how they work, prices, autonomy, refueling, weaknesses and risks

Although it sounds like science fiction, the presence of hydrogen in vehicles has a long history. The electronic instruments of the modules used in the NASA Apollo missions were already powered by 3 hydrogen fuel cells more than sixty years ago. Today they aim to become the protagonists of urban mobility. Both the authorities and the main vehicle brands are committed to hydrogen as an alternative to battery cars and predict its boom in just 10 years.

Cells that replace batteries

Like electric vehicles, fuel cell vehicles use electricity to power an electric motor. In this case, that electricity is produced by means of a fuel cell powered by hydrogen, instead of using the energy that comes from a battery.

The most common type of fuel cell for transport applications is the proton exchange membrane, sandwiched between a positive (cathode) and a negative (anode) electrode. Its chemical function is explained in two strokes. To begin with, hydrogen is introduced at the anode and oxygen from the air is introduced at the cathode. Hydrogen (H₂) molecules are broken down into protons (H⁺) and electrons through an electrochemical reaction on the catalyst (usually platinum).

The protons pass through the membrane to the cathode, and the electrons are conducted to an external circuit to produce work (powering the car’s electric motor). Subsequently, protons, electrons, and oxygen molecules combine at the cathode to generate water.

More efficient and without emissions

Electric vehicles that run on hydrogen are much more efficient (60%) than conventional internal combustion ones (20-30%) and do not generate emissions (they only emit water vapor and hot air).

In addition, these vehicles do not emit any noise, even at the speed reached on highways, since they have no mechanical gears and no combustion occurs. They also have the advantage that they allow easy scaling, since fuel cells can be accumulated to move anything from small vehicles to buses or trucks.

Refueling in 4 minutes and 700 km of autonomy

During vehicle design, the manufacturer defines its power through the size of the electric motor. This engine receives electrical power from the fuel cell and from a battery. Although the battery could theoretically be designed to be recharged by plugging it in, it is normal to recharge by recovering braking energy. This battery supplies extra power at certain times. It also allows smoothing of the power supplied by the fuel cell. Thus it is possible to isolate or shut down the fuel cell when power needs are low.

Apart from the electric motor, the fuel cell and the battery that recovers braking energy, an electric car powered by hydrogen needs a low-voltage auxiliary battery to start the car and power the vehicle’s accessories.

These vehicles are charged with pure hydrogen, which is stored in a tank inside the vehicle. Like conventional internal combustion cars, they can be refueled in less than 4 minutes and have a range of around 700 km.

How much do they cost and what help do they have?

One of the main problems is that this technology is still expensive. The price of these vehicles is high and is within the reach of few pockets. At the moment there are only three models of mass-produced hydrogen cars for sale in the world. Two of them are sold in Spain, with a price ranging between €70,000 and €76,000. However, they can benefit from the Moves III aid plan and have the DGT Zero label.

The infrastructure to distribute the hydrogen is still in the early stages of implementation. This hydrogen is usually obtained by steam reforming the methane present in natural gas, although it would be preferable to obtain it from the electrolysis of water using renewable energy sources (solar photovoltaic, wind, etc.).

The hydrogen must be compressed (to 700 atmospheres of pressure) so that it does not occupy a lot, which requires enormous resources for its refinement before reaching the hydrogen.

Your Achilles heel

Precisely here lies another weak point of this technology: the difficulty of refueling. Currently there are only six hydrogen refueling stations in Spain, located in the provinces of Albacete, Ciudad Real, Huesca, Madrid, Seville and Zaragoza. Of them, only 3 are for public use.

The current price of hydrogen is around €10/kg and the typical consumption of these vehicles is 0.8 kg/100 km. We would be talking about a cost of about €8/100 km. It is lower than for a gasoline car, but it is still higher than the consumption of an electric car, whose domestic recharging cost is €1-2/100 km. Of course, recharging an electric car is much slower.

Another aspect of concern is security. Hydrogen is a colorless, odorless, non-toxic gas that is easily dispersed and has a very high autoignition temperature (585ºC). In contrast, it has a wide range of concentrations in air (between 4-75% by volume) in which ignition can occur. However, the hydrogen concentration from which the mixture is flammable is higher than that of the propane in our homes or gasoline vapors.

In addition, the refining industry has decades of experience in its production, transport and use, and car manufacturers have spent a lot of time designing hydrogen tanks that are strong enough, even in the face of potential accidents.

All this makes us optimistic about a medium-term application of this technology. Proof of this is the creation of the National Center for Experimentation of Hydrogen and Fuel Cell Technologies (CNH2) in Puertollano (Ciudad Real) in 2007, and the recent holding of the H2 Revolution international congress in this same city.

Rafael Camarillo Blas, Full Professor of Chemical Engineering, Castilla-La Mancha university

This article was originally published on The Conversation. Read the original.