cells and batteries

how a cell works

electrochemical cells are made up of two electrodes in contact with an electrolyte. electrodes are made of metal and electrolyte contains free ions to react with them. chemical reactions between them set up a charge difference which flows through a wire to produce electricity.

what the voltage of a cell depends on

charge difference affected by type of metal used for electrodes as they react differently with electrolyte. the bigger the difference in reactivity of the electrodes, the bigger the voltage of the cell.
also affected by electrolyte used as different ions react differently.

how is a battery formed

connecting two or more cells together in series to increase the voltage.

Non-rechargeable batteries

if chemical reactions in the cell are irreversible, once ions in electrolyte and metal ions are used up and turned into products then no electricity is produced. cell cant be recharged because products cant be turned back. in a rechargeable cell, reaction can be reversed by connecting it to an external electric current.

what is a fuel cell

an electrical cell that is supplied with a fuel and oxygen. it efficiently produces electrical energy from the energy released when they react. the fuel becomes oxidised and sets up a potential difference.

what happens in a hydrogen-oxygen fuel cell

electrolyte is usually an acid. electrodes are usually carbon with a catalyst.
1. hydrogen goes in to anode compartment (is the negative electrode in a fuel cell) and oxygen goes into cathode compartment ( positive electrode in a fuel cell).
2. hydrogen is oxidised and loses electrons to produce H+ ions at anode, and ions in electrolyte move to cathode.
3. oxygen is reduced and gains electrons from the cathode, reacting with H+ ions to make water.
4. electrons flow through an external circuit from anode to cathode producing an electric current.

overall reaction in a hydrogen oxygen fuel cell

hydrogen plus oxygen produces water.

why are hydrogen-fuel cells useful

as conventional fuels for vehicles are a finite supply, hydrogen-oxygen fuel cells provide a cleaner alternative that dont produce any greenhouse gases- only water and heat. although electric vehicles dont produce many pollutants either their batteries are more polluting to dispose of- made from highly toxic metal compounds.
cheaper than batteries to make and batteries have a limit to number of times they can be recharged before replacing.
fuel cells store more energy- batteries need to be recharged more often.

disadvantages of using fuel cells

as hydrogen is a gas it takes up more space to store than a rechargeable battery.
it is explosive when mixed with air so hard to store safely.
it is often made from hydrocarbons or by electrolysis of water which uses electricity, which is generated by burning fossil fuels.