8/3/2019 Preparation of Tri-metallic Catalyst for Direct Ethanol Fuel Cell

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PREPARATION OF TRI-METALLIC CATALYST FOR DIRECT

ETHANOL FUEL CELL

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Introduction of fuel cell:-A fuel cell is an electrochemical device (a galvanic cell) which convertsfree energy of a chemical reaction into electrical energy (electricity); by

product depends upon fuel used.

Types of Fuel Cell:-

PEMFC- Proton Exchange Membrane Fuel Cell.DMFC- Direct Methanol Fuel Cell.AFC - Alkaline Fuel Cell.

( for space program for producing electricity and drinking waterfor austronaughts.)

PAFC - Phosphoric Acid Fuel Cell.MCFC- Molten Carbonate Fuel Cell.SOFC - Solid Oxide Fuel Cell.

DISADVANTAGES OF THESE FUEL CELL:-

PEMFC -For a fuel cell system using pure hydrogen as fuel, high hydrogenutilization operation is required because the exhausted hydrogen from thefuel cell is not used as a heat source for a reformer. While the hydrogenutilization is very high, any minor imbalance in the distributed flowcauses a shortage of hydrogen gas.

DMFC -

Methanol is toxic so it creates bad effect on human body.Methanol fuel cells use platinum in large quantities as a catalyst.

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8/3/2019 Preparation of Tri-metallic Catalyst for Direct Ethanol Fuel Cell

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Platinum is aprecious metal, thus making it expensive to run them.

SOFC -The high temperatures and the electrolyte chemistry has disadvantages.

The high temperature requires significant time to reach operatingconditions and responds slowly to changing power demands.

MCFC -The carbonate electrolytes cause electrode corrosion problems.Furthermore, since CO2 is consumed at the anode and transferred to thecathode, introduction of CO2 and its control in air stream becomes anissue for achieving optimum performance that is not present in any otherfuel cell.

AFC -Alkaline fuel cells allow the use of non precious metal catalysts becauseOf facile oxygen reduction kinetics at high pH conditions, but suffer fromthe problem of liquid electrolyte management and electrolyte degradation

WHY WE NEED DIRECT ETHANOL FUEL CELL

(DEFC)?

Ethanol is the most promising one because it is a safe moleculecomparatively to methanol. As a liquid it is easier to be stored andhandled when comparing to hydrogen. Moreover, ethanol has a hightheoretical mass energy(8 kWh/kg for ethanol versus 6.1 kWh/kg formethanol)

It is pollution free; the CO2 generated entered the carbon cycle again.

High energy density of ethanol (6.1KWh/litre) makes it more feasible.

Low cost (1.3$ per gallon) of ethanol makes it more feasible.

Large scale production of ethanol is possible from agricultural waste.

Eco-friendly, since no combustion reaction occurs. It is useful for mobile & stationary applications (viz. for vehicles and

in villages).

Objective:-To break the C-C bond of Ethanol and complete oxidation of ethanol intoCO2 in fuel cell and to avoid the formation of acetic acid (AA) by

promoting the C-C breaking route from the early adsorption steps.

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8/3/2019 Preparation of Tri-metallic Catalyst for Direct Ethanol Fuel Cell

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Description:-Direct alcohol fuel cell (DAFC) appears to be the most promising system

because either methanol in a DMFC or ethanol in a DEFC is not reformedinto hydrogen gas but is oxidized directly in the cell however, DEFCs

suffer from difficulties associated with the complete oxidation of ethanolto CO2. The catalytic challenge is the breaking of C-C bond, which is noteasily achieved at low temperatures. To achieve this goal, it is necessaryto increase the effective surface area of the catalysts, that is, to increasethe surface contact between the catalyst, the electronic conductor(carbon), the electrolyte (Nafion) and the reactant (ethanol). Theelectrochemical reaction occurs in this active part of the electrodes andthus the performances depend greatly on the kinetics of interfacial

phenomena. Usually, electrodes for PEMFCs (polymer exchange

membrane fuel cells) are constituted of black carbon powder which actsas a catalyst support and solid electrolyte such as Nafion. In this case, toincrease the performance of the electrodes (i.e. the true surface area of thecatalyst) one needs either to increase the thickness of the active layer, fora given catalyst loading, or to increase the amount of catalyst in thecatalytic powder. Increasing the thickness of the active layer leads to adecrease in the diffusion rate of the reactant towards the catalytic sites,whereas increasing the weight loading generally leads to an increase inthe particle size of the catalysts, thus decreasing their efficiency.Moreover, the most used methods of preparation of carbon supportedcatalysts by impregnation method.

Catalyst prepared for complete oxidation of ethanol

PtSnIr/C

PtRuIr/C

PtSnOs/C

PtSnHf/C

PtSnTa/C

PtRuTa/C

PtRuHf/C

Basis of selection of Precursor:-In order to increase the electro catalyst activity towards oxidation ofethanol Platinum was often modified with other metals like Ru .Addition of Tin increases the activity of platinum towards oxidation of

ethanol.

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Catalyst Preparation Method:-The catalyst was prepared by impregnation method. The carbon black

powder (Vulcan XC-72) used as a support for the catalyst. The carbonblack was preheated in ultra-sonicated bath to disperse the C-particles.

The precursor (H2PtCl6 or IrCl3xH2O with 0.1 mol dm-3 solutiondissolved in Aldrich) is taken in a beaker in the ratio of 100(40-40-20).Propanol is added in the precursor to dissolve the particles and sonicatedit in ultra-sonicated bath for 4-5 hours. After 4-5 hours both (precursor &C-powder) are mixed and then placed it in magnetic stirring bath for onehour till convection starts in the slurry. The slurry was left for drying inoven till it dry. The catalyst powder was scrapped from beaker and wasground in agate-mortar. Then from TPR (Temperature ProgrammedReduction) hydro-choric acid comes out as a fumes and catalyst is taken

out. After this procedure prepared catalyst is sent for TEM (Temp.Electron Microscopy) , SEM (Scanning Electron Microscopy) & XRD(X-ray Diffraction, for particle size determination) analysis.

Results & Discussion:-After several analysis of catalyst like TEM, XRD, CV analysis it is foundthat addition of Sn , Ru , Ir increases the activity of catalyst as well as tri-

metallic catalyst perform better than bi-metallic catalyst. Also efficiencyof ethanol fuel cell increases.

References:- A new trend in fuel cell by S. Basu

Journal of Applied Electrochemistry by F. Vigier , C. Coetaneous ,A. Perrard , E.M. Belgsir & C. Lamy.

Wikipedia encyclopedia.

** Analysis of catalyst is remain to do.