Fuel CellsFuel CellsCourse:Course: Environmental Catalysis Environmental Catalysis

Mass and Heat Transfer Process LaboratoryMass and Heat Transfer Process Laboratory

2828thth April 2008 April 2008

Seelam Prem KumarSeelam Prem Kumar

Fuel CellFuel Cell

DefinitionDefinition::

A fuel cell is an electrochemical energy conversion device.

H2 + O2 == Electricity + Heat+H2O

It converts chemical energy to electrical energy using catalyst.

Fuel Cell HistoryFuel Cell History 1776-1800: 1776-1800: Electrochemistry founded by J.W.Ritter.Electrochemistry founded by J.W.Ritter. 1802: 1802: Simple fuel cell by Sir Humphrey Davy.Simple fuel cell by Sir Humphrey Davy. 1843: 1843: Sir William Grove First Fuel cell Type by electrolysis Sir William Grove First Fuel cell Type by electrolysis

of Hof H22O (today’s PAFC).O (today’s PAFC). 1899: 1899: Ceramic fuel cell (solid oxide electrolytes) discovered by Ceramic fuel cell (solid oxide electrolytes) discovered by

Sir Nernst.Sir Nernst. 1920’s1920’s First gas diffusion electrode by A.Schmid First gas diffusion electrode by A.Schmid 1937: 1937: Operation of first ceramic Fuel cell at 1000Operation of first ceramic Fuel cell at 1000ooC.C. 1955: 1955: Modified the original fuel cell design by using a Modified the original fuel cell design by using a

sulphonated polystyrene ion-exchange membrane as the sulphonated polystyrene ion-exchange membrane as the electrolyte.electrolyte.

19591959 British engineer Francis Thomas successfully developed British engineer Francis Thomas successfully developed a 5 kW stationary fuel cell.a 5 kW stationary fuel cell.

1960’s1960’s Pratt and Whitney licensed Bacon's U.S. patents for use Pratt and Whitney licensed Bacon's U.S. patents for use in the U.S. space program to supply electricity and drinking in the U.S. space program to supply electricity and drinking water.water.

1970’s1970’s First PAFC systems for stationary power. First PAFC systems for stationary power. 1980’s1980’s MCFC systems MCFC systems 1990’s1990’s SOFC systems SOFC systems 1990 1990 Ballard used series of fuel cells in transit busesBallard used series of fuel cells in transit buses.. Today many R and D’s , applications in various fields like Today many R and D’s , applications in various fields like

space, millitary, portable, home power, large power genration space, millitary, portable, home power, large power genration etc.etc.

Sir William Robert Grove 1811-1896

Parts of a Fuel CellParts of a Fuel Cell Anode (Negative post of the fuel cell)

Electrons that are freed from the hydrogen molecules used in an external circuit. Etched channels disperse hydrogen gas over the surface of catalyst.

Cathode (Positive post of the fuel cell) Etched channels distribute O2 to the surface of the catalyst. Electrons back from the external circuit to the catalyst Recombine with the hydrogen ions and oxygen to form H2O

Electrolyte Proton exchange membrane. Specially treated material, only conducts +ions Membrane blocks electrons.

Catalyst Facilitates reaction of oxygen and hydrogen Usually platinum powder very thinly coated onto carbon Rough & porous maximizes surface area exposed to hydrogen or oxygen The platinum-coated side of the catalyst faces the PEM.

Electrochemical Reactions Anode side:

2H2 4H+ + 4e-

Cathode side: O2 + 4H+ +4e- 2H2O

Overall net reaction: 2H2 + O2 2H2O

Thermodynamically: ΔGo =-nFEo

ΔGo= standard gibbs free energy of the cell reaction n=2 electrons for hydrogen,

F= fradays constant (96500Cmol-1), Eo = standard cell voltage.

Fuel Cell ChemistryFuel Cell Chemistry

Fuel Cell WorksFuel Cell Works

ΔH

ΔG

TΔS

Types of Fuel CellsTypes of Fuel Cells Alkaline Fuel Cells (AFC)Alkaline Fuel Cells (AFC)

Molten Carbonate Fuel Cells (MCFC)Molten Carbonate Fuel Cells (MCFC)

Phosphoric Acid Fuel Cells (PAFC)Phosphoric Acid Fuel Cells (PAFC)

Solid Oxide Fuel Cells (SOFC)Solid Oxide Fuel Cells (SOFC)

Proton Exchange Membrane Fuel Cells (PEMFC)Proton Exchange Membrane Fuel Cells (PEMFC)

Polymer electrolyte fuel cells (SPFC)Polymer electrolyte fuel cells (SPFC)

Direct Methanol Fuel Cells (DMFC) Direct Methanol Fuel Cells (DMFC)

Fuel cell types and differencesFuel cell types and differencesTypeType Temp. Temp.

((ooC)C)

FuelFuel ElectrolyteElectrolyte Mobile Mobile ion ion

(charge (charge carrier)carrier)

Electrode Electrode materialmaterial

EfficienEfficiency-cy-

(%)(%)

AFCAFC 60-110 60-110 (200)(200)

HH22 Aq. KOH or Aq. KOH or NaOHNaOH

OHOH-- Metal or Metal or carboncarbon

6060

PEMFCPEMFC 70-11070-110 HH22 Sulfonated Sulfonated (Nafion) (Nafion) polymerpolymer

HH++ Polymers Polymers

(H(H22O)O)xx

Pt on Pt on Carbon or Carbon or

CNTsCNTs

6060

PAFCPAFC 80-11080-110

(200)(200)

HH2 reformate2 reformate HH33POPO44 HH++ Pt on Pt on Carbon or Carbon or

CNTsCNTs

5555

MCFCMCFC 500-700500-700 HH22/CO /CO reformatereformate

HC’s,HC’s,

LiCOLiCO33-K-K22COCO33, ,

and and COCO22,O,O22,air ,air

oxidantsoxidants

COCO332-2- Ni+CrNi+Cr 55-6555-65

SOFCSOFC 700-1000700-1000 HH22/CO /CO reformatereformate

HC’s,HC’s,

ZrOZrO22 with with

YY220033

OO2-2- Ni/YNi/Y220033 -ZrO -ZrO22 60-6560-65

DMFCDMFC 70-11070-110 CH3OHCH3OH Polymer Polymer membranemembrane

(H(H22O)O)xx H H++ Pt on Pt on Carbon Carbon or CNTsor CNTs

6060

Direct Methanol Fuel CellDirect Methanol Fuel Cell

Anode:Anode:

CHCH33OH + HOH + H22O → COO → CO22 + 6H + 6H++ + 6e + 6e--

methanolmethanol

Cathode:Cathode:

(3/2)O(3/2)O22 + 6H + 6H++ + 6e + 6e-- → 3H → 3H22O (No reforming)O (No reforming)

Overall reaction:Overall reaction:

CHCH33OH + (3/2)OOH + (3/2)O22 → CO → CO22 + 2H + 2H22OO

Efficiency of Fuel CellEfficiency of Fuel Cell Efficiency of a cell is almost proportional to its voltage.Efficiency of a cell is almost proportional to its voltage.

Polarisation leads to voltage drop in electrolyte and it Polarisation leads to voltage drop in electrolyte and it

occurs at both electrodes.occurs at both electrodes.

Polarisation caused by obstruction of ePolarisation caused by obstruction of e--’s transfer ’s transfer

between electrode and reactant molecules.between electrode and reactant molecules.

Charge-transfer Polarization by limitations M.T Charge-transfer Polarization by limitations M.T

(concentration and diffusion polarisation) or else slow (concentration and diffusion polarisation) or else slow

reactions (rxn polarization) or also Ohmic polarisation reactions (rxn polarization) or also Ohmic polarisation

(electrical resistance)(electrical resistance)

Hydrogen FuelHydrogen Fuel

Fuel Cells require highly purified hydrogen Fuel Cells require highly purified hydrogen as a fuelas a fuel

Researchers are developing a wide range Researchers are developing a wide range of technologies to produce hydrogen of technologies to produce hydrogen economically from a variety of resources in economically from a variety of resources in environmentally friendly ways.environmentally friendly ways.

Hydrogen FuelHydrogen Fuel Hydrogen can be produced from a wide variety of energy Hydrogen can be produced from a wide variety of energy

resources including:resources including: Fossil fuels, such as natural gas and coalFossil fuels, such as natural gas and coal Nuclear energyNuclear energy Renewable resources, such as solar,water, wind and Renewable resources, such as solar,water, wind and BiomassBiomass

Mainly it can be produced by the following processes.Mainly it can be produced by the following processes. Thermal Processes : Thermal Processes : Natural gas reforming, Gasification, Biomass liquid ref.Natural gas reforming, Gasification, Biomass liquid ref. Electrolyte ProcessesElectrolyte Processes Photolytic ProcessesPhotolytic Processes

Electrolytic ProcessesElectrolytic Processes

Electrolytic processes use an electric current to split water into hydrogen Electrolytic processes use an electric current to split water into hydrogen and oxygenand oxygen

The electricity required can be generated by using renewable energy The electricity required can be generated by using renewable energy technologies such as wind, solar, geothermal and hydroelectric powertechnologies such as wind, solar, geothermal and hydroelectric powerBio-Hydrogen

BiofuelsBiofuels reformingreforming

Hydrogen storageHydrogen storage

Hydrogen is difficult to store and distributeHydrogen is difficult to store and distribute

The hydrogen can be stored in many ways:The hydrogen can be stored in many ways: Compression in gas cylindersCompression in gas cylinders

A metal absorber as a metal hydrideA metal absorber as a metal hydride

Cryogenic liquidCryogenic liquid

Potentially in carbon nano-fibres (still under development)Potentially in carbon nano-fibres (still under development)

Glass micro-spheres etc.Glass micro-spheres etc.

ReformerReformer

A reformer turns hydrocarbon or alcohol fuels into A reformer turns hydrocarbon or alcohol fuels into hydrogen which is then fed to the fuel cells.hydrogen which is then fed to the fuel cells.

Unfortunately, reformers are not perfect. They generate Unfortunately, reformers are not perfect. They generate heat and produce other gases besides hydrogen. heat and produce other gases besides hydrogen.

They use various devices to try to clean up the hydrogen, They use various devices to try to clean up the hydrogen, but even so, the hydrogen that comes out of them is not but even so, the hydrogen that comes out of them is not pure, and this lowers the efficiency of the fuel cell.pure, and this lowers the efficiency of the fuel cell.

Internal reformingInternal reforming Direct and in-direct internal reformingDirect and in-direct internal reforming

Direct internal reforming:Direct internal reforming: a porous ceramic anode a porous ceramic anode comprising a reforming catalyst, such as Pt, Rh, Ru and comprising a reforming catalyst, such as Pt, Rh, Ru and mixtures thereof, to intimately integrated the reforming mixtures thereof, to intimately integrated the reforming reaction with electrochemical reactions, high efficient reaction with electrochemical reactions, high efficient coupling of reactions can be achieved.coupling of reactions can be achieved.

In-direct Iinternal refroming:In-direct Iinternal refroming: its between the direct and its between the direct and convention reforming with a separated reforming catalyst convention reforming with a separated reforming catalyst bed but close to anode side of a fuel cell, eg,: SOFC.bed but close to anode side of a fuel cell, eg,: SOFC.

External ReformingExternal Reforming

Reforming

Steam Reforming UnitSteam Reforming Unit

WGSR to removeCO < 10ppm or PROX

Or Inorganic membrane

Fuel

Water

Advantages and Benifits Fuel CellAdvantages and Benifits Fuel Cell

3 E’s3 E’s EEnergy securitynergy security EEconomic growthconomic growth EEnvironmental protectionnvironmental protection

Water vapor is the only emission No noise, No air pollution More flexible High efficiency than batteries Constant power production Reliability

Fuel Cell ApplicationsFuel Cell Applications Stationary devices like portabel power Stationary devices like portabel power

generation, computer’s, server’s, data generation, computer’s, server’s, data generation, mobile phone battery, power generation, mobile phone battery, power plants etc.plants etc.

Mobile or transport devices like trucks, Mobile or transport devices like trucks, buses, transit systems etc.buses, transit systems etc.

Emission minimisation or elimination

www.fueleconomy.gov/feg/fcv_pem.shtml

Fuel cell transit bus

Laptops can be poweredLaptops can be powered for 20 hours without rechargingfor 20 hours without recharging

Fuel cell chip for cell phone andFuel cell chip for cell phone andCell phones can be powered forCell phones can be powered for 30 days without recharging30 days without recharging

FUEL CELLSTACK

Challenges to Fuel Cell TechnologyChallenges to Fuel Cell Technology

CostCost Durability and ReliabilityDurability and Reliability Etc….Etc….

Conclusions………Conclusions………

ReferencesReferences• http://www.ucsusa.org/assets/animation/fuelcell8.swf

• Environmental Catalysis-by E.J.J.G.Janssen and R.A.Van

Santen, vol-1.

• http://www.doitpoms.ac.uk/tlplib/fuel-cells/case.php

• A. Boudghene Stambouli et al, Renewable and

Sustainable Energy Reviews 6 (2002) 297–306. • www.fueleconomy.gov/feg/fcv_pem.shtml etc

BioBio-Hydrogen-A Clean, Renewable, Efficient Energy.-Hydrogen-A Clean, Renewable, Efficient Energy.