Ameer Randolph
Hydrogen fuel cell vehicles (HFCVs) are powered by combining hydrogen with oxygen from the air to produce electricity, which then powers an electric motor. Hydrogen fuel cell vehicles are therefore technically a type of electric car, but with a different method of electricity generation. Hydrogen fuel cell cars are energy-efficient, produce no emissions, and have a similar range and performance to gasoline cars. However, they are more expensive to acquire than comparable conventional cars, and the production and transportation of hydrogen are energy-intensive processes.
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What You'll Learn
Hydrogen fuel cell vehicles (HFCV) use oxygen from the air
Hydrogen fuel cell vehicles (HFCV) are powered by a fuel cell stack in which hydrogen passes through a membrane to combine with oxygen from the air, producing electricity and water vapour. This electricity powers the vehicle's electric motor and turns the wheels.
HFCVs use the same type of electric motor as battery-electric cars, but instead of a large, heavy battery, they are powered by a fuel cell stack. This makes them technically a series hybrid, and they are sometimes classified as fuel-cell hybrid electric vehicles (FCHEV).
The process of creating the electricity that powers HFCVs involves taking pure hydrogen (H2) and passing it through a membrane where it combines with oxygen (O2) from the air. This chemical reaction produces electricity and water vapour. The water vapour is emitted through the exhaust, making the vehicle emission-free.
The production of hydrogen for HFCVs requires a significant amount of energy to "crack" compounds like natural gas (CH4) into pure H2, with CO2 as a byproduct. This process can also be done using electrolysis, where electrical energy is used to break down water into its separate hydrogen and oxygen components. If the electricity used comes from renewable sources, hydrogen production can have a neutral carbon footprint. However, if fossil fuels are used, it can negatively impact the climate footprint of the vehicle.
HFCVs offer several advantages, including quiet operation, high energy efficiency, and no emissions. They also have a similar range and performance to gasoline cars and can be refuelled quickly. However, they are generally more expensive to acquire than comparable conventional cars.
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Hydrogen is stored in thick-walled, high-pressure tanks
Hydrogen fuel-cell vehicles (HFCVs) are powered by a fuel-cell stack in which hydrogen combines with oxygen from the air to produce electricity and water vapour. Hydrogen is highly flammable and prone to reacting uncontrollably with oxygen. Therefore, it must be carefully stored to prevent explosions.
Hydrogen can be stored physically as either a gas or a liquid. Gas storage typically requires high-pressure tanks (350–700 bar, or 5,000–10,000 psi). Liquid storage requires cryogenic temperatures because hydrogen has a boiling point of −252.8°C at one atmosphere pressure.
Compressed gas storage is the most common method for hydrogen tanks used in industrial applications. These tanks are often made of carbon fibre resin with polymer-based liners, such as high-density polyethylene (HDPE). The fibre is generally layered helically, with more layers added circumferentially to increase strength. Type-IV tanks, for example, can withstand pressures as high as 750 bar.
To store hydrogen safely in vehicles, high-pressure composite vessels are used. These thick-walled, high-pressure tanks are made of fibre-reinforced composites capable of reaching 700 bar pressure. They are designed to prevent hydrogen leaks and have been validated through numerous crash tests. However, high-pressure storage remains a challenge for transportation applications due to the large storage volumes required.
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Hydrogen and oxygen combine to make water
Hydrogen fuel cars use hydrogen as their fuel source. Hydrogen is a highly flammable gas that can be converted into electrical energy. To prevent explosions, the hydrogen in these cars is stored in thick-walled tanks. In a process called electrolysis, electrical energy is used to break down water into its components of hydrogen and oxygen.
Hydrogen fuel cars work by passing hydrogen through a fuel cell, where it combines with oxygen from the air to form water vapour. This reaction produces electricity, which powers the car's electric motor. The car then emits this water vapour out of its exhaust pipe.
The process by which hydrogen and oxygen combine to make water is called an oxyhydrogen reaction. This reaction occurs when two hydrogen atoms fuse with one oxygen atom. In this process, each hydrogen atom donates its single electron to the oxygen atom. This results in the oxygen atom having 10 electrons instead of 8. However, it is important to note that molecules share electrons, and they do not "belong" to any particular atom.
The positive and negative charges of hydrogen and oxygen atoms attract each other, preventing the random movement that would keep them as gases. This attraction allows them to combine to form water.
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Hydrogen fuel cells produce electricity
Hydrogen fuel cells use pure hydrogen fuel, which is combined with oxygen from the air to generate electricity. This process occurs at the anode site, where a catalyst splits the hydrogen molecules into electrons and protons. The protons pass through a porous electrolyte membrane, while the electrons are forced through a circuit, generating an electric current and excess heat. At the cathode, the protons, electrons, and oxygen combine to produce water molecules.
The electricity generated by hydrogen fuel cells can be used to power vehicles, such as cars, and other applications like portable power and telecommunications. Hydrogen fuel cells are related to electric cars but have unique advantages and disadvantages. For example, hydrogen fuel cells can be more energy-intensive and complex to transport and store than gasoline or diesel. However, hydrogen can be produced anywhere with access to electricity and water, and it can be used to store and deliver energy produced from other sources.
The production of hydrogen fuel can be achieved through several methods, including natural gas reforming, electrolysis, and solar-driven processes. Electrolysis involves using electrical energy to break down water into its separate hydrogen and oxygen components. If renewable energies are used in this process, hydrogen production can have a neutral carbon footprint. However, if fossil fuels are used, it can adversely impact the climate footprint of a hydrogen car.
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Hydrogen fuel cells are safe
Hydrogen fuel tanks in cars are designed to be extremely safe. They are built to withstand extreme temperatures and pressures and are subject to rigorous testing standards. For example, Toyota's Mirai fuel cell vehicle has undergone extensive road testing, crash testing, and safety testing, passing all tests with no issues. The hydrogen fuel tanks have even been shot at by high-velocity weapons without sustaining damage. BMW, another manufacturer of hydrogen fuel cell cars, also emphasizes the safety of its hydrogen vehicles, stating that they meet the same high safety standards as all other vehicles in their group.
The safe handling and use of hydrogen focus on preventing situations where the three combustion factors—ignition source (spark or heat), oxidant (air), and fuel—are present simultaneously. Hydrogen's properties make it safer to handle and use than traditional fuels. For instance, hydrogen is non-toxic and lighter than air, allowing for rapid dispersal in the event of a leak. Additionally, hydrogen's combustion results in water vapor, making it a carbon-free and non-hazardous energy source.
While hydrogen is highly flammable and has a low ignition energy, engineering controls and guidelines have been developed to mitigate these risks. Hydrogen fueling stations, for instance, are equipped with sensors for leak detection, and hydrogen storage tanks are designed to withstand high pressures. Furthermore, the refuelling process has built-in safety measures, such as disconnecting the car's ignition until the fuel nozzle is replaced and the fuel cap closed.
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Frequently asked questions
Yes, hydrogen fuel cars require oxygen to function. Hydrogen and oxygen are combined in a fuel cell to generate electricity, which powers the car's electric motor.
The process involves separating hydrogen atoms into electrons and protons. The electrons are collected by a conductive current collector, which sends them through the car's circuitry to power the motors. The protons combine with oxygen from the air to create water vapour, which is released through the exhaust.
Hydrogen fuel cars offer several advantages. They produce no emissions, have a long range on a single refuelling, and their refuelling time is comparable to that of standard gas tanks. Additionally, hydrogen burns cleaner than gasoline or methane, reducing air pollution from transportation.
