (%) 20 10 20 40 60 t (min)

Water uptake into Nafion N1110 T = 25oC T = 30oC T = 40oC T = 60oC t (min) 20 40 60 10 30 weight increase (%)

Water uptake into Nafion N1110 T = 25oC T = 30oC T = 40oC T = 60oC T = 80oC t (min) 20 40 60 10 30 weight increase (%)

Water uptake into Nafion N1110 T = 25oC two processes: relative weight increase: T = 30oC T = 40oC T = 60oC slow T = 80oC T = 100oC very fast t (min) 20 40 60 10 30 weight increase (%)

Water uptake into Nafion N1110 absorption kinetics – two processes: very fast process slow process characteristic time t2  10-60 min T ( o C) 20 40 60 80 100 120 t2 (min) characteristic time t1 = (11 ± 1) s filling of ionic clusters with water expansion of ionic clusters into free volumes T ( o C) 20 40 60 80 100 120 t1 (s) 4 6 8 10 12 14 16 18 22

Water uptake into Nafion N1110 - PAS positron components boiled in water 2 h boiling in water 2 h  both fast & slow process influence of water on free volumes in Nafion water content (wt.%) 10 20 30 40 50 lifetime (ps) 150 200 250 300 350 400 450 500 t1 t2 volume expansion  increase of t1, t2 boiled in water 30 s boiling in water 30 s  very fast process only water content (wt.%) 10 20 30 40 50 Intensity (%) 60 80 100 I1 I2

Water uptake into Nafion N1110 - PAS o-Ps component water content (wt.%) 10 20 30 40 50 to-Ps (ns) 2.75 2.80 2.85 2.90 2.95 3.00 3.05 3.10 3.15 lifetime influence of water on free volumes in Nafion boiled in water 30 s boiled in water 2 h to-Ps decreases so-Ps firstly increases and then decreases water content (wt.%) 10 20 30 40 50 so-Ps (ns) 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 dispersion boiled in water 30 s water 2 h IPs increases water content (wt.%) 10 20 30 40 50 IPs (%) 12 14 16 18 22 intensity boiled in water 30 s water 2 h

Water uptake into Nafion N1100 - PAS influence of water on distribution of free volumes as-received 1.8 1.6 1.4 1.2 H (R) * IPs 1.0 0.8 0.6 0.4 0.2 0.0 0.0 0.2 0.4 0.6 0.8 1.0 R (nm)

Water uptake into Nafion N1110 - PAS influence of water on distribution of free volumes dried at 130oC / 2h as-received 1.8 1.6 1.4 1.2 H (R) * IPs 1.0 0.8 0.6 0.4 0.2 0.0 0.0 0.2 0.4 0.6 0.8 1.0 R (nm)

Water uptake into Nafion N1110 - PAS influence of water on distribution of free volumes ionic clusters filled with water & incomplete splitting of free volumes boiled in water 30s dried at 130oC / 2h as-received R (nm) 0.0 0.2 0.4 0.6 0.8 1.0 H (R) * IPs 1.2 1.4 1.6 1.8

Water uptake into Nafion N1110 - PAS influence of water on distribution of free volumes boiled in water 2h splitting completed boiled in water 30s narrow distribution of free volumes dried at 130oC / 2h as-received R (nm) 0.0 0.2 0.4 0.6 0.8 1.0 H (R) * IPs 1.2 1.4 1.6 1.8

Water uptake into Nafion N1110 - PAS o-Ps component to-Ps decreases water content (wt.%) 10 20 30 40 50 to-Ps (ns) 2.75 2.80 2.85 2.90 2.95 3.00 3.05 3.10 3.15 boiled in water 2 h water 30 s lifetime influence of water on free volumes in Nafion so-Ps firstly increases and then decreases water content (wt.%) 10 20 30 40 50 so-Ps (ns) 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 dispersion boiled in water 30 s water 2 h IPs increases water content (wt.%) 10 20 30 40 50 IPs (%) 12 14 16 18 22 intensity boiled in water 30 s water 2 h water absorption in ionic clusters: volume expansion splitting of free volumes

Water uptake into Nafion N1110 - PAS o-Ps component water content (wt.%) 10 20 30 40 50 to-Ps (ns) 2.75 2.80 2.85 2.90 2.95 3.00 3.05 3.10 3.15 lifetime influence of water on free volumes in Nafion boiled in water 30 s boiled in water 2 h water content (wt.%) 10 20 30 40 50 so-Ps (ns) 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 dispersion boiled in water 30 s water 2 h very fast process water content (wt.%) 10 20 30 40 50 IPs (%) 12 14 16 18 22 intensity boiled in water 30 s water 2 h

Water uptake into Nafion N1110 - PAS o-Ps component water content (wt.%) 10 20 30 40 50 to-Ps (ns) 2.75 2.80 2.85 2.90 2.95 3.00 3.05 3.10 3.15 lifetime influence of water on free volumes in Nafion boiled in water 30 s boiled in water 2 h water content (wt.%) 10 20 30 40 50 so-Ps (ns) 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 dispersion boiled in water 30 s water 2 h slow process water content (wt.%) 10 20 30 40 50 IPs (%) 12 14 16 18 22 intensity boiled in water 30 s water 2 h

Water uptake into Nafion N1110 - PAS mean free volume Vmean Nafion-N1110 210 200 190 180 Vmean (Å3) 170 160 150 140 10 20 30 40 50 water content (%)

Water uptake into Nafion N1110 - PAS fast process: Vmean decreases due to expansion of ionic clusters & splitting of holes broad distribution of free volumes Nafion-N1110 210 200 190 180 Vmean (Å3) 170 160 150 140 10 20 30 40 50 water content (%)

Water uptake into Nafion N1110 - PAS slow process: splitting completed  most of free volumes are split narrow distribution of free volumes Nafion-N1110 210 200 190 180 Vmean (Å3) 170 160 150 140 10 20 30 40 50 water content (%)

Water uptake into Nafion N1110 - PAS mean free volume Nafion-N117, H.S. Sodaye et al. J. Polymer Sci. B 35, 771 (1997) Nafion-N1110 water content (%) 10 20 30 40 50 Vmean (Å3) 140 150 160 170 180 190 200 210

Ethanol uptake into Nafion N1110 weight increase t (min) 10 20 30 40 50 60 relative weight increase (%) 100 200 300 400 500 600 T = 25oC

Ethanol uptake into Nafion N1110 weight increase t (min) 10 20 30 40 50 60 100 200 300 400 500 600 T = 35oC T = 25oC relative weight increase (%)

Ethanol uptake into Nafion N1110 weight increase t (min) 10 20 30 40 50 60 100 200 300 400 500 600 T = 40oC T = 35oC T = 25oC relative weight increase (%)

Ethanol uptake into Nafion N1110 weight increase t (min) 10 20 30 40 50 60 100 200 300 400 500 600 T = 50oC T = 40oC T = 35oC T = 25oC relative weight increase (%)

Ethanol uptake into Nafion N1110 weight increase t (min) 10 20 30 40 50 60 100 200 300 400 500 600 T = 60oC T = 50oC T = 40oC T = 35oC T = 25oC relative weight increase (%)

Ethanol uptake into Nafion N1110 weight increase t (min) 10 20 30 40 50 60 100 200 300 400 500 600 T = 70oC T = 60oC T = 50oC T = 40oC T = 35oC T = 25oC relative weight increase (%)

Ethanol uptake into Nafion N1110 weight increase t (min) 10 20 30 40 50 60 100 200 300 400 500 600 T = 78oC T = 70oC T = 60oC T = 50oC T = 40oC T = 35oC T = 25oC relative weight increase (%)

Ethanol uptake into Nafion N1110 weight increase t (min) 10 20 30 40 50 60 100 200 300 400 500 600 T = 78oC T = 70oC T = 60oC T = 50oC T = 40oC T = 35oC T = 25oC relative weight increase (%) relative weight increase:

Ethanol & water uptake into Nafion N1110 comparison of water and ethanol absorption in Nafion N 1110 at room temperature t (min) 10 20 30 40 50 60 relative weight increase (%) 80 100 120 140 160 ethanol water

Ethanol uptake into Nafion N1110 relative weight increase: absorption kinetics – two processes: fast process T ( o C) 20 40 60 80 100 120 2 4 6 8 10 12 14 16 18 t2 (min) slow process characteristic time t2  10 t1 penetration of ethanol into PTFE parts characteristic time t1 < 1.5 min absorption of ethanol in ionic clusters both processes  substantial increase of rate at elevated temperatures T ( o C) 20 40 60 80 100 120 t1 (min) 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

Ethanol uptake into Nafion N1110 absorption kinetics – two processes: fast process slow process characteristic time t1 < 1.5 min characteristic time t2  10 t1 absorption of ethanol in ionic clusters penetration of ethanol into PTFE parts both processes  substantial increase of rate at elevated temperatures relative weight increase: T ( o C) 20 40 60 80 100 120 relative contribution 0.0 0.2 0.4 0.6 0.8 1.0 slow process, x2 relative contributions: fast process, x1

Ethanol uptake into Nafion N1110 - PAS distribution of free volumes H(R) decrease of the mean radius of free volume holes increase in concentration of free volume holes 2.5 as-received dried 135 o C / 2h 2.0 T = 25 o C in ethanol T = 40 o C in ethanol T = 60 o C in ethanol 1.5 H (R) * IPs 1.0 0.5 0.0 0.2 0.3 0.4 0.5 0.6 0.7 R (nm)

Ethanol & water uptake into Nafion N1110 - PAS distribution of free volumes H(R) comparison of water and ethanol influence on distribution of free volume holes water absorption  smaller size & lower concentration of free volume holes R (nm) 0.2 0.3 0.4 0.5 0.6 0.7 0.0 1.0 1.5 2.0 2.5 as-received dried 135 o C / 2h T = 60 C in ethanol T = 100 C in water H (R) * IPs

Kinetics of ethanol uptake – intensity of o-Ps component in-situ positron lifetime measurement of Nafion N1110 immersed in ethanol T = 21oC t (h) 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 IPs (%) 15 25 -4 -2 2 4 residuals (s) T = 25oC T = 25oC

Kinetics of ethanol uptake – intensity of o-Ps component in-situ positron lifetime measurement of Nafion N1110 immersed in ethanol T = 42oC T = 21oC t (h) 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 15 25 -4 -2 2 4 6 IPs (%) residuals (s) T = 40oC T = 25oC T = 40oC T = 25oC

T = 60oC T = 40oC T = 25oC T = 60oC T = 60oC T = 40oC T = 42oC t (h) 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 14 16 18 22 24 26 28 32 34 -4 -2 2 4 6 IPs (%) residuals (s) T = 60oC T = 40oC T = 25oC T = 60oC T = 40oC T = 25oC

Kinetics of ethanol uptake – PAS two processes: slow process ( 70 %) splitting of free volumes due to expansion of ionic clusters & penetration into PTFE part T = 42oC T = 21oC T = 60oC t (h) 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 14 16 18 22 24 26 28 32 34 IPs (%) T = 25oC T = 40oC

Kinetics of ethanol uptake – PAS two processes: slow process ( 70 %) at elevated temperatures (T  40oC) t2 comparable with that of weight increase splitting of free volumes due to expansion of ionic clusters & penetration into PTFE part T ( o C) 20 40 60 80 100 120 t2 (min) 50 150 200 PAS weight measurement

Kinetics of ethanol uptake – PAS two processes: very slow process ( 30 %) slow process ( 70 %) t3  25 – 30 h splitting of free volumes due to expansion of ionic clusters & penetration into PTFE part further redistribution of free volumes T = 42oC T = 21oC T = 60oC t (h) 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 14 16 18 22 24 26 28 32 34 IPs (%) T = 25oC T = 40oC

Conclusions Nafion N1110 water concentration in as-received state: (6.7 ± 0.8) wt.% water absorption: up to 40 wt.% ethanol absorption: up to 500 wt.% water & ethanol up-take occurs by two processes (fast & slow) effect of absorbed water & ethanol on free volume holes - increase in concentration of free volume holes - decrease in the mean size of free volume holes expansion of ionic clusters  splitting of free volumes

Ethanol uptake into Nafion N1110 - PAS in-situ positron lifetime measurement intensity of Ps component ethanol uptake T = 60oC 35 ethanol uptake T = 40oC drying T = 25oC 30 ethanol uptake T = 25oC 25 drying T = 40oC IPs (%) 20 15 virgin T = 25oC 10 100 200 300 400 500 t (h)

As-received Nafion N1110 – positron lifetime results scaled size distribution of free volumes – comparison of PTFE and Nafion compared to PTFE, Nafion exhibits lower concentration and sharper size distribution of free volume holes PTFE (teflon) ionic clusters R (nm) 0.0 0.2 0.4 0.6 0.8 1.0 H (R) * IPs 1.2 1.4 1.6 1.8 Nafion, as-received

Ethanol uptake into Nafion N1110 - PAS mean free volume Vmean ethanol content (wt. %) 100 200 300 400 Vmean (Å3) 190 195 205 210 215 T = 40oC