Regan Brown
Hydrogen fuel cells are an alternative to battery-powered electric vehicles. Hydrogen fuel cell vehicles (FCVs) are powered by compressed hydrogen gas and a fuel cell that powers the electric motor. The size of the hydrogen fuel tank determines the amount of energy stored onboard. Hydrogen fuel cells are available in popular vehicle types, including sedans and compact SUVs. They can be refuelled in about five minutes and have a driving range of over 300 miles.
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What You'll Learn
Hydrogen fuel cell vehicles (FCVs) use compressed hydrogen gas
Hydrogen fuel cell vehicles (FCVs) are powered by hydrogen gas stored in carbon-fibre high-pressure tanks. They are fuelled with pure hydrogen gas, which combines with oxygen from the air to produce electricity, powering the vehicle's electric motor. This electricity, along with the energy from the battery, controls the speed and torque of the electric motor.
FCVs have a driving range of over 300 miles and can be refuelled in about five minutes. They are more efficient than conventional internal combustion engine vehicles and produce no harmful tailpipe emissions, only emitting water vapour and warm air. They are also similar to conventional vehicles in appearance.
However, producing hydrogen gas uses some of the energy it creates, and more energy is lost when the hydrogen is converted into electricity within fuel cells. This means that only around 25% of the energy is available for practical use. In addition, there are safety challenges associated with hydrogen, and a lack of storage and refuelling infrastructure.
Despite these challenges, FCVs have the potential to significantly reduce our dependence on foreign oil and lower harmful emissions that contribute to climate change. Major automobile manufacturers are offering an increasing number of FCVs to the public, and the US Department of Energy leads research efforts to make hydrogen-powered vehicles an affordable, environmentally friendly, and safe transportation option.
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The fuel cell stack combines hydrogen and oxygen to generate electricity
Hydrogen fuel cell vehicles (HFCVs) use electric motors to turn their wheels, much like battery-electric cars. However, instead of a large, heavy battery, they are powered by a fuel cell stack. This fuel cell stack combines hydrogen and oxygen to generate electricity, which turns the wheels, and produces water vapour as a by-product.
The hydrogen fuel tank stores hydrogen gas onboard the vehicle until it is needed by the fuel cell. Hydrogen gas is highly flammable and kept under extremely high pressure, at 10,000 pounds per square inch (psi) or 700 bar. The fuel filler is a nozzle that attaches to the vehicle's receptacle to fill the tank.
The fuel cell stack is an assembly of individual membrane electrodes. Hydrogen atoms enter the fuel cell stack at the anode, where they are stripped of their electrons. The positively charged protons then pass through a membrane to the cathode, while the negatively charged electrons are forced through a circuit, generating electricity. After passing through the circuit, the electrons combine with the protons and oxygen from the air to produce water and heat. This process is completely carbon-free, with electricity, heat, and water as the only by-products.
There are several types of fuel cells, including Proton Exchange Membrane Fuel Cells (PEMFCs), Direct Methanol Fuel Cells (DMFCs), Molten Carbonate Fuel Cells (MCFCs), and Alkaline Fuel Cells (AFCs). PEMFCs are commonly used in cars due to their ability to handle large and sudden shifts in power output and operate at cooler temperatures than other fuel cells. MCFCs, on the other hand, operate at much higher temperatures, allowing them to utilize non-platinum catalysts and natural gas as a fuel source. AFCs are highly efficient, with electrical efficiency potentials of up to 60%, but they are sensitive to carbon dioxide and thus primarily used in controlled aerospace and underwater applications.
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Hydrogen fuel tanks are made of carbon-fibre
Hydrogen fuel tanks are made of carbon fibre to store hydrogen gas at high pressures. The hydrogen gas is stored at high pressures of 10,000 pounds per square inch (psi) or 700 bar, and the carbon fibre is wrapped around an aluminium or plastic liner. The tensile strength of the carbon fibres is a key factor in determining the burst pressure of the tank.
Carbon fibre is the only material that can withstand such high pressures while remaining light enough to be installed in an automobile. The use of carbon fibre allows for a more flexible design and a smoother manufacturing process. The high tensile strength of carbon fibres strengthens the tank and makes it safer.
The amount of energy stored onboard a hydrogen fuel-cell vehicle is determined by the size of the hydrogen fuel tank, which can vary. For example, Cimarron Composites has tested 25-inch and 40-inch-diameter tanks and is working on a 5000-litre tank.
One challenge with using carbon fibre for hydrogen fuel tanks is that carbon composite materials can be chemically reactive with oxygen, so the resins and fibres must be carefully selected to ensure leak-tightness. Additionally, the low thermal conductivity of carbon fibre-reinforced plastic (CFRP) means that it takes longer for the tank to cool down compared to metallic tanks.
Despite these challenges, the use of carbon fibre for hydrogen fuel tanks is becoming more common. Universal Hydrogen, for example, uses carbon fibre-wrapped pressure vessels to store hydrogen gas for aircraft.
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Hydrogen fuel cells power the electric motor
The electricity generated by the fuel cell can take two routes, depending on the driving situation. It can flow directly to the electric motor to drive the vehicle, or it can charge a battery that acts as temporary storage until the energy is needed for driving. This "buffer" battery is significantly smaller and lighter than the battery of an all-electric car. Automakers could design an HFCV with plug-in capabilities to charge the battery, but most HFCVs today use the battery for recapturing braking energy, providing extra power during short acceleration events, and smoothing out the power delivered from the fuel cell.
The amount of energy stored in an HFCV is determined by the size of the hydrogen fuel tank, which stores hydrogen gas onboard the vehicle until it is needed by the fuel cell. The hydrogen comes from one or more armoured, carbon-fibre tanks in the car, which hold pure hydrogen under extremely high pressure: 10,000 pounds per square inch (psi) or 700 bar in metric. The fuel tank is filled through a fuel filler, a receptacle on the vehicle to which a nozzle from a fuel dispenser attaches.
Hydrogen vehicles are powered purely by electricity and drive with zero local emissions. They have a similar driving experience to electric cars, with dynamic, virtually silent acceleration, as electric motors provide their full torque even at low speeds. They also have the advantage of a short refuelling time of around 3 to 5 minutes, compared to the longer and more variable charging times of electric vehicles.
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Hydrogen fuel cell vehicles emit water vapour and warm air only
Hydrogen fuel cell vehicles are related to electric cars but differ in their power source. While electric cars are powered by large, heavy batteries, hydrogen fuel cell cars are powered by a fuel cell stack that combines hydrogen and oxygen to produce electricity. This electricity then powers the electric motor, turning the wheels. The by-products of this process are simply warm air and water vapour, emitted through the exhaust.
The water vapour is a result of the reaction between hydrogen and oxygen in the fuel cell stack, a process known as reverse electrolysis. This reaction also produces electricity and heat. The electricity generated takes two routes: it can either flow directly to the electric motor, or it can charge a small "buffer" battery for later use. This battery is constantly recharged by the fuel cell and is used to capture energy from regenerative braking, providing additional power to the electric motor.
The amount of energy stored on board a hydrogen fuel cell vehicle is determined by the size of its hydrogen fuel tank. These tanks are typically made of carbon fibre and hold pure hydrogen under extremely high pressure: 10,000 pounds per square inch (psi) or 700 bar. The hydrogen is stored in these tanks until it is needed by the fuel cell.
Hydrogen fuel cell vehicles have several advantages over electric cars. They produce no carbon dioxide or harmful tailpipe emissions and do not suffer from long charging times, as refuelling typically takes just five minutes for a range of 300 to 400 miles. However, they also have disadvantages, most notably the limited availability of hydrogen fuel and the higher cost of the vehicles themselves.
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Frequently asked questions
The size of a hydrogen fuel cell in a car depends on the power of the vehicle, which is defined by the size of the electric motor(s) that receive electric power from the fuel cell. The amount of energy stored onboard is determined by the size of the hydrogen fuel tank.
Hydrogen fuel cells are smaller than conventional car gas tanks as they do not store as much fuel. Hydrogen fuel cell vehicles can carry enough fuel for 300-400 miles of range and their tanks can be refilled in about 5 minutes, similar to conventional cars.
A fuel cell stack is an assembly of individual membrane electrodes that use hydrogen and oxygen to produce electricity. The electricity generated powers the car's electric motor.
