1 T.Maiyalagan and Prof. B. Viswanathan Department of Chemistry, Indian Institute of Technology, Madras Chennai , India Nitrogen containing carbon nanotubes as supports for Pt – alternate anodes for Fuel cell applications.

2 Thermal Energy Mechanical Energy Chemical Energy Electrical Energy FUEL CELLS Fuel Cell ICE Direct Energy Conversion Vs Indirect Technology

3 Batteries –Needs recharging –Dangerous chemicals Internal combustion engines - Carnot limitations - Moving parts and hence friction - Noisy C. K. Dyer, J. Power. Sources, 106 (2002) 245 BATTERIES/ICE /FUEL CELLS

4  EFFICIENCY  RELIABILITY  CLEANLINESS  UNIQUE OPERATING CHARACTERISTICS  PLANNING FLEXIBILITY  FUTURE DEVELOPMENT POTENTIAL FUEL CELLS – ADVANTAGES

5 VARIOUS TYPES OF FUEL CELLS dadf

6 2H 2 + O 2  2H 2 O 2H 2  4H + + 4e - O 2 + 4H + + 4e -  2H HOW DOES PEMFC WORK ?

7 Electrolyte frameBipolar plate Anode catalyst Cathode catalyst O2O2 H2H2 Stack of several hundred

8 ADVANTAGES OF LIQUID FUELS Higher volumetric and gravimetric densities Easier to transport Storage and handling

9 CHEMICAL AND ELECTROCHEMICAL DATA ON VARIOUS FUELS FUEL  G 0, kcal/mol E 0 theor (V)E 0 max (V)Energy density (kWh/kg) Hydrogen Methanol Ammonia Hydrazine Formaldehyde Carbon monoxide Formic acid Methane Propane

10 High specific energy density Clean liquid fuel Larger availability at low cost Easy to handle and distribute Made from Natural gas and renewable sources Possible direct methanol operation fuel cell Economically viable option WHY METHANOL ? Heinzel et al, J. Power Sources 105 (2002) 250

11 Direct Methanol Fuel Cell (DMFC) CH3OH + H2O  CO2 + 6H+ + 6e- Eo = V (electro-oxidation of methanol) Driven Load AnodeCathode Methanol + Water Carbon Dioxide Anode Diffusion Media Anode Catalyst Layer e- H+ Oxygen Water Acidic Electrolyte Solid Polymer Electrolyte: PEM (Proton Exchange Membrane) Cathode Catalyst Layer Cathode Diffusion Media 3/2O2 + 6H+ + 6e-  3H2O Eo = 1.23 V Overall Reaction CH3OH + 3/2O2 +H2O  CO2 + 3H2O Ecell = 1.18 V Acidic electrolytes are usually more advantageous to aid CO2 rejection since insoluble carbonates form in alkaline electrolytes Nafion117

12 Advantages of DMFC Technology Longer membrane lifetime due to operating in aqueous environment Reactant humidification is not required Compared to H 2 Systems with Methanol Reformer Low operating temperature of DMFC results in low thermal signature DMFC system has faster start-up and load following DMFC system is simpler and has lower weight and volume Can use existing infrastructure for gasoline G.G. Park et al., Int.J. Hydrogen Energy 28 (2003) 645

13 Status of DMFC Technology Large number of companies working on DMFC technology for consumer applications Commercialization of DMFCs for cell phones and laptops expected within 2-3 years Cost of DMFCs is coming down, and becoming competitive with Li batteries

14 DIFFICULTIES IN DMFC POOR ANODE KINETICS FUEL CROSSOVER ELECTROCATALYSTS

15 Challenges for DMFC Commercialization  COST Cost of stacks DECREASE OF NOBLE METAL LOADINGS Utilization  Stability  Template synthesised CNT as the support for Pt, Pt-Ru, Pt-MoO 3 Present objective Overall objective: Reduce catalyst cost for direct methanol fuel cells  Reduce catalyst cost for direct methanol fuel cells CNT: Concentric shells of graphite rolled into a cylinder

16 High Temperature Why Supported Catalyst? What is the support? How to choose better Support ?

17 THE PROMISE OF NANOTUBES SUPPORT ● Single walled nanotubes are only a few nanometers in diameter and up to a millimeter long. ● High conductivity. ● High accessible surface area. ● High dispersion. ● Better stability.

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19 Why Nitrogen containing carbon nanotubes? Good electronic conductivity. Electronic structure and band gap can be tuned by varying the nitrogen content. Addition of nitrogen increases the conductivity of the material by raising the Fermi level towards the conduction band. Catalytic properties of the surface are determined by the position of the Fermi level of the catalyst. Consequently Fermi level acts as a regulator of the catalytic activity of the catalyst. The nitrogen functionality in the carbon nanotube support determines the the size of Pt by bonding with lone pairs of electrons at the nitrogen site. Pt bound strongly to nitrogen sites so sintering doesn’t takes place. The increased electron donation from nitrogen bound carbon nanotubes to Pt might be responsible for enhancement in kinetics of methanol oxidation.

20 PVP N=12.9% PPY N=21.2% PVI N=33.0% PPP N= 0% Present work Present work Synthesis Of Nitrogen containing carbon nanotubes NITROGEN CONTAINING POLYMERS

21 impregnation Polymer solution ALUMINA MEMBRANE carbonization 48 % HF 24 HRS CNT Schematic Diagram Polymer

22 SYNTHESIS OF PVP-CNT Carbonization Ar atm 48% HF 24 hrs PVP In DCM PVP/alumina Alumina membrane CNT PVP

23 Carbonization apparatus

24 Thermogravimetric analysis

25 ELEMENTAL ANALYSIS CALCULATED EXPERIMENTAL at C SAMPLE% C% N% H% C% N% H PPP-CNT PVP-CNT

26 SEM PICTURE OF PVP -CNT (a) The top view of the CNTs.

27 (b) The lateral view of the well aligned CNTs ( Low magnification). SEM PICTURE OF PVP -CNT

28 SEM PICTURE OF PVP -CNT (c) The lateral view of the well aligned CNTs ( High magnification).

29 HR-TEM images of carbon nanaotubes obtained by the carbonisation of polyvinyl pyrolidone (a-b) Carbonisation at 1173 K, 4hrs TEM PICTURES OF PVP -CNT 200nm

30 RAMAN SPECTRUM G -Band D-Band

31 FT – IR SPECTRUM

32 FT – IR SPECTRUM C=N C=C C-N O-H

33 XPS - SPECTRA

34 Loading of catalyst inside nanotubes 73mM H 2 PtCl 6 12 hrs H K 3 hrs 48% HF 24 hrs

35 TEM PICTURE OF Pt/CNT EDX spectrum

36 TEM PICTURE OF Pt/CNT

37 Electrode Fabrication Ultrasonicated, 30 min Dispersion (10  l) / Glassy Carbon (0.07 cm 2 ) Dried in air 5  l Nafion (binder) Solvent evaporated ELECTRODE 10 mg CNT/ 100  l water ELECTROCHEMICAL STUDIES

38 METHANOL OXIDATION Cyclic Voltammograms of (a) Pt in 1 M H 2 SO 4 /1 MCH 3 OH run at 50 mV/s

39 Cyclic Voltammograms of (b) GC/ETek 20 % Pt/C Nafion in 1 M H 2 SO 4 /1 MCH 3 OH run at 50 mV/s

40 Cyclic Voltammograms of (c)GC/CNT pvp -Pt- - Nafion in 1 M H 2 SO 4 /1 MCH 3 OH run at 50 mV/s

41 Electrochemical activity of the electrodes based on carbon nanotubes in comparison with commercial catalysts for methanol oxidation Electrode Activity I pa (mA/cm 2 ) Pt GC/CNT-Pt-Naf GC/ETek20%Pt/C-Naf  Data evaluated from cyclic voltammogram run in 1M H 2 SO 4 /1M CH 3 OH at 50 mV/s

42 Conclusions Conclusions 1.The template aided synthesis of carbon nanotubes using polymer as a carbon source yielded well aligned carbon nanotube with the pore diameter matching with the template used. 2.The higher electrochemical surface area of the CNT and the highly dispersed catalytic particles may be responsible for the better utilization of the catalytic particles. The tubular morphology might be the reason for the better dispersion. 3.The higher activity of the nitrogen containing carbon nanotube catalyst suggest that the Nitrogen present in the carbon nanotube (after carbonisation) plays an important role not only in the dispersion, but also in increasing the hydrophilic nature of the catalyst. 4. There is a correlation between the catalytic activity of the carbon nanotube electrode material and the nitrogen concentration (at%). Future work will be focused on ways to enrich the N content on the surface of CNT supports.

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