Polybenzimidazole及其奈米複合材料薄膜在直接甲醇燃料電池的應用

Polybenzimidazole及其奈米複合材

料薄膜在直接甲醇燃料電池的應用

許聯崇 教授

國立成功大學材料科學及工程學系

中華民國97年3月19日

遠東科技大學材料科學與工程系專題演講

Outline

{

Fuel Cells and Proton Exchange

Membranes

{

Synthesis of Polybenzimidazoles (PBIs)

{

Research work regarding PBI, PBI/clay

and PBI/silica nanocomposite membranes

at our Lab

Introduction of Fuel Cells and

Proton Exchange Membranes

燃料電池之優點(Ⅰ)

內燃機︰

經由熱能轉換，效率低

燃料電池︰

燃料電池之優點(Ⅱ)

{

低噪音

{

低污染

{

多用途

{

多種進料選擇

{

免充電

PEMFC Membrane Electrode Assembly

(MEA)

Motorcycle

powered with a

fuel cell

Direct Methanol Fuel Cell ( DMFC)

¾

目前以氫氣與氧氣為反應進料的質子交換膜燃料

電池組，因為其堆疊串聯方式與氫氣鋼瓶體積的限

制，尚無法達到真正輕薄短小的要求。

¾

因此近年來開始研究使用甲醇為進料的直接甲醇

燃料電池(DMFC)，並設計微小型燃料電池組的串聯

方式與製作方法以及燃料卡匣，使其能達到輕薄短

小的目的。

DMFC

Notebook

Computer

The Desired Properties of PEMFC Membranes

{

High proton conductivity

{

Low electronic conductivity

{

Low permeability of fuel or oxygen

{

_{Low electro-osmotic drag coefficient}

{

Good mechanical properties

{

Thermal, oxidative and hydrolytic stability

Category of Polymers Used in PEMFC

Membranes

{

Perfluorinated polymers: Nafion

®

{

Partially fluorinated polymers:

PVDF-g-PSSA

{

Non-fluorinated hydrocarbon polymers:

PVA/PWA

{

Non-fluorinated aromatic polymers: PSSA,

S-PEEK, S-polyimide, S-PPO,S-PPS, S-PPP

etc.

Commercial Proton Exchange Membrane

-Nafion

®

CF₂ CF₂ CF₂ CF O CF₂ CF O CF₃ CF₂ CF₂ SO₃-H+ n x m

Problems of Nafion

®

for PEMFC and DMFC

{

_Nafion

®

_{relies on water for proton conductivity,}

so it cannot operate at high temperatures (> 80

℃

_).

{

_Nafion

®

_{has a lot of methanol crossover when}

used in DMFC. That causes loss of fuel and

reduces cathode voltage.

Necessary Properties of New Proton

Exchange Membranes for DMFC

{

_{High thermal stability at high temperature.}

(＞100℃)

{

_{High proton conductivity under an anhydrous}

condition at high temperatures.

Synthesis of Polybenzimidazole (PBI)

NH₂ NH₂ H₂N H₂N X COOH HOOC X N N N N H H in PPA 170~200 o C

Synthesis of Polybenzimidazole (PBI)

HOOC

_NH

2

NH

₂

N

N

H

n

PPA

200 o

C

(2) AB type PBI

Commercial PBI

N N N N H H n poly[2,2’-(m-phenylene)-5,5’-bibenzimidazole] PMPBI

Advantages of PBI membranes for PEMFC

and DMFC

¾

_{High thermal stability and good mechanical}

properties at high temperatures

¾

_{High proton conductivity under an anhydrous}

condition through hopping mechanism.

¾

_{Low electro-osmotic drag coefficient (near zero).}

¾

_{They can be operated at higher temperatures (up to}

200 ℃) than Nafion (< 80 ℃).

¾

_{High CO tolerance (up to several percent)}

¾

_{Low methanol crossover.}

Conductivity of PMPBI Film doped with Acids

Research work of PBI, PBI/clay and

PBI/silica nanocomposite membranes

at our Lab

Problems of PMPBI for DMFC

¾

Although the PMPBI has very good

mechanical properties, it has a very rigid

molecular structure, which is not good for

proton transfer.

¾

The PMPBI is difficult to dissolve in common

organic solvents for the preparation of

membranes by solution casting.

¾

After doping with acids, the PMPBI membrane

becomes brittle.

Objectives of Our Research

{

Synthesis of organosoluble, flexible and

tough PBI membranes for DMFC application

{

_{Preparation of PBI/clay and PBI/silica}

nanocomposite membranes to improve PBI’s

performance in DMFC application

Part 1

Synthesis and properties of a new

fluorine-containing polybenzimidazole for high

temperature fuel cell applications

Shih-Wei Chuang, Steve Lien-Chung Hsu*,“Journal of Polymer Science, Polymer Chemistry Edition, 2006, 44(15) 4508

Synthesis of fluorine-containing PBI for DMFC

NH₂ NH2 H2N H2N CF3 CF3 COOH HOOC N N H CF3 + PPA Polyphosphoric acid ，200 ℃

{

_{An amorphous, organosoluble, flexible fluorine-containing}

PBI was synthesized through molecular modification that

still retains enough thermal and mechanical properties.

inherent viscosity =2.5 dL/g (conc.=0.5g/dL at 30 o_C)

1

_{H-NMR of fluorine-containing PBI}

N N N N H CF₃ CF₃ H n

IR Spectra of PBI membranes doped with

different amounts of phosphoric acid

Tr ansm it ta n ce ( % ) PBI-3.0H₃PO₄ PBI-2.1H₃PO₄ PBI-1.7H₃PO₄ PBI-1.2H₃PO₄ PBI N N N N H CF3 CF3 H n 1631 cm-1 3100~3250 cm-1

Wide angular X-ray diffraction (XRD)

pattern of fluorine-containing PBI

0 10 20 30 40 0 1500 3000 4500 6000 7500 In te n s ity 2θ (Degree)

amorphous

Solubility of the PBI Polymer

-Acetone -Chloroform -THF -Methanol + MSA + DMF + DMSO + DMAc + NMP PBI Polymerb Solventa

TGA thermograms of PBI membranes doped

with different amount of phosphoric acid in air

200 400 600 800 0 20 40 60 80 100 W e ight ( % ) Temperature (oC) PBI PBI-1.2H₃PO₄ PBI-1.7H₃PO₄ PBI-2.1H₃PO₄ PBI-3.0H₃PO₄

The 5% weight loss is at 520 ℃

Mechanical properties of PBI membranes

18.0 23.0 0.31 PBI-3.0H₃PO₄ 16.4 32.6 0.53 PBI-2.1H₃PO₄ 14.6 36.7 0.78 PBI-1.7H₃PO₄ 12.5 46.4 0.95 PBI-1.2H₃PO₄ 11.9 55.0 1.19 PBI Elongation (%) Stress (MPa) Modulus (GPa)

Methanol permeability of PBI membranes

1300 Nafion®117 99 PBI-3.0H₃PO₄ 52 PBI-1.2H₃PO₄ 9.8 PBI Permeabilitya (10-9 cm2/sec)

-6.0

-5.5

-5.0

-4.5

-4.0

-3.5

-3.0

log (

σ

/ S

c

m

-1

)

Nafion117 PBI-3.0H 3PO4 PBI-2.1H 3PO4 PBI-1.7H 3PO4

Proton conductivity of PBI membranes doped with

different amount of phosphoric acid at different

temperatures

Conclusions of our research (1)

{ _{An amorphous, organosoluble fluorine-containing polybenzimidazole (PBI)}

can be synthesized from 3,3’-diaminobenzidine and 2,2-bis(4-carboxyphenyl)-hexafluoropropane.

{ The PBI can be easily dissolved in common organic solvents for the preparation of membranes by solution casting.

{ The PBI membrane has good thermoxidative stability (5% weight loss temperature of the polymer is at 520 ℃) and good mechanical properties.

{ _{The PBI membrane has low methanol permeability (9.8×10}-9 _cm2_{/sec at 6}

wt% methanol).

{ After doping with phosphoric acid, the PBI membranes show higher proton conductivity than Nafion® _{117 membrane at high temperatures (}

Part 2

Synthesis and properties of fluorine-containing

polybenzimidazole/montmorillonite

nanocomposite membranes for direct methanol

fuel cell applications

Organic/Inorganic Hybrid Membranes

For Fuel Cell Application

{

Increase of mechanical properties

{

Improvement of conductivity

{

Improvement of thermal stability

{

_{Increase of water adsorption}

Preparation of Fluorine-Containing

PBI/Clay Nanocomposites for DMFC

{

_{A modified montmorillonite}

_{(m-MMT) was}

incorporated into the organo-soluble,

fluorine-containing PBI. The PBI has good compatibility with

the m-MMT. The high aspect ratio of MMT is

expected to decrease the methanol permeation through

polymer membranes due to a winding diffusion

pathway for methanol.

Modification of Clay

{

_{The modified montmorillonite (m-MMT) was formed}

by a cation exchange reaction between montmorillonite

and an ammonium salt of dodecylamine.

„ RNH₂ + HCl → RNH₃+ _Cl- _{R= CH}

3(CH2)11

XRD patterns of MMT and m-MMT

Intensity

m-MMT MMT 4.89(d=1.8nm) 6.95(d=1.27nm)

WAXD patterns of PBI/m-MMT

nanocomposite membranes

0 4 8 12 16

θ (Degree)

Intensity

PBI PBI/3 wt% m-MMT PBI/5 wt% m-MMT PBI/7 wt% m-MMT 6.28 0

TEM micrographs of PBI/m-MMT

nanocomposites

Mechanical properties of the

PBI/m-MMT nanocomposite membranes

7.8 66.5 1.55 PBI/7 wt% m-MMT 7.9 70.4 1.68 PBI/5 wt% m-MMT 8.0 66.8 1.54 PBI/3 wt% m-MMT 11.9 55.0 1.19 PBI Elongation (%) Stress (MPa) Modulus (GPa)

Mechanical properties of PBI/m-MMT nanocomposite

membranes and phosphoric acid doped PBI/m-MMT

nanocomposite membranes

11.4 ± 2.2 32.4 ± 2.1 0.77 ± 0.05 PBI/7 wt% m-MMT -3.0H₃PO₄ 11.2 ± 1.8 47.3 ± 3.8 0.98 ± 0.07 PBI/5 wt% m-MMT -3.0H₃PO₄ 13.8 ± 0.2 46.2 ± 3.8 0.81 ± 0.01 PBI/3 wt% m-MMT -3.0H₃PO₄ 18.0 ± 1.4 23.0 ± 1.5 0.31 ± 0.02 PBI -3.0H₃PO₄ 7.8 ± 1.2 66.5 ± 5.7 1.55 ± 0.06 PBI/7 wt% m-MMT 7.9 ± 0.6 70.4 ± 4.7 1.68 ± 0.03 PBI/5 wt% m-MMT 8.0 ± 1.5 66.8 ± 3.3 1.54 ± 0.01 PBI/3 wt% m-MMT 11.9 ± 1.9 55.0 ± 4.7 1.19 ± 0.08 PBI Elongation (%) Stress (MPa) Modulus (GPa) 41% increase

Methanol permeability of the PBI/m-MMT

nanocomposite membranes in 6 wt% methanol

aqueous solution at room temperature

0 2 4 6 8 0 10 20 30 40 Methanol permeability (10 -9cm 2/s ec ) 81% decrease

Proton conductivity (σ) of PBI/m-MMT nanocomposite

membranes doped with different amounts of phosphoric acid

at 160

o

C under anhydrous condition

-5.5 -5.0 -4.5 -4.0 lo g ( σ / S c m -1 ) PBI PBI/3 wt% m-MMT PBI/5 wt% m-MMT PBI/7 wt% m-MMT 21~27% decrease

Conclusions of our research (2)

{ The amorphous, fluorine-containing PBI has good compatibility with m-MMT.

{ WAXD and TEM analyses showed that the nano-scaled silicate layers were well dispersed in the PBI matrix up to 5 wt% loading.

{ _{The addition of m-MMT can significantly enhance the mechanical}

properties of the acid-doped PBI membranes.

{ _{The methanol permeability of the PBI/5 wt % m-MMT}

nanocomposite membrane was decreased by approximately 81 % with respect to the pure PBI membrane.

{ The conductivity of the acid-doped PBI/m-MMT nanocomposite membrane was decreased by 21~27 % relative to the acid-doped

Part 3

Synthesis of polybenzimidazole/silica nanocomposite

membranes by sol-gel process for high temperature

proton exchange membrane fuel cells

Sol gel process

Methanol barrier

H5C2 O Si O O O C2H5 C₂H₅ C2H5 H2O HO Si OH OH OH Hydrolysis - H₂O Si O O O Si O Si O Si O O Si O Condensation Si O Si O O O Si Si O O O O Si Si O Si O Si Tetraethyl orthosilicate (TEOS)

The problem of polymer/silica composites

Si O O O Si O Si O Si O O Si O Si O Si O O O Si Si O O O O Si Si O Si O Si

organic

inorganic

phase separation

polymer

silica

bonding agent

Synthesis of PBI copolymers

NH₂ NH₂ H2N H₂N CF₃ CF₃ COOH HOOC + PPA H N N N N H CF₃ CF₃ OH H N N N N H x y OH HOOC COOH + PBI10OH --- x=0.1n, y=0.9n PBI30OH --- x=0.3n, y=0.7n

PBI/silica hybrid materials

IR spectra of PBI copolymers

4000 3000 2000 1000 -(CH₂ )-O C O NH (a) PBI10OH

PBI10OH with bonding agent

T ran s m it tan c e (% ) Wavenumber (cm-1) 4000 3000 2000 1000 -(CH 2 )-O C O NH (b)

PBI30OH with bonding agent PBI30OH Tr a n sm it ta nc e ( % ) Wavenumber (cm-1) H N N N N H CF₃ CF₃ O H N N N N H x y C O N H CH₂ Si 3 OC2H5 OC2H5 OC₂H₅

TEM micrographs of PBI10OH/silica

nanocomposite membranes

PBI10OH/10 wt% Silica

TEM micrographs of PBI30OH/silica

nanocomposite membranes

PBI30OH/10 wt% Silica

Mechanical properties of PBI10OH/Silica

nanocomposite membranes

PBI10OH/15%SiO -25.7 ± 3.1 49.9 ± 3.7 0.84 ± 0.10 PBI10OH/10%SiO₂ -3.0H₃PO₄ 26.2 ± 1.8 48.3 ± 4.8 0.70 ± 0.04 PBI10OH/5%SiO₂ -3.0H3PO4 32 ± 1.3 42.0 ± 6.8 0.55 ± 0.12 PBI10OH-3.0H3PO4 11.4 ± 1.0 90.3 ± 5.8 1.30 ± 0.04 PBI10OH/15%SiO2 11.5 ± 0.6 99.0 ± 6.6 1.37 ± 0.05 PBI10OH/10%SiO2 12.1 ± 0.7 84.2 ± 5.0 1.29 ± 0.07 PBI10OH/5%SiO₂ 13.7 ± 2.5 80.1 ± 5.4 1.17 ± 0.13 PBI10OH

Elongation (%)

Stress (MPa)

Modulus (GPa)

17% increase

Mechanical properties of PBI30OH/silica

nanocomposite membranes

14.8 ± 3.3 51.9 ± 2.7 1.11 ± 0.04 PBI30OH/15wt%SiO₂ -3.0H₃PO₄ 10.9 ± 3.6 57.5 ± 1.3 1.15 ± 0.01 PBI30OH/10wt%SiO2 -3.0H₃PO₄ 20.1 ± 4.7 41.2 ± 1.4 0.88 ± 0.04 PBI30OH/5wt%SiO2 -3.0H₃PO₄ 34.9 ± 4.5 41.4 ± 0.6 0.83 ± 0.06 PBI30OH-3.0H3PO4 8.3 ± 2.1 92.2 ± 5.9 2.15 ± 0.06 PBI30OH/15wt%SiO2 10.8 ± 1.0 113.8 ± 5.0 2.22 ± 0.07 PBI30OH/10wt%SiO2 11.0 ± 0.7 102.7 ± 4.8 1.81 ± 0.09 PBI30OH/5wt%SiO₂ 11.7 ± 1.5 89.8 ± 4.8 1.62 ± 0.12 PBI30OH Elongation (%) Stress (MPa) Modulus (GPa) 37% increase

Mechanical properties of PBI30OH/silica

nanocomposite membranes

8.3 ± 2.1 92.2 ± 5.9 2.15 ± 0.06 PBI30OH/15 wt% SiO 10.8 ± 1.0 113.8 ± 5.0 2.22 ± 0.07 PBI30OH/10 wt% SiO₂ 9.5 ± 1.7 84.4 ± 5.9 1.80 ± 0.13 PBI30OH/10 wt% SiO₂

(without bonding agent)

11.0 ± 0.7 102.7 ± 4.8 1.81 ± 0.09 PBI30OH/5 wt% SiO₂ 11.7 ± 1.5 89.8 ± 4.8 1.62 ± 0.12 PBI30OH Elongation (%) Stress (MPa) Modulus (GPa) 11% increase 37% increase

Methanol permeability of PBI copolymer/silica

nanocomposite membranes in 6 wt% methanol

aqueous solution at room temperature.

0 4 8 12 16 1 1.5 2 2.5 3 PBI30OH/SiO2 PBI10OH/SiO2 Methanol permeability (10 -8cm 2/sec) SiO content (wt%) 58 % decrease 39 % decrease

Proton conductivity (

σ

) of PBI30OH/Silica

nanocomposite membranes doped with different amounts

of phosphoric acid at 160 ℃ under anhydrous condition.

2.0 2.2 2.4 2.6 2.8 3.0 3.2 -5.75 -5.50 -5.25 -5.00 -4.75 -4.50 -4.25 -4.00 log ( σ / S c m -1 ) PBI30OH PBI30OH/5 wt% SiO₂ PBI30OH/10 wt% SiO₂ PBI30OH/15 wt% SiO₂ 22~28% decrease

Conclusions of our research (3)

{ The PBI copolymer with a bonding agent had good compatibility with silica.

{ TEM analyses showed that nano-scaled silica particles were dispersed in the PBI copolymer matrix and particle size decreased with the increase of hydroxy group in PBI chain.

{ _{The tensile modulus of PBI30OH/10 wt % silica nanocomposite}

membranes had a 37 % increase compared to the pure PBI30OH films.

{ _{The methanol permeability of the PBI30OH/10 wt % silica}

nanocomposite films had a 58 % decrease relative to the pure PBI 30OH membranes.