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Experimental Study of Diffusion of Carbon Dioxide, Methanol and Formic acid through PTFE Membrane.
Salman Zafar
Content
• Objectives
• Literature Survey
• Experimental Setup
• Results and Comparisons
• Summary
Indian Institute of Technology Roorkee -- 2
Objectives
• Better understanding of the transport of selected species
through the PTFE membrane using DEMS
• Studying the Effect of change in Pore size of the membrane
• Studying the Effect of movement of solution in the cell
• Studying the Effect of temperature change
• Studying the Effect of presence of Catalyst
Indian Institute of Technology Roorkee -- 3
Content
• Objectives
• Literature Survey
• Experimental Setup
• Results and Comparisons
• Summary
Indian Institute of Technology Roorkee -- 4
Literature Survey
• Ashton, S., J. (2011)
The Design, Construction and Research Application of a
Differential Electrochemical Mass Spectrometer (DEMS),
PhD Dissertation TU Munich.
The work deals with the design, construction and characterization of DEMS
which has emerged as an important tool for the analysis of the half-cell
studies in the fuel cells and other electro-chemical areas of application. The
study uses the DEMS to elucidate the chemical reactions that occur while
the oxidation of methanol on carbon based Pt-Ru catalyst. And the
corrosion of the high surface area carbon based catalysts. The study
presents a detailed discussion about the various operational features of
DEMS
Indian Institute of Technology Roorkee -- 5
Literature Survey
• Lindermeir, A., Rosenthal, G., Kunz, U. (2004)
On the question of MEA preparation for DMFCs. J. Power
Sourc., Vol. 129(2), pp. 180-187
The study presents two methods of preparation of the membrane electrode
assembly. In the first method the preparation started with the carbon
backing, then the substrate along with some PTFE is added to it, followed
by spraying of the catalyst mixture. This is then combined with the
membrane to give the MEA. In the second method the catalyst mix is
applied directly to the membrane. The assemblies from the second method
were found to be better due to a greater availability of active sites of the
catalyst.
Indian Institute of Technology Roorkee -- 6
Literature Survey
• Cappiello, A., Famiglini, G., Palma, P. (2003)
Peer reviewed: electron ionization for LC/MS. Anal. Chem.,
Vol. 75, pp. 496A–503A
The study highlights the use of Teflon membranes in DEMS studies. The
Teflon membrane being hydrophobic in nature is able the separate out the
aqueous medium from going into vacuum, resulting in the ionic species
being the majority of what goes into the DEMS. The output data from the
DEMS may be converted to quantitative data by calibrating the ion current
to actual mass or actual quantity of a specific ion or species.
Indian Institute of Technology Roorkee -- 7
Literature Survey
• Sundmacher K. (1999)
Cyclone flow cell for the investigation of gas-diffusion
electrodes, App. Eletroche., Vol. 3 (29), pp. 919-926
The study throws light on a new design for the electrochemical half cell
studies that is well suited for the Gas diffusion Electrodes. The design
earlier used for the study of surface electrochemical reactions was the
rotating disc electrode, but this is not suited well with GDE’s. The cylcone
flow cell suggested by Sundmacher, makes use of cyclone vortex flow over
a stationary electrode surface that is diffusive in nature to the gas phase.
Indian Institute of Technology Roorkee -- 8
Literature Survey
• Wang, H., Rus, E., Abruna, H.D. (2010)
Letters to Analytical Chemistry New Double-Band-
Electrode Channel Flow Differential Electrochemical Mass
Spectrometry Cell: Application for Detecting Product
Formation during Methanol Electro-oxidation. Anal. Chem.,
Vol. 82, pp. 4319–4324
The study shows the behaviour of mass spectrometer ion current with change in flow
rate of the solution over the electrode surface. The mass current is plotted as a
function of the flow rate for carbon dioxide, methanol and other species. The trends
given in this study were observed to be similar to one found in experiments.
Indian Institute of Technology Roorkee -- 9
Content
• Objectives
• Literature Survey
• Experimental Setup
• Results and Comparisons
• Summary
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Apparatus
Cyclone Flow Cell
Membrane
PTFE Membranes
0.2μm and 0.45μm
Mass Spectrometer
Vacuum Pumps
Vacuum Pump 1 80 l.s-1
Vacuum Pump 2 200 l.s-1
Solution Pump
Peristaltic Pump
Operation Range- 24RPM(27.3 ml/min) to 600RPM(579ml/min)
Indian Institute of Technology Roorkee -- 12
Experiments
Carbon Dioxide 1. De-ionized water bubbled with Nitrogen for 15min
2. Then bubbled with CO2 for 30min
3. Cell and connections set up, vacuum pumps started (with vacuum valve
closed).
4. Solution bottle bubbled and stirred continuously
5. Cell filled with solution
6. Vacuum valve is opened to evacuate the space between membrane and the
valve, valve closed again.
7. Pump is started and cell fills with ‘fresh’ solution
8. Pump is closed, and the valve is opened (1min Delay)
9. Record the diffusion curve and close the valve
10. Repeat from step 7 again
Indian Institute of Technology Roorkee -- 13
Experiments
Methanol and Formic Acid
1. De-ionized water bubbled with Nitrogen for 15min
2. 0.5M Solution Made
3. Cell and connections set up, vacuum pumps started (with vacuum valve
closed).
4. Cell filled with solution
5. Vacuum valve is opened to evacuate the space between membrane and the
valve, valve closed again.
6. Pump is started and cell fills with ‘fresh’ solution
7. Pump is closed, and the valve is opened (1min Delay)
8. Record the diffusion curve and close the valve
9. Repeat from step 6 again
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Content
• Objectives
• Literature Survey
• Experimental Setup
• Results and Comparisons
• Summary
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Results
Carbon Dioxide – Diffusion Through 0.2μm Membrane
Almost similar transport – no significant effect of catalyst presence.
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Results
Carbon Dioxide – Diffusion Through 0.45μm Membrane
Presence of catalyst slows down the transport
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Results
Carbon Dioxide – Diffusion Membrane Comparison
Transport through 0.2μm membrane is slower
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Results
Carbon Dioxide – Diffusion at different temperatures
No significant effect on the diffusion curve
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Results
Carbon Dioxide – Diffusion with varying degree of solution convection
No significant effect on the diffusion curve
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Results
Methanol – Diffusion Through 0.2μm Membrane
Presence of catalyst slows down the transport
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Results
Methanol – Diffusion Through 0.45μm Membrane
Presence of catalyst slows down the transport
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Results
Methanol – Membrane Comparison
Greater and faster diffusion for bigger pore size
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Results
Methanol – Effect of convection on Mass signal
The shape of the Diffusion Curve remains the same
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Results
Formic Acid – Diffusion Through 0.2m Membrane
Presence of catalyst slows down the transport significantly
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Results
Formic Acid – Diffusion Through 0.45μm Membrane
Presence of catalyst slows down the transport significantly
Indian Institute of Technology Roorkee -- 27
Results
Formic Acid – Membrane Comparison
Greater and faster diffusion for bigger pore size
Indian Institute of Technology Roorkee -- 28
Results
Formic Acid – Membrane Comparison
Greater and faster diffusion for bigger pore size
Indian Institute of Technology Roorkee -- 29
Results
Formic Acid – Membrane Comparison
Greater and faster diffusion for bigger pore size
Indian Institute of Technology Roorkee -- 30
Results – Conformation with Earlier Study
New Double-Band-Electrode
Channel Flow Differential
Electrochemical Mass
Spectrometry Cell: Application for
Detecting Product Formation
during Methanol Electro-oxidation
Wang, H., Rus, E., Abruna, H.,D.
(Analytical Chemistry, Vol. 82, No.
11, June 1, 2010)
Indian Institute of Technology Roorkee -- 31
Results – Conformation with Earlier Study
Carbon Dioxide - Hydrodynamic Behaviour of MS signal
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Results – Conformation with Earlier Study
Methanol - Hydrodynamic Behaviour of MS signal
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Results – Conformation with Earlier Study
Formic Acid - Hydrodynamic Behaviour of MS signal
Indian Institute of Technology Roorkee -- 34
Content
• Objectives
• Literature Survey
• Experimental Setup
• Results and Comparisons
• Summary and Further Developments
Indian Institute of Technology Roorkee -- 35
Summary
• The flux for non polar species (CO2) is higher compared to polar species
(Methanol and formic acid).
• The flux and rate of diffusion for 0.45μm membrane is greater than 0.2 μm
membrane.
• The presence a catalyst has a little effect on transport for 0.2 μm membrane
in case of CO2 as compared to methanol and formic acid .
• The speed of pump has no significant effect on the diffusion curve for all the
species.
• The temperature dependence is not profound over range of 10 °C
• Hydrodynamic behaviour of the species in the system was in conformation
with an earlier study.
Indian Institute of Technology Roorkee -- 36
Further Developments
• The data of the MS may be used
quantitatively and be compared
with a model if the system is
calibrated for the three species
giving a calibration constant that
would relate the mass currents to
actual mass flow rates.
• The diffusion curve can be
studied in an exact manner when
the dead space between the
membrane and the vacuum pump
can be removed some how.
Indian Institute of Technology Roorkee -- 37
References
• Sundmacher K. (1999)
Cyclone flow cell for the investigation of gas-diffusion electrodes, App.
Eletroche., Vol. 3 (29), pp. 919-926
• Lindermeir, A., Rosenthal, G., Kunz, U. (2004)
On the question of MEA preparation for DMFCs. J. Power Sourc., Vol.
129(2), pp. 180-187
• Cappiello, A., Famiglini, G., Palma, P. (2003)
Peer reviewed: electron ionization for LC/MS. Anal. Chem., Vol. 75, pp.
496A–503A
• Ashton, S., J. (2011)
The Design, Construction and Research Application of a Differential
Electrochemical Mass Spectrometer (DEMS), PhD Dissertation TU
Munich.
Indian Institute of Technology Roorkee -- 38
References
• Wang, H., Abruña, H.D. (2011)
Electrocatalysis of direct alcohol fuel cells: quantitative DEMS studies.
Struct. Bond., Vol. 141, pp. 33–83
• Planes, G.A., García, G., Pastor, E. (2007)
High performance mesoporous Pt electrode for methanol
electrooxidation. A DEMS study. Electrochem. Commun. Vol. 9, pp. 839–
844
• Wolter, O., Heitbaum, J. (1984)
Differential Electrochemical Mass Spectroscopy (DEMS) — a New
Method for the Study of Electrode Processes. Ber. Bunsenges. Phys.
Chem., Vol. 88, pp. 2– 6
Indian Institute of Technology Roorkee -- 39
References
• Munk, J., Christensen, P.A., Hamnett, A., Skou, E. (1996)
The electrochemical oxidation of methanol on platinum and platinum +
ruthenium particulate electrodes studied by in-situ FTIR spectroscopy
and electrochemical mass spectrometry. J. Electroanal. Chem., Vol. 401,
pp. 215-222
• Wang, H., Rus, E., Abruna, H.D. (2010)
Letters to Analytical Chemistry New Double-Band-Electrode Channel
Flow Differential Electrochemical Mass Spectrometry Cell: Application
for Detecting Product Formation during Methanol Electro-oxidation. Anal.
Chem., Vol. 82, pp. 4319–4324
---xxx---
Indian Institute of Technology Roorkee -- 40
Extra - Catalyst Coating
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• The nanoparticles are mixed with distilled water and isopropanol and then with nafion solution which acts as a binder.
• The mixture is then sonicated and it ensures evenly dispersed particles.
• The suspension is then directly sprayed on the PTFE membrane.
• The catalyst loading is then directly calculated by the difference in the weights of the naked membrane and the coated membrane.
MATLAB Model for Carbon Dioxide
Assumptions
• Diffusion is purely Diffusive in nature.
• Concentration gradient across the
membrane is linear
• Tortuosity of the membrane is ≈ 1
• Initially the concentration of CO2 is
uniform (At saturation)
• The Diffusion is one dimensional
Indian Institute of Technology Roorkee -- 47
MATLAB Model
Development of the Model
Mass Balance Equation (Unsteady State)
Finite Difference method was used to define the derivates, and equation were written for 1st, i th and last
element and the membrane and solved simultaneously
Indian Institute of Technology Roorkee -- 48