Yes hydrogen makes near zero pollutants if we use fuel cells which are still very costly partly because they use platimum as the catalyst. We already use enough hydrogen for 10 million cars, mostly made from natural gas and water. The other product carbon dioxide is released into our atmosphere, so hydrogen is worse than gasoline until we start making hydrogen some other way, which will make hydrogen twice as costly as gasoline; Likely more than twice. Hydrogen is better only if the electricity for electroysis is free and a use can be found for a huge amount of oxygen. At high cost we could obtain enough hydrogen (for one million cars) that is presently leaking into Earth's atmosphere, but Earth needs thousands of times more vehicles than one million.
Yes but where are they going to get the hydrogen from? Hydrogen is not a fuel.
Molly you ask a very interesting question. The real issue is with the meaning of the word burning. Taken in its common denotative (or dictionary) definition, burning means combining with oxygen in a rapid chemical reaction. With this definition you are being asked to compare what is chemically happening when hydrogen combines with oxygen relative to when fossil fuels combine with oxygen. When fossil fuels burn there are by products that are released to the atmosphere. Carbon is a big one. When hydrogen burns the result is water. Some might quibble about what is a pollutant but so far carbon seems to be more of a problem than water. But some would consider this definition as just narrow thinking. There is another sense of the word burning that is closer to using rapidly. For example we could say that we burned through all our money in a week. This implies more than just the chemical reaction, and might be similar to the words, use or consume. Hydrogen does not exist freely on Earth. It musty be made and it usually takes more energy to make it than we get by burning it. 96% of industrial hydrogen is made from fossil fuels. It is usually more efficient to use something directly than to convert it first to something else. Hydrogen is then less efficient than burning fossil fuels directly. Less efficiency typically means more pollution. When we consider the entire usage process of hydrogen it can then be overall more polluting than burning fossil fuels directly. The reason we don't hear more about this is that many are advocating that hydrogen could be made from water. But so far this is very inefficient and very costly. The sad economic reality is that the cheapest way to make hydrogen is from fossil fuels.
