1. Vitamin E Assisting Polymer Electrolyte Fuel Cells
Jianguo Liu, Yingfang Yao, Zhigang Zou
National Laboratory of Solid State Microstructures
Vitamin E (α-TOH) was one of
the best candidates for PEMFC
use!
Benefiting from O2 in the atmosphere, people
suffers from reactive oxygen species (ROS) that leads
to disorder, diseases, cancer, and aging;
Similarly working in the atmosphere of O2, Proton
exchange membranes (PEMs) in fuel cells (FCs) were
also attacked with reactive oxygen species (ROS),
Leading to chemical degradation that causes PEMs
failure and performance loss;
As we learned from human bodies, natural
antioxidant was suspected as an effective free radical
scavenger that can resolve the oxidative stress
appeared in PEMFCs, and offers the possibility of
worldwide commercialization of PEMFCs.
Background
Physics:
Zero Drain;
Good Compatibility/solubility in Nafion;
Chemistry:
Protection Efficiency toward Free Radicals;
Recyclability.
Antioxidative Additives Standard
Oily and water insoluble, zero dissolving drain;
Thermally Stable (Tdecomposition>530 K).
Sustainable in complex PEMFC working condition.
Zero Drain
Sandwiched Pt Wire as
Detecting Electrode;
Membrane at Cathode
Side as Detecting PEM;
CV scans to Detect H2O2
generation and transport.
In-situ Detectionα-TOH can be well dispersed in Nafion matrix.
Solution-cast
Nafion
Nafion+
0.5% α-TOH
Nafion+
1.0% α-TOH
Nafion+
3.0% α-TOH
Compatibility/Solubility
Great Performance Retention (OCV Holding Tests);
Great Membrane Protection (OCV Holding Tests);
Inhibition of H2O2 Generation/Transport (in-situ);
Protection Efficiency
0 200 400 600 800 1000 1200
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1st
Cycle
2nd
Cycle
3rd
Cycle
4th
Cycle
5th
Cycle
6th
Cycle
Voltage(V)
Current Density (mA·cm-2
)
PowerDensity(mW·cm-2
)
0
100
200
300
400
500
600
0 200 400 600 800 1000 1200 1400
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Voltage(V)
Current Density (mA·cm-2
)
PowerDensity(mW·cm-2
)
0
100
200
300
400
500
600
700
1st
Cycle
2nd
Cycle
3rd
Cycle
4th
Cycle
5th
Cycle
6th
Cycle
7th
Cycle
8th
Cycle
9th
Cycle
10th
Cycle
11th
Cycle
12th
Cycle
13th
Cycle
14th
Cycle
15th
Cycle
16th
Cycle
Performance
Solution-cast Nafion Nafion + 1.5% α-TOH
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
-16
-14
-12
-10
-8
-6
-4
-2
0
2
4
6
8
PercentageChanged(%)
Cycle Number
Nafion
Nafion + 1.5% α-TOH
Potential@1200 mAcm-2
after each OCV holding
tests normalized with
Cycle 1 as denominator.
Membrane Thickness
Solution-cast
Nafion
Nafion +
1.5% α-TOH
Before
OCVTest
After
OCVTests
Inhibition of H2O2
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
-0.2
0.0
0.2
-0.2
0.0
0.2
-0.2
0.0
0.2
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Potential (V v.s. Anode)
613mV
800mV
H2
O2
Oxidation
H2
O2
Reduction
H2
O2
Oxidation
H2
O2
Reduction
H2
O2
Reduction
OCV
DetectedCurrent(mA)
H2
O2
Oxidation
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
-0.4
-0.2
0.0
0.2
0.4
-0.4
-0.2
0.0
0.2
0.4
-0.4
-0.2
0.0
0.2
0.4
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
DetectedCurrent(mA)
Potential (V v.s. Anode)
613mV
800mV
OCV
Solution-cast Nafion Nafion + 1.5% α-TOH
Recyclability
0.0 0.2 0.4 0.6 0.8 1.0 1.2
-6
-5
-4
-3
-2
-1
0
1
CurrentDensity(mA·cm-2
)
Potential (V v.s. RHE)
N2
Circumstance
O2
Circumstance
0.0 0.2 0.4 0.6 0.8 1.0 1.2
-6
-5
-4
-3
-2
-1
0
1
CurrentDensity(mA·cm-2
)
Potential (V v.s. RHE)
N2
Circumstance
O2
Circumstance
w/α-TOHNoα-TOH
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
-0.4
-0.2
0.0
-0.8
-0.6
-0.4
-0.4
-0.2
0.0
-0.2
0.0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
DetectedCurrent(mA)
Potential (V v.s. Aonde)
Nafion/α-TOHAfter H2
Reduction
Nafion/α-TOHAfter 12hr OCV
H2
O2
Oxidation
Nafion/α-TOHInitial
Nafion
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
0.2
0.4
0.6
0.2
0.4
0.6
0.0
0.2
0.4
0.6
0.8
1.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Time (hr)
RecastedNafion
DetectedCurrent(mA)
1%α-TOH/Nafion
H2
/Air H2
/AirH2
/N2
Potential(V)
Cathodic Potential
H2
/N2
Ex-situ In-situ Ex-situ and in-situ detection
proved the possibility of α-TOH
regeneration from H2;
Preferentially oxidized by ROS,
α-TOH could be reduced by
permeated H2;
The recyclability of α-TOH enables PEMFC long term operation.
Conclusion
In-situ
Detection
indicates
H2O2
generation at
various
cathodic
potentials.
••
TO-α+OH→TOH-α+HOO 22
TO)OOH-(α→TO-α+HOO ••
••
TO-α+OH→TOH-α+OH 2
TO)OH-(α→TO-α+OH ••
TOH-α2→H+TO-α2 2
•
+
2
+
H+TOH-α→H+TO-α
Anti-
oxidation
Regeneration
Vitamin E is a great antioxidant
candidate for PEMFCs long-term use.