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 typeOp. Temp. ( o C) Transported ion Membrane usedPower density mW/cm 2 Fuel cell efficiency Polymer electrolyte membrane fuel cell (PEMFC) 50-80H+H+ Polymeric membrane Alkaline fuel cell (AFC)60-90OH - Aqueous alkaline solution Phosphoric acid fuel cell (AFC) H+H+ Molten phosphoric acid Molten carbonate fuel cell (MCFC) CO 3 2- Molten alkaline carbonate Solid oxide fuel cell (SOFC) O 2- Ceramics Int. J. Hydrogen Energy, 35, 2010,

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: C  Power density: 240 mW/cm 2  Fuel cell efficiency: ~60%  Power output: 0.1 – 15W

Contd..... Why methanol is preferred over hydrogen fuel ?  Energy density: Methanol: 4.8 Wh/cm 3 Hydrogen: 2.7 Wh/cm 3  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 CH 3 OH + H 2 O CO 2 + 6H + + 6e - Cathodic reaction (Reduction): 1.22 V 3/2 O 2 + 6H + + 6e - 3H 2 O Overall reaction: 1.19 V CH 3 OH + 3/2 O 2 CO 2 + 2H 2 O (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 150 o C 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 cm 3 Concentration of NaCl0.1 M/0.01 M Maximum cell voltage0.118 V Photographic image of diffusion cell EIS specifications Frequency range1Hz- 1 MHz AC voltage5 mV Area of membrane12.56 cm 2 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/TEOS Power density= 29 mW/cm 2 OCV= 0.65 V 1.5 PWA/TEOS Power density= 35 mW/cm 2 OCV= 0.75 V Experimental specifications: Cell temperature= 25 o C MeOH flow rate= 5 ml/min Oxygen 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 (32 o C) Proton conductivity for inorganic membranes being used in DMFC is in the range of mScm -1 Maximum obtained power density was 35 mW/cm 2 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

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