Fuel Cells: – The energy solution for Future

Imagine

A future with no wars over limited supplies of Oil

A future when every country is energy self-sufficient

Earth with no Acid rains, Ozone depletion or warming

Hydrogen EnergyHydrogen is the simplest and the most plentiful element in the universe. Despite its simplicity and abundance, hydrogen doesn't occur naturally as a gas on the Earth — it's always combined with other elements.

Hydrogen is high in energy, yet an engine that burns pure hydrogen produces almost no pollution. NASA has used liquid hydrogen since the 1970s to propel the space shuttle and other rockets into orbit. Hydrogen fuel cells power the space shuttle's electrical systems, producing a clean byproduct—pure water.

What is a Fuel Cell ?

Fuel cells are electrochemical devices like batteries that convert the chemical energy of a fuel directly and very efficiently into electricity (DC) and heat, thus doing away with combustion.

Unlike a battery, a fuel cell does not run down or require recharging. It will produce energy in the form of electricity and heat as long as fuel is supplied.

Electrodes Electrolyte

Electricity

History

• The principle of the fuel cell was discovered by German scientist Christian Friedrich Schönbein in 1838

• Based on this work, the first fuel cell was developed by Welsh scientist Sir William Robert Grove in 1843. The fuel cell he made used similar materials to today's Phosphoric-acid fuel cell.

Todys’s Fuel Cell

A fuel cell system which includes a "fuel reformer" can utilize the hydrogen from any hydrocarbon fuel - from natural gas to methanol, and even gasoline.

A modern Fuel Cell Assembly

For a fuel cell

• Chemicals constantly flow into the cell so it never goes dead.

As long as there is a flow of chemicals into the cell

the electricity flows out of the cell.

• Most fuel cells in use today use hydrogen and oxygen as the chemicals.

Fuel Cell Descriptions

• Fuel Cells generate electricity through an

electrochemical process

In which the energy stored in a fuel is converted

directly into DC electricity.

• Because electrical energy is generated without

combusting fuel.

Fuel cells are extremely attractive from an

environmental stand point.

How Fuel Cells Work

What is the Principle ?

A fuel cell consists of two electrodes sandwiched around an electrolyte. Oxygen passes over one electrode and hydrogen over the other, generating electricity, water and heat. 

Working Principle

Hydrogen gas(H2)flows into channels on one face of the cell and migrates through that electrode, while the same occurs with

oxygen gas (O2, typically from the ambient air) along the opposite electrode.

Contd…

But this wouldn't continue for long without a complete electrochemical cycle. As the electrical current begins to flow, hydrogen protons pass through the membrane from the anode to the cathode.

When the electrons return from doing work—lighting your house, charging a battery, or powering your car's motor, for example—they react with oxygen and the hydrogen protons at the cathode to form water. Heat emanates from this union (an exothermic reaction), as well as from the frictional resistance of ion transfer through the membrane. This thermal energy can be utilized outside the fuel cell.

Anode Reaction: H2 —> 2 H+ + 2 e-

Cathode Reaction: ½ O2 + 2 H+ + 2 e- —> H2O

Layers of materials with distinct

electrochemical properties are sandwiched together to form a single galvanic cell. At the heart lies a membrane that can only be crossed by charged molecules. Gas-permeable electrodes coated with a catalyst adhere to this membrane, adding a layer on either side. These electrodes are in turn connected to a device that can utilize electricity— a load— which creates a complete electrical circuit.

Fuel Cell TypesFuel Cell type Electrolyte Anode gas Cathode

gasTemp oC

Efficiency %

Proton Ex Membrane (PEMFC)

Solid polymer

membrane

Hydrogen Pure or Atm

Oxygen

75 35 - 60

Alkaline (AFC)

Potassium Hydroxide

Hydrogen Pure Oxygen

< 80 50 - 70

Direct Methanol

(DMFC)

Solid polymer

membrane

Methanol soln in Water

Atm Oxygen

75 35 - 40

Phosphoric Acid (PAFC)

Phosphorus Hydrogen Atm Oxygen

210 35 - 50

Molten Carbonate

(MCFC)

Alkali Carbonate

Hydrogen / Methane

Atm Oxygen

650 40 - 55

Solid Oxide ( SOFC)

Ceramic Oxides

Hydrogen / Methane

Atm Oxygen

800 - 1000

45 - 60

All fuel cells have the same basic operating principle.

• An input fuel is catalytically reacted (electrons removed from the fuel elements) in the fuel cell to create an electric current.

• Fuel cells consist of an electrolyte material which is sandwiched in between two thin electrodes (porous anode and cathode).

• The input fuel passes over the anode (and oxygen over the cathode) where it catalytically splits into ions and electrons.

• The electrons go through an external circuit to serve an electric load while the ions move through the electrolyte toward the oppositely charged electrode.

• At the electrode, ions combine to create by-products, primarily water and CO2. Depending on the input fuel and electrolyte, different chemical reactions will occur.

Basic Configuration

PEMFC

Animation of PEMFC

PEMFC Technology and issues

• Expected life of PEMFC is very short (5,000 hours) and not suitable for Distributed Generation (DG).

• The most commonly used catalyst (Pt) is very expensive.

• The most commonly used membrane (Nafion – a sulfonated tetrafluorethylene copolymer is also very expensive).

• PEMFCs are very expensive.

• CO poisoning diminishes the efficiency. Carbon monoxide (CO) tends to bind to Pt. Thus, if CO is mixed with hydrogen, then the CO will take out catalyst space for the hydrogen.

• Hydrogen generation and storage is a significant problem.

• Additional issues to be discussed when comparing other technologies: dynamic response and heat production.

• The main advantage is that they use a liquid fuel.• Reactions:

• Anode• Cathode

• Voltages: 0.046 V at anode, 1.23 V at cathode, 1.18 V overall.

• Methanol has high energy density so DMFC are good for small portable applications.

• Issues:• Cost• Excessive fuel crossover (methanol crossing the membrane)• Low efficiency caused by methanol crossover• CO poisoning• Low temperature production• Considerable slow dynamic response

Direct Methanol Fuel Cells (DMFC)

3 2 2 6 6CH OH H O CO H e 2 21/ 2 2 2O H e H O

• One of their main advantages is their long life in the order of 40,000 hours.

• The phosphoric acid serves as the electrolyte.

• The reactions are the same than in a PEMFC. Hence, the reversible voltage is 1.23 V

• The most commercially successful FC: 200 kW units manufactured by UTC

• They produce a reasonable amount of heat

• They support CO poisoning better than PEMFC

• They have a relatively slow dynamic response

• Relative high cost is an important issue

Phosphoric Acid Fuel Cells (PAFCs)

• The main advantage is that their cost is relatively low (when considering the fuel cell stack only without “accessories”.• Reactions:

• Anode• Cathode

• Developed for the Apollo program.

• Very sensitive to CO2 poisoning. So these FCs can use impure hydrogen but they require purifying air to utilize the oxygen.

• Issues:• Cost (with purifier)• Short life (8000 hours)• Relatively low heat production

Alkaline Fuel Cells (AFCs)

2 22 2 2H OH H O e

2 21/ 2 2 2 2O H O e OH

• One of the main advantages is the variety of fuels and catalyst than can be used.• Reactions:

• Anode• Cathode

• They operate at high temperature. On the plus side, this high temperature implies a high quality heat production. On the minus side, the high temperature creates reliability issues.

• They are not sensitive to CO poisoning.

• They have a relatively low cost.

• Issues:• Extremely slow startup• Very slow dynamic response

22 3 2 2 2H CO H O CO e

22 2 31/ 2 2O CO e CO

Molten Carbonate Fuel Cells (MCFCs)

Solid Oxide Fuel Cells (SOFCs)• One of the main advantages is the variety of fuels and catalyst than can be used.• Reactions:

• Anode• Cathode

• They operate at high temperature with the same plus and minus than in MCFCs.

• They are not sensitive to CO poisoning.

• They have a relatively low cost.

• They have a relatively high efficiency.

• They have a fast startup

• The electrolyte has a relatively high resistance.

22 2 2H O H O e

221/ 2 2O e O

PEMFC DMFC AFC PAFC MCFC SOFC

Fuel H2 CH3OHH2 H2

H2, CO,

CH4,

hydrocarbons

H2, CO,

CH4,

hydrocarbons

Electrolyte

Solid polymer(usually Nafion)

Solid polymer(usually Nafion)

Potasium hydroxide

(KOH)

Phosporic acid

(H3PO4

solution)

Lithium and

potassium carbonate

Solid oxide (yttria,

zirconia)

Charge carried in electrolyte

H+ H+ OH- H+ O2-

Operational temperature (oC)

50 – 100 50 - 90 60 - 120 175 – 200 650 1000

Efficiency (%) 35 – 60 < 50 35 – 55 35 – 45 45 – 55 50 – 60

Unit Size (KW) 0.1 – 500 << 1 < 5 5 – 2000 800 – 2000 > 2.5

Installed Cost ($/kW)

4000 > 5000 < 1000*3000 – 3500 800 – 2000 1300 - 2000

Fuel cell technologies

2-3CO

• U

Potential Applications

• Stationary power generation • Residential • Transportation – No pollution• Portable power – Miniature Fuel

Cells • Land fill Waste treatment – Power

from Methane in-situ .

Stationary Power

• More than 2500 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.

Residential Power

• Ideal for residential power generation, either to provide supplemental power and backup for critical areas, or installed as independent generator in areas that are inaccessible by power lines.

• Operating silently, they reduce noise & air pollution and the waste heat can be used to provide hot water or room heating for a home.

• Prototypes being tested & demonstrated for residential use extract hydrogen from propane or natural gas.

Powering Transportation

• All the major automotive manufacturers have a fuel cell vehicle either in development or in testing right now.

• Honda and Toyota have already begun leasing vehicles in California and Japan.

• Fuel cells are also being incorporated into buses, locomotives, airplanes, scooters and golf carts.

Landfills and Waste Water Treatment

• Fuel cells currently operate at landfills and wastewater treatment plants across USA.

• Providing a valid technology for reducing emissions and generating power from the methane gas they produce.

Benefits

No other energy generating technology holds the combination of

benefits that fuel cells offer

• Energy Security : Abundant Source• Supply Security : Efficient, modular and fuel flexible• Physical security : resources evenly distributed in nature• High Reliability• High quality power• High Efficiency – as high as 85%• ENVORONMANTALLY FRIENDLY

Energy Security

• Being efficient, modular and fuel flexible, fuel cells can enable a transition to a secure, renewable energy future, based on the use of hydrogen.

• A fuel cell system that includes a "fuel reformer" can utilize the hydrogen from any hydrocarbon or alcohol fuel - natural gas, ethanol, methanol, propane, and even gasoline or diesel.

• Hydrogen can also be produced from electricity from conventional, nuclear or renewable sources.

• Hydrogen can be extracted from novel feed stocks such as landfill gas or anaerobic digester gas from wastewater treatment plants, from biomass technologies, or from hydrogen compounds containing no carbon, such as ammonia or borohydride.

• Fuel cells and Electrolysis, in combination with solar or wind power, or any renewable source of electricity offer the promise of a totally zero-emission energy system that requires no fossil fuel and is not limited by variations in sunlight or wind flow.

• This hydrogen can supply energy for power needs and for transportation.

High Reliability

• Fuel cells can be configured to provide backup power to a grid-connected customer, if the grid fail.

• They can be configured to provide completely grid-independent power.

• They can also use the grid as the backup system. • Modular installation (several identical units to

provide a desired quantity of electricity) provides extremely high reliability .

• In specialized applications, fuel cells can achieve up to 99.9999% reliability, less than one minute of down time in a six year period.

High Quality and Efficiency

• Fuel cells offer high quality power, crucial to an economy that depends on increasingly sensitive computers, medical equipment and machines.

• High Efficiency as they make energy electrochemically, and do not burn fuel.

• Fuel cells are fundamentally more efficient than combustion systems.

Environmental Benefits

• Air pollution continues to be a primary health concern in the industrialized world.

• Exposure to ozone, particulate, or airborne toxic chemicals has substantial health consequences.

• Scientists are now directly linking air pollution to heart disease, asthma and cancer.

• Recent health studies suggest polluted urban air is a comparable health threat to passive smoking.

Fuel cells can reduce pollution today and offer the promise of eliminating pollution

tomorrow

Hydrogen - Tomorrow

Production Storage

Use

Bio-mass & Electrolysis

Innovative Tank Designs

Fuel for FUEL CELLS

Hydrogen production for Future

Photo-electrochemical

Algal Production

Solar powered Electrolysis