请认真阅读下列短文，并根据所读内容在文章后表格中的空格里填入最恰当的单词。 注意：每空格1个单词。 For years, the automobile industry has been testing vehicles that use hydrogen as fuel. Now, people across the United States have had a chance to see and even drive cars that get power from hydrogen fuel cells (燃料电池). But the hydrogen fuel cell is not a new idea. The fuel cell was first invented by Sir William Grove of Britain in 1839. Since then, many different designs, have been invented. There is one place where fuel cells are a proven technology: in space. The American space agency used fuel cells in its Apollo spaceships in the twentieth century. The most useful fuel cell for transportation purposes is the Polymer Electrolyte Membrane, or P.E.M. fuel cell. It is simple and can operate at temperatures of sixty to eighty degrees Celsius. That is much lower than other fuel cell designs. A P.E.M. fuel cell has two sides divided by a thin membrane (膜). Hydrogen gas is forced through one side where it comes in contact with a reactive material containing the metal platinum(铂). The membrane separates the electrons(电子) from the protons(质子) in the hydrogen atoms. The protons pass through it to the other side of the fuel cell. But the electrons are captured to do work; like powering a motor. Oxygen from the air is forced into the other side of the fuel cell. There, the gas meets the protons that have passed through the membrane. They combine to form water and heat. A single fuel cell does not produce a lot of electricity. But when many fuel cells are combined, they can produce enough electricity to power a vehicle. The product of the chemical reaction that powers fuel cells is water. This makes fuel cells a very clean technology. Hydrogen fuel cell cars have been slow to develop because of many technical problems that have to be solved. For example, it is unclear how long the membranes in P.E.M. fuel cells will last. Also, fuel cells need water for their chemical reactions. They must be designed to start easily at low temperatures and in dry climates. And smaller, less costly fuel cells must be designed before they can truly take the place of gasoline engines. Now more models of fuel cell vehicles are being tested than ever before. The threat of climate change and the high cost of oil have increased interest in these vehicles that do not cause pollution.
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