In its push to become climate-neutral by 2050, the European Commission has unveiled an industrial strategy called the Clean Hydrogen Alliance. The public-private partnership among the EC, Europe’s fuel-cell and hydrogen industry, and research organizations will drive the region’s efforts to ensure Europe’s energy independence and develop zero-emission cars.
Next-generation vehicles that produce less harmful substances and less noise are universal goals, and as a result, the whole world is experimenting with electric vehicles (EVs). But a drawback of EVs, which belong to the electro-mobility sector, is their long charging times.
That’s a problem that might be solved by hydrogen fueling, also called cell fueling. Hydrogen cells exploit the same energy used by spacecraft to reach Earth’s orbit. But how do hydrogen cars work? What are the strengths and weaknesses?
Hydrogen vehicles convert chemical energy into mechanics. A hydrogen internal combustion engine vehicle (HICEV) uses a hydrogen-fueled version of the traditional internal combustion engine. Alternatively, hydrogen can be used to cause a reaction with oxygen in a fuel cell, thus producing electricity. This type of vehicle is called a fuel-cell electric vehicle (FCEV), and in recent years, FCEVs have drawn the attention of many manufacturers. FCEVs are powered by an electric engine and have an on-board power plant to allow the production and management of hydrogen.
An environmental argument for hydrogen-powered vehicles is that they do not generate polluting emissions; rather than greenhouse gases and fine particles, they emit water vapor (Figures 1 and 2). However, the overall environmental impact of hydrogen mobility depends on the energy source used to produce it. Hydrogen is the most abundant chemical element in the universe, but not in natural form. For this reason, it is not exactly a renewable resource and must be produced. If you use renewable energy sources to produce hydrogen, the environmental impact is minimal. Conversely, if fossil sources are used, the environmental impact is much higher.
Hydrogen can be produced through two production processes and technologies: reforming and electrolysis. Reforming has a higher environmental impact because it involves the extraction of crude oil, transportation, and refining. Electrolysis is the process of splitting H₂O water molecules into individual hydrogen and oxygen atoms via the chemical reaction induced by electricity. This production process does not emit polluting gases but requires a large amount of power. The electrolysis process consists of a low-voltage current that flows through the water to release oxygen and hydrogen in a gaseous form.
One of the qualities of hydrogen is its very high specific energy density, 40,000 Wh/kg, or 236× the specific energy of lithium-ion batteries. This means that hydrogen-powered vehicles are lighter than battery-powered vehicles and have a more extended range. Also, hydrogen refueling takes just a few minutes, compared with several hours for battery-powered cars.
Figure 1 shows a general layout of a hydrogen vehicle. Reverse electrolysis takes place in the fuel cell: Hydrogen comes from a tank, air from the surrounding environment. Fuel cells do not provide thermal combustion but an electric current that produces non-altered water as the only waste.
Fuel cells receive two incoming flows: hydrogen from the negative pole and oxygen from the positive pole. The catalyst contained in the hydrogen engine causes the electrons to separate from the nucleus, and this reaction releases electricity. The electrons move to the positive pole and join the oxygen atoms, which receive a negative charge. The union of hydrogen with oxygen produces a chemical reaction whose final product is water. What is emitted is water vapor, which can be released directly into the atmosphere by hydrogen-fueled cars (Figures 3 and 4).
The current generated in the fuel cell can directly power the vehicle or charge a battery (smaller than a conventional battery) that acts as an intermediate accumulator. As in other hybrid vehicles, hydrogen-powered vehicles also use energy harvesting to recharge the battery. The battery is used to cover possible engine energy demands and to recover braking energy, as in electric and hybrid cars. The voltage produced by fuel cells must be up to 600 V.
