“PREPARATION AND CHARACTERIZATION OF NIOBIUM DOPED ZIRCONIA AS SOLID OXIDE ELECTROLYTE FOR SOLID OXIDE FUEL CELL APPLICATIONS”

Prepared By,

Arathy. S. R

CONTENTS

FUEL CELL

A fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent.

The first fuel cell were invented in 1838 by William Robert Grove, arranging two platinum electrodes electrodes with one end of each immersed in a container of sulfuric acid and the other ends separately sealed in containers of oxygen and hydrogen, a constant current would flow between the electrodes. The sealed containers held water as well as the gases, and he noted that the water level rose in both tubes as the current flowed. By combining several sets of these electrodes in a series circuit, he created what he called a “gas battery” the first fuel cell. In 1959 Bacon and Frost developed a first practical fuel cell.

The first commercial use of fuel cells came more than a century later in NASA space programs to generate power for probes, satellites and space capsules. Since then, fuel cells have been used in many other applications. Fuel cells are used for primary and backup power for commercial, industrial and residential buildings and in remote or inaccessible areas. They are also used to power fuel-cell vehicles, including forklifts, automobiles, buses, boats, motor cycles and submarines.

There are many types of fuel cellsThey all consist of an anode, a cathode and an electrolyte that allows charges to move between the two sides of the fuel cell. Electrons are drawn from the anode to the cathode through an external circuit, producing direct current electricity. As the main difference among fuel cell types is the electrolyte, fuel cells are classified by the type of electrolyte they use followed by the difference in startup time ranging from 1 sec for PEMFC to 10 min for SOFC

Fuel cells come in a variety of sizes. Individual fuel cells produce relatively small electrical potentials, about 0.7 volts, so cells are "stacked", or placed in series, to increase the voltage and meet an application's requirements. In addition to electricity, fuel cells produce water, heat and, depending on the fuel source, very small amounts of nitrogen dioxide and other emissions. The energy efficiency of a fuel cell is generally between 40–60%, or up to 85% efficient in cogeneration if waste heat is captured for use.

Fuel cell stack

Types of fuel cells

1) alkaline fuel cell (AFC)2) proton exchange membrane (PEM) fuel

cell3) direct methanol fuel cell (DMFC)4) molten carbonate fuel cell (MCFC)5) phosphoric acid fuel cell (PAFC)6) solid oxide fuel cell (SOFC)

SOFC

Made up of three adjacent segments: the anode, the electrolyte, and the cathode.Two chemical reactions occur at the interfaces of the three different segments. The net result of the two reactions is that fuel is consumed, water or carbon dioxide is created, and an electric current is created, which can be used to power electrical devices, normally referred to as the load.

At the anode, catalyst oxidizes the fuel, usually hydrogen, turning the fuel into a positively charged ion and a negatively charged electron. The electrolyte is a substance specifically designed so ions can pass through it, but the electrons cannot. The freed electrons travel through a wire creating the electric current. The ions travel through the electrolyte to the cathode. Once reaching the cathode, the ions are reunited with the electrons and the two react with a third chemical, usually oxygen, to create water or carbon dioxide.

At anode:

H2 2H+ +2e-

At cathode:

2H + + 1/2O2 +2e- H 2O

The most important design features in a fuel cell are

the electrolyte substance. The electrolyte substance usually defines the type of fuel cell. The most common fuel is hydrogen.The anode catalyst is usually made up of very fine platinum powder. The cathode catalyst is often made up of nickel but it can also be a nanomaterial-based catalyst.

Solid oxide fuel cells (SOFCs) use a solid material, most commonly a ceramic material called yitrium-stabilized zirconia (YSZ), as the electrolyte. They require high operating temperatures (800–1000 °C) and can be run on a variety of fuels including natural gas.Due to high temperature

Restrictions in choice of material

Electrode sintering problem

Mechanical stress due to difference in thermal expansion

To over come this problem, intermediate temperature SOFC ,operating at 600-8000c was introduced.A new material named Pyrochlore oxides (Ba RE 4Zr4NbO17.5 ) having equivalent conductivity value in IT range were synthesized.

SOFCS ARE

Pollution free

Reliable

High efficiency

Convert wide variety of fuels

Vibration free

Next generation energy source………

Applications Power

used for commercial, industrial and residential primary and backup power generation.

Cogeneration

used to generate both electricity and heat for homes

Fuel cell electric vehicles Automobiles Portable power systems Markets and economics

RESULTS AND DISCUSSION

3.2.1 Powder X –ray Diffraction Results

Sample 1: Zr2NbO7-δ

20 40 60 80

0

2000

4000

6000

8000

10000

12000

2 theta

(angle

)

Intensity (count)

Zr2NbO

7-

(1 1 0)

(1 1 0)(1 1 1)

(2 0 0)

(2 1 1)

(2 2 0)

(2 2 1)(3 1 0)

THANK YOU