Leah Douglas1,3, Michael Bright1, Doug Aaron1, Alexander B. Papandrew1, and Thomas A. Zawodzinski, Jr.1,2
1Department
of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, TN
2Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN
³The University of Memphis, Memphis, TN
OBJECTIVE The
objective of this experiment was to increase electrode
surface area and reduce the contact resistance between the membrane and
the electrode. This was done by attaching a microporous electrode directly to
the membrane. Variations of carbon inks, amounts of ink and types of carbon
paper were considered in this effort.
Flow batteries are a potential technology for energy storage
because they allow for large amounts of energy to be stored and flexibility in
size. Energy and power capacity can be independently scaled. One type of
flow battery is the vanadium redox battery (VRB). An advantage of the VRB is
that crossover only results in loss of charge, not cross contamination and all
charge is stored in the electrolyte.
MOTIVATION
Cathode
Anode
1.8
IR-FreePotential(V)
Membrane
Graphite Plate
Gold Current Collector
• Electrolyte: 2M vanadium in 5M
SO⁴⁻
• Flow rate: 20mL/min
• Potentiostat: Biologic HCP-803
up to 80 amps
• Membrane: N117 for thickness
• Carbon paper electrodes (SGL
group)
Electrode Mass
6.8 mg (5 layer), 17.4 mg (10 layer)
Carbon:Ionomer
2:1 C:I, 50:1 C:I
Carbon Paper
5% treated, untreated, none
• 2:1 C:I composition
• N117 membrane
• No carbon paper present
1.6
1.4
1.2
1
0.8
0.6
2:1,5layer,ncp
2:1,10layer,ncp
0.4
0.2
0
0
50
100
150
200
Current(mA/cm²)
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
correct
raw
0
100
200
300
400
Current flowing in electrochemical cells experiences intrinsic resistance (iR).
To correct for this resistance, the high frequency resistance (HFR) is found
Finding the areal specific resistance (ASR) allows for the calculation of an iRfree polarization curve. This is done by taking the HFR and multiplying it with
the area of the membrane.
Electrode: 5 layers, 50:1 C:I ink
Electrode: 10 layers, 2:1 C:I ink
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
50:1 C:I
2:1 C:I
0
100
200
300
• 10 layer decal
• 2:1 C:I composition
• N117 membrane
1.6
1.4
1.2
1
0.8
0.6
0.4
Untreated carbon paper
5% PTFE
No Carbon Paper
0.2
0
0
50
100
150
200
250
300
Current (mA/cm²)
Different layers of ink were tested to see if, by adding more ink, performance would
improve. Increased electrode surface area could result in better performance.
However, the thicker electrode did not exhibit better performance.
Potential (V)
Cell Potential (V)
Polarization curves allow for the determination of the dominant loss mechanisms in a battery.
Activation loss is the result of slow reaction kinetics at low current. Ohmic loss is attributed to
charge transport in the battery. Mass transport limitation is the inability to increase rate of
electrolyte delivery to match increase in current.
1.8
IR-Free Potential (V)
Setup
Electrode Configuration
400
Current (mA/cm²)
Different compositions of carbon and ionomer ink were considered. The goal
here was to increase electrode surface area and improve the electrical
conductivity of the electrode.
Different types of carbon paper were tested to determine the effect on the
battery. There was no discernable difference between the different carbon
papers .
Summary
• Increased carbon content in the electrode
resulted in improved performance.
• No great performance improvement was observed
when doubling the number of layers of ink used to
make the electrodes.
• Wet-proofed carbon paper performed similarly to
non-wet-proofed carbon paper.
• Lack of carbon paper resulted in noticeably
greater activation loss.
Acknowledments to NSF grant #1004083 for making this research possible.