Ready for Production
By Jacques Gordon
We use two different technologies to make electricity. One is mechanical; physically manipulating magnetic fields, such as with a generator or an ignition coil. The other is chemical, in which a chemical reaction produces ions. An ion is an atom that has an extra electron or one less electron that it normally would. This makes it somewhat unstable, and when exposed to the right conditions, the atom will either attract or give up an electron to become stable again. Creating ions and moving electrons from one atom to another produces the energy we call electricity.
A standard lead/acid battery makes electricity (moves electrons) with a chemical reaction, but first we need to make some ions by “charging” the battery. The lead plates in a lead/acid battery are actually lead sulfate, a compound made of lead and sulfur. Charging the battery forces electrons to flow from one set of plates to the other, transforming one set into lead (with fewer electrons) and the other into lead oxide (‘charged’ with extra electrons). It also ionizes the electrolyte (sulfuric acid), increasing its ability to conduct electricity. The plates are insulated from each other, so when a circuit is connected across the battery terminals, electrons flow from the ‘charged’ plates (cathode) through the circuit to the ‘uncharged’ plates (anode) and into the acid. Eventually both sets of plates and the acid have a balanced (stable) number of electrons again and the chemical reaction ends.
In a fuel cell, instead of storing ions on metal plates, we create them continuously by pumping fuel through porous metal plates. There are several different types of fuel cell, each using different metals, fuels and electrolytes, but they pretty much all work the same way.
The hydrogen fuel cell is the most common type. Hydrogen is pumped through pores in the anode, and a chemical reaction between the hydrogen and the metal anode strips away electrons. These electrons flow out through the anode into the circuit, leaving a positively-charged hydrogen ion which flows through the electrolyte to the cathode. There it reacts with oxygen (in the air) to recover an electron from the electrical circuit. These two chemical reactions working together generate direct current (DC) and water.
A typical fuel cell produces about 0.7 volts, so just like the lead/acid battery which produces 1.2 volts per cell, the cells are ‘stacked’ together to provide the desired voltage. Honda recently installed a one-megawatt fuel cell stack at its Torrance, California campus that will meet about 25 percent of their total power requirements. The fuel is natural gas, so there is still some CO2 emission as the gas is broken down into hydrogen and carbon, but the emissions are about 20% less than burning the gas needed to make the same amount of electricity.
As for mobile applications, lots of development work has gone into fuel cell vehicles of all types. So far the most successful are spacecraft that use hydrogen fuel cells to generate electricity, heat and water. Here on Earth, Honda is currently leasing fuel cell cars in California that run on pure hydrogen, and Hyundai put their fuel cell-powered Tucson SUV into small-volume production earlier this year. BMW, Mercedes-Benz and Toyota are also ready to begin limited production of fuel cell vehicles by 2020. So far there are only a few dozen hydrogen filling stations in the world, mostly in Europe, but if development continues and hydrogen becomes widely available (a real possibility), hydrogen-powered fuel cell vehicles will eventually become at least as common as today’s hybrid vehicles.
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