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Many experts think that by 2040 most of us will be driving a fuel-cell hydrogen vehicle (FCHV) because the concept makes a lot of sense.
By Jake Venter on ToyotaZone
The FCV-R concept car shows what a future Corolla-sized energy-efficient vehicle could look like.
Fuel cells generate electricity from oxygen and hydrogen with the result that it uses renewable fuel. These units are small enough to be fitted to a vehicle so that the electricity can be used to power a car. I’ve driven such a vehicle, and it feels just like a plug-in electric, except that you stop for fuel instead of recharging the battery.
Many of us have seen a school science experiment that shows how water can be broken down into oxygen and hydrogen by passing an electric current through it. Fuel cells perform the opposite trick. They combine oxygen and hydrogen in the presence of a catalyst to form water and generate electricity.
The basis of a fuel cell is a stack of cells called a membrane electrode assembly. Each cell has an anode (negative terminal) at one end and a cathode (positive terminal) at the other end, and is filled with an electrolyte that allows charges to move between the two sides of the cell. Both the anode and the cathode are surrounded by catalysts, and these terminals are connected by means of an external circuit.
To operate the cell hydrogen is supplied to the anode. Here the catalyst causes the hydrogen to release electrons that travel outside the cell from the anode to the cathode, thus forming an electrical current. The molecules that have released their electrons are called ions, and these travel through the polymer electrolyte membrane to the cathode. Here the ions bond with airborne oxygen and electrons on the catalyst to from water and heat.
Each cell yields less than one volt, so that hundreds of cells are connected in series to increase the voltage. This is called a stack or fuel cell unit. The conversion efficiency is over 55%, but if the waste heat is utilised their efficiency can be as high as 80%.
Toyota has built a series of experimental fuel cell vehicles called FCHV-adv, series 1 to 4 and made them available to selected customers in Japan and the USA on a lease basis. They were all based on the Highlander SUV platform.
The fuel cell powers a 90 kW AC electric motor that drives the wheels when power is demanded, but becomes an alternator during braking and coasting to capture kinetic energy. An auxiliary battery is provided to store the electricity generated this way. It is used to supplement the output from the fuel cell to deliver a power boost during acceleration.
The power control unit consists of a DC (from the fuel cell) to AC (for the power unit) converter plus a high voltage DC to low voltage DC converter for the vehicle accessories. The unit also exercises precision control over the fuel cell output and the auxiliary battery charging state under all driving conditions.
The hydrogen is stored in liquid form in a 70 MPa high-pressure carbon fiber tank. It has a polyamide resin inner liner that reduces hydrogen molecule leakage through the walls of the container.