MAKING ANODES FOR SOLID OXIDEFUEL CELLS USING TAPE CASTING

METHOD

Semester Project on ENE401 Fuel Cell Technology-Autumn 2013

Bernard Sisara Gunawardana Dimuthu Dharshana Arachchige

Overview Introduction

Methodology

Tape casting

Sintering

Results and discussion

Future works

Conclusion

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IntroductionWhat is a SOFC..?

In a SOFC, the electrolyte is a solid ceramic material. The anode and cathode are made from special inks that coat the electrolyte. Unlike other types of fuel cells, no precious metals, corrosive acids, or molten materials are required

 Solid Oxide Fuel Cell (SOFC) is an electrochemical conversion device that produces electricity directly from oxidizing a fuel at a higher temperature(6500C-10000C)

Application in stationary power, marine power or Aircraft APUs If a SOFC operates continuously a long period then it has a long operating life, unless parts of the fuel cell would break down so often due to the higher temperature

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Introduction Cont…..How SOFC Operates..?

 Steam reforming CH4+ H2O = 3H2 +CO

CO2 reforming CH4 + CO2 = 2H2 +2CO

In a typical SOFC,Efficiency is about 60%Operating temperature is about 1,000°C. Output is up to 100 kW

CH4

Anode Reactions

Cathode Reactions

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Methodology Formulation of slurry for anode

Ingredient Description Weight/(g)Powder NiO-YSZ 5Binder PVA 30% 3.5Solvent Distilled Water 2.2Plasticizer Glycerol 1Dispersant Tween 80 0.4Total 12.1

Ingredient Description Weight/(g)Powder NiO-YSZ 5Binder PVA 30% 3.5Solvent Propanol 1.4Plasticizer Glycerol 1Dispersant Tween 80 0.4Total 11.3

a) Solvent as distilled water

b) Solvent as propanol

Formulation of slurry for electrolyteIngredient Description Weight/(g)Powder YSZ 10.15Binder PVA 30% 10Solvent Distilled Water 5.85Plasticizer Glycerol 3.15Dispersant Tween 80 0.7Total 29.85

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Methodology Contd.. Experimental mixing

Ball milling machine was used for proper mixing of the slurry with Zirconia balls

Zirconia grinding medium in the form of balls were used to mill the slurry and disperse agglomerations.

Removing bubbles using a vacuum chamber

Having bubbles may cause to form defected and non uniform casted layers

a) Air bubbles in slurry foam

b) Removing air bubbles by vacuum chamber

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Tape casting

1) Tape caster is placed above the film carrier

2) Gap between film carrier and the casting plate is set to desired value

3) An amount of slurry is poured to the glass plate

4) Pipet edge is kept as close as to the film carrier

in order to minimize the formation of air bubbles5) Tape caster is pushed slowly and

steadily along the guided width of the glass plate

Tape casting steps

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Tape casting contd.. Tape casted layersa) Nio-Ysz layer without

vacuumingb) Ysz layers with vacuuming

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Sintering To check high temperature properties of the tape casted samples

3x3 cm2 samples on the ceramic plates

Colored ceramic plates; NiO casting

Samples with powder beds

Powder beds

First few test runs, sintering was unsuccessful Ceramic plates showed sign of reactivity towards NiO-YSZ samples A thin flat powder bed of YSZ was laid between the sample and the support plates

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Carbolite Muffle Furnace (CMF)

Removing additives in non-violent way under low temperature conditions, prevents any formation of cracks, rapid gas expansions, etc.

Sintering programme in the CMFCarbolite Muffle Furnance

10Sintering cont..

Results and discussionResults on tape casting

a) Unsuccessfully sintered Nio-Ysz samples

b) Sintered YSZ layer at 14000C

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Results contd……Microstructural observation

a) Microstructure of NiO-YSZ layer before sintering observed

through optical microscope

b) Microstructural observation of sintered NiO-YSZ through SEM

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Future worksMicrostructural analysis and validation

Microstructural analysis using Atomic Force Microscope (AFM) will help to study the degree of dispersity, particle size, porosity and the tendency of agglomeration.

Possible to control the mechanical strength and conductivity of anode. Substrate tests to obtain desired V-I characteristic, thermal andredox stability The samples are hydrogen thermal reduced in the test furnace in a temperature about 800 °C and voltage is measured against variable current.

Optimizing slurry composition Performance of different slurry compositions for better thermal

stability and conductivity properties. Conductivity as a function of volume of Ni Foreign additives; Cu, Zn

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Conclusion

It is required to modify, test and repeat the slurry samples in an iterative manner to obtain an optimized composition

Optimum Sintering Temperature (OST) has to be decided based on grain size, and boundariesEg: OST is changed with the volume of % Ni : 1400 0C for 40% Ni

Adjustable tape casting device is a well designed apparatus for low cost tape casting ,allowing to control the thickness of anode and electrolyte down to a desired value.

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Thank You..!!

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