ELASTIC PROTON CONDUCTING INORGANIC-ORGANIC ELECTROLYTES
M. Mí
Míka1, M. Maš
Mašinová
inová1, S.Š
S.Švarcová
varcová1, M. Paidar1, K. Bouzek1, B. Klá
Klápště2, and Jiř
Jiří Vondrá
Vondrák2
1Institute of Chemical Technology in Prague, Czech Republic
2
Institute of Inorganic Chemistry, Academy of Sciences of the Czech
Czech Republic
100 – 200°
200°C
Introduction
The developed phosphosilicate polymer is a promising material for
for intermediate
temperature H2/O2 fuel cells and gas sensors.
H2
(fuel)
Hybrid phosphosilicate (HPS) membranes:
membranes:
• high proton conductivity in dry atmosphere at elevated temperatures
temperatures
O2
(or air)
Fuel cell Advantages:
Advantages:
• working temperature range 100 - 150 °C
• viscovisco-elastic material – good contact with electrodes
Membrane
• effective – direct conversion of chemical energy to electric power
• membrane backbone – polydimethylsiloxane
• ecological – the emission is pure H2O (g);
(g); operates silently
• phosphorous heteroatoms embedded into the siloxane polymer
• applications – mobile sources (e.g., electric vehicles, notebooks, cameras)
• proton conductivity at 130°
130°C is about 18 mS·
mS·cm-1
stationary sources (e.g., power plants, houses)
Anode
H2O
(vapor)
Cathode
Medium Temperature H2/O2 Fuel Cell
Structures of Polysiloxanes
Derived from silica
• -SiSi-O-SiSi- (454 kJ/mol)
• -C-C- (349 kJ/mol)
Softening
• hard, fragile; tm=1720°
=1720°C
by organic
groups ((-R)
• temperature stability
• chemical durability
Structure of Silica
• -SiSi-O-SiSi- (52% ionic) -> stabilizes organic groups
• stability of polysiloxanes -90 to 250°
250°C
CrossCross-Linked Polydimethylsiloxane Rubber
Model of a Spiral Structure of the Polydimethylsiloxane Chain
Linear and Branched Chains
(H-White, O-Red, C- Black (Left Picture) or Grey (Middle and Right Picture), Si- Grey
(Left Picture) or Blue (Middle and Right Picture), and Lone Electron Pair-Pink)
Synthesis of HPS Membranes
OH
CH3
OC2H5
|
|
|
H 2O
HO — P — OH + Cl — Si — Cl + C2H5 — O — Si — O —C2H5
||
|
|
-HCl
OC2H5
-C2H5OH
O
CH3
OH
CH
OH
CH3
|
|
|
HO — P — O — Si — O — Si —OH
||
|
|
O
CH3
OH
Flexible Membrane 4x4cm
• starting compounds: H3PO4, dichlorodimethylsilane,
dichlorodimethylsilane, tetraethoxysilane (TEOS)
• low temperature synthesis (50 to 200°
200°C) – high concentration of –OH groups
• in the melt of H3PO4 – very low fraction of a solvent –> low porosity
• casting into a Teflon mould
Pictures from Electron Microscope
-SiSi-O-P-O-Si Chain
Transparent Material
Thermal Analysis
TG, DTG (First Derivative), and DTA Curves
Mass Spectroscopy Curves for H2O and HCl
Proton Conductivity
C1/F
7.39·10-5 γ1 /Ω·s1/2
8.375·103
R1/Ω 9.42
C2/F
62.9
γ2 /Ω·s1/2
3.959·105
R2/Ω 31.41
C3/F
4.89·10-2 γ3 /Ω·s1/2
4.112·103
9.93·10-5
L1/H
23°C
140
115
HPS Membrane Conductivity
1.8
1.4
1.2
90
Autolab PGSTAT30; 2 probe method with Pt electrodes
f = 10 mHz – 1 MHz; U = 10 mV; ambient atmosphere
65
40
• conductivity calculation
-10
0
50
100
150
200
250
300
350
400
450
σ=
S = 2.54·10
2.54 10-4 m2 d = 0.5 mm
500
Typical High Frequency Impedance Spectrum with an Equivalent Circuit
Circuit
9
d
R1 ⋅ S
2
0.6
P [mW/cm ]
6
5
0.5
4
0.4
3
0.3
0.2
2
0.1
1
0.0
0
0
5
10
15
20
j [m A /cm 2 ]
25
30
35
25
20
15
10
5
0
0
1
2
3
4
5
6
t [h]
t = 60°
60°C
U = 0.5 V
40
Current/Voltage Characteristic and Power Density (Left) and Time Dependence of Current (Right) Generated by
HPSHPS-Based Laboratory FC at 60°
60°C Using Standard ELAT EE-TEK Electrodes Pt/C, 5g Pt/m2, Nafion 7g/m2.
7
0
20
40
60
80
100
120
140
t [°C]
Temperature Dependence of Conductivity for Different HPS
Membranes at Indicated Humidity
3.0
100
110
0.7
30
I [mA]
0.7
U [V]
35
5
0
0.8
40
7
10
0.0
0.9
45
8
15
0.6
0.2
• activation Energy of Conduction ~ 18 – 28 kJ/mol
U [V]
1st scan
5th scan
P ower
t = 60°
60°C
0.8
20
0.4
Testing in a Fuel Cell at Elevated Temperatures with Dry H2 and O2 Gas Streams
1.0
25
0.8
2.5
120
0.6
130
0.5
120 d
0.4
110 d
0.3
100 d
2
Z1 / ohm
1.0
p [mW/cm ]
15
0.9
30
M6-8
M6-10
M6-13
RH
1.6
0.2
2.0
1.5
1.0
0.5
0.1
0.0
0
0
2
4
6
8
2
j [mA/cm ]
10
12
14
0
2
4
6
8
10
12
14
2
j [mA/cm ]
Current/Voltage Characteristic and Power Density as a Function of
of Increasing Temperature from 100 to
130°
130°C and Decreasing Temperature Down to 100°
100°C (with “d” in the Legend). QuinTech FC, S = 4.84
cm2, Using Commercial Pt/C 10 wt% Electrodes with SiC Matrix.
Conclusions
•
•
•
RH [%]
-Z2 / ohm
165
σ≅ [S/m]
190
Mass Spectroscopy Curves for P and NO
Parameters of the Equivalent Circuit
Prepared HPS membranes possess fast proton conductivity at elevated temperatures in the atmosphere of very low humidity.
humidity. Dry atmosphere does not significantly affect the migration of protons.
Thermal analysis indicates that water is bonded by two different types of bonds (of different strength). Complex analysis of impedance
impedance spectra indicates probable migration of protons through two
two different environments.
environments.
First tests of the membranes in fuel cells at temperatures above 100°
results. The performance of the fuel cell improved in time at 130°
130°C that is probably caused by
100°C using dry H2 and O2 gas streams gave promising results.
the establishment of better contacts between the electrodes and the membrane when the membrane reaches its viscovisco-elastic state at this temperature. The experiments revealed that our hybrid phosphosilicate polymer is
a promising material for membranes operating in intermediate temperature fuel cells using dry H2 and O2 gases.
This work was supported by the Czech Science Foundation (grant No.
No. GA ČR 106/04/1279),
106/04/1279), Ministry of Environment (grant VaV SN/171/05), and Ministry of Education (grant CEZ: MSMT 2231 00002).
00002).