Alternatives to oil
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Clean and efficient hydrogen is a much-vaunted alternative power source. Iceland has already embarked on its journey to become the first hydrogen economy.
Hydrogen occurs naturally in water, so resources are vast
Hydrogen fuel cells are silent
The only by-product is water vapour, in contrast to the burning of fossil fuels, which emits greenhouse gases and other pollutants.
The biggest problem is getting at the hydrogen. This is done either by electrolysis - using electricity to split water molecules into oxygen and hydrogen - or by reforming fossil fuels.
Electrolysis creates no harmful by-products directly, but is only as clean as the process used to generate the electricity in the first place It is also expensive – costing about $2.40 for a kilogram of hydrogen
The more widely used method is to split the hydrocarbons in fossil fuels into hydrogen and carbon. This is much cheaper – about $0.65 a kilogram. But it defeats the point somewhat as it still uses fossil fuels and creates carbon dioxide as a by-product. Even using hydrocarbons, however, hydrogen fuel cells would still reduce air pollution.
Hydrogen is a flammable gas, so there are safety concerns
Hydrogen is bulky to transport
How it works
Pure hydrogen is a gas. But hydrogen atoms are widely found combined with oxygen in water molecules, or with carbon in hydrocarbons such as coal and oil. If hydrogen and oxygen are combined in uncontrolled conditions, an explosion results – energy is released.
A fuel cell allows this reaction to take place under control. It works like a constantly replenished battery, generating a current from the reaction between the two gases. Hydrogen is fed to a positive electrode (anode) and oxygen to a negative one (cathode). A catalyst helps the hydrogen atoms split into electrons and hydrogen ions. A membrane between the two electrodes allows the ions to pass from the anode to the cathode to combine with the oxygen, but blocks the path of the free electrons also trying to do so. These electrons flow instead through an external circuit, creating an electrical current. Water forms at the cathode as the electrons, hydrogen ions and oxygen atoms combine.