How do Fuel Cells Work
For some time I have been interested in the idea of cars that run on hydrogen fuel cells rather than petroleum, but I wanted to know how these fuel cells actually work? The hydrogen, presumably, isn't being "burned" in the normal sense, so what's going on?
Let's take a look at that most common of electrical sources, the battery. Batteries usually consist of two metal "poles", with an acid or salt solution sandwiched between them. The chemical reaction of these components makes electrons collect on the negative (-) terminal of the battery and, when an electrical item is attached to the battery, these electrons are used for power. At the same time, though, the chemical reaction within the battery is continuing, which eventually reduces the difference in charge between the positive (cathode) and negative (anode) poles and the battery stops producing power.
How about a fuel cell? There are a number of different types of fuel cell, but we'll look at hydrogen cells here. Fuel cells still work by transferring electrons, but the source of those electrons is different from in a battery: the electrons are stripped from the hydrogen fuel itself. The fuel cell consists of two catalyst-coated electrodes, separated by a membrane which only allows charged particles to pass through. The two electrodes are also connected to an electrical load, such as a car's motor. Hydrogen is fed into the cell at one end, where the catalyst prompts the Hydrogen to become positively charged H+. The dropped electron from the Hydrogen is picked up by the electrode (which becomes the negative anode), and used to power the load (i.e. the car). Meanwhile, the positively charged H+ passes through the membrane to the other electrode (the cathode), where it is combined with oxygen from the air, and the returning electrons, to become water.
I did wonder what happens when the catalysts are used up, but then I remembered that catalysts, while playing a part in aiding chemical reactions, are not actually used up in them. So the catalysts just sit there, merrily helping to convert the hydrogen to H+, and then into water.
What is quite amazing about this set up is that none of the mechanical components of the fuel cell are used up. The electrodes don't corrode, and there is no electrolyte slowly reducing in effectiveness. So long as Hydrogen is fed in the fuel cell will continue to generate.
One question facing proponents of fuel cell technology, though, is "How can we generate pure hydrogen cleanly?" Whilst a full answer is not within the scope of this article, one option is Honda's proposed solar filling station. This electrolyses water using solar energy, cleanly separating it into Hydrogen and Oxygen. Whatever method is used, however, it will need to be clean if we are to avoid simply replacing fossil-fuel based pollutants with new ones.
