Advantages of polymer wrapping on to the carbon black toward improved Pt utilization efficiency in polymer electrolyte membrane fuel cell (PEMFC)

1. 0
0.1
0.2
0.3
0.4
0.5
0.6
0 0.5 1 1.5 2 2.5 3 3.5
dV
p
/
dd
0
0.1
0.2
0.3
0.4
0.1 0.2 0.3 0.4
K 6.5 3.9
Cdl / mF cm-
2 0.34 0.28
R / Ω cm2 14.6 4.4
0
0.1
0.2
0 0.5 1 1.5 2 2.5 3 3.5
Pore size / nm
KB Vulcan AB
0 0.2 0.4 0.6 0.8
0 0.2 0.4 0.6 0.8
Voltage / V
Introduction
ü High energy conversion
efficiency
ü High power density
ü No pollutant emission
üCapping for micropore gates T. Fujigaya et al., J Power
Sources, 2015, 300, 175.
Polymer Electrolyte Membrane Fuel Cell (PEMFC)
ü Homogeneous
Nafion coating
Inhomogeneous Nafion
distribution
Target
Advantages of polymer wrapping on to the carbon black toward
improved Pt utilization efficiency in polymer electrolyte membrane
fuel cell (PEMFC)
1Samindi Jayawickrama and 1-4Tsuyohiko Fujigaya
1Department of Applied Chemistry, Graduate School of Engineering, Kyushu University
2WPI-I2CNER, 3JST-PRESTO, 4CMS, Kyushu University
CB
Micropore
Polybenzimidazole
(PBI)
Conventional
catalyst
New
catalyst
Improved Pt utilization
(catalyst layer)
Experimental and Results
q N2 Adsorption – Specific surface area
Anode: H2 (0.1 L min-1), Cathode: N2 (0.5 L min-1), 40 °C, RH: 100%
TEM KB Vulcan AB
PBI-wrapped
Non-wrapped
q Cyclic voltammetry - ECSA
Non-
wrapped
H+
PBI-wrapped
H+
H+
üImproved ECSA in PBI-wrapped CBs
üPrevention of Pt deposition into pores
üECSA increment is higher when the degree
of capping of micropore gates is higher in
Vulcan and KB
q Impedance Spectroscopy – H+ resistance of the catalyst layer
üHomogeneous Nafion coating
v PBI wrapping aided the well dispersion of Pt on the CB/PBI.
1.Prevention of Pt deposition into pores
2. Reduced H+ resistance in the catalyst layer due the homogeneous
distribution of Nafion
v We successfully improved the Pt utilization efficiency in all polymer
wrapped CBs by,
Long range H+ conduction
Prevent deposition of Pt into pores
Pt loading
Addition of
Nafion
Conclusion
20 nm
q Fuel cell test – Polarization losses
üImproved power density in PBI-wrapped CBs
ü Capping of micropore gates for KB and Vulcan
Pt loading
2.34 ± 0.53 3.06 ± 0.50 3.49 ± 0.68
CB/PBI/Pt
2.33 ± 0.57 4.39 ± 1.21
3.10 ± 0.60
CB/Pt
PBI wrapped-CB
(CB/PBI)
CB/PBI/Pt
CB/Pt CB/Pt+Nafion
CB/PBI/Pt+Nafion
No
Interaction
Interaction
ü Prevent deposition
of Pt into pores
Energy source for next
generation
Polyol method : H2PtCl6.6H20, 140 °C, 60 vol% Ethylene glycol aq.
-80
-60
-40
-20
0
20
40
60
80
0 0.2 0.4 0.6 0.8
Current
/
A
g
-1
PBI wrapped
+15 %
PBI wrapped
+27 %
PBI wrapped
+16 %
49.2 m2g-1 62.4 m2g-1 87.4 m2g-1
49.3 m2g-1
42.1 m2g-1 73.0 m2g-1
0
0.5
1
1.5
2
2.5
3
0 10 20 30 40 50
1336 m2g-1
1126 m2g-1
206 m2g-1
83 m2g-1
60 m2g-1
53 m2g-1
Vulcan
KB/
PBI
Vulcan/
PBI
AB/
PBI
KB
AB
PBI wrapping
Micropore
reduction
-22 %
Micropore
reduction
-83 %
Micropore
Reduction: ND
N2, 77 K, 1 atm
1. Ketjen black (KB)
2. Vulcan
3. Acetylene black (AB)
Types of CB used
CB (CB/PBI)
DMAc
PBI
KB Vulcan AB
H+
H+
PBI-wrapped
Non- wrapped
Lower H+
resistance
Higher H+
resistance
K = √ Rp/Cdl
|Z| = √ Rp/Cdl * ω-1/2
High frequency
T. Fujigaya et al., ACS Appl. Mater. Interfaces, 2016, 8, 14494.
Vulcan/Pt vs Vulcan/PBI/Pt
üWell dispersed Pt particles in PBI wrapped catalyst
T. Fujigaya et al., ACS Appl. Mater. Interfaces, 2016, 8, 14494.
0
5
10
15
20
0 1 2 3 4 5 6 7 8
Vulcan/Pt
Vulcan/PBI/Pt
Z"
Ohm
cm
-2
Z Ohm cm2
Anode: H2, Cathode: N2, 80 °C, RH: 100%
0
0.2
0.4
0.6
0.8
1
0 0.5 1 1.5 2
Voltage
/
V
0 0.5 1 1.5 2
Current density / A cm
-2
+19 %
+25 %
KB/PBI/Pt
0.59 Wcm-2
Vulcan/PBI/Pt
0.70 Wcm-2
Vulcan/Pt
0.59 Wcm-2
KB/Pt
0.47 Wcm-2
Anode: H2 (0.1 L min-1), Cathode: Air (0.2 L min-1), 80 °C , RH: 100%
KB Vulcan AB
0 0.5 1 1.5 2
+10 %
AB/Pt
0.71 Wcm-2
AB/PBI/Pt
0.78 Wcm-2
e-
H＋
electrode
catalyst
electrolyte
membrane
electrode
Nafion ionomer
Reduced Pt utilization
(catalyst layer)
Pt
Current situation
Carbon black (CB)
Ununiform Nafion
distribution
Nafion
Carbon
L. Haro et al. Nature Commun.
2014, 5, 5229
Reduced Pt
utilization
All Pts are not contributed
for the electrochemical
reactions
2H2 4H+ + 4e-
Anode - Hydrogen Oxidation
Cathode - Oxygen Reduction
O2 + 4H+ + 4e- 2H2O
H+
O2
H+
O2
q Oxygen reduction reaction
-6
-5
-4
-3
-2
-1
0
1
0 0.2 0.4 0.6 0.8 1 1.2
@ 1600 rpm
VulcanPBI/Pt
Vulcan/Pt
Current
density
/
mA
cm
-2
Voltage vs RHE / V
Tafel slop
(mV dec.-1)
65
64
üSame catalytic behavior
üBetter ORR of Vulcan/PBI/Pt
üThinner Nafion layer
O2
50 mV
gain
Strategy – Polymer Wrapping
Pt in pore
KB
Carbon
Outer Pt
Inner Pt
Vulcan
E. Padgett et al. J. Electrochem.
Soc. 2018, 165, F173-F180