Wenzhen LiDepartment of Chemical Engineering
Michigan Technological University, Houghton, MI 49931
Highly Active and Durable Nano-electrocatalysts for PEMFC
PEMFC Operation Mechanism
Solid proton exchange membrane working as electrolyte, PEMFCs are electrochemical energy conversion devices, which directly change the chemical energy of fuel (H2 or methanol) into electrical energy.
Advantages:Higher Power density (than other types of fuel cells)High energy conversion efficiency (cell: 50-70%)Environmental friendly (no noise, zero NOX emissions)Low temperature operation (< 100oC)
………
Proton Exchange Membrane Fuel Cell (PEMFC): a promising sustainable energy
Pt/carbon nanotube(CNTs)
PtRu/CNTs
Pt/CNTs film
Pt/polyaniline nanotube Pt-NTs
PdFe-Nanorods(NR)
Self-developed 1-D PEMFC Electrocatalysts(nanotube, nanowire, nanorods, etc)
Pt/Carbon Nanofibers
PtCo/CNTs
20 nm
Nanomaterials Based System for Sustainable Energy Applications
Future Research Plans
1.Design and Synthesis of Highly Performing and Stable Catalytic Active Phase (1-D & core shell)
2. Exploring Durable Catalyst Support 3. Development of Support-less Catalyst System 4. Nanomanufacture of membrane electrode assembly (MEA)
device
Nanotechnology CatalysisEngineering
Surface/Colloidal Chemistry
Challenges in PEMFC CommercializationLow Pt utilization in MEA (<30%)
New efficient design and fabrication of ordered MEA with high Pt utilization and long life-time
Polymer membrane electrolyteHigh operation temperature (>120oC) and less water dependence
The stability & durability of fuel cell componentsCatalysts (Pt nanoparticle, carbon support), membrane, MEA, etc
CostPt or PtRu catalysts in the electrodes (0.5gPt/KW = $18/KW to $7/KW) Nafion membrane electrolyte ($250/m2 to $20/m2), Graphite bipolar plates
Slow kinetics of cathode oxygen reduction reaction (ORR) Pt-M alloy (M = Fe, Co, Ni, etc) catalystsNovel carbon nanomaterials as catalyst support
1) The significant over-potential for ORR: @ OCV: more than 250 mV (on the most active Pt surface), iexchange=10-9 mA/cm2 (six magnitude lower than hydrogen oxidation reaction HOR)
2) An approximate 5-fold reduction of the amount of Pt(platinum loading: from 0.5 mgPt/cm2 to 0.1 mgPt/cm2
$7/kW, 2015 DOE target)
3) The dissolution / loss of Pt surface area in the cathode must be greatly reduced.My Solution: One Dimensional (1-D) PEMFC Electrocatalyst
@ OCV: > 250 mV overpotential
Catalyst Issues
Portable electronicsStationary Automobile
GM Chevy PEMFC powered SUV run more than 300 miles without refuel!
50 nm
PtFe-Nanowires(NW)
Wenzhen LiDepartment of Chemical Engineering
Michigan Technological University, Houghton, MI 49931
High Performance Carbon Nanotube (CNTs) Supported Catalysts for Fuel Cell Application
98
103
108
113
118
123
128
133
1000150020002500300035004000
Wavenumber (cm-1)
Tran
smitt
ance
(arb
. unit
s)
Background Pristine 1 hour 2 hour 3 hour 4 hour
20 nm
HO
HOHO
CO
HOCO
HOCOOH
OCCO
Purified CNTs
Surface oxidized CNTs
4N HNO3-H2SO4
120oC refluxing
PtCl6
2–EG
135oC
,refluxing
PtCl6
2–EG
135oC
, refluxing
Pt/CNT(oxidized)
Pt/CNT(unoxidized)
Ethylene Glycol (EG) Synthesis Method
EG concentration-H2O effect
EG Mechanism
4.0-7.4 125 0
5.0 (vertical)200-2500 (horizontal)
Carbon black (CB)(Vulcan XC-72) Graphite
Carbon nanotubes (CNT)
Electrical conductivity (s/cm)
Surface area (m2/g) 250 50-1000Micro-pores (%) > 50% 0 %
Specific corrosion current (mA/g) (@0.9V, 60oC)0.5 0.3
High electrical conductivity and high aspect ratio (giving long range conduction paths)
Advantages for CNT as fuel cell electrocatalysts support
Superior morphology & pore structure – better mass transport
High corrosion resistant ability in electrochemical environment
* Xin Wang, Wenzhen Li, et al,Journal of Power Sources, 2006, 158, 154
Water Effects on Pt Average Particle Size
20 nm
a b
d e
20 30 40 50 60 70 80
edcba
Pt (3
11)
Pt (2
20)
Pt (2
00)
Pt (1
11)
grap
hite
(100
)
grap
hite
(004
)grap
hite
(002
)
Inte
nsity
(a.u
.)
2 theta degree (o)
64 66 68 70 72
Pt/MWNTs-EG Pt (220)
e, 4.5 nm
d, 4.0 nm
c, 3.2 nm
b, 2.5 nm
a, 2.0 nm
Inte
nsity
(a.u
.)
2 theta degree (o)
Debye-Scherrer formula:
10 20 302
3
4
5
6
Grain
size
(nm)
Water content (vol.%)
Microwave method 30wt% Pt-CNT 30wt% Pt-CNF 10wt% Pt-CNT 10wt% Pt-CNF
Conventional method 10wt% Pt-CNT 10wt% Pt-CNF 30wt% Pt-CNT
Water in synthesis system
Pt particle size
0 50 100 150 200 250 300 350 400 4500.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Pt/CB
Pt/CNTCNT
E catho
de / V
.vs.DH
E
i / mA.cm-2
64 66 68 70 72
Pt/CNT
Pt/CB
Pt (220)
2-theta (o)
Pt/CB
CNTs: unique electrical property, tubular structure, Pt-CNTs interaction
02468
10121416182022
Pt/CB
Pt/CNT
i [mA.
mg-1 Pt
] 0.7 V vs. DHE
ORR activity
Durability
* Xin Wang, Wenzhen Li, et al,Journal of Power Sources, 2006, 158, 154
Wenzhen Li, et al. Carbon, 2002, 40, 791-794. Wenzhen Li, et al. Journal of Physical Chemistry. B, 2003, 107, 6292-6299.
Wenzhen Li, et al.Carbon, 2004, 42, 436-439.
Pt/CNT
Pt/CB
The ECSA is improved 3 times for Pt/CNT catalyst than Pt/C
Pros:SimpleLow temperatureEasy to scale up
… … …
Seth Knupp, Wenzhen Li, et al, Carbon, 2008, 46, 1276-1264
Seth Knupp, Wenzhen Li, et al, Carbon, 2008, 46, 1276-1264
Wenzhen Li, et al. Journal of Physical Chemistry. B, 2003, 107, 6292-6299.
Wenzhen LiDepartment of Chemical Engineering
Michigan Technological University, Houghton, MI 49931
Design and Synthesis of Special Nano-Structured Electrocatalysts with High Activity and Durability for Fuel Cells
Large Scale Solution phase synthesis methodM1(acac)x+M2 (acac)y+ROH+RCOOH+RNH2+Ph2O
Nucleation T1/ M2 (CO)z
Growth & aging T2
Core-shell Nanorod Nanocube
Deposition & ‘activation’
Nano-Catalysts
10 nm
4.9 nm
2.7 nm1.1
Pt core-Co3O4 shell nanoparticles
PtFe-nanowire50 nm
50 nm
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1-1.6
-1.4
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
Curre
nt / m
A
Potential / V vs. RHE
PtFe nanowire Pt/CB
0 100 200 300 400 500 600 700 800 900 1000 11000
10
20
30
40
50
60
70
80
90
100
110
Pt/CB
Supportless PtFe NW
Relat
ive EC
SA %
CV Cycle No.
0 1 2 3 4 5 6 7 8 9 10 110
20406080
100120140160180200220240
Pt-NR
Pd-NR
Surfa
ce A
rea
/ m2 /g
Nanorod Diameter / nm
Advantages:* Accurate control of shape, composition, morphology, etc* Solution phase synthesis– simple & easy to scale up* Multi-components catalyst system
… … …
Measured ECSA of PdFe-NR : 55-60 m2/g
Theoretical calculation TEM XRDA: B = 1A: B = 1/3
A only
NP Only10 nm NR
60 nm NR
30 35 40 45 50 55 60 65 70 75 80
Pd-Pd bond distance 0.2729 nm
PdFe-NR
Inten
sity /
a.u.
2 theta degree (o)
* Pd-Pd distance of Pd nanoparticles: 0.2753 nm
ORR activity Test
Support-less PdFe nanorod electrocatalyst
0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0-6
-5
-4
-3
-2
-1
0
60nm PdFe-NR Pt/C Pd Nanoparticle
i / mA
.cm-2
E / V vs. RHE0 100 200 300 400 500 600 700 800
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Pt/C, 0.4mgPt/cm2 (commercial electrode)
Pt/C, 0.5mgPt/cm2 (commercial MEA)
60nm PdFe-NR, 0.22mgPd/cm2
E cell / V
i / mA.cm-2
Advantageous Pd-Pd bond distance -- higher ORR activity
Super thin catalyst layer -- lower resistance &
better mass transport
Other nanostrcutured materials
Nanotube
Core-shellNanoparticle
NanowiresNanotube
Zhongwei Chen, Mahesh Waje, Wenzhen Li, Yushan Yan, Angewandte Chemie International Edition, 2007, 46, 4060.
Future work
Firstly demonstrated higher mass transport and lower resistance using
support-less catalyst!
* Experiment: de-alloying & post-treatment (annealing)
* Theoretical calculation / model: structure vs. activity
* Surface fuctionalization: bonding with nanostructures
* Multiple simulation on nanostructured catalysts: Pt dissolution / aggregation mechanism
Ni nano-particles PtCo/CNTs
Ni
0
5
10
15
20 Pt skin layer
Pt core-shellPtCo/CPt/C
Spec
ific ac
tivity
/ A.cm
-2
Sample
Research Target
Ideal core-shell structure with ultra-high electrochemical activity and long life-time in real world !
* A & B : two surfactants
Pt-nanotube
a b
c d
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.20.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Aligned Pt/CNTs film (0.20 mg Pt/cm2, no PTFE) Pt/C (E-TEK, 0.25mg Pt/cm2, 30wt% PTFE) Pt/C, (E-TEK, 0.25mg Pt/cm2, no PTFE)
Cellp
poten
tial /
V
Current density / A cm-2
Wenzhen LiDepartment of Chemical Engineering
Michigan Technological University, Houghton, MI 49931
20 nm
TEMAcknowledgements
20 30 40 50 60 70 80
200
400
600
800
1000
Graphite (100)
Pt (1
11)
Grap
hite (
002)
PtRu/MWNTs-30wt%
PtRu/DWNTs-50wt%
PtRu/DWNTs-30wt%
DWNTs
Inten
sity (
a.u.)
2 theta degree (o)
0 50 100 150 200 250 300 350 400 450 5000.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Cell v
oltag
e / V
Current denisty / mA cm-2
PtRu/C-40wt% (E-TEK), 2.0 mgPtRu/cm2
PtRu/C-40wt% (E-TEK), 0.50 mgPtRu/cm2
PtRu/SWNTs-30wt%, 0.52 mgPtRu/cm2
PtRu/MWNTs-30wt%, 0.47 mgPtRu/cm2
PtRu/DWNTs-30wt%, 0.50 mgPtRu/cm2
Conclusions• Polyol catalyst synthesis method: small particle size (2-3 nm) and uniform sizedistribution.
• MEA for PEMFC: oriented super-hydrophobic Pt/MWNTs film of 20 um and super-hydrophobicity (153o); MEA for DMFC: uniform thin catalyst layer of 5-20 um, 75%noble metal loading reduction & 68% peak power density improvement.
-0.2 0.0 0.2 0.4 0.6 0.8
-0.010
-0.005
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
Curre
nt d
ensit
y (m
A/cm
2 Pt)
Potential (V vs. Ag/AgCl)
PtRu/C-40wt% (E-TEK) PtRu/DWNT-30wt% PtRu/MWNT-30wt% PtRu/SWNT-30wt%
Contact angleSuperhydrophobic: 153o
Oriented Pt/CNTs film for high perform PEMFC
PtRu/CNTs film for High perform DMFC Load
H2 gas diffusion
O2 gas diffusion
Proton conduction
Water out
Anode Nafion CathodeMembrane
e- e-
Load
CH3OH diffusion
O2 gas diffusion
Proton conduction
Water out
Anode Nafion CathodeMembrane
e- e-
Methanol crossover
Schematic illustration of fuel cell operation principle
PEMFC DMFCAnode:2H2 4H+ + 4e-
Cathode:O2 + 4H+ + 4e- 2H2O
Total:2H2 + O2 2H2O
Anode:CH3OH + H2O CO2 + 6H+ + 6e-
Cathode:O2 + 6H+ + 6e- 3H2O
Total:CH3OH + 3/2O2 CO2 + 3H2O
23
Novel membrane electrode assembly (MEA) fabrication method: Filtration
SEM
TEM
XRDCV: methanol oxidation activity
DMFC single cell performance
PEMFC single cell performance
SEM & EDAX
Wenzhen Li, Xin Wang, Zhognwei Chen, Mahesh Waje, Yushan Yan, Langmuir, 2005, 21, 9386-9389.
Wenzhen Li, Xin Wang, Zhognwei Chen, Mahesh Waje, Yushan Yan., Journal of Physical Chemistry-B, 2006,110, 15353.
Catalyst Applied to Membrane
Catalyst Applied to Gas Diffusion Layer
Screen(hot pressing)
Spray(hot pressing)
Direct Thin FilmDecal
Spray
MEA
Cross section view of a MEA
MEA Fabrication Methods
* Profs. Qin Xin (DICP, CAS), Yushan Yan (University of California-Riverside), Masahiro Watanabe (University of Yamanashi, Japan) & former colleagues* A Packard Postdoctoral Fellowship to W.Z. Li* National Natural Science Foundation of China (No.29976006, 20173060) * GM China Natural Science Foundation * DOD - SBIR & Pacific Fuel Cell Corp.* UC-Discovery/Smart Grant & California Energy Commission
GDL
GDL
Catalyst layer
Catalyst layer
Brush
Filtration
Pros for filtration methodOrdered CNTs filmSimple & cheapEasy to scale up… … …
Screenprinting
Issues: membrane wrinkle, Catalyst cracking