section 12scsc

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12. The Direct Methanol Fuel Cell



Use of hydrogen as fuel for transport has severe weight penalty.

Methanol has comparable energy density to petrol, (6 cf . 14

kWh kg-1)

DMFC (1)



Schematic of a Direct Methanol Fuel Cell

As opposed to ‘Indirect’ where methanol is reformed to H2:

CH3OH + H2O CO2 + 3H2

DMFC (2)



In the DMFC Methanol is oxidized directly at the anode (as

opposed to H2 as in the PEMFC).

High energy density.

Liquid CH3OH is preferred over vapour due to the

simplicity of design offered; existing liquid fuel distributionnetwork.

CH3OH is considered by some of have lower market entry

barriers than H2 (eg . less explosive).

Cheap and easy to manufacture.

Low temperature operation – N2 does not burn so no NOx.

DMFC (3)



Cell Reactions

Anode: CH3OH(l) + H2O → 6e- + 6H+ + CO2(g) E0 = 0.046V

PtRu catalyst

Cathode: 1.5 O2(g) + 6e- → 3H2O(l) E0 = 1.23V

Pt catalyst

Overall: CH3OH(l) + 1.5 O2(g) → 3H2O(l) + CO2(g)

(E°=1.2 V, 90°C)

DMFC (5)



CH3OH CH2OH x CHOH

xx COH xxx

CH2O CHO x CO

x (COL)

HCOOH COOH x

CO2 The mechanism of methanol electro-oxidation at Pt. From V. S. Bagotzky, Yu.

B. Vassilyev and O. A. Khazova, J. Electroanal. Chem., 81 (1977) 229.

DMFC (6)



DMFC’s are usually based on porous carbon electrodes and the construction of

the fuel cells is very similar to that of the PEMFC, differing primarily in the

pattern and depth of the flow channels of the bipolar plates.

DMFC (7)



The structure of Gas Diffusion Electrodes (GDE’s)

(Porous carbon area up to 1000 m2 g-1)

FlowField

GasDiffusion

Layer

Catalyst Layer

Gases:Wettability

Flooding/conductivity

3-phase interface

DMFC (8)



Schematic of an experimental vapour-fed single cell DMFC showing the component

parts.

DMFC (9)



0 50 100 150 200 250

0.0

0.2

0.4

0.6

0.8

1.0

DMFC

PEMFC

C e l l v o l t a g e / V

Current density /mA cm-2

Typical ‘good’ polarisation curves for DMFC and PEMFC operating with

ambient air at 60 ºC & 90 ºC, respectively.

DMFC (10)



11

The Polymer Electrolyte Membrane employed (Nafion) is

permeable to methanol.

Methanol reacts at cathode (as well as O2) lowering the cathode

potential and hence the cell voltage- BIG problem. Also swellsNafion.

Consequently, major research effort on methanol-tolerant cathode

catalysts for the DMFC.

DMFC (11)



12

Catalysts for Oxygen Reduction (Cathode)

Ruthenium-based chalcogenides

(RhRuxSy , RuSe, etc )

Transition metal macrocycles

(mostly porphyrins and phthalocyanines)

Pt and its alloys with different transition metals

Other noble metals such as Pd and Au

DMFC (12)



13

In Newcastle:

Catalysts based on Chevrel phase chalcogenides MxM’6-xX8, M,

M’ = Mo, Ru, Re etc, X = S, Se or Te

MoxRuySz (MoV), RhxRuySz (RhV) and RexRuySz (ReV) dispersed

on porous carbon.

DMFC (13)



14

For the first time could measure methanol crossover directly!

DMFC (14)



15

Effect of anode methanol feed concentration and cathode loading on the

performance of a liquid-feed DMFC operating at 90°C with ambient pressure

oxygen. All anodes: Pt – Ru (1:1); 2 mg Pt cm2 (60 wt % on Vulcan XC-72R).

Pt cathodes 0.75 mg cm-2,

2M & 4M methanol

RhRu5.9S4.7

2M & 4M methanol,

0.75 mg cm-2

RhRu5.9S4.7

4M methanol,

1.5 mg cm-2

4M

2M

DMFC (15)



16

Effect of oxidant pressure on the power characteristics of a liquid-feed DMFC operating

at 90 C with 4 M methanol feed. Anode E-TEK PtRu, 60 w/o on XC-72, 2 mg cm-2 Pt.

Cathode = 1.5 mg cm-2 Rh2

Ru11.8

S9.4

, 60 w/o Ketjen 600 or 0.75 mg cm-2 Pt, 60 w/o XC-

72.

0 100 200 300 400

0

10

20

30

40

50

0.5 barg air

0.1 barg O2

0.5 barg O2

Pt, (Atm. O2)

P o w e r d e n s i t y / m W

c m - 2

Current density /mA cm-2

Rh2Ru11.8S9.4

DMFC (16)

C (1 )



17

Catalysts highly active and selective.

Also – an added benefit – do not oxidize methanol so

methanol permeation across Nafion membrane can be

measured via GLC.

DMFC (17)

DMFC (18)



18

• GCD Chromatograph (Pye Unicam) incorporating a flame ionizer

detector and a Shimadzu Chromatopac C-E1B integrator.

•Analysis was carried out on exhausts sampled from both Pt and sulfidecathode-based MEAs over a range of cell operating and polarization

conditions.

• Each sample was mixed with a 2% n -propan-1-ol internal standard in

order to normalize the signals, and then compared with a curve obtained

from a range of methanol standards.

DMFC (18)

DMFC (19)



19

Effect of current density and anode methanol feed concentration on the

concentration of methanol in the cathode exhausts of: MEA-Pt (∆, 2 M; ▲, 4

M); MEA-MoV (◊, 2 M; , 4 M); MEA-ReV (*, 2 M). Cell operated with

ambient pressure oxygen.

Pt

2M MeOH MoV

4M MeOH MoV

2M MeOH ReV

DMFC (19)

DMFC (20)



DMFC problems

• 60 – 100 C = Low temperature- poor kinetics atanode and cathode-much lower power density than

H2/O2.

•Needs Ru co-catalyst- Pt poisons otherwise.

• Methanol cross over through membrane to

cathode, Pt active for methanol oxidation, hence

mixed potential.

• Durability: membrane, agglomeration of Pt…

DMFC (20)

F l ll f t



Ballard Power Systems, Inc.: Canada based, global leader in PEM

(proton exchange membrane) fuel cell technology. Back up power,Distributed Generation, Vehicles (bus, material handling trucks)

http://www.ballard.com/files/PDF/ProductPortfolio.pdf

Intelligent Energy: UK based, H2

fuel cells. Aerospace, Military,

Motive systems. http://www.intelligent-energy.com/

Fuel cell manufacturers

F l ll li ti


http://www.intelligent-energy.com/







Fuel Cell Applications

Transportation and Automotive Industry

Fords Adavanced Focus FCV

(2002)

fuel cell battery hybrid

85 kW PEM

~50 mpg (equivalent)

4 kg of compressed H2 @ 5000psi

Car companies: GM, Honda, Daimler-Chrysler, Mitsubishi etc.

2011 buses running on route RV1

between Covent Garden and Tower

Gateway Station, London

Submarine Typ 212 in Docks at HDW/Kiel (Germany).

Fuel cell applications

F el cell applications



Stationary Power Supply Units

Fuel Cell Applications

More than 2500 stationary fuel cell systems

have been installed all over the world In

large-scale building systems,

A fuel cell installed at McDonald’s restaurant,Long Island

HotModule System

installed at theUniversity Hospital

in Magdeburg

• Molten Carbonate

Fuel Cell: MCFC

• 342 Cells, 250 kW

Electrical Power

• ca. 48% Electrical

Efficiency

• Feed Gas: NaturalGas

• Size (L x W x H): 7,3

m x 2,5 m x 3,2 m

• Mass 15 t

Residential Power Units

Plug Power 7000 unit cost $5000 - $10 000.

Fuel cell applications

Portable applications



Fuel Cell Applications Portable applications

• portable appliances and power tools

• small personal vehicles

• Consumer electronics like laptops, mobile phones

• Backup power

Toshiba fuel cell charger 2009

Fujitsu fuel cell powered

laptop. The methanol

powered laptop has a batterylife of 8 to 10 hours

http://pr.fujitsu.com/jp/news/2004/01/26-1.html

http://pr.fujitsu.com/jp/news/2004/01/26-1.html

section 12scsc

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