novel middle temperature pem fuel cell … · novel middle temperature pem fuel cell membranes -...
Post on 03-Jul-2018
238 Views
Preview:
TRANSCRIPT
NOVEL MIDDLE TEMPERATURE PEM FUEL CELL MEMBRANES - POLYBENZIMIDAZOLE
CONTAINING IMMOBILIZED PHOSPHONIC OR SULFONIC ACID GROUPS
V. Sinigersky1, H. Penchev1, F. Ublekov1, M. Staneva1,
D. Budurova1, I.Radev2, V. Peinecke2
1 Institute of Polymers – Bulgarian Academy of Sciences, Sofia, Bulgaria 2 Zentrum für BrennstoffzellenTechnik ZBT GmbH, Duisburg, Germany
PIERO LUNGHI EFC CONFERENCE 11-13.12.2013, ROME, ITALY
OUTLOOK
Ø Introduction – Nafion and PA doped PBI
Ø Objectives
Ø Starting materials
Ø Preparation of membranes:
m-PBI containing cross-linked PVPA
p-PBI containing cross-linked PVSA
Ø Characterization of the membranes
Ø Proton conductivity measurements
Ø Summary
PIERO LUNGHI EFC CONFERENCE 11-13.12.2013, ROME, ITALY
Nafion® and PA Doped PBI – Limitations
Nafion®: - Low working temperatures – up to 80oC, 100% RH - Water management (min. 7 molecules H2O/-SO3H group) - Relatively high methanol cross-over - Expensive (over 600 USD/m2)
Phosphoric acid doped PBI : - Can be operated only at temperatures above 100oC (usually 160oC) - If operated under 100oC the drained water (reaction product) washes the electrolyte (phosphoric acid) out – the proton conductivity decreases
y
SO3H
CF2CF2 x
CF
CF3
O OCF2 CF2 n
CF2CF
m
N
NN
N* *n P
H
H OH
OHO OH
pKa = - 6 Superacid !
pKa1= 2.1 pKa2 = 7.2 pKa3 = 12.6 Middle strong, buffering acid
Piero Lunghi EFC Conference 11-13.12.2013, Rome, Italy
PBI/PA N
NN
N* *n P
H
H OH
OHO OH 5 – 40 H3PO4
per PBI unit
Polymeric acid alternative: Polyvinylphosphonic acid (PVPA) Problem: PVPA is water soluble
n CH2 CH
P(O)(OH)2
CH2 CH
P(O)(OH)2
Polymerisation of Vinylphosphonic acid
Solution: In order to become water insoluble PVPA has to be - Grafted to the PBI backbone - Cross-linked in the PBI matrix
Known: Membrane Celtec V® (BASF Fuel Cell GmbH) – PBI, containing grafted/ crosslinked PVPA. Prepared by Electron beam irradiation of a PBI film, containing VPA. Outperforms Nafion in therm of methanol cross-over. Proton conductivity – 100 mS.cm-1 (100oC, wet)
In
PBI containing –PO3H2 groups
PIERO LUNGHI EFC CONFERENCE 11-13.12.2013, ROME, ITALY
Preparation of membranes, comprising semi interpenetrating networks – PBI, containing cross-linked polyvinyl phosphonic or polyvinylsulfonic acid (PVPA or PVSA)
Synthetic concept:
Introduction of vinylphosphonic acid (VPA) or polyvinylsulfonic acid (VSA) , cross-linker and initiator in porous PBI film. Polymerization/cross-linking of the acid in the PBI matrix.
Objectives
PIERO LUNGHI EFC CONFERENCE 11-13.12.2013, ROME, ITALY
N
NN
N*n
N
NH
N
NH
n
Starting materials
NN
CH3
CH3CH3
CH3
NH
NH2
NH
NH2.2HCl
N
N
N
O
O
O
PO3H2
SO3Na
m-PBI
p-PBI
VPA
VSNa
Initiator (V50) Cross-linker Trially triazin trion
PIERO LUNGHI EFC CONFERENCE 11-13.12.2013, ROME, ITALY
Membranes, containing cross-linked PVPA (PBI crossPVPA membranes)
Dry PBI film
PBI containing VPA, Initiator and Cross-linker
PBI membrane, containing
cross-linked PVPA
VPA
swelling PBI containing VPA
exchange VPA, Initiator Cross-linker
UV irradiation, Δ
Polymerization/ cross-linking
Preparation of membranes
PIERO LUNGHI EFC CONFERENCE 11-13.12.2013, ROME, ITALY
Step 1: Introduction of VPA in the dry PBI film In a closed vessel a piece of dry PBI film, was swollen in a bath containing VPA and 3-5% water for 2 hours (70 oC) . Dimensions increase: up to 100% Weight uptake: up to 1000%
Preparation of membranes
Step 2: Introduction of VPA, initiator and cross-linker
The film prepared in Step 1 was transferred in a a bath, containing VPA, Cross-linker (5%), initiator (1.5%) and 10% water. Exchange was completed for 3h at RT.
Step 3: Polymerization/cross-linking of VPA in the PBI matrix
The film prepared in Step 2 was irradiated with UV light (intensity 0.08 W/cm2) The temperature rises to 60-80°C. Irradiation time: 5-15 min
Membranes, containing cross-linked PVSA (PBI crossPVSA membranes)
p-PBI/PA membrane
PBI containing VSNa, Initiator and Cross-linker
PBI membrane, containing
cross-linked PVSNa
exchange
VSNa, Initiator Cross-linker
UV irradiation, Δ
Polymerization/ cross-linking
Preparation of membranes
Porous PBI filled with
water
Washing with water
5% HCl
Water
PBI membrane, containing
cross-linked PVSA
Step 1: Preparation of porous PBI film, filled with water: A PBI membrane, doped with PA (prepared by the sol-gel method from the reaction mixture (5 wt.% PBI) was washed with ammonia and water.
Preparation of membranes
Step 2: Introduction of VSNa, initiator and cross-linker: The film prepared in step 1 was transferred into a bath, containing 25%water solution of VSNa, cross-linker (2-5 wt.%), initiator (1-2% wt.) and ethanol. Exchange was completed in 3h at RT
Step 3: Polymerization/cross-linking of VSNa in the PBI matrix: The film prepared in Step 2 was irradiated with UV light (up to 4h) or heated in a furnace (80 oC) for up to 96h.
Step 4: Acidification – transfer of the –SO3Na group in –SO3H: The film from step 3 was washed subsequently with 5%HCl and water.
PIERO LUNGHI EFC CONFERENCE 11-13.12.2013, ROME, ITALY
Characterization
Before characterization the membranes were washed subsequently with aqueous ammonia (removing unreacted reagents and homopolymer PVPA) and water, then dried.
Contents of cross-linked polyacid (water insoluble): determined gravimetrically from the weight uptake according to the Weight of the starting PBI film. From the weight ratio cross-linked polyacid /PBI the number of PVPA/ PVSA units per PBI repeating unit was calculated. 1H NMR (H2SO4-d2, 80 oC),
ppm (f1) 1.02.03.04.05.06.07.08.09.0
8.686
8.475
8.345
8.259
6.337
6.121
5.904
3.112
3.077
2.528
2.515
2.497
10.00
14.04
Ar H -CH2-CH-
PIERO LUNGHI EFC CONFERENCE 11-13.12.2013, ROME, ITALY
TGA
Membranes prepared
Using the procedures described membranes of very
good quality (smooth, flexible) were obtained. Very high contents of immobilized –PO3H2 and –SO3H
groups in the PBI matrix has been achieved:
- Membranes, containing cross-linked PVPA – 8.8 to
15.4 VPA groups per PBI repeat unit
- Membranes, containing cross-linked PVSA - 0.8 to
4.6 VSA groups per PBI repeat unit
All membranes exhibit good mechanical properties and thermal stability
PIERO LUNGHI EFC CONFERENCE 11-13.12.2013, ROME, ITALY
Proton conductivity measurements
All proton conductivity measurements were performed at
Zentrum für BrennstoffzellenTechnik ZBT GmbH, Duisburg,
Germany. The EasyCellTest method, developed at Institute of
Electrochemistry and Electrical Sources, Bulgarin Academy of
Sciences, has been used.
Membranes, containing cross-linked PVPA:
Measurements at 80oC and 100oC, RH 20-100%,
Membranes, containing cross-linked PVSA:
Measurements at 60oC, 80oC and 95oC,
Wet cell (the measuring cell immersed in water)
PIERO LUNGHI EFC CONFERENCE 11-13.12.2013, ROME, ITALY
Proton conductivity measurements
Membrane Weight ratio PBI/Cross-
linked PVPA
VPA units per PBI
σ,
mS.cm-1
PC 1 1/3.1 8.8 65.0
PC 2 1/4 11.4 62.1 PC 3 1/4.7 13.3 80.2
PC 4 1/5.4 15.4 86.7
Nafion 117 105.0
Proton conductivity of PBI membranes, containing cross-linked PVPA and Nafion 117, measured at 80 ºС и 100% RH
Proton conductivity measurements
Membrane
VPA units per PBI
σ, mS.cm-1
RH 100% RH 80% RH 50% RH 20%
PC 1 8.8 59.3 50.5 15.3 3.2
PC 2 11.4 53.9 44.7 37.1 5.0
PC 3 13.3 80.3 69.1 27.8 8.7
PC 4 15.4 82.6 80.8 60.5 8.3
Proton conductivity of PBI membranes, containing cross-linked PVPA measured at 100 ºС and 20 - 100% RH
PIERO LUNGHI EFC CONFERENCE 11-13.12.2013, ROME, ITALY
Proton conductivity measurements
Proton conductivity of PBI membranes, containing cross- linked PVSA measured at different temperatures (wet cell)
Mem-‐brane
Method of polymeriza4on/ Cross-‐linking
VPA units per PBI
σ, mS.cm-1
60 oC 80 oC 95 oC
T1 Thermal, 80 oC, 72h
3.0 25.0 29.2 31.5
T2 Thermal, 80 oC, 96h
3.6 28.0 38.2 45.2
UV1 UV, 3h 3.7 29.1 37.3 42.2
UV2 UV, 4h 4.6 51.3 55.3 61.8
PIERO LUNGHI EFC CONFERENCE 11-13.12.2013, ROME, ITALY
Summary
Ø Using an original procedure, PBI membranes, containing cross- linked PVPA or PVSA have been prepared
Ø High concentrations of immobilised (water insoluble) –PO3H2 and -SO3H groups have been achieved – up to 15 VPA and up to 4.6 VSA groups per PBI repeating unit
Ø The membranes prepared are of good qulity and thesmaly stable
Ø Proton conductivity increases with increasing the contents of –PO3H2 and -SO3H groups in the mebrane
Ø The highest proton conductivity was measured for the membrane with 15 VPA groups per PBI repeating unit - 86.7 mS.cm-1 at 100%RH, 60.5 mS.cm-1 at 50% RH and 8.3 mS.cm-1 at 20% RH
Ø The membranes, containing -SO3H exhibit high proton conductivity only in the wet state and 80-95 oC
Ø In the fully hydrated state the PBI membranes, containing cross- linked PVPA exhibit proton conductivities close to these of the Celtec V® (BASF Fuel Cell GmbH) and Nafion 117 membranes
PIERO LUNGHI EFC CONFERENCE 11-13.12.2013, ROME, ITALY
PIERO LUNGHI EFC CONFERENCE 11-13.12.2013, ROME, ITALY
Acknowledgement: The authors would like to thank the Bulgarian Science Fund
(Project PemHydroGen, ДТК 02/68) for funding the research
and EU project POLINNOVA, № 316086 for funding this
presentation
THANK YOU VERY MUCH FOR YOUR KIND ATTENTION
top related