2. WhatareFuelCells?
Devices that convert chemical
potential energy into
electrical energy
• Characterized by type of
electrolyte used
• Reactions at electrodes
• Electrolytes carry charged
particles
• Catalysts speed reactions
• Electrical current directed
out of fuel cell (FC)
K. Tran, T. Nguyen, A. Bartrom, A. Sadiki and J. Haan, "A Fuel-Flexible Alkaline
Direct Liquid Fuel Cell", Fuel Cells, vol. 14, no. 6, pp. 834-841, 2014.
3. PreviousWork
Y-shaped paper-based
microfluidic fuel cells (MFCs)
But…
they’refragile.
Advantages:
• Capillary action means no
need for external pump
= inexpensive to make
• Easy to fabricate
• Environmentally friendly
Disadvantages:
• Wet paper tears easily
• 1.5 hours+ for optimal values
• 0.6-0.8 mA, rarely 1mA
• 0.8-1 V
• Low current
4. WhyCottonandPolyester?
Have the highest wicking rates
and is most commonly found
M. Reches, K. Mirica, R. Dasgupta, M. Dickey, M. Butte and G.
Whitesides, "Thread as a Matrix for Biomedical Assays", ACS
Appl. Mater. Interfaces, vol. 2, no. 6, pp. 1722-1728, 2010.
Whylaminate?
Lamination was shown to
increase fluid flow speed
laminated
non-laminated
5. • Two-strip stacked design. Each
strip carries its own anolyte and
catholyte streams.
• Plastic wrap barrier
• Thermally laminated at 120°C
with laminating sheets
NewPlatformDesign
Front, side, and back views
Active area
6. Materials Tested:
100% Cotton:
• Shoelace
• Flannel
• Canvas
Cotton-Poly Blend:
• 60-40 cotton-poly knit
• 65-35 cotton-poly shoelace
Experiment Details
Anode
Fuel: 5M HCOOH
Catalyst: Pd/C
Cathode
Fuel: 30% H2O2
Catalyst: Active Carbon
Current Collectors
Silver epoxy & steel mesh
Anode Reaction (Oxidation)
Cathode Reaction (Reduction)
T. Copenhaver, K. Purohit, K. Domalaon, P. Linda, B. Burgess, N. Manorothkul, V. Galvan, S. Sotez, F. Gomez and J.
Haan, "A microfluidic direct formate fuel cell on paper", Electrophoresis, vol. 36, no. 16, pp. 1825–1829, 2015.
(Left) 60C-40P Knit.
(Middle, Top to Bottom) 100C Canvas,
65C-45P Shoelace, 100C Shoelace.
(Right) 100C Flannel
7. 0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0
0.2
0.4
0.6
0.8
1
1.2
0 2 4 6 8 10
PowerDensity(mW/cm2)
Potential(V)
Current Density (mA/cm2)
100% Cotton
(CD 3.1.2) canvas (PD 3.1.2) canvas (CD 4.4) flannel
(PD 4.4) flannel (CD 1.3.3) shoelace (PD 1.3.3) shoelace
shoelace
• Highest CD and PD
shoelaces
• Highest potential
flannel
• High SD due to amount of fuel
at inlets, and fuel crossover
100% Cotton
Current Density
(mA/cm2)
Power Density
(mW/cm2)
Potential
(V)
shoelace
AVG 9.43 1.35 0.62
SD 1.96 0.44 0.15
flannel
AVG 4.68 0.99 0.98
SD 3.13 0.55 0.09
canvas
AVG 0.11 0.02 0.63
SD 0.14 0.03 0.43
Results
100% Cotton
flannel
canvas
*Graph is from one test and was selected
based on how best it reflected average
values. For illustration purposes only
8. Applications
Two in Series
Two 100% cotton
shoelace FCs producing
1.9V at 1mA powers:
• 1 red LED
• 1 yellow LED
• Handheld
calculator
9. Applications
Four in Series
Four 100% cotton shoelace FCs
producing 3.2 V at 0.9 mA powers:
• 1 red, yellow, blue, pink, green,
and white LED individually
10. 0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0
0.2
0.4
0.6
0.8
1
1.2
0 5 10 15 20 25
PowerDensity(mW/cm2)
Poential(V) Current Density (mA/cm2)
Cotton Polyester Blends
(CD 3.3) shoelace (CD 3.1) knit (PD 3.3) shoelace (PD 3.1) knit
•Highest CD and PD
shoelaces
• Highest potential
shoelaces
• High SD due to amount of
fuel at inlets, and fuel
crossover
Cotton-Poly
Blends
Current Density
(mA/cm2)
Power Density
(mW/cm2)
Potential
(V)
knit
AVG 5.45 1.24 0.95
SD 1.95 0.34 0.04
shoelace
AVG 15.18 2.75 0.67
SD 8.50 2.00 0.25
shoelace
knit
Results
Cotton-Polyester Blends
*Graph is from one test and was selected
based on how best it reflected average
values. For illustration purposes only
11. 0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0
0.2
0.4
0.6
0.8
1
1.2
0 5 10 15 20 25
PowerDensity(mW/cm2)
Poential(V)
Current Density (mA/cm2)
100C and Cotton-Poly Blend
(CD 3.1.2) 100C canvas (PD 3.1.2) 100C canvas (CD 4.4) 100C flannel
(CD 1.3.3) 100C shoelace (CD 3.3) 65C-35P shoelace (CD 3.1) 60C-40P knit
(PD 4.4) 100C flannel (PD 1.3.3) 100C shoelace (PD 3.3) 65C-35P shoelace
(PD 3.1) 60C-40P knit
Results
Overall
100C
shoelace
• Highest CD
65C-35P shoelace
at 15.18 mA/cm2
• Highest PD
65C-35P shoelace
at 2.75 mW/cm2
• Highest potential
100C flannel at 0.98 V
*Graph is from one test and was selected
based on how best it reflected average
values. For illustration purposes only
65C-35P
shoelace
12. Conclusion
> Additional tests needs to be performed with more materials. For future
work, other barriers, the material’s weaving and thickness, the FC’s size and
active area size will need to be further investigated to optimize this FC.
• No FC’s were torn
• Material’s thickness and weave are
also important parameters –
shoelace type works best
• Introduction of lamination + new
materials found cotton-poly
shoelace to be better than paper FC
Max PD
(mW/cm2)
Max CD
(mA/cm2)
Y-shaped
paper FC
2.53 11.50
65C-35P
shoelace
2.75 15.18
+8.7% +32.0%
Let’s start out with what fuel cells are. Fuel cells are devices that converts chemical potential energy (energy stored in molecular bonds) into electrical energy. There are many types of fuel cells, and mainly they are characterized by the type of electrolyte they use. The figure shown on the right is an alkaline direct liquid fuel cell, which is the kind that this research focuses on. Oxidation and reduction occurs on the electrodes, the anode and cathode, and is sped up by catalysts. As hydroxide crosses the anion exchange membrane from cathode to anode, it completes the circuit. The electrical current that has been directed out of the fuel cell can be used to power applications.
On our previous work, we worked with paper based microfluidic fuel cells, or paper MFCs. Because paper has the ability to facilitate laminar flow with capillary action, it eliminates the need to have an external pump, which lowers the fuel cell’s overall costs. It’s environmentally friendly, and inexpensive and easy to make compared to traditional fuel cells.
As shown in the picture here, We previously examined these Y-shaped fuel cells that were fabricated with chromatography paper as the platform. Fuel flows from these inlets to react with the catalysts at the electrodes to produce the electrical energy, which is collected with steel mesh and silvery epoxy. However, with these paper MFCs, they were very fragile because wet paper rips easily. Also, these FC’s produced low current—it rarely reached 1 milli amp.
Therefore, the objective was to design a new platform to mitigate these issues. To increase durability and current, two things were done to the MFC: lamination was introduced, and paper was changed to cotton-polyester blend fabrics.
So why laminate? Not only would laminating increase durability, but in a preliminary test comparing a laminated and non-laminated strip of cotton fabric as shown here, it was observed that the fuel flowed faster in the laminated strip due to the increased surface contact. Because this means that more fuel can be brought to the catalyst, which it would help increase the MFC’s current as the reaction is sped up.
So why cotton and polyester? Fabrics were chosen as an alternative to paper because they are more durable, and also some of them can demonstrate capillary action. Cotton and polyester were one of the types that had the highest wicking rate, and their blends are more common to find.
In this new design, small strips of material are stacked with plastic wrap in between as the membrane, so that each strip carries its own anolyte and catholyte streams that reacts with at its respective electrodes. The stack is laminated at 120°C with thermal laminating sheets. Afterwards, the current collector and catalyst is added on. Over here is the active area which the catalyst reacts with the fuel.
For the experiment, we used 5M formate and Pd/C for the anode fuel and catalysts, and 30% hydrogen peroxide and active carbon for the cathode fuel and catalyst. The oxidation and reduction reactions on the anode and cathode are shown as the following. Five different materials were tested—shoelace, flannel, and canvas that were all 100% cotton, and 60-40 knit and 65-35 shoelace that were cotton polyester blends.
The data is obtained about 1 hour into the run.
The results compiled here are averages between two FCs from the same material, in which each FC was tested three times.
It is then graphed, with the potential and power density plotted with respect to current density.
The densities are taken with respect to the active area’s size.
In comparison with the three materials that were made with 100% cotton, the shoelace had the highest CD and PD, however, the flannel had the highest potential. The high standard deviation found in current density is due to fuel crossing over, and also the fact that some materials were more sensitive to the amount of fuel at the inlets. For instance, there were times when shoelace performed better with more fuel, but also sometimes the values fluctuated greatly with more fuels.
This is a graph to just give an idea on the difference between the performances of the materials. How you read this graph, is that the highest point on this curve (parabola) tells you the power density which is read from this axis, and where the curve ends at the horizontal axis tells you the current density, and following this line to intersect the axis here tells you the potential.
With two 100% cotton shoelaces connected together in series, which means each FC voltage adds up, it produces 1.9V at about 1mA. It powers a red and yellow LED light, and a handheld calculator.
With two more of the cotton FC’s added to the series, the total voltage now increased to 3.2V. With this higher number, it can power more LED colors.
In comparison with the two materials that were made with cotton-polyester blends, the shoelace also had the highest power and current density, but the knit had the highest potential. As shown here on the graph,
Over all, between the 5 materials, the shoelaces had the highest power and current density in both 100% cotton and cotton-polyester blends. The highest potentials were still the flannel and knit, and the 100%C was the worst overall.
In conclusion, no FC’s ripped in these experiments. However, we did come to realize that the material’s thickness and how it’s woven also affects the performance of the fuel cell, and perhaps these parameters are just as important (if not more) than the actual composition of the fabric. The shoelace-type was found to work best.
With the introduction of lamination, and the substitute of paper with fabrics, we found a design that succeeded the previous Y shaped paper fuel cells, and that is with the cotton poly shoelace. Its power density was greater by about 109 percent, and current density was greater by about 132 percent. Additional test needs to be performed with more materials because some of these FC’s are still inconsistent. For future work, other barriers, the fabric’s weaving, and the fuel cell’s size and active area's size, will need to be further investigated to optimize this fuel cell.
