3. Overview
• This research project sought to understand how well Birnessite can reduce NOx
electrocatalytically in a solution of NaNO3.
• The samples were first prepared by depositing MnOx on Fluorine-doped tin oxide (FTO)
substrates.
• A potentiostat was then used to apply a current to the cell containing the Birnessite
electrode to observe the amount of reduction occurring
• The results were then compared to that of platinum tin oxide substrates (PTO), which is
already known to reduce some amount of nitrate.
4. Anode Sample Preparation
• The samples were prepared following the same procedure as a paper in The Journal of
Physical Chemistry.
• Pinaud, Blaise A., et al. “Thin Films of Sodium Birnessite-Type MnO2: Optical Properties, Electronic
Band Structure, and Solar Photoelectrochemistry.” The Journal of Physical Chemistry C, vol. 115,
no. 23, 2011, pp. 11830–11838., doi:10.1021/jp200015p
Materials:
- 3D printed cell
- FTO glass
- Graphite counter electrode
- Ag/AgCl reference electrode
Equipment:
- Ultrasonic Cleaner
Solution
- 0.002 M MnSO4
- 0.05 M NaClO4
Process:
• Fluorine-doped tin oxide (FTO) substrates on glass supports were ultrasonically
cleaned.
• Na birnessite-type MnO2 films were prepared by potentiostatic electrodeposition.
• Cyclic voltammetry (CV) technique used:
• Cycled from {-1.0 V to 1.0 V} vs Ag/AgCl
• The number of cycles was arbitrarily chosen – Typically, as the scan rate
increased, more cycles were implemented.
5. Experimental Procedure
• The prepared samples were tested
in a solution of 0.01 M NaNO3 and
0.1 M NaOH
• The set-up, shown in the picture,
includes the cell and the 3
electrodes (working, counter,
reference).
• Two tests were completed with the
same set-up, but the first test
included the sodium nitrate from the
start, whereas the second test
exhibited the addition of sodium
nitrate after an arbitrary number of
cycles carried out in sodium
hydroxide. Test 2 was also
evacuated using argon to avoid
oxidation of O2
7. -10.00
-5.00
0.00
5.00
10.00
15.00
-1.00 -0.80 -0.60 -0.40 -0.20 0.00 0.20 0.40 0.60 0.80 1.00
<I>/mA
Ewe/V vs. Ag/AgCl
Test 1: Nitrate Reduction of Birnessite-type MnOx
PTO Sample a MnOx_FTO Sample a MnOx_FTO Sample b
Not much reduction has occurred for the Birnessite samples compared to PTO
Test 1
8. -1.20
-1.00
-0.80
-0.60
-0.40
-0.20
0.00
0.20
0.40
0.60
0.80
1.00
-1.00 -0.50 0.00 0.50 1.00
<I>/mA
Ewe/V vs. Ag/AgCl
Nitrate Reduction by Birnessite-type MnOx
Before Addition of nitrate
Mn-FTO_Sample A1 Mn-FTO_Sample A2
Mn-FTO_Sample A3 PTO_Sample A1
-1.20
-1.00
-0.80
-0.60
-0.40
-0.20
0.00
0.20
0.40
0.60
0.80
1.00
-1.00 -0.80 -0.60 -0.40 -0.20 0.00 0.20 0.40 0.60 0.80 1.00
<I>/mA
Ewe/V vs. Ag/AgCl
Nitrate Reduction by Birnessite-type MnOx
After Addition of nitrate
Mn-FTO_Sample A1 Mn-FTO_Sample A2
Mn-FTO_Sample A3 PTO_Sample A
Test 2
9. Conclusion
Both tests do not demonstrate significant activity for reducing solution species when compared
to PTO samples.
11. Overview
This research project sought to understand how the solution pH affects the activity of
ozone generated on Nickel-Antimony doped Tin Oxide anodes. These anodes were first
prepared using a titanium substrate and the solution below:
Ethanoic Solution: (Sn:Sb:Ni ratio = 10:6:1)
- 0.1 M Tin(IV) Chloride Pentahydride
- 0.06 M Antimony(II) Chloride
- 0.01 M Nickel(II) Chloride Hexahydrate
All from Sigma-Aldrich
The anodes were then tested under acidic and neutral conditions to observe the activity.
This test involved the use of a potentiostat to send a current through the cell containing
the anode samples. Simultaneously, UV absorbance was measured. Ozone is known to
absorb UV light at 258 nm, so activity was analyzed about this wavelength.
12. Anode Sample Preparation
The catalysts were prepared using similar methods to the 2013 paper shared by Paul
Christensen, Khalid Zakaria, Heneriette Christensen, and Taner Yonar in the Journal of The
electrochemical Society
• Christensen, P. A., et al. “The Effect of Ni and Sb Oxide Precursors, and of Ni Composition, Synthesis
Conditions and Operating Parameters on the Activity, Selectivity and Durability of Sb-Doped SnO2
Anodes Modified with Ni.” Journal of the Electrochemical Society, vol. 160, no. 8, Feb. 2013,
doi:10.1149/2.023308jes.
Materials:
- Titanium foil (thickness: 0.1 mm)
- Titanium wire (diameter: 0.25 mm)
Equipment:
- Spot Welder
- Hot plate
- Furnace
13. Process:
1. Wash substrate materials: 10% Oxalic Acid wash for 15 min
2. Create Samples: Spot welded 0.5 cm2 Ti foil samples on Ti wires
3. Heating and calcination coating cycle (7 total)
a. Samples dip-coated then immediately dried on hot plate
b. Hot plate:
i. 100 C
ii. 15 min
c. Transfer immediately to furnace
d. Calcination in furnace:
i. 550 C
ii. 5 min
e. Repeat
Anode Sample Preparation con’t…
15. Experimental Procedure
First, the cyclic voltammetry technique (CV) was applied for a few cycles to observe if normal
activity was exhibited by samples. Both samples were cycled through a range of 0 V to 2.3 V to
observe the amount of oxidation occurring.
-5.00
0.00
5.00
10.00
15.00
20.00
25.00
0.00 0.50 1.00 1.50 2.00 2.50
<I>/mA
Ewe/V
CV – NiATO – 0.5 M H2SO4 (Acidic)
I vs Ewe
Cyclic Voltammetry applied just before start of the chronopotentiometry technique (CP). Both indicate oxidation occurring
around 1.7 to 2.3 V. It is apparent that the acidic solution produces a higher current at the same potential, indicating that lower pH
facilitates oxidation.
As a reference, the evolution of oxygen and ozone are known
to occur at anodic potentials given by the following reactions:
-5.00
0.00
5.00
10.00
15.00
20.00
25.00
0.00 0.50 1.00 1.50 2.00 2.50
<I>/mA
Ewe/V
CV - NiATO - 0.15 M Na2SO4 (Neutral)
<I>/mA
16. Experimental Procedure con’t…
• Following the CV, the potentiostat allowed the sample to exhibit open-circuit
voltage, allowing the cell activity to settle.
• At this point, the UV vis was autozeroed. This established the baseline
absorbance for the remaining absorbance readings. After completion, the
actual test was then ready to proceed.
• The potentiostat now applied the CP technique at a desired current. The current
steps were arbitrarily taken for both solutions:
• Acidic: 15 mA, 25 mA, 20 mA, 30 mA, 35 mA, 40 mA, and 45 mA
• Neutral: 0.1 mA, 0.5 mA, 1.0 mA, and 5.0 mA
• During each applied current value, an arbitrary number of UV-vis readings were
measured in the range of 200-300 nm. One measurement involves a set of
absorbance readings within the specified range. I will be referring to each
measurement as an “absorbance set”.
• The applied current and the resulting potential throughout the experiment can
be observed in the graphs labelled “CP”.
• Each data series (t#) is one absorbance set taken at a particular time (t1, t2,
t3,…) relative to the start of the experiment.
22. 0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
45.00
50.00
0.00 500.00 1000.00 1500.00 2000.00 2500.00 3000.00 3500.00
<Ewe>/V
I/mA
time/s
CP – NiATO Sample - H2SO4
I/mA <Ewe>/V
Applied current steps and corresponding cell potential over time. Multiple UV-
vis sets were taken at each current step, which can be observed on later slides.
That drop in potential and current was a result of me pausing EC Lab to change
the current. I mistakenly resumed the current at the same amperage as shown
above.
23. 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
200 210 220 230 240 250 260 270 280 290 300
Absorbance
Wavelength
NiATO Sample - H2SO4 - CP_15.0 mA
t1 t2 t3 t4 t5 t6 t7 t8 t9 t10 t11 t12
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
200 210 220 230 240 250 260 270 280 290 300
Absorbance
Wavelength
NiATO Sample - H2SO4 - CP_20.0 mA
t19 t20 t21 t22 t23 t24 t25 t26 t27 t28
For the time range of current = 20.0 mA
Between t23 and t 24, I paused EC-Lab to change the current
but mistakenly forgot to lock the settings upon resuming. So
t24-t28 is the absorbance at the same current but after a
pause in the current flow.
27. • The spectrophotometer was only autozeroed once, in between applying the CV
and first CP techniques.
• Hence, all of the raw absorbance values were accumulated with respect to the cell
at the state during which it was autozeroed. With this in mind, I had to correct the
absorbance values by subtracting out unnecessary background data.
• Since we are comparing the absorbance as a function of applied current, we want
to observe how absorbance is changing over time at the particular current value.
• To accomplish this, I took each absorbance set under the same applied current and
subtracted the last absorbance set of the previous applied current. For example, (see
acidic data) for the 6 absorbance sets taken at 30 mA, the last absorbance set taken
at 25 mA was subtracted from each.
• This results in absorbance values varying with respect to the applied current step
Results: Calculation Details
28. Results: Current Efficiency
• To calculate efficiency, we must find the amount of charge consumed by O3 generation (Qo3)
per total amount of charge consumed by the cell (Qmeas). The latter is provided by EC Lab.
• The number of moles of O3 produced can be found using the absorbance data:
• Absorbance, 𝐴 = 𝜖ℓ𝑐 ⇒
𝐴
𝜖ℓ
= 𝑐 ⇒ 𝑐 ⋅ 𝑉 =
𝐴𝑉
𝜖ℓ
𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑜𝑧𝑜𝑛𝑒 𝑝𝑟𝑜𝑑𝑢𝑐𝑒𝑑
• 𝜖 = 𝑚𝑜𝑙𝑎𝑟 𝑒𝑥𝑡𝑖𝑛𝑐𝑡𝑖𝑜𝑛 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 𝑓𝑜𝑟 𝑜𝑧𝑜𝑛𝑒 = 3000
𝐿
𝑚𝑜𝑙⋅𝑐𝑚
• ℓ = 𝑝𝑎𝑡ℎ 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑐𝑒𝑙𝑙 = 1 𝑐𝑚
• 𝑐 = 𝑜𝑧𝑜𝑛𝑒 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛
• 𝑉 = 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝑖𝑛 𝑐𝑒𝑙𝑙 = 3.75 𝑚𝐿
• The theoretical charge consumed by ozone can be found using the moles of ozone
produced times the number of electron equivalents times Faraday’s constant
• 6 (
𝑒𝑞𝑣
𝑚𝑜𝑙 𝑂3
) comes from the number of electrons consumed by ozone
• Faradays constant , 𝐹 = 96480(
𝑄
𝑒𝑞𝑣
)
• 𝑄 =
𝐴𝑉
𝜖ℓ
⋅ 6 ⋅ 𝐹 = 𝑇ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝐶ℎ𝑎𝑟𝑔𝑒 𝑐𝑜𝑛𝑠𝑢𝑚𝑒𝑑 𝑏𝑦 𝑂3 𝑔𝑒𝑛𝑒𝑟𝑎𝑡𝑖𝑜𝑛
• Efficiency, Φ =
𝑄 𝑂3
𝑄 𝑚𝑒𝑎𝑠
=
𝐴𝑉
𝜖ℓ
⋅6⋅𝐹
𝑄 𝑚𝑒𝑎𝑠
• The results can be observed on the following slide
29. 0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
0.00 500.00 1000.00 1500.00 2000.00 2500.00 3000.00 3500.00
ΦCurrentEfficiency/%
Recorded Time / s
Φ Current Efficiency - NiATO - 0.5 M H2SO4
(acidic)
Current Efficiency
Clearly, there is a decrease in efficiency as time proceeds with a higher produced efficiency
occurring under acidic conditions. Although, it appears that the decreasing rate of efficiency is
about the same for both conditions.
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
0.00 500.00 1000.00 1500.00 2000.00 2500.00 3000.00 3500.00 4000.00 4500.00
ΦCurrentEfficiency/%
Recorded Time / s
Φ Current Efficiency - NiATO - 0.15 M Na2SO4
(neutral)
30. Conclusion
• Overall, there are three parameters that can be analyzed from this experiment:
▪ Absorbance activity
▪ Current Efficiencies
▪ Solution pH
• Although the results of pH on solution are different, a conclusion cannot be formed since
the neutral samples were tested at lower applied currents.
• The absorbance activity about 258 nm was absent for the neutral sample and very
minimal for the acidic sample. If much ozone as produced, one would expect greater
absorbance about 258 nm relative to other parts of the spectral range. This was not the
case, so significant ozone formation cannot be concluded to have occurred.
• The current efficiency appeared to decrease as the experiments progressed. If ozone was
being produced, you would expect the opposite result. This indicates that a) the samples
might have reached their limit very quickly, b) the samples might have been breaking
down throughout the tests, c) or not much ozone was being produced in the first place
and the starting efficiency is not reliable. It is important to note that these calculations
can be easily skewed by the physical parameters of the cell and the experimental set-up.
• Errors:
• A significant error could have resulted from the incorrect starting ratio. This was
realized after the completion of the experiment! The research paper referenced here
actually proposed a ratio of Sn:Sb:Ni = 100:6:1 opposed to 10:6:1 in this test.
