Hydrogen, the most abundant element in the universe, is a promising energy source for our transportation needs.  Understanding its potential helps prioritize its place in decarbonizing our energy mix.

What is hydrogen?

Hydrogen is the smallest chemical element.  It is most commonly known to us as a part of water as in good ol'  H-two-O (H2O).   Hydrogen also combines with carbon to create the building blocks associated with all organic matter including fossil fuels such as coal, crude oil, and natural gas.  However by itself, hydrogen is a gas and one that is highly flammable.  

How is hydrogen a fuel?

While we can burn hydrogen like we burn gasoline to power our cars, most hydrogen energy research is in the form of fuel cells that generate power using a chemical reaction called a redox reaction.  With a supply of hydrogen and air, the beauty of this reaction is its output - electricity and water.  

How is hydrogen sourced?

There are only small amounts of pure hydrogen on Earth.  Therefore, to have hydrogen as a fuel source, it must be extracted from other sources.  The common sources are water, fossil fuels, and ammonia.  

The process that extracts hydrogen from water is called electrolysis.  The process that extracts hydrogen from natural gas is called steam methane reforming (SMR).  The generic term for extracting hydrogen from ammonia is called cracking.  Each of these processes requires energy.  Therefore, the source of the energy used to create hydrogen is a significant issue.

What do the colors mean?

When talking about hydrogen, you will often hear of colors.  The colors define the energy used to create the hydrogen.

• Green hydrogen employs renewable electricity.
• Blue hydrogen is sourced from natural gas with carbon capture and storage.
• Grey hydrogen is produced from natural gas with no carbon capture.
• Black or brown hydrogen uses coal with no carbon capture. Black from bituminous and brown from lignite. 
• Turquoise hydrogen is extracted from natural gas by a technique called  methane pyrolysis with carbon  removed as a solid instead of CO2 gas.
• Purple, Pink, and Red hydrogen is made using nuclear power.
• White hydrogen refers to naturally occurring hydrogen.

How are hydrogen fuel cells applied?

Hydrogen fuel cells, like electric vehicle (EV) batteries, power transportation vehicles with electricity.  Unlike batteries that store and discharge electricity to power a car, fuel cells generate electricity on demand which means the hydrogen is stored in a car's gas tank like gasoline.  So why are we seeing EVs  instead of hydrogen fuel cell cars?  In a nutshell, it is the lack of a hydrogen infrastructure.

Hydrogen fuel cells need hydrogen to be created on a massive scale relative to current production levels.  The hydrogen needs to be transported in pipelines from hydrogen generating stations to distribution centers where it can be trucked and dispensed to filling stations so vehicle tanks can be finally filled.  None of this currently exists.  With EVs, we already have a significant headstart with the electricity generating scale and transportation needed (although we need more).  Distribution and charging stations, while not as far along, is gaining traction.

However, hydrogen fuel cells can make a significant contribution with other transportation modes like trucks, buses, large air and marine transport.  The reason centers on an attribute called energy density or the amount of energy per weight.  Fuel cells generate more power with less weight than lithium batteries.  As Brian Lindgren, who heads up Kenworth's research and development puts in a TruckingInfo.com article , “The heaviest part of [a hydrogen fuel cell system for a tractor trailer] is the storage tanks at about 4,000 pounds, but we’re still way below the 16,000 pounds of batteries you’d need for the same distance.  And then there’s recharge time. Charging the batteries would take several hours, but you can fill 120 pounds of hydrogen in about 15 minutes."  The same thinking of weight, distance, recharge/fill up time applies to buses, large air and marine transport.

Conclusion

So what does the future hold for hydrogen as a transportation fuel?  I think we will see hydrogen fuel cells used for large transportation needs.  The energy density alone is enough to drive forward in this direction.  (No pun intended.)  I have my doubts about hydrogen fuel cells for cars as I think lithium batteries' "first-to-market" position will be hard to unseat as the needed hydrogen infrastructure for personal transportation will take too long to develop.  Regardless, movement away from carbon based to non-carbon based transportation fuel is clear.