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FUEL CELL

An upgraded version of Batteries

WHAT IS A FUEL CELL?

A fuel cell is an electrochemical energy conversion device that converts hydrogen and oxygen into electricity, heat, and water as a result of a chemical reaction.

WHAT DOES A FUEL CELL ACTUALLY CONTAINS?

1. CATHODE- the positive electrode2. ANODE- the negative electrode3. ELECTROLYTE- in which the reactions

take place4. AN INTERCONNECT(in case of a stack)-

for electron transfer5. SEALS- To act as barrier between

components

SALIENT FEATURES

Highly efficient electric power generation system (can be as high as 70-80%)

Effective utilization high temperature waste heat

Environmental friendly power generation

WHETHER A SINGLE FUEL CELL IS ENOUGH ? A single fuel cell generates a tiny

amount of direct current (DC) electricity. In practice, many fuel cells are usually assembled into a stack. Cell or stack, the principles

are the same.

REQUIREMENTS OF ELECTROLYTE

Ionically conductive -oxygen ion transport

Chemically stable (at high temperatures as well as in reducing and oxidizing environments)

Gas tight/free of porosity Uniformly thin layer (to minimize ohmic

losses)

ELECTROLYTEMost widely used electrolyte is Yttrium

doped zirconium oxide (YSZ) Advantages of YSZi. ionic conductivityii. chemical stabilityiii. mechanical strength Disadvantages of YSZi. low ionic conductivity

ELECTROLYTE SolutionI. Decrease the thickness of the YSZ

electrolyte II. Find other materials to replace the

yttrium like Scandium-doped zirconium oxide has higher conductivity than YSZ but high cost of scandium is a disadvantage

CATHODE-REQUIREMENTS

High electronic conductivity Chemically compatible with neighboring

cell component (usually the electrolyte) Should be porous Stable in an oxidizing environment Large triple phase boundary Catalyze the dissociation of oxygen Adhesion to electrolyte surface

CATHODELanthanum strontium manganite(LSM) is the cathode

Advantages of LSM

I. Compatibility with doped zirconia electrolytes

II. Similar coefficient of expansion to YSZ and thus limits stresses

CATHODE Disadvantages of LSMI. LSM is a poor ionic conductor, and so

the electrochemically active reaction is limited to the triple phase boundary (TPB) where the electrolyte, air and electrode meet.

II. LSM works well as a cathode at high temperatures, but its performance quickly falls as the operating temperature is lowered below 800 °C.

ANODE-REQUIREMENTS

Electrically conductive High electro-catalytic activity Large triple phase boundary Stable in a reducing environment Can be made thin enough to avoid mass transfer

losses, but thick enough to provide area and distribute current

Thermal expansion coefficient similar neighboring cell component

Chemically compatible with neighboring cell component

Fine particle size

ANODE Ceramic anode layer must be very

porous to allow the fuel to flow towards the electrolyte

The most common material used is a cermet made up of nickel mixed with the ceramic material that is used for the electrolyte

The anode is commonly the thickest and strongest layer

The anode’s job is to use the oxygen ions that diffuse through the electrolyte to oxidize the hydrogen fuel

ANODEADDITIONAL USES:

Function of the anode is to act as a catalyst for steam reforming the fuel into hydrogen.

This provides another operational benefit to the fuel cell stack because the reforming reaction is endothermic, which cools the stack internally.

INTERCONNECT-REQUIREMENTS

Stable under high temperature oxidizing and reducing environments

Very high electrical conductivity High density with “no open porosity” Strong and high creep resistances for planar

configurations Good thermal conductivity Phase stability under temperature range Resistant to sulfur poisoning, oxidation and

carburization Low materials and fabrication cost

INTERCONNECT The interconnect can be either a metallic or

ceramic layer that sits between each individual cell.

It connects each cell in series, so that the electricity each cell generates can be combined.

a metallic 95Cr-5 Fe alloy is the most commonly used interconnect

Ceramic materials are also under considerations

DRAWBACKS: these ceramic interconnect materials are very

expensive as compared to metals.

SEALS-REQUIREMENTS

Electrically insulating Thermal expansion compatibility with

other cell components Chemically and physically stable at high

temperatures Gastight Chemically compatible with other

components Provide high mechanical bonding strength Low cost

HOW DO FUEL CELLS WORK? PURPOSE produce an electrical current that can

be directed outside the cell to do work GENERAL WORKING OF FUEL CELLS1. Hydrogen atoms enter a fuel cell at

the anode 2. Hydrogen atoms are now ionized, and

carry a positive electrical charge.3. Negatively charged electrons provide

the current through wires to do work.

In some cells, Oxygen enters the fuel cell at the cathode and combines with the electrons and hydrogen.

In other cell types the oxygen picks up electrons and then combines with hydrogen

Electrolyte must permit only the appropriate ions to pass between the anode and cathode

Fuel cells create electricity chemically. Therefore, fuel cells are more efficient in extracting energy from a fuel

TYPES Alkali fuel cells Molten Carbonate fuel cells (MCFC) Phosphoric Acid fuel cells (PAFC) Proton Exchange Membrane (PEM) fuel

cells Solid Oxide fuel cells (SOFC)

CHARACTERISTICS OF SOFC Fuel cells can continuously make

electricity if they have a constant fuel supply.

SOFCs that operate at higher temperatures -- between about 1100 and 1800 degrees Fahrenheit

Can run on a wide variety of fuels, including natural gas, biogas, hydrogen and liquid fuels such as diesel and gasoline

CHARACTERISTICS OF SOFC Each SOFC is made of ceramic

materials, which form three layers: the anode, the cathode and the electrolyte

The big advantage to fuel cells is that they're more efficient than traditional power generation

SOLID OXIDE FUEL CELL

GENERAL WORKING

WORKING PRINCIPLE

SOFC – WORKING PRINCIPLE SOFC essentially consists of two

porous electrodes separated by a dense, oxide ion conducting electrolyte.

Oxygen supplied at the cathode (air electrode) reacts with incoming electrons from the external circuit to form oxide ions

 These ions migrate to the anode (fuel electrode) through the oxide ion conducting electrolyte.

SOFC – WORKING PRINCIPLE At the anode, oxide ions combine with

hydrogen (and/or carbon monoxide) in the fuel to form water (and/or carbon dioxide), liberating electrons. 

Electrons (electricity) flow from the anode through the external circuit to the cathode.

SOLID OXIDE FUEL CELLSADVANTAGES high efficiency, long-term stability, fuel flexibility, low emissions, and relatively low cost. DISADVANTAGES high operating temperature which

results in longer start-up times and mechanical and chemical compatibility issues.

APPLICATIONS SOFC are being targeted for use in power and heat

generation for homes and businesses as well as auxiliary power units for electrical systems in vehicles.

SOFC also can be linked with a gas turbine, in which

the hot, high pressure exhaust of the fuel cell can be

used to spin the turbine, generating a second source of

electricity. Using planar SOFCs, stationary power generation

systems of from 1-kW to 25-kW size have been fabricated and tested by several organizations

APPLICATIONS Rolls-Royce Fuel Cell Systems Ltd is

developing a SOFC gas turbine hybrid system fueled by natural gas for power generation applications on the order of a megawatt (e.g. Futuregen).

Ceres Power Ltd. has developed a low cost and low temperature (500–600 degrees) SOFC stack using cerium gadolinium oxide (CGO) in place of current industry standard ceramic, yttria stabilized zirconia (YSZ), which allows the use of stainless steel to support the ceramic.

APPLICATIONS Solid Cell Inc. has developed a unique, low cost cell

architecture that combines properties of planar and tubular designs, along with a Cr-free cermet interconnect.

The high temperature electrochemistry center (HITEC) at the University of Florida, Gainesville is focused on studying ionic transport, electro catalytic phenomena and micro structural characterization of ion conducting materials.

SiEnergy Systems, a Harvard spin-off company, has demonstrated the first macro-scale thin-film solid-oxide fuel cell that can operate at 500 degrees.

APPLICATIONS Delphi Automotive Systems are

developing an SOFC that will power auxiliary units in automobiles and tractor-trailers

Research is also going on in reducing start-up time to be able to implement SOFCs in mobile applications

ADVANCEMENTS

ADVANCEMENTS

ADVANCEMENTS

THANK YOU!!!!