Microfluidic fuel cells
Jin Xuan, Ph.D.
Assistant Professor
School of Engineering and Physical Sciences
Heriot-Watt University, Edinburg, U.K.
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Outline
•  Introduction
•  Our research on microfluidic fuel cells
–  Principle understanding
–  Modeling
–  Experiment
•  Conclusions
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Microfluidics
• All flow is laminar
• Surface tension becomes significant
• Little inertia effects
• Apparent viscosity increases
• Gradient increases
• S/V ratio increases
q  Application of microfluidics in chemical industry
Intensification
Picture Source: Bayer microreactors New function
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Fuel cells
an important role in low-carbon energy economy
v
High overall efficiency
45%～60% v.s. 30%～40% for nuclear &
thermal systems.
v
Low environmental impacts
Quiet operation; Ultra-low emissions of SOx,
NOx and CO2.
v
Fuel diversity
Fuels such as oil, natural gas, alcohols, and
biomass-derived fuels are applicable.
v
Wide-range power supplies
Power supplies at different scales from
MEMS to a whole city.
Energy efficiency comparison by www.fuelcells.org.au Fuel cell power generation
is regarded as a 4th
generation technology
following thermal, nuclear
and hydraulic power.
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The membrane
Membrane: 40% cost
Low catalytic efficiency
Membrane: acid preferred
High overpotential
Membrane: 40% voltage loss
Hard in miniaturization
MEA structure
Reason
Bottleneck
High cost
High cost
Water
management
Fuel
crossover
Membrane
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Membraneless fuel cells?
v
Conventional fuel cell Fuel
Anode
H+
PEM
Cathode
Oxidant
v
M
E
A
PEM functions
•  To separate fuel and oxidant
•  To maintain a good ionic
conductivity
M2FC Fuel
w
How to be membraneless?
•  Laminar nature of micro flows
•  Naturally separates the reactant
streams
•  Keeps a good ionic conductivity
Oxidant
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Basic cell structure
J Power Sources 2013; 231: 1 Distinctly Global
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Fluid-fluid interface:
the virtual membrane
Ø  The interface is the key to the success of MFC
Ø  Investigation techniques developed in our lab:
Numerical modeling
Fluoresce microscope
Laser confocal
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Understanding and controlling the
crossover
v
2012: Fuel crossover and
parasitic current successfully
predicted
v
Developed and Integrated
mixed potential theory
v
2013: Nonlinear transport
characteristics at the interface
successfully predicted
v
Adopting Maxwell–Stefan law
Applied Energy 2012; 90: 87 Applied Energy 2013; 112: 1131. Distinctly Global
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Focusing the reactants
•  A qualitative leap: fuel utilization and
current density be simultaneously
enhanced;
•  After optimization: I > 100 mA cm-2 with FU
> 50%, un-optimized value: FU = 5-8 %.
Int J Hydrogen Energy 2011; 36: 11075 Distinctly Global
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In-situ visualization of temperature
distribution
(a) 31 30 29 28 27 26 25 24
H& electrode
Anolyte
1000 µμm
(b)
0 mA/cm&
20 mA/cm&
40 mA/cm&
60 mA/cm&
80 mA/cm&
100 mA/cm&
0 mA/cm&
20 mA/cm&
40 mA/cm&
60 mA/cm&
80 mA/cm&
100 mA/cm&
(c)
Catholyte
O& electrode
(d)
200 µL/min
500 µL/min
800 µL/min
1100 µL/min
1400 µL/min
1700 µL/min
2000 µL/min
2300 µL/min
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Design and prototyping
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Prototypes in our lab (1)
Microfluidic fuel cell
density by 3 times
environmental
compatibility
v
Applications ranging from
on-chip power to EVs
0
0
50
J / mA cm-2
100
1.8
0
20
15
Cell voltage / V
operation, low cost, good
5
0
E / V vs. Ag/AgCl(satd)
Room-temperature
MAlAFC in literature 0.6
•  Increases the current
density by 5 times
v
10
1.2
-0.6
Cathode
10
0.6
-1.2
Anode
-1.8
0
50 cm-2
J / mA
5
0
100
P / mW cm-2
1.2
•  Increases the power
P / mW cm-2
New cell architecture
15
Cell voltage / V
v
1.8
0
0
60
J / mA cm-2
120
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Prototypes in our lab (2)
An integrated fuel processor & fuel cell system
v
Simple & cheap fuel cell system integrated with Al-based H2 generator
v
H2 conversion yield up to 96.2%
v
Electrochemical performance comparable to the M2FC system fed with
compressed H2 in a gas cylinder
v
The M2FC performed stably until Al was consumed up
Prototype of 36188 mAh
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245th ACS MeeNng, New Orleans, 2013 www.hw.ac.uk
Prototypes in our lab (3)
Microfluidic CO2 reduction cell
v
v
CFD analyses Proof-of-concept prototype
CFD analyses of transport and reactions
Calculated efficiency D ua l
A c id
A lk a li
350
250
200
C e ll P ote ntia l (V )
-­‐2
C urre nt de ns ity (m A c m )
300
150
100
50
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
D ua l C a thode
D ua l A node
A c id C a thode
A c id A node
A lk a li C a thode
A lk a li A node
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
-­‐0.2
-­‐0.4
-­‐0.6
-­‐0.8
-­‐1.0
-­‐1.2
-­‐1.4
-­‐1.6
C e ll pote ntia l (V )
Applied Energy 2013, 102, 1057. 0
50
100
150
200
250
-­‐2
C urre nt de ns ity (m A c m )
300
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Scale-out the MFC
16-­‐cell sStack
tack prototype
Ø  Control methods
q Pressure redistribution
q Local current blocking
Ø  Significantly reduced
scale-out losses
Ø  Stack efficiency > 90%
US Provisional Patent 61886413;
Electrochimica Acta, 2014, 135:467
Efficiency over 90%
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Summary
•  Microfluidic fuel cell is an alternative cell type
without the need of a membrane
•  The L-L interface is the key to the success of
MFC. Both model and experiment are conducted
to understand and optimize it.
•  MFC appears to be a promising power source
for portable electronic devices.
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Our recent book
Micro & Nano-­‐Engineering of Fuel Cells Series: Sustainable Energy Developments Published: July 15, 2014 by CRC Press Editors: D.Y.C. Leung, Jin Xuan hYp://www.crcpress.com/product/isbn/9780415644396 Features
q  First book focused on the micro and nanoscale engineering science of fuel cells
q  Comprehensive introduction to general engineering principles applied to various
fuel cell types
q  Both theoretical and practical approach
q  Contributors are leading experts and researchers in their field
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Thanks very much
You are welcome to contact us via
Dr. Jin Xuan
Email: j.xuan@hw.ac.uk
School of Engineering and Physical Sciences
Heriot-Watt University, Edinburg, EH14 4AS
United Kingdom
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