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Studies on Direct Methanol Fuel Cell: An electro-chemical energy conversion device
Jay Pandey
Research Scholar
Department of Chemical Engineering
Indian Institute of Technology Delhi, New Delhi
Outline
Introduction
Objectives
Experimental details
Membrane characterization
DMFC performance
Conclusions
Fuel Cell
Electrochemical device which converts chemical
energy into electrical energy
Invented by W.R.Groove, 1839 Introduced the IEMs in FCs (1963, J.W.Niedrach)
Fuel cell type Op. Temp. (oC)
Transported ion
Membrane used Power density mW/cm2
Fuel cell efficiency
Polymer electrolyte membrane fuel cell (PEMFC)
50-80 H+ Polymeric membrane 350 45-60
Alkaline fuel cell (AFC) 60-90 OH- Aqueous alkaline solution
100-200 40-60
Phosphoric acid fuel cell (AFC)
150-200 H+ Molten phosphoric acid 200 55
Molten carbonate fuel cell (MCFC)
600-700 CO32- Molten alkaline
carbonate
100 60-65
Solid oxide fuel cell (SOFC) 800-1000 O2- Ceramics 240 55-65
Int. J. Hydrogen Energy, 35, 2010, 9349-9384
Direct Methanol Fuel Cell (DMFC)
Sub-category of PEMFC
Fuel at anode: Methanol ; Oxidant at cathode: Oxygen
Membrane used: Proton exchange membrane (PEM)
Operating temperature: 50-1200C
Power density: 240 mW/cm2
Fuel cell efficiency: ~60%
Power output: 0.1 – 15W
Contd.....
Why methanol is preferred over hydrogen fuel ?
Energy density: Methanol: 4.8 Wh/cm3
Hydrogen: 2.7 Wh/cm3
Easy transportation and handling Readily available, relatively lesser cost Stable at all atmospheric conditions
(Silva et al, 2005)
Electrochemical reactions involved in DMFC
Anodic reaction(Oxidation): 0.03 V
CH3OH + H2O CO2 + 6H + + 6e-
Cathodic reaction (Reduction): 1.22 V3/2 O2 + 6H+ + 6e- 3H2O
Overall reaction: 1.19 VCH3OH + 3/2 O2 CO2 + 2H2O
(Silva at al. 2005)
Applications of DMFC
All kinds of portable, automotive and mobile applications like,
• Powering laptop, computers, cellular phones, digital cameras
• Fuel cell vehicles (FCVs)
• Spacecraft applications
• Any consumables which require long lasting power compare to Li-ion batteries
(Dyre et al., 2002)
Objectives
Synthesis of proton conductive PWA membrane for potential application in
DMFC
Physico-chemical characterization of membrane in order to characterize the
surface morphology, phase identification, intermolecular bonding, thermal
stability of the membrane
Electrochemical characterization of the membrane to analyze the
electrochemical behavior of membrane such as specific conductivity,
transport number, areal resistance of the membrane
Study of the DMFC performance using synthesized PWA membrane
Synthesis protocol of PWA membrane
PWA membrane
Physico-chemical characterization
FT-IR spectra of PWA membrane
XRD patterns of PWA membrane
FT-IR spectra confirms the stable intermolecular interaction between silica and tungustate ions.
Silanol ion peak ~1532 cm-1
Tungstate ion peak~1079, 984, 828, 815 cm-1
XRD patterns show the presence of silica and phosphotungustic acid in the membrane even after the heat treatment up to 150oC for 2 h.
PWA peak
Silica Peak
SEM analysis of membrane
SEM images of PWA membrane
SEM images of graphite support
The SEM images show the surface uniformity as well as proper dispersion of active sol (PWA and TEOS) on graphite support.
Electrochemical characterization
Membrane potential and transport number measurements
Experimental specifications
Volume of each compartment
27 cm3
Concentration of NaCl 0.1 M/0.01 M
Maximum cell voltage 0.118 V
Photographic image of diffusion cell
EIS specifications
Frequency range 1Hz- 1 MHz
AC voltage 5 mV
Area of membrane 12.56 cm2
Concentration of NaCl in both the compartments
0.5 M
Specific conductivity (S/cm) measurements
Nyquist Plot for resistance measurement
Nyquist plot
Membrane potential and transport number
*As the PWA/TEOS ratio is increased the transport as well as the membrane potential is increased significantly due to increase in the surface charge density of the synthesized membrane
Specific conductivity and water uptake
As the wt% of PWA was increased specific conductivity was also found to be increased i.e. more ionic conduction occurred through the PWA membrane.
Maximum value of water uptake was found around 30% for 1 molar ratio of PWA and TEOS. It indicates that membranes has high hydration content at higher wt% of PWA that will result into high proton conduction.
Fig. 1: Variation of specific conductivity with molar ratio of PWA and TEOS
Fig. 2: Variation of water uptake with molar ratio of PWA and TEOS
Experimental Setup for DMFC
DMFC performance
0.5 PWA/TEOSPower density= 29 mW/cm2
OCV= 0.65 V
1.5 PWA/TEOSPower density= 35 mW/cm2
OCV= 0.75 V
Experimental specifications:Cell temperature= 25oCMeOH flow rate= 5 ml/minOxygen flow rate= 100 ml/min
*It can be inferred that 1.5 PWA/TEOS has better DMFC performance than 0.5 PWA/TEOS membrane, mainly due to high proton conductivity of membrane for 1.5 PWA/TEOS
Conclusions
• The PWA membrane was synthesized using sol-gel method followed by solution casting on graphite support
• The highest obtained value of transport number was 0.90 for the synthesized PWA membrane
• Higher value of transport number indicates that maximum current is being carried across the membrane
• The maximum value of specific conductivity was found 5 mScm-1 at room temperature (32oC)
• Proton conductivity for inorganic membranes being used in DMFC is in the range of 5-14 mScm-1
• Maximum obtained power density was 35 mW/cm2 for 1.5 PWA/TEOS, and OCV was 0.75 V
• Synthesized PWA membrane has the potential for wide applications in DMFC
• The membrane properties can be further improved by changing the synthesis protocol or final treatment methods
References
S.K., Kamarudin, F., Achmad, W.R.W., Daud. Overview on application of direct methanol fuel
cell (DMFC) for portable electronic devices. Int. J. Hydrogen Energy, 34, 6902-6916. 2009.
U.S.D., Energy. Fuel cell handbook. Science Applications International Corporation E&G
Services, 5th ed., Parson Inc., 2000.
R., O’Hayre, S.W., Cha. Fuel cell fundamentals. Wiley, 113, 267-268, 2007.
S.Q., Song, W.J., Jhou, W.J., Li. Direct methanol fuel cells: Methanol crossover and its
influence on single DMFC performance. Solid State Ionic, 10, 458-462. 2004.
Z.G., Shao, P., Joghee, I.M., Hsing. Preparation and characterization of hybrid Nafion-silica
membrane doped with phosphotungustic acid for high temperature operation of PEMFC. J.
Membr. Sci. 229, 43–51, 2004.