Fuel Cells

Extra chapter with a topic test

Fuel cell

a type of galvanic cells that generates electricity from redox reactions

How do fuel cells produce electricity?

Fuel cells use the chemical energy of hydrogen or other fuels to cleanly and efficiently generate electricity almost with no pollution

The hydrogen economy

where hydrogen could become a major source of energy and replace fossil fuels

Fuel cell design

• 2 compartments or oxygen and hydrogen

• Electrolyte in between acting as a salt bridge

• Anode = oxidation of hydrogen

  • Cathode = reduction of oxygen

Characteristics of electrodes

• Conducting - allows ions to come in contact with hydrogen and oxygen gas

• Porous - increasing surface area of the electrode, allowing spontaneous redox reactions to happen on the surface

Function of the electrolyte

carries ions from one electrode to the other

Products of fuel cells

• water and heat

• 1 volt

Efficiency of fuel cells

• are 60% efficient

• Petrol and engines are only 25-30% efficient

• using steam that can heat a turbine can increase cell efficiency to 85%

Catalyst

employed to enhance the rate of reaction an the current produced from the cell

Catalysts at the anode and cathode

Anode: Platinum metal- increases the rate of oxidation

Cathode: NIckel powder - increases rate of reduction

Advantages of fuels cells

• Efficient energy conversion (of chemical → electrical)

• No greenhouse gases released

• Continuous supply of energy (with reactants continuously supplied)

• can use a variety of fuels

• Electricity can be generated onsite

  • Waste heat can be recycled

Disadvantages of fuel cells

• Requires constant supply of gas

• Expensive, as technology is still developing

• Some catalysts and electrolytes are expensive

• Infrastructure need to be created such as H2 filling stations

• Fuel cells generating DC, homes using AC

• Most H2 is sourced from fossil fuels

• H2 is dangerous to use, hence the storage and safety

Why is a fuel cell described as ‘zero emission’ device?

water is only produced apart from electricity and heat when hydrogen fuel itself is made renewably

Steam reforming

• 95% of hydrogen is produced from fossil fuels

• steam reacts with fossil fuels at high temperatures

• Carbon monoxide generated can be use to generate more hydrogen gas

Disadvantages of hydrogen production

• hydrogen produced has lower energy content

• carbon dioxide emissions produced

Alternative hydrogen production methods

• using electrical energy to convert water to hydrogen

• collecting biogas and converting methane in the gas to hydrogen using the steam reforming process

Hydrogen storage

• Liquid hydrogen - less energy than petrol and needs a large tank for insulation

• Compressed hydrogen - stored in high pressure tanks and inconvenient due to being bigger than a car boot

Alternatives for hydrogen storage

• Surface absorption of hydrogen molecules

• Absorption into a solid lattice as hydrogen atoms

Safety issues of hydrogen gas

• will ignite and explode at any combination of hydrogen and air

• Low density of hydrogen causes dangerous leakage which need hydrogen sensors as it quickly disperses