chemical cells and fuel cells

• Cells contain chemicals which react to produce electricity.
• The voltage produced by a cell is depended upon a number of factors such as type of electrode & electrolyte.
• A simple cell can be made by connecting two different metals in contact with an electrolyte.
• Batteries are two or more cells connected together in series to provide a greater voltage.
• Non-rechargeable cells & batteries stop chemical reactions when one of the reactants has been used up.
• Alkaline batteries are non-rechargeable.
• Rechargeable cells & batteries can be recharged because the chemical reactions are reversed when an external electrical current is supplied.
• Fuel cells are supplied by an external source of fuel (e.g hydrogen) and oxygen or air, where the fuel is oxidised electrochemically within the fuel cell to produce a potential difference.
• Overall reaction in a hydrogen fuel cell involves the oxidation of hydrogen to produce water.
• Hydrogen fuel cells offer a potential alternative to rechargeable cells & batteries as they can be used constantly provided fuel keeps being put in and can be recharged by reversing reaction, so fuel doesn’t need to keep being supplied.
• Hydrogen is a gas so needs to be stored at high pressure and so is harder to transport and dispose of.
• Hydrogen fuel cells only produce water when burnt and will eventually stop working.
• Equations for each half cell: At the cathode (negative electrode): H 2 (g) –> 2e – +2H + (aq) At the anode (positive electrode): 4H + (aq) + O 2 (g) + 4e – → 2H 2 O(g).