How Do Fuel Cell Electric Vehicles Work?

While on the surface, a fuel cell may seem like a mysterious box that turns hydrogen into electricity, the reality of how fuel cells work is really interesting and less complicated than you might think. In the simplest terms, a fuel cell breaks hydrogen molecules apart into protons and electrons. The electrons get sent off to a battery and the protons bond with the oxygen molecules in air to make water. Of course, that’s just the start of things, so let’s break it down.

How fuel cells work

A basic hydrogen fuel cell uses two electrodes — anode and cathode — surrounded by an electrolyte. The negative side (anode) gets fed with hydrogen and the positive side (cathode) gets fed with air. 

The hydrogen at the anode interacts with a catalyst and separates into protons (positive) and electrons (negative). The negative electrons are directed into a circuit that then can be used to power things. The protons wander through the electrolyte to bond with the oxygen in the air to create heat and water. Cool, right?

So now that we’ve got all this electricity from our chemical reaction, we need to either store it or use it. That’s where the EV part comes in. Typically, hydrogen fuel cell-powered vehicles use a small traction battery — often less than 2 kWh — or what’s called a supercapacitor to store the electricity provided by the fuel cell and direct it to the vehicle’s motors. A supercapacitor is like a battery, only it’s meant to charge and discharge extremely quickly and not be as good at holding energy for a long period. Another advantage of supercapacitors is that they’ll tolerate many, many more charge-and-discharge cycles than a battery.

Speaking of batteries, one of the most appealing features of fuel cell technology is the current charging times for lithium batteries. A full tank of hydrogen will give you a similar driving range as many EVs, like a Tesla Model 3. When that Tesla has to recharge, however, it can take up to an hour to get a partial recharge, depending on a bunch of factors. A hydrogen FCEV can refill its tanks in a matter of minutes, much like an internal combustion engine vehicle.

What FCEVs are available? 

Currently there are two fuel cell electric vehicles available to the public, and both are only available in the state of California. Buyers now can choose between the Toyota Mirai, which is probably the best-known FCEV, and the Hyundai Nexo. 

Honda is set to release its latest fuel cell vehicle, the CR-V e:FCEV. This is cool because it does the fuel cell thing a little differently than the other vehicles we’ve seen so far. The e:FCEV is able to be plugged into a wall and driven on pure battery electric power for a short distance before the vehicle will fire up the fuel cell and start running on hydrogen. This transition is more or less seamless for the driver and helps to keep the car mobile in the (not especially uncommon) event that hydrogen is unavailable.

The problem with hydrogen 

Hydrogen availability is arguably the biggest problem for fuel cell technology at present. There is very little hydrogen infrastructure outside of California, and even in California, some companies that once offered hydrogen filling stations, such as Shell, have gotten out of the game entirely. Also, because the hydrogen filling network is so small, it’s subject to significant swings in price and availability, making it hard to depend on. These price swings are partly why Toyota, for example, subsidizes a significant amount of hydrogen for Mirai buyers.

How far can I go?

As with any other kind of vehicle, the fuel consumption of an FCEV depends on a number of factors. The EPA lists fuel cell vehicles' estimated range, miles per gallon equivalent (MPGe), and the amount of hydrogen used per 100 miles. The latter may seem like an odd way to describe economy, but that’s actually how much of the world does it with internal combustion engine vehicles, and it makes extra sense here given the relatively small tanks that FCEVs have.

So, if you compare the 2023 Toyota Mirai and 2023 Hyundai Nexo, you’ll see that the Mirai is by far the more efficient with a combined 74 MPGe and a range of 330 miles. The Nexo is the less efficient, offering just 57 MPGe but with bigger tanks, a range of 354 miles. Using the hydrogen per 100 miles standard, the Mirai uses 1.4 kilograms, while the Nexo takes 1.8 kg per 100 miles, which is a pretty sizable delta.

A non-hydrogen fuel cell

If the doom and gloom state of America’s hydrogen filling infrastructure has you down, you might be happy to know that there are other kinds of fuel cells that run on different chemicals. Nissan, for example, has been hard at work on what it’s calling its E-Bio Fuel Cell, but which is better described as a solid-oxide fuel cell. This works somewhat differently than a hydrogen fuel cell and is instead powered by ethanol.

This is especially cool because, while the ethanol infrastructure in America is nowhere near as robust as that for gasoline or even diesel, it’s considerably better than hydrogen. It’s also an established industry already for vehicle fuels, so it’s more stable when it comes to price.

Nissan started testing its E-Bio Fuel Cell in a stationary power generation station in its Tochigi facility in Japan back in March. This means it may not be too far off from being ready to see duty in passenger vehicles (think decade instead of decades).