In 2003, President George W. Bush announced his $1.2 billion Hydrogen Initiative, which called for mass production of hydrogen fuel cell vehicles by 2020. The enormous hurdles facing the wholesale switch to a hydrogen economy remain, but the technology needed to build the cars is advancing every year. There are thousands of working prototypes that deliver on the promise of hydrogen power that convert the abundant element to electricity, leaving behind only water vapor from the tailpipe.
Fueling the Car
The problem of fueling a hydrogen-powered car lies not in the mechanics of injecting the fuel into an onboard storage tank but in the infrastructure required to make fueling as convenient as it is with traditional internal combustion engines.
The hydrogen pump features a conduit for the hydrogen itself and a communicator harness. Both components must be inserted into the vehicle. The communicator harness plugs into a separate outlet near the fuel intake valve. Once communication between the computerized pump and the vehicle is established, the nozzle can be locked into place in the intake and hydrogen flows automatically until the tank is full.
Storing the Fuel
Awaiting the fresh influx of hydrogen is the onboard fuel tank, a device far different from one in the average Chevy. There are three types of hydrogen storage in development featuring three distinct technologies; pressurized gas, cryogenic liquid and solid state.
Hydrogen is far less dense than gasoline at standard temperature and pressure, so in order to fit enough hydrogen on board to give the car a viable range, the gas must be compressed at pressures up to 10,000 pounds per square inch (psi). The Honda FCX Clarity uses a medium-sized tank pressurized to 5,000 psi. Hydrogen can also be transformed to liquid at temperatures near absolute zero (-459.67 degrees Fahrenheit) and there is promising advancement in solid-state storage that uses metal hydrides to absorb hydrogen gas. Carbon nanotubes, by virtue of their microscopic size and shape which increases surface area, can absorb even more gas.
Generating the Power
The heart of the hydrogen car is the fuel cell. In it, hydrogen gas is used to generate the electricity needed to power the car's electric motor. One type of fuel cell for the passenger car segment of the transportation sector is of the proton exchange membrane variety.
In an electronic circuit, energy flows from the anode to the cathode as electrical current. The PEM cell generates this current by allowing the hydrogen protons to pass through a membrane on the anode side of the cell, leaving the electrons free to move around the membrane to the cathode and rejoin the protons. This passage of electrons is the electrical current. The re-formed hydrogen combines with oxygen from the air after completing the circuit to produce water, the cell's only emission.
"Piloting" the Car
One of the benefits of hydrogen-powered vehicles is that they contain very few moving parts, which reduces the weight and the need for lubricants. This concept extends beyond the workings of the fuel cell and motor to the actual driving of the car.
"Drive-by-wire" technology means that the steering, "gas" pedal and brake are not connected mechanically to their respective components but instead send computerized instructions over wires. For example, when you step on the accelerator, the car's computer processor interprets the input and sends the information to the motor to carry out the action.
Recapturing Lost Energy
Maximizing the amount of energy onboard is one of the keys to a successful, long-range hydrogen car. Like the electric and hybrid vehicles that preceded them, hydrogen cars recapture lost kinetic energy when the car brakes by converting the stopping power back to electricity by means of two-way motors connected to the wheels. This reclaimed energy is stored on board in lithium ion batteries and used for peripheral electronics and supplemental power to the motor.
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