Temperature influence on PANI growth as a protective coating for PEMFC bipolar … ·...
1
Temperature influence on PANI growth as a protective coating for PEMFC bipolar plates Daniel Gonzalez, Surbhi Sharma Centre for Hydrogen and Fuel Cell Research, School of Chemical Engineering, University of Birmingham, Edgbaston, B15 2TT, Birmingham, U.K. Email: [email protected] www.fuelcells.bham.ac.uk Introduction One of the most promising ways to cut down the price size and weight of present PEMFC stacks is to use stamped metallic bipolar plates (BPP) instead of graphite BPP. However, the acidic environment of the fuel cell tends to induce corrosion on metallic bipolar plates and for this reason they require protective coatings. In terms of durability and long term fuel cell performance, stainless steel coated with gold is the combination that is presented as the state of the art. However, this is not economically viable and hence the need to explore other cheaper and effective coatings including intrinsically conductive polymers like polyanilne (PANI). This work explores the effect of growth temperature on PANI coating thickness and morphology and consequently its effect on corrosion resistance. 3 electrode electrochemical coating setup • Substrate: Stainless steel 316L partially masked • Coated area: 6.3 cm 2 • Jacketed cell: constant temperature • Reference electrode: Ag/AgCl (KCl saturated) • Counter electrode: Pt wire • Electrolyte: 0.5M H 2 SO 4 + 0.1M aniline • Coating mode: cyclic voltammetry 50mV/s d: estimated coating thickness (nm) Q: integrated charge of the characteristic peak (mC) Mw: Aniline molecular weight (93.13 g/mol) z: No electrons in the polymerization reaction (0.5) F: Faraday constant A: electrode area (6.3 cm 2 ) : estimated density of the polymer (1.022 g/cm 3 ) 0 1 2 3 4 5 6 7 8 9 10 0 5 10 15 20 Integrated charge (mC Cycle No 3 ºC 29 ºC 15 ºC 0 50 100 150 0 5 10 15 20 Integrated charge (mC) Cycle No 3 ºC 29 ºC 15 ºC 0.E+00 5.E-07 1.E-06 2.E-06 2.E-06 3.E-06 3.E-06 4.E-06 4.E-06 0 50 100 150 200 Current density (A/cm 2 ) Time (min) Chronoamperometry Uncoated 316L SS316L+PANI 3CV cycle 1.0V SHE 80°C H 2 SO 4 1mM purged with air -8 -7.5 -7 -6.5 -6 -5.5 -5 -4.5 -4 -3.5 -3 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 Current density log (A/cm 2 ) Potential (V SHE ) Potentiodynamic corrosion test Uncoated 316L SS316L+PANI 3CV cycle From -0.32V SHE to +1.28V SHE at 1mV/s 12CV cycles, 3 °C 5CV cycles, 15 °C 3CV cycles, 29 °C Coating process Growth analysis at 3, 15 & 29 °C Thin coatings comparison Growth morphology at 29 °C Corrosion analysis Conclusions • Colder temperatures delays the nucleation of PANI on SS 316L and reduces the growth rate. • At 29 °C A thin PANI layer is deposited on SS but the polymer tends to form aggregates that leads to porous layers if the coating thickness increases beyond. • In order to get similar thickness and coating morphology different number of CV cycles are required at 3, 15 and 29 °C. • Thin PANI layers can decrease the corrosion current in acid electrolyte and positively displace the corrosion potential. 3CV cycles 29 °C 8CV cycles 29 °C 40 nm 150 nm
Transcript of Temperature influence on PANI growth as a protective coating for PEMFC bipolar … ·...
Temperature influence on PANI growth as a protective
coating for PEMFC bipolar plates
Daniel Gonzalez, Surbhi Sharma
Centre for Hydrogen and Fuel Cell Research, School of Chemical Engineering,
University of Birmingham, Edgbaston, B15 2TT, Birmingham, U.K.
Email: [email protected]
www.fuelcells.bham.ac.uk
Introduction
One of the most promising ways to cut down the price size and weight of present PEMFC stacks is to use stamped metallic bipolar plates (BPP) instead
of graphite BPP. However, the acidic environment of the fuel cell tends to induce corrosion on metallic bipolar plates and for this reason they require
protective coatings. In terms of durability and long term fuel cell performance, stainless steel coated with gold is the combination that is presented as the
state of the art. However, this is not economically viable and hence the need to explore other cheaper and effective coatings including intrinsically
conductive polymers like polyanilne (PANI). This work explores the effect of growth temperature on PANI coating thickness and morphology and
consequently its effect on corrosion resistance.
3 electrode electrochemical coating setup • Substrate: Stainless steel 316L partially masked
• Coated area: 6.3 cm2
• Jacketed cell: constant temperature
• Reference electrode: Ag/AgCl (KCl saturated)
• Counter electrode: Pt wire
• Electrolyte: 0.5M H2SO4 + 0.1M aniline
• Coating mode: cyclic voltammetry 50mV/s
d: estimated coating thickness (nm)
Q: integrated charge of the characteristic peak (mC)
Mw: Aniline molecular weight (93.13 g/mol)
z: No electrons in the polymerization reaction (0.5)
F: Faraday constant
A: electrode area (6.3 cm2)
𝜌: estimated density of the polymer (1.022 g/cm3)
0
1
2
3
4
5
6
7
8
9
10
0 5 10 15 20
Inte
gra
ted
ch
arg
e
(mC
Cycle No
3 ºC
29 ºC
15 ºC
0
50
100
150
0 5 10 15 20
Inte
gra
ted
ch
arg
e
(mC
)
Cycle No
3 ºC
29 ºC
15 ºC
0.E+00
5.E-07
1.E-06
2.E-06
2.E-06
3.E-06
3.E-06
4.E-06
4.E-06
0 50 100 150 200 Cu
rren
t d
en
sit
y
(A/c
m2)
Time (min)
Chronoamperometry
Uncoated 316L SS316L+PANI 3CV cycle
1.0VSHE 80°C
H2SO4 1mM purged with air
-8 -7.5
-7 -6.5
-6 -5.5
-5 -4.5
-4 -3.5
-3
-0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2
Cu
rren
t d
en
sit
y l
og
(A
/cm
2)
Potential (VSHE)
Potentiodynamic corrosion test
Uncoated 316L
SS316L+PANI 3CV cycle
From -0.32VSHE to +1.28VSHE at 1mV/s
12CV cycles, 3 °C 5CV cycles, 15 °C 3CV cycles, 29 °C
Coating process
Growth analysis at 3, 15 & 29 °C
Thin coatings comparison
Growth morphology at 29 °C
Corrosion analysis
Conclusions
• Colder temperatures delays the nucleation of PANI on SS 316L and reduces the growth rate.
• At 29 °C A thin PANI layer is deposited on SS but the polymer tends to form aggregates that leads to porous layers if the coating
thickness increases beyond.
• In order to get similar thickness and coating morphology different number of CV cycles are required at 3, 15 and 29 °C.
• Thin PANI layers can decrease the corrosion current in acid electrolyte and positively displace the corrosion potential.
3CV cycles 29 °C
8CV cycles 29 °C
40 nm 150 nm
