If you are not already sensitized to hydrogen as a possible fuel for cars, you will be. Hydrogen is being touted as a source fuel for large trucks, delivery vans, and buses. In addition, Toyota is also looking at hydrogen cars to compete with battery electric passenger vehicles (BEVs). Let's look at why hydrogen is an attractive fuel for cars.  Is it a challenge to BEVs?

The primary energy source to a hydrogen car is the fuel cell. Think of it as the equivalent to the internal combustion engine. Instead of gasoline stored in a tank, a hydrogen car has a tank of...hydrogen. Rather than converting the potential energy of gasoline into kinetic energy by ignition (see What is Energy? for more on potential and kinetic energy), hydrogen cars convert the potential energy in the hydrogen to kinetic energy by a chemical reaction in the fuel cells that generate electricity. Fuel cells generating electricity on demand is in contrast to BEVs where the batteries have stored electricity in them. 

Hydrogen cars also have batteries. However, they are much smaller. To give you a sense of how much smaller, the battery on the 2022 Toyota Mirai (a hydrogen based car that has limited availability) is 1.24 kWh. The battery on the Tesla S is 82 kWh. The reason the battery for a hydrogen car is smaller is the role they play in moving the car. One responsibility is to get the car moving from a dead stop before the fuel cells kick in. It also adds to acceleration when needed. Lastly, it powers the car when the car is cruising at a steady speed. Recharging occurs when the brakes are applied or from the fuel cells when needed. 

There are a number of advantages that hydrogen cars brings to the table over BEVs:

Range - The Toyota Mirai is documented to go 402 miles on a tank of hydrogen. 

Refuel time - It takes just under five minutes to fill up the Mirai's hydrogen tank.

Energy density - Hydrogen has an energy density of  35,000 watts per kilogram compared to 200 watts per kilogram for Lithium ion batteries.

Even with these advantages, there are good reasons why you do not see automakers showing hydrogen cars in their showrooms. In fact, in the US, only two car models are available and both are only available from select California dealers - the Toyota Mirai and Hyundai Nexo. Most of the reasons center around maturity of the technology:

Availability of refueling infrastructure - There are 48 publicly available hydrogen filling stations in the US with 47 of them in California. (One is in Hawaii.)

Availability of hydrogen - The primary means of generating hydrogen is by a process called electrolysis. This is where hydrogen is stripped away from water (aka H2O).  While electrolysis is scalable, it takes electricity to work. The issue then becomes  "Where does the electricity come from?"

If the electricity comes from burning fossil fuels, it is called grey hydrogen. If the electricity comes from burning fossil fuels where the CO2 is captured, then it is called blue hydrogen. Lastly, if the electricity comes from  non-carbon sources (e.g. solar, wind, nuclear, geothermal), then it is called green hydrogen. Currently, most of the hydrogen created is non-green hydrogen. 

So, are hydrogen cars a challenge to BEVs? Not in the short term. Too much time is needed to build up the required infrastructure relative to how quickly we need to reduce CO2 emissions. While upgrades to the grid are needed to fully take advantage of BEVs, we can at least begin to reduce emissions with the current infrastructure. 

This does not mean there is no future for hydrogen fuel cell technology in the transportation sector. As noted in the introduction, hydrogen is seen as a viable option for large trucks, delivery vans, and buses due to the energy density of hydrogen. And as hydrogen technology matures, it may provide an option for consumers just like we currently have with diesel as an option to gasoline.