Chapter 5 - Hydrogen & Fuel Cell Vehicle

MOHD FAIRUS JAMIDfairus@icam.edu.my

Is an electrochemical reactions device that combines hydrogen and oxygen to produce electricity, with water and heat as its by-product.

Unlike a battery, chemicals are not stored in the fuel cell; they must be replenished

Using a fuel and an oxidant

Possible fuel sources: hydrogen, alcohols, hydrocarbons, gasoline

Possible oxidants: oxygen, chlorine, chlorine dioxide

Structural characteristics of PEMFC membranesStructural characteristics of PEMFC membranes

Anode (-) and Cathode (+) on each side of the fuel cell, divided by an electrolyte

Hydrogen gas is channeled through anode side; oxygen passes through cathode

Platinum catalyst oxidizes hydrogen atoms into H+ and electrons

Electrons pass along external circuit; conduct electricity before entering cathode

Electrolyte allows H+ to pass into the cathode In cathode, catalyst combines H+ , O2- and electrons,

forming H2O and heat

• Anode:2H2 => 4H+ + 4e-

• Cathode: O2 + 4H+ + 4e- => 2H2O

• Net Reaction:2H2 + O2 => 2H2O

• Exact opposite of electrolysis

Fuel cell stack componentsFuel cell stack components

The P2000, zero-emission vehicle that utilizes a direct The P2000, zero-emission vehicle that utilizes a direct hydrogen polymer electrolyte fuel cell.hydrogen polymer electrolyte fuel cell.

i. Polymer Electrolyte Membrane (PEM) Fuel Cells

ii. Direct Methanol Fuel Cells

iii. Alkaline Fuel Cells

iv. Phosphoric Acid Fuel Cells

v. Molten Carbonate Fuel Cells

vi. Solid Oxide Fuel Cells

vii. Regenerative Fuel Cells

Fuel Cell Electrolyte Operating Conditions

Alkaline FC (AFC) Aq. KOH Operates at room temp. to 80 0C

Apollo fuel cell

Proton Exchange

Membrane FC (PEMFC)

Sulfonated Polymers

Operates best at 60-90 0C

Hydrogen fuel

Originally developed by GE for space

Phosphoric Acid FC (PAFC)

H3PO4 Operates best at ~200 0C

Hydrogen fuel

Stationary energy storage device

Molten Carbonate FC (MCFC)

(Na, K, Li)2CO3 Operates best at 550 0C

Nickel catalysts, ceramic separator membrane

Hydrocarbon fuels reformed in situ

Solid Oxide FC (SOFC) YSZ Operates at 900 0C

Conducting ceramic oxide electrodes

Hydrocarbon fuels reformed in situ

Direct Methanol Fuel Cell

(DMFC)

Operates best at 60-90 0C

Methanol Fuel

For portable electronic devices

Proton Exchange Membrane (PEM)

This is the leading cell type for passenger car application

Uses a polymer membrane as the electrolyte

Operates at a relatively low temperature, about 175 degrees

Has a high power density, can vary its output quickly and is suited for applications where quick startup is required making it popular for automobiles

Sensitive to fuel impurities.

• Hydrogen is a secondary energy resource, meaning it must be made from another fuel

• Hydrogen can be produced from a wide variety of energy resources including:– Fossil fuels, such as natural gas and coal– Nuclear energy– Renewable resources, such as solar,water, wind

and biomass

• The biggest challenge regarding hydrogen production is the cost• Reducing the cost of hydrogen production so as to compete in the

transportation sector with conventional fuels on a per-mile basis is a significant hurdle to Fuel Cell’s success in the commercial marketplace

• There are three general categories of Hydrogen production– Thermal Processes– Electrolyte Processes– Photolytic Processes

• Thermal Processes– Natural Gas Reforming– Gasification – Renewable Liquid Reforming

• Natural Gas Reforming– Steam Methane Reforming

• Hydrogen is produced from methane in natural gas using high-temperature steam

• Methane reacts with the steam in presence of a catalyst to produce hydrogen

• This process accounts for about 95% of the hydrogen used today in the U.S.

– Partial oxidation • Produces hydrogen by burning methane in air

• Gasification– Process in which coal or biomass is converted into gaseous components by

applying heat under pressure and in the presence of steam– A subsequent series of chemical reactions produces a synthesis gas which

reacts with steam to produce more hydrogen that can be separated

• Renewable Liquid Reforming– Biomass is processed to make renewable liquid fuels, such as ethanol or

bio-oil, that are then reacted with high-temperature steam to produce hydrogen

– This process is very similar to reforming natural gas• Electrolytic Processes

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

– The electricity required can be generated by using renewable energy technologies such as wind, solar, geothermal and hydroelectric power

• Photolytic Processes– Uses light energy to split water into hydrogen and oxygen– These processes are in the very early stages of research but offer the

possibility of hydrogen production which is cost effective and has a low environmental impact

• Developing safe, reliable, compact and cost-effective hydrogen storage is one of the biggest challenges to widespread use of fuel cell technology

• Hydrogen has physical characteristics that make it difficult to store large quantities without taking up a great deal of space

• Hydrogen will need to be stored onboard vehicles, at hydrogen production sites, refueling stations and stationary power sites

• Hydrogen has a very high energy content by weight (3x more than gasoline) and a very low energy content by volume (4x less than gasoline)

• If the hydrogen is compressed and stored at room temperature under moderate pressure, too large a fuel tank would be required

• Researchers are trying to find light-weight, safe, composite materials that can help reduce the weight and volume of compressed gas storage systems

• Liquid hydrogen could be kept in a smaller tank than gaseous hydrogen, but liquefying hydrogen is complicated and not energy efficient

• Liquid hydrogen is also extremely sensitive to heat and expands significantly when warmed by even a few degrees, thus the tank insulation required affects the weight and volume that can be stored

• If the hydrogen is compressed and cryogenically frozen it will take up a very small amount of space requiring a smaller tank, but it must be kept supercold- around -120 to -196 degrees Celsius

• Fuel cells require specific humidity, pressure, etc.

• Catalysts are pricey and sensitive to poisoning

• Difficult to produce hydrogen

• Difficult to store optimum amounts of Hydrogen

• If fuels other than hydrogen are used, some greenhouse gasses are emitted

• Very few cars currently running on hydrogen

• Environmental Benefits - Reduce air pollution.

– Create less than one ounce of pollution per 1,000 kilowatt-hours of electricity produced

– Conventional combustion generating systems produce 25 pounds of pollutants for the same electricity

– The only byproducts of these Fuel Cell vehicles are water and heat

• Battery replacement/alternative

– Fuel Cell replacements for batteries would offer much longer operating life in a packaged of lighter or equal weight

– Additionally, Fuel Cell replacements would have an environmental advantage over batteries, since certain kinds of batteries require special disposal treatment

• It is a clean, quiet and highly efficient process- two to three times more efficient than fuel burning.

• Hydrogen fuel cells are efficient, and clean• Also expensive, and require specific humidity, temperature,

pressure• With more technological advancements, could be used in

mass production for various applications• Not an instant fix for the energy crisis, but definitely a major

component• Promising technology• Most viable for niche market use in the near future• Widespread marketplace acceptance and use is still many

years away

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