A novel heterogeneous precipitation method for

the synthesis of highly percolated fine NiO/Ni

particles in 8YSZ matrix for IT-SOFC application

Subrat K. Mohanty1+, Bibhuti B. Nayak1#, R. D. Purohit2, P. K. Sinha2

1Department of Ceramic Engineering, National Institute of Technology, Rourkela

ODISHA-769008, INDIA

2Energy Conversion Materials Section, Chemical Engineering group

Bhabha Atomic Research Centre, Vashi Complex, Navi Mumbai – 400075, INDIA

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ICMAT13-A-3388

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Solid oxide fuel cell

Solid oxide fuel cells (SOFC) are the devices

which directly and efficiently convert the

chemical energy of a fuel into electrical energy

without any intermediate steps.

Applications

Stationary electric power

Distributed generation

Vehicle motive power

Space and other closed

environment power

Fuel cell auxiliary power

systems

Derivative application

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• The oxygen gas enters the cathode and moves through its porous structure towards the cathode-

electrolyte interface.

• The oxygen molecule picks up four electrons and gets converted into oxygen ion.

• The oxygen ion moves through the oxide ion conducting electrolyte into the anode electrolyte interface.

• There it combines with the fuel (H2) producing water and electrons.

• The electrons moves through the external circuit giving rise to electricity.

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Thermodynamic principles (Nernst’s equation)

At cathode: O2(c)+4e´= 2O´´(e)

At anode: 2O´´(e) = O2(a)+4e´

Overall cell reaction: O2(c) = O2(a)

Reversible cell voltage: 𝑹𝑻𝟒𝑭

𝒍𝒏𝑷

𝑶𝟐(𝒄

)𝑷𝑶𝟐

(𝒂

)

Er=

For H2(a)+1/2O2(c) = H2O(a)

𝑹𝑻

𝟒𝑭 𝒍𝒏𝑷𝑶

𝟐(𝒄

)+ Er= E0 +

𝑹𝑻𝟐𝑭

𝒍𝒏𝑷

𝑯𝟐(𝒂

)𝑷𝑯𝟐𝑶

(𝒂

)

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Advantages

Internally reforms light hydrocarbon fuels

Promote rapid reaction kinetics

Minimizes polarization losses

Minimizes noise pollution

Imposes constraints on materials selection

Electrolyte conducts at high temperature

Causes thermal mismatch between the components

Interconnect presents major proportion of the cost of the stack

Longer start up time

Chemical compatibility issues

Disadvantages

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Intermediate temperature SOFC

Facilitates the use of inexpensive materials thereby reducing the cost

Offers the potential for more rapid start up and shut down procedures

Simplifies the design and material requirement

Reduces corrosion rates

Challenges

The conductivity of the electrolyte decreases.

The catalytic activity of the electrodes reduces.

The power density of the cell decreases.

To overcome all these challenges the anode requires special

attention as it makes an oxidation of fuel to generate electricity

and is responsible for majority of voltage loss of SOFC

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The Anode Hydrogen Water

Electrons

Oxygen ions

Anodic reaction steps

Overall anodic reaction: O´´(electrolyte)+H2(fuel gas) H2O (fuel gas)+2e´ (anode)

Anodic electrochemical reaction Ox

o (Electrolyte)+ H2 ads (TPB) H2O (Fuel gas)+2e´(Anode)+V¨o(Electrolyte)

Adsorption of H2 on the surface of anode H2 (Fuel gas) H2 ads (Anode)

Surface diffusion of adsorbed H2 to TPB H2 ads (Anode) H2 ads (TPB)

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Triple Phase Boundary

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OBJECTIVES

To adopt a cost effective heterogeneous precipitation method to develop

NiO/Ni: 8YSZ composites with 20, 30 and 40 vol % Ni content for IT-

SOFC application.

Where

Smaller size Ni will be uniformly distributed and well connected in

8YSZ matrix

Better percolation of Ni (as low as possible)

Better electrical conductivity (for lower Ni content)

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How to achieve

Direct strike (DS) technique

Reverse strike (RS) technique

Dispersion solution containing 8YSZ and NiCl2·8H2O was continuously stirred in a magnetic stirrer at a temperature around 70°C – 80°C and mixture of N2H5OH and NaOH were added drop wise to a beaker containing dispersion solution.

Reverse way of DS technique

Samples prepared through DS and RS techniques are designated as NX0DS/RS UR/R, where N represent nickel, ‘X0’ represents vol % of Ni, and DS represents direct strike, RS represents reverse strike, UR and R represents before and after reduced under H2 atmosphere.

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RESULTS AND DISCUSSION

Thermal properties

Phase analysis

Sintering behavior

Microstructure

Electrical conductivity

Compositions NX0DS/RS UR/R

Where X0 = 20, 30 and 40 vol % of Ni

0 200 400 600 800 1000-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

93

94

95

96

97

98

99

100

Mass

(g

)

mW

/mg

Temperature (°C)

N20DS

N20RS

(a)

0 200 400 600 800 1000-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Temperature (°C)

mW

/mg

87

90

93

96

99

102

105

108(b)

N30DS

N30RS

Mass

(g

)

0 200 400 600 800 1000-0.5

0.0

0.5

1.0

1.5

2.0

N40DS

N40RS

Temperature (°C)

Ma

ss

(g

)

mW

/mg

(c)

98

100

102

104

106

108

110

112

114

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Thermal Analysis

20 30 40 50 60 70 80

N30RS

YSZ Ni Ni(OH)2

Inte

ns

ity (

a.u

.)

(a)

2 (degree)

N30DS

20 30 40 50 60 70 80

N30RS

NiOYSZ

(b)

2 (degree)

Inte

ns

ity

(a

.u.)

N30DS

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Phase analysis

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Sinterability and particle morphology

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Microstructure

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Microstructure

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Microstructure

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Electrical conductivity

300 450 600 750 900

10

100

1000 N20 RS R

N30 RS R

Co

nd

ucti

vit

y (

S/c

m)

Temperature (°C)

N20 DS R

N30 DS R

N40 DS R

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N20 DS R

N20 DS R

EDS mapping

N20 RS R

N20 RS R

EDS mapping shows N20DS R sample has higher Ni connectivity than N 20 RS R

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EDS mapping

N20 DS R

N20 DS R

N40 DS R

N40 DS R

EDS mapping shows N40DS R sample has higher porosity with lower Ni connectivity than N 20 DS R

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Important Findings

Highly percolated fine NiO/Ni particles in 8YSZ matrix was successfully prepared through a novel heterogeneous precipitation method using DS and RS techniques.

DS technique shows better electrical conductivity than RS technique with same Ni content in Ni: 8YSZ composites.

Better percolation with higher conductivity was observed in lower Ni (20 vol%) content in Ni: 8YSZ composites prepared through DS technique.

Presence of Ni(OH)2 in the as-prepared samples play a role for better percolation and better conductivity for N20DS R.

However, both techniques show comparable electrical properties, which predict the suitability of these techniques for the synthesis of Ni-8YSZ anode material for intermediate temperature SOFC application.

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Acknowledgements

Department of Ceramic Engineering, NIT Rourkela

Board of research in nuclear sciences (BRNS), Govt. of INDIA

Council of scientific and industrial research (CSIR), Govt. of INDIA

Department of Science and Technology (DST), Govt. of INDIA

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THANK YOU