Fuel cells are a type of primary cell in that they are not recharged, However, they are unique because they never run out, if the reactants are constantly supplied. They are relatively efficient sources of energy, since they transform chemical energy directly into electrical energy, enabling efficient use of energy released by spontaneous redox reactions. Energy losses such as those that occur in coal-fired power stations and combustion engines would be avoided, with a consequential reduction in the volume of greenhouse gases produced.
A hydrogen-oxygen fuel cell is made up of two compartments, one for \(H_2\) and the other for \(O_2\). They are both separated by two porous electrodes and an electrolyte solution. The electrode at the \(H_2\) compartment is the anode, while the electrode at the \(O_2\) compartment is the cathode. The nature of the electrodes is crucial to the efficiency of the fuel cell, they must be both conducting and porous to allow the hydrogen and oxygen to come into contact with the ions in the electrolyte and to allow the redox half-reactions to occur at their surface. Catalysts are employed to enhance the rate of the reaction and the current that can be produced from a cell.
Hydrogen Fuel Cell
|Fuel cells convert chemical energy directly to electrical energy. This is then clearly more efficient than coal-fired power stations as there aren’t as many energy transformations that need to occur||Fuel cells are expensive – as they are still developing and there are no economies of scale associated with making a large number of fuel cells|
|No greenhouse gases, such as \(CO_2\) are produced since hydrogen fuel cells only produce water and heat as by-products||Fuel cells require a constant fuel supply|
|Fuel cells will generate electricity as long as fuel is supplied – conventional batteries need to be replaced or recharged||Fuel cells generate DC current – electrical appliances require AC current|
|Electricity can be generated on site – users are not reliant on connection to an electricity grid||Issues associated with the storage and safety of hydrogen fuel|
|Galvanic Cells||Fuel Cells|
|A galvanic cell that converts chemical energy to electrical energy from spontaneous redox reactions. The reactants of primary and secondary cells are contained within the cell and consequently, they can produce power for only a limited time until their reactants are depleted||A fuel cell is a galvanic cell that converts the chemical energy of a fuel into electrical energy. The fuel and air or oxygen is supplied continuously|
|A source of portable electrical energy||Useful as a continuous source of high electric current for both portable and fixed applications|
|60-90% efficiency||40-60% efficient; up to 85% if the heat produced by the cell is also used to generate electricity|