Fuel cells and batteries

Why do alkaline batteries eventually stop working

They stop working when all the reactants have been used up and when they have used up all their energy

How do batteries work

Batteries are stores of chemical energy. When being used in portable electrical devices like your phone, they transfer chemical energy into electrical energy.

Why do batteries stop working?

When a battery stops working, it is because the chemicals in it have been used up. Some batteries are rechargeable and when they are being recharged, electrical energy (from the mains) is transferred back to chemical energy (in the battery) to be used again.

Advantages of batteries

• They are portable and have changed how we live and work.

• Some batteries are a clean method of generating electricity for transport as they do not produce carbon dioxide.

• Batteries are used to store electricity that is surplus to requirements. This means that energy is not being wasted.

Disadvantages of batteries

• They are expensive to use.

• They (usually) store only a small amount of energy.

• They contain finite resources such as precious metals. This is why it is essential that we recycle batteries.

• Mining precious metals and making batteries produce toxic waste which is dangerous to the environment.

• They can leak corrosive chemicals (from the electrolyte).

Advantages of using hydrogen for a fuel cell

• petrol comes from a non renewable source or there are renewable ways of producing hydrogen, electrolysis of water

• Its combustion only produces water

• Combustion of hydrogen does not produce carbon dioxide or does not contribute to climate change

Disadvantages of hydrogen fuel cells

• hydrogen has to be stored at high pressure if there is a risk of explosion or larger volume needed for storage

• Much less energy produced from the combustion of Hydrogen or need to refuel more often

• Most methods of producing Hydrogen need fossil fuels

Chemical cells

Usually a battery is made up of cells. The cell is what converts the chemical energy into electrical energy.

A simple cell contains two different metals (electrodes) separated by a liquid or paste called an electrolyte. When the metals are connected by wires an electrical circuit is completed.

One metal is more reactive than the other. Negatively-charged electrons flow from the more reactive metal through the wires to the less reactive metal. In the graphic above, electrons flow from the magnesium to the copper. Positively-charged ions flow from the copper through the electrolyte to the magnesium.

Electricity will continue to flow until there is no more magnesium left to react.

Rule for potential difference in chemical cells

The greater the difference in reactivity between the metals the higher the potential difference.

when do non-rechargeable batteries stop working

They stop working when the reactant is used up

How are rechargeable batteries recharged

The chemical reactions are reserved using an external electrical current

Describe what a hydrogen fuel cell is and how it works

A fuel such as Hydrogen is fed to the anode and air is fed to the cathode. In a hydrogen fuel cell a catalyst at the anode separates hydrogen molecules into protons and electrons which take different paths to the cathode. the electrons go through an external circuit creating a flow of electricity. The protons migrate through the electrolyte to the cathode where they unite with oxygen and the electrons produce water and heat.

The __________ that is produced by a chemical cell depends on the type of electrode and electrolyte.

voltage

True or false? Hydrogen-oxygen fuel cells have no moving parts.

true

What happens to the voltage produced by a cell if the metals used are further apart in the reactivity series?

it increases, The larger the difference in reactivity between the 2 metals in a cell, the greater the voltage.

what is a cell

composed of two electrodes dipped in a electrolyte solution. It produces electricity from a chemical reaction.

what is a battery

a battery consists of two or more cells connected in series

rechargeable batteries

chemical reactions are reversed when an external current is supplied

non-rechargable batteries

reactants are used up, cannot be recharged

what is a fuel cell

supplied by fuel and oxygen to oxidise the fuel to generate electricity

Why can alkaline batteries not be recharged?

the reaction is not reversible

Why can a rechargeable cell be recharged?

reaction is reversible

why are some fuel cells described as alkaline fuel cells

contain OH- ions