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