Fuel Cell Technology

Curtis LentzAPPH 573

April 13, 2004

Topics1. A Very Brief History2. Electrolysis3. Fuel Cell Basics

- Electrolysis in Reverse- Thermodynamics- Components- Putting It Together

4. Types of Fuel Cells- Alkali- Molten Carbonate- Phosphoric Acid- Proton Exchange Membrane- Solid Oxide

5. Benefits6. Current Initiatives

- Automotive Industry- Stationary Power Supply Units- Residential Power Units

7. Future

A Very Brief History

Considered a curiosity in the 1800’s. The first fuel cell was built in 1839 by Sir William Grove, a lawyer and gentleman scientist. Serious interest in the fuel cell as a practical generator did not begin until the 1960's, when the U.S. space program chose fuel cells over riskier nuclear power and more expensive solar energy. Fuel cells furnished power for the Gemini and Apollo spacecraft, and still provide electricity and water for the space shuttle.(1)

Electrolysis“What does this have to do with fuel cells?”

By providing energy from a battery, water (H2O) can be

dissociated into the diatomic molecules of hydrogen (H2)

and oxygen (O2).

Figure 1

Fuel Cell Basics“Put electrolysis in reverse.”

fuelcell

H2OO2

H2

heat

work

The familiar process of electrolysis requires work to proceed, if the process is put in reverse, it should be able to do work for us spontaneously.

The most basic “black box” representation of a fuel cell in action is shown below:

Figure 2

Fuel Cell BasicsThermodynamics

H2(g) + ½O2(g) H2O(l)

Other gases in the fuel and air inputs (such as N2 and CO2) may be present, but as they are not involved in the electrochemical reaction, they do not need to be considered in the energy calculations.

69.91 J/mol·K205.14 J/mol·K130.68 J/mol·KEntropy (S)

-285.83 kJ/mol00Enthalpy (H)

H2O (l)O2H2

Table 1 Thermodynamic properties at 1Atm and 298K

Enthalpy is defined as the energy of a system plus the work needed to make room for it in an environment with constant pressure.

Entropy can be considered as the measure of disorganization of a system, or as a measure of the amount of energy that is unavailable to do work.

Fuel Cell BasicsThermodynamics

Enthalpy of the chemical reaction using Hess’ Law:ΔH = ΔHreaction = ΣHproducts – ΣHreactants

= (1mol)(-285.83 kJ/mol) – (0)

= -285.83 kJ

Entropy of chemical reaction:ΔS = ΔSreaction = ΣSproducts – ΣSreactants

= [(1mol)(69.91 J/mol·K)] – [(1mol)(130.68 J/mol·K) + (½mol)(205.14 J/mol·K)]

= -163.34 J/K

Heat gained by the system:ΔQ = TΔS

= (298K)(-163.34 J/K)= -48.7 kJ

Fuel Cell BasicsThermodynamics

The Gibbs free energy is then calculated by:

ΔG = ΔH – TΔS = (-285.83 kJ) – (-48.7 kJ) = -237 kJ

The external work done on the reaction, assuming reversibility and constant temp.W = ΔG

The work done on the reaction by the environment is:

The heat transferred to the reaction by the environment is:

W = ΔG = -237 kJ

ΔQ = TΔS = -48.7 kJ

More simply stated: The chemical reaction can do 237 kJ of work and produces 48.7 kJ of heat to the environment.

Fuel Cell BasicsComponents

Anode: Where the fuel reacts or "oxidizes", and releases electrons.

Cathode: Where oxygen (usually from the air) "reduction" occurs.

Electrolyte: A chemical compound that conducts ions from one electrode to the other inside a fuel cell.

Catalyst: A substance that causes or speeds a chemical reaction without itself being affected.

Cogeneration: The use of waste heat to generate electricity. Harnessing otherwise wasted heat boosts the efficiency of power-generating systems.

Reformer: A device that extracts pure hydrogen from hydrocarbons.

Direct Fuel Cell: A type of fuel cell in which a hydrocarbon fuel is fed directly to the fuel cell stack, without requiring an external "reformer" to generate hydrogen.

Fuel Cell BasicsPutting it together.

Figure 3

Types of Fuel Cells

The five most common types:AlkaliMolten CarbonatePhosphoric AcidProton Exchange MembraneSolid Oxide

Alkali Fuel Cell

compressed hydrogen and oxygen fuel

potassium hydroxide (KOH) electrolyte

~70% efficiency

150˚C - 200˚C operating temp.

300W to 5kW output

requires pure hydrogen fuel and platinum catylist → ($$)liquid filled container → corrosive leaks

Figure 4

Molten Carbonate Fuel Cell (MCFC)

carbonate salt electrolyte

60 – 80% efficiency

~650˚C operating temp.

cheap nickel electrode catylist

up to 2 MW constructed, up to 100 MW designs exist

Figure 5

The operating temperature is too hot for many applications.

carbonate ions are consumed in the reaction → inject CO2 to compensate

Phosphoric Acid Fuel Cell (PAFC)

phosphoric acid electrolyte

40 – 80% efficiency

150˚C - 200˚C operating temp

11 MW units have been tested

sulphur free gasoline can be used as a fuel

Figure 6

The electrolyte is very corrosive

Platinum catalyst is very expensive

Proton Exchange Membrane (PEM)

thin permeable polymer sheet electrolyte

40 – 50% efficiency

50 – 250 kW

80˚C operating temperature

electrolyte will not leak or crack

temperature good for home or vehicle use

platinum catalyst on both sides of membrane → $$

Figure 7

Solid Oxide Fuel Cell (SOFC)

hard ceramic oxide electrolyte

~60% efficient

~1000˚C operating temperature

cells output up to 100 kW

high temp / catalyst can extract the hydrogen from the fuel at the electrode

high temp allows for power generation using the heat, but limits use

SOFC units are very large

solid electrolyte won’t leak, but can crack

Figure 8

Benefits

Efficient: in theory and in practice

Portable: modular units

Reliable: few moving parts to wear out or break

Fuel Flexible: With the a fuel reformer fuels such as natural gas, ethanol, methanol, propane, gasoline, diesel, landfill gas,

wastewater treatment digester gas, or even ammonia can be used

Environmental: produces heat and water (less than combustion in both cases)near zero emission of CO and NOx

reduced emission of CO2 (zero emission if pure H2 fuel)

Current InitiativesAutomotive Industry

Most of the major auto manufacturers have fuel cell vehicle (FCV) projects currently under way, which involve all sorts of fuel cells and hybrid combinations of conventional combustion, fuel reformers and battery power.

Considered to be the first gasoline powered fuel cell vehicle is the H20 by GM:

GMC S-10 (2001)fuel cell battery hybridlow sulfur gasoline fuel25 kW PEM40 mpg112 km/h top speed

Figure 9

Fords Adavanced Focus FCV (2002)fuel cell battery hybrid85 kW PEM~50 mpg (equivalent)4 kg of compressed H2 @ 5000 psi

Approximately 40 fleet vehicles are planned as a market introduction for Germany, Vancouver and California for 2004.

Current InitiativesAutomotive Industry

Figure 10

Figure 11

Daimler-Chrysler NECAR 5 (introduced in 2000)

85 kW PEM fuel cell

methanol fuel

reformer required

150 km/h top speed

version 5.2 of this model completed a California to Washington DC driveawarded road permit for Japanese roads

Current InitiativesAutomotive Industry

Figure 12

Mitsubishi Grandis FCV minivan

fuel cell / battery hybrid

68 kW PEM

compressed hydrogen fuel

140 km/h top speed

Plans are to launch as a production vehicle for Europe in 2004.

Current InitiativesAutomotive Industry

Figure 13

Current InitiativesStationary Power Supply Units

A fuel cell installed at McDonald’s restaurant, Long Island Power Authority to install 45 more fuel cells across Long Island, including homes.(2) Feb 26, 2003

More than 2500 stationary fuel cell systems have been installed all over the world - in hospitals, nursing homes, hotels, office buildings, schools, utility power plants, and an airport terminal, providing primary power or backup. In large-scale building systems, fuel cells can reduce facility energy service costs by 20% to 40% over conventional energy service.

Figure 14

Current InitiativesResidential Power Units

There are few residential fuel cell power units on the market but many designs are undergoing testing and should be available within the next few years. The major technical difficulty in producing residential fuel cells is that they must be safe to install in a home, and be easily maintained by the average homeowner.

Residential fuel cells are typically the size of a large deep freezer or furnace, such as the Plug Power 7000 unit shown here, and cost $5000 - $10 000.

If a power company was to install a residential fuel cell power unit in a home, it would have to charge the homeowner at least 40 ¢/kWh to be economically profitable.(3) They will have to remain a backup power supply for the near future.

Figure 15

Future

“...projections made by car companies themselves and energy and automotive experts concur that around 2010, and perhaps earlier, car manufacturers will have mass production capabilities for fuel cell vehicles, signifying the time they would be economically available to the average consumer.” Auto Companies on Fuel Cells, Brian Walsh and Peter Moores, posted on www.fuelcells.org

Technical and engineering innovations are continually lowering the capital cost of a fuel cell unit as well as the operating costs, but it is expected that mass production will be of the greatest impact to affordability.

A commercially available fuel cell power plant would cost about $3000/kW, but would have to drop below $1500/kW to achieve widespread market penetration. http://www.fuelcells.org/fcfaqs.htm

Future

internal combustion obsolete?

solve pollution problems?

common in homes?

better designs?

higher efficiencies?

cheaper electricity?

reduced petroleum dependency?

...winning lottery numbers?

References

(1) FAQ section, fuelcells.org(2) Long Island Power Authority press release: Plug Power Fuel Cell Installed at McDonald’s Restaurant, LIPA to Install 45 More Fuel Cells Across Long Island, Including Homes, http://www.lipower.org/newscenter/pr/2003/feb26.fuelcell.html(3) Proceedings of the 2000 DOE Hydrogen Program Review: Analysis of Residential Fuel Cell Systems & PNGV Fuel Cell Vehicles, http://www.eere.energy.gov/hydrogenandfuelcells/pdfs/28890mm.pdf

Figures1, 3 http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/electrol.html4 – 8 http://fuelcells.si.edu/basics.htm10 http://www.moteurnature.com/zvisu/2003/focus_fcv/focus_fcv.jpg11 http://www.granitestatecleancities.org/images/Hydrogen_Fuel_Cell_Engine.jpg12 http://www.in.gr/auto/parousiaseis/foto_big/Necar07_2883.jpg13 http://www3.caradisiac.com/media/images/le_mag/mag138/oeil_mitsubishi_grandis_big.jpg14 http://www.lipower.org/newscenter/pr/2003/feb26.fuelcell.html15 http://americanhistory.si.edu/csr/fuelcells/images/plugpwr1.jpg

Table 1 http://hyperphysics.phy-astr.gsu.edu/hbase/tables/therprop.html#c1

Fuel cell data from: Types of Fuel Cells, fuelcells.org

Fuel Cell Vehicle data primarily from: Fuel Cell Vehicles (From Auto Manufacturers) table, fuelcells.org