Hydrogen cars, or, to be more precise, fuel cell cars, are electric vehicles. The difference to the “normal” e-car:
A fuel cell with a hydrogen tank is installed in the vehicle, which generates electricity for the driver while driving.
A small battery acts as a buffer or temporary storage and covers peak loads, e.g., when accelerating. It also absorbs and stores recuperation energy (kinetic energy when braking).
In the fuel cell, electricity is generated from hydrogen. This is done by reversing the electrolysis. Hydrogen and atmospheric oxygen react to form water, generating heat and electrical energy. The latter drives the electric motor.
So-called PEM (polymer electrolyte membrane) fuel cells are used in vehicles. How it works:
The membrane separates the hydrogen and the oxygen from the air, which flows around the anode and cathode, respectively.
The membrane is only permeable to hydrogen ions. At the anode, the hydrogen molecules separate into ions and electrons.
The hydrogen ions migrate through the PEM to the cathode and combine with the oxygen in the air to form water.
However, because the PEM represents an impenetrable barrier for them, the hydrogen electrons have to take a detour via a line from the anode to the cathode: the resulting electrical current flow charges the traction battery or drives the vehicle’s electric motor.
How is the fuel stored in the car?
The storage of fuel cell vehicles differs significantly from that of conventional cars with petrol or diesel tanks.
Hydrogen is stored either in gaseous form under high pressure (350 bar or 700 bar) or in liquid form at minus 253 degrees Celsius. In this state of aggregation, a very high energy density is achieved.
This requires super-insulated, double-walled tanks.
Insulation materials are located in a vacuum between the two shells of the tank, which keep the tank cold and minimize evaporation losses. Filling stations store hydrogen in both gaseous and frozen forms.
Are hydrogen cars emission-free?
That depends on how the hydrogen is produced. Before the law, hydrogen cars are considered Zero Emission Vehicles (ZEV):
The electrochemical process occurs locally without emissions, and heat and water vapor are released, as well as very small amounts of NOx. The latter is because ambient oxygen is used in the process – and it is contaminated.
However, the emissions that occur during the production of hydrogen must also be taken into account. Then there are enormous differences:
If hydrogen is produced with natural gas, the balance is miserable – if the electricity for it comes from renewable energies, things look much better.
In the search for a long-term replacement for fossil fuels, hydrogen and fuel cell cars certainly offer opportunities.
However, only if the energy comes from regenerative energy sources such as photovoltaics, wind and water power, solar thermal energy, geothermal energy, and biomass.
What is hydrogen anyway?
Hydrogen has the chemical formula H₂ and is considered the oldest, simplest, and most common element in the universe.
It is colorless, odorless, gaseous under normal conditions, and lighter than air. In nature, hydrogen only occurs in bound form – for example, as a component of water.
How To Produce Hydrogen Fuel?
H₂ can be obtained from water by electrolysis. Direct current and electrolyte are required for this: When they are used, water (H₂O) is broken down into its components, i.e., hydrogen and oxygen.
Oxygen is produced at the anode (positive electrode), and hydrogen is made at the cathode (negative electrode).
Only two percent of the global hydrogen requirement of 600 billion cubic meters is produced with regenerative energy.
In contrast, 98 percent is obtained from hydrocarbons – such as natural gas, oil, and coal. Around 40 percent of this is a by-product of chemical processes, natural gas synthesis, and crude oil processing.
The most economical way of producing hydrogen from these fossil raw materials is steam reforming. Natural gas is pressurized, heated, and mixed with water vapor – hydrogen is released.
Are Fuel Cell Cars Safe?
The non-toxic, invisible, and volatile hydrogen places different demands on developers in terms of safety than, for example, petrol: hydrogen has a wider range of ignitability.
Therefore, stipulates basic requirements for the type approval of vehicles with hydrogen technology, for the type approval of components and hydrogen systems that use hydrogen, and for the installation of such components and systems.
Strict requirements for the safety of these vehicles and components are also defined here, and various tests are stipulated (e.g., pressure, leak, bursting, and fire safety tests).
Does hydrogen also work in a combustion engine?
BMW engineers have designed bivalent Otto engines that can burn gasoline and hydrogen. A BMW 7 series equipped in this way was even officially included in the BMW price list.
The hydrogen combustion engines are based on the regular series engine and, like these, are characterized by high comfort, dynamics, and power density. However, they differ in the modified intake system, which on the one hand, enables direct fuel injection and, on the other hand, hydrogen injection into the intake manifold.
Another difference lies in the changed combustion control and the exhaust after treatment. With the hydrogen combustion engine, practically only water and small amounts of NOx from the combustion are emitted as emissions while driving. However, BMW stopped developing hydrogen vehicles with combustion engines in 2009.
