Transcript Slide 1

‘Direct’ alcohol fuel cells:
Eocell (V)
6n e–
n = 1 [MeOH]
n = 2 [EtOH]
6n H+; H2O
n CO2,(g)
3n H2O
CnH2n+1OH
(3n/2) O2
CnH2n+1OH + (2n – 1) H2O
Anode (-)
PEM: proton exchange membrane
PEM
Cathode (+)
1.20
1.14
‘Direct’ borohydride fuel cell:
Eocell (V)
8e-
NaBO2 + 6H2O
4H2,(g)
1.64
8 Na+; H2O
H2O
8NaOH
NaBH4 + 2H2O
2O2
NaBH4 + 8NaOH
Anode (-)
PEM: proton exchange membrane
PEM
Cathode (+)
Highlights of direct fuel cells
 Advantages
 Ethanol and methanol are primary liquid fuels obtainable from
renewable, agricultural, resources: sustainable energy
 Canada is a leader in both ethanol (~240 million liters
annually from agricultural resources) and methanol production
(Methanex)
 The borohydride fuel cell (DBFC) is a zero-carbon emission
power source
 Higher theoretical energy densities compared to H2:
H2-O2 fuel cell: 550 kWh m-3H2 (at 200 atm, 293 K)
– DMFC 4,800 kWh m-3 CH3OH
– DEFC 6,300 kWh m-3 C2H5OH
– DBFC 2,000 kWh m-3 (20% wt NaBH4 in 2 M NaOH)
Disadvantages

Poor anode performance




Problems to be solved
Sluggish fuel electro-oxidation kinetics / electrocatalysis
– CH3OH oxidation: Pt-Ru
– C2H5OH oxidation: Pt-Sn
– NaBH4 oxidation: Au, Pt, Metal-Hydrides
– Effect of catalyst composition, operating conditions
Low catalyst layer utilization efficiency
– Catalyst preparation method
particle size
dispersion on
and interaction with various supports
ionomer network /
catalyst interface
Two-phase flow in the porous anode
– For alcohol fuel cells: CO2 disengagement from the catalyst layer
mass transfer overpotential and effective ionic conductivity
Fuel crossover from the anode to the cathode
 Membrane permeable to alcohols
mixed potential on the cathode
Research strategy
Colloidal
precursor method
Liquid crystal
templated
/surfactant
assisted
electrodep.
Nano-scale
electrocatalyst
synthesis and
deposition on
substrates
Electrodeposition from
microemulsions and
micellar media
Surface analytical
studies:
- surface area,
composition etc.
Evaluation of
electro-catalytic
activity
Electrochemical
methods:
Voltammetry, impedance,
chrono-techniques
Cell Design
variables
Fuel cell
testing and
optimization
Operating
conditions
Typical gas diffusion anode structure for direct fuel cells:
Might not be the best engineering solution we are looking at alternatives
~ 100 – 300 m
~ 5 – 25 m
CO2,(g)
H 2O
H+; H2O;
R-OH
C
A
T
H
O
D
Na+; H2O; E
NaBO2, H2,(g)
CH3OH, C2H5OH
O2
~BH4-
NaBH4
Carbon fiber
diffusion layer
Catalyst layer Ionomer
(e.g. proton exchange
membrane)
Acknowledgement
 NSERC
 Discovery Grant
 Equipment Grant
 BC ASI
 Provincial Research Fellow
 WED / CFI
 Auto 21
 Industrial collaborations
 Consultant for: Vizon Sci Tech. (2002-2003)
Colgate-Palmolive USA (2005)
Tekion (2006-2007)