Preparation and characterization of sulfonated styrene pentablock copolymer (Nexar TM ) membrane for PEM fuel cell.

Transcription

1 Preparation and characterization of sulfonated styrene pentablock copolymer (Nexar TM ) membrane for PEM fuel cell. 1

2 2 Outline of Presentation Fuel Cell & PEM Fuel Cell MEA & Membrane for PEMFC Membrane Material Nexar TM as a membrane material Synthesis of Nexar TM membrane Characterization of Nexar TM membrane Conclusion Future Recommendation

3 3 Fuel Cell: What & Why Fuel cell is an electrochemical device that convert chemical energy of fuel in to electrical energy without using any moving parts as in the case of internal combustion engine. The efficiency of fuel cell is higher than the thermodynamic efficiency of internal combustion engine. There are no emission of green house gas or harmful gases from fuel cell, therefore, it is considered as clean and environmental friendly device.

4 4 PEM Fuel Cell: PEM Fuel Cell: Proton Exchange Membrane Fuel Cell or Polymer Electrolyte Membrane Fuel Cell. It is one of the type of fuel cell using polymeric material for electrolyte and allow only proton (H + ) ion to cross over it. Merits of PEM Fuel Cell Low Temperature Operation Mobile Application No Harmful Product Environmental Friendly

5 5 Membrane Electrode Assembly (MEA) Gas Diffusion Layers (GDL) Porous and conductive material for H 2 and current flow. Catalyst Layers Anode and Cathode for electrochemical reaction Proton Exchange Membrane (PEM) GDL Catalyst Membrane Catalyst GDL Proton conductive material Barrier for electron Membrane Electrode Assembly

6 6 Types of the ion exchange membranes based on their development time Tongwen X. Review - ion exchange membranes: state of their development and perspective. J Membr Sci 2005;263:1e29

7 7 Proton Exchange Membrane (PEM) One of the important part of Fuel cell. For a good performance, PEM should contain following properties High proton conductivity Zero electronic conductivity Zero Fuel Crossover Adequate mechanical strength and stability Chemical and electrochemical stability under operating conditions All these parameters should be considered before the selection of membrane material

8 8 Materials for Membrane Main objective for material is proton conductivity (H + ) Polymer based materials are the most common type of electrolyte used in PEMFC To facilitate proton conductivity acidic groups has to be attached in polymer such as sulfonic group (-SO 3 H) Polymer Membrane for PEMFC Sulfonic Acid

9 9 Commercial cation-exchange membranes Peighambardoust, S. J., Rowshanzamir, S. & Amjadi, M. Review of the proton exchange membranes for fuel cell applications. Int. J. Hydrogen Energy 35, (2010).

10 10 Nafion Nafion is a sulfonated tetrafluoroethylene based fluoropolymercopolymer It is developed by DuPont But It is very costly Fuel cross over problem at high temperature Low proton conductivity at high temperature

11 11 Sulfonated styrene pentablock copolymer (Nexar TM ) It is a non-perfluorinated, pentablock copolymer of (t-butyl-styrene)-b- (ethylene-r-propylene)-b- (styrene-r-styrene sufonate)-b- (ethylene-r-propylene)-b- (t-butyl-styrene) It is developed and patented by Kraton Polymers LLC, USA and known as Nexar TM

12 12 Nexar TM : Uses & Application Majority of work that has been carried out using this material is alcohol pervaporation [J. Zuo et al, 2014; G. M. Shi et al, 2015] Desalination [G. M. Geise et al, 2010] IPMC actuator [R. Gao et al, 2012; Inamuddin et al, 2014, ] oil water separation [P. H. H. Duong et al, 2014] water purification [G. M. Geise et al, 2010] No literatures are available for Nexar TM as a material for PEM fuel cell.

13 13 Synthesis of Nexar TM Membrane Membrane preparation The Nexar solution was diluted with a fixed amount of THF at room temperature with continuous stirring. A homogenous solution is obtained after three hours. Membrane is developed by solution casting method

14 14 Characterization Analysis Characterization of polymer material is carried out to check its properties. Characterization of membrane is carried out to check feasibility of material for fuel cell.

15 15 X-ray diffraction (XRD) X ray diffraction is a very useful tool to examine the crystallinity of the membrane and hence their symmetry & regularity The diffraction patterns were recorded over a range of 2Ɵ from 10 o to 80 o. From the XRD result, it can be concluded that the Nexar material is amorphous as no clear peak was shown in the figure. CY Chen et.al, 2007 & other researcher reported XRD of Nafion & its nature as crystalline

16 16 FTIR Spectrophotometer It is an analytical technique used to identify organic materials. The infrared absorption bands identify molecular components and structures. Fourier transform infrared (FTIR) spectrum of sample was studied using Perkin Elmer, USA in the range of cm -1 The band at 3414 cm-1 is showing O-H stretching. Bands at around ~1411 and ~1223 cm-1 are due to presence of S=O stretching vibration which are confirming the existence of block styrene sulfonate unit of Nexar polymer.

17 17 Thermogravimetric analysis (TGA) Thermogravimetric analysis (TGA) of sample was carried out by Shimadzu, Model No DTG-60H. The TGA curve of the NX showed weight loss up to 350 ºC is about 22%, which is represented the presence of moisture. A sharp weight loss from 22 to 85 % at around 400 ºC may be due to the thermal degradation of sulphonic acid groups. At 480 ºC onwards, almost smooth horizontal section are shown, which represents the complete formation of the oxide form of the membranes.

18 WATER UPTAKE, % 18 Water Uptake, % Water uptake is an indication of holding capacity of water in membrane. Hydrated condition of membrane is required to transport H + ion Nexar can hold more water than Nafion as shown in figure Water Uptake, % This is due to high degree of 40 sulfonation & IEC of Nexar than Nafion 20 0 Nafion 117 MEMBRANE MATERIAL Nexar Water Uptake, % = Weight Wet Weihght Dry Weihght Dry 100

19 SWELLING RATIO, % 19 Swelling Ratio, % Swelling is an indication of distortion of membrane from its original shape. High value of swelling means higher distortion of membrane shape. Too high value of swelling is not desirable as it weaken the strength of membrane. Swelling ratio is related with water uptake. Nexar swelling is more than Nafion due to high water uptake of Nexar Swelling Ratio, % Nafion 117 Nexar MEMBRANE MATERIAL Swelling Ratio, % = Length Wet Length Dry Length Dry 100

20 IEC, MEQ/GM 20 Ion exchange capacity (IEC) Titration method is used to determine IEC values of membrane. Ion exchange capacity indicates the moles of SO 3 present per gm of dry membrane. Higher value of IEC is always recommended. The IEC value of Nexar MD9200 was calculated by titration method and found as 2.0±0.03 meq/gm whereas Nafion is showing 0.95±0.04 meq/gm Nafion is having almost half the value of IEC Nexar MD IEC, meq/gm Nafion 117 Nexar MEMBRANE MATERIAL

21 21 Proton conductivity measurement: Ionic conductivity is measured by Autolab potentiostat PGSTAT30 (Autolab Metrohm, Netherland) equipped with frequency response analyser (FRA) module. ionic conductivity, σ S cm = l R A where l = the distance between electrodes (cm), A is the cross-sectional area of membrane (cm2) and R is the membrane resistance (Ω) Width Thickness

22 22 Result: Proton Conductivity Temperature, oc Membrane Nafion Nexar TM Proton Conductivity increases with temperature Nexar showing high conductivity than Nafion This is due to higher IEC and water uptake as compared to Nafion.

23 23 Activation Energy The activation energy (Ea, which is the minimum energy required for proton transport) is calculated based on Arrhenius plot using the following equation. Ln ρ = E a RT Where Ea = activation nergy, KJ/mol, T= Temperature, o K, R = Gas constant Activation energy was found as13.27 kj/mol and 5.37 kj/mol for Nafion and Nexar respectively

24 24 Proton conduction mechanisms Grotthus mechanism or proton hopping Vehicular mechanism Nexar TM having high water uptake & low activation energy support vehicle mechanism Nafion with low water uptake and high activation energy support Grotthus mechanism. Ueki, T.; Watanabe, M. Macromolecules in ionic liquids: Progress, challenges, and opportunities. Macromolecules 2008, 41,

25 25 Conclusion Membrane casting was successfully carried out by solution casting method Material characterization was carried out Membrane characterization was carried out to explore potential application in fuel cell. Nexar TM membrane showing better result than Nafion 117 in all the important characterization test It was found that Nexar has 4 times higher conductivity than Nafion for all temperatures. Activation energy was found as13.27 kj/mol and 5.37 kj/mol for Nafion and Nexar respectively.

26 26 Future Recommendation Mechanical stability of Nexar TM is required to analyze. Need to explore its application as a membrane for DMFC (Direct methanol fuel cell). Development of MEA and single fuel cell stack performance based on Nexar TM membrane

27 27 Acknowledgment This work was made possible by TEQIP-II & TEQIP-III Grant from the World Bank, monitored by MHRD, Govt of India. Dr Inamuddin, Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia. Dr S Javed Rizvi, Department of Petroleum Studies, Zakir Husain College of Engineering & Technology, AMU, Aligarh, UP, India

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29 29 Abstract Proton exchange membrane fuel cell (PEMFC) have special attention because of high power density, easy start up, portable and cleanliness. The membrane used in PEM fuel cell is considered as the heart of the cell and cell performance depends upon it. The most widely used material for the membrane is Nafion, but due to its limitations, other materials are also explored. In aromatic hydrocarbon, particularly block copolymer have been very attractive for membrane material due to its implicit properties. In this work sulfonated styrene pentablock copolymer (Nexar TM ) has been explored as an alternative to Nafion for PEMFC membrane. The membrane of sulfonated styrene pentablock copolymer was developed by casting method. Characterization and structure property relationship of material was carried out with the help of FTIR spectroscopy, X-ray powder diffraction (XRD) and thermogravimetric analysis (TGA). Water uptake, ion exchange capacity (IEC) of the sample was carried out and found higher value than Nafion. Proton conductivity at different temperatures was also evaluated and it was found that Nexar has 4 times higher conductivity than Nafion for all temperatures. Conductivity temperature relationship are used to calculate activation energy and it was found kj/mol and 5.37 kj/mol for Nafion and Nexar respectively. The mobility of proton was also predicted using activation energy.

30 30 Basic Reaction of PEMFC Reaction at Anode H 2 2H + + 2e Reaction at Cathode O 2 + 4H + 2H 2 O Overall Reaction 2H 2 + O 2 2H 2 O E = 0V E = 1.23V E = 1.23V

31 31 Type of Fuel Cell

32 32 Numb Name of electrode er 1 Working electrode 2 Source 3 Reference electrode 4 Counter electrode

33 33 Nafion Structure