Hydrogen is the most abundant chemical element in the known universe, so why isn’t it widely used to power our transportation?
Though there are hydrogen fuel cell vehicles and buses, the technology has not been widely commercialized. We will explore two of the reasons for the lack of adoption in this article.
The first reason for the slow adoption of hydrogen is that it has to be manufactured (even though it is the most abundant chemical element in the universe). Why is this?
Hydrogen gas is very rare in the Earth’s atmosphere because it is so light, and this enables it to escape Earth’s gravity more easily than other gases. On the Earth’s surface, most of the hydrogen has reacted with other elements to form substances such as water and hydrocarbons. This means that in order to use pure hydrogen as an energy source, we would have to produce it. All of the hydrogen production methods we have costs energy, so pure hydrogen is more of an energy “carrier” than an energy “source”. If we are able to mass produce hydrogen with renewable technology such as solar, then it might make sense for us to go down that path.
Once the pure hydrogen is produced, we run into the second reason for its slow adoption – the fact that it is hard to store hydrogen for use in vehicles.
The main issue with storage is that at normal temperatures and pressures hydrogen is a gas. This means that it is much less dense than a liquid such as gasoline, and can carry much less energy per unit volume. If we want to effectively store hydrogen for use in a vehicle, we essentially have to increase its density by using one of the following techniques.
- Liquid H2: This method creates the densest form of H2, but is also the most expensive to produce. The technology involves cooling and pressurizing hydrogen gas. How cold do we have to make the hydrogen before it becomes a liquid? Roughly -253C if we keep the storage vessel at atmospheric pressure. As you can imagine, it is not very practical to carry around a tank full of -253C liquid hydrogen as fuel in your car. Can you imagine if an accident caused the tank to burst?
- Compressed H2 Gas: This method involves compressing the hydrogen gas in order to increase its density, but does not turn the gas into a liquid. However, most people would not want a pressurized tank of flammable gas as part of their car. This storage method is what is currently used in most hydrogen fuel cell vehicles, and the gas is store at more than 5,000 PSI.
- Solid H2: This method involves dissolving H2 molecules into a metal matrix. The hydrogen gets turned into a hydride and stored between the metal molecules. This method is not as effective as Liquid H2 or Compressed H2 Gas when it comes to increasing the density of hydrogen storage. Furthermore, the resulting metal-hydrides are not healthy for humans.
Despite these challenges, researchers are still working diligently on making hydrogen vehicles viable. The current consensus is that Solid H2 is the preferred form of hydrogen storage for future research as it does not require low temperatures or high pressures. However, much work has to be done in order to increase the H2 density as well as decreasing health risks of the metal-hydrides.