Fuel Cell Technology

Fuel Cell Technology

While hydrogen fuel cell vehicles may look like conventional cars from the outside, inside they contain a highly advanced fuel cell that converts hydrogen gas stored onboard with oxygen from the air into electricity to drive the electric motor that propels the vehicle. A fuel cell converts hydrogen and oxygen into water and in the process, it produces electricity. Most fuel cells designed for use in vehicles produce less than 1 volt of electricity, far from enough to power a vehicle. To get this voltage up to a reasonable level, many separate fuel cells must be combined to form a fuel cell stack.

Polymer exchange membrane fuel cell (PEMFC)

Polymer exchange membrane fuel cellPEMFC is the best candidate for transportation applications. The PEMFC has a high power density and low operating temperature ranging from 60 to 80 degrees Celsius. Due to the low operating temperature, it does not take very long for the fuel cell to warm up and generate electricity.

Hydrogen gas (H2) enters the fuel cell on the anode (negative) side. When an H2 molecule comes in contact with the platinum on the catalyst, it splits into two H+ ions and two electrons (e-). The electrons are conducted through the anode, where they make their way through the external circuit (doing useful work such as turning a motor) and return to the cathode (positive) side of the fuel cell.

Meanwhile, on the cathode side of the fuel cell, oxygen gas (O2) is being forced through the catalyst, where it forms two oxygen atoms. Each of these atoms has a strong negative charge. This negative charge attracts the two H+ ions through the membrane, where they combine with an oxygen atom and two of the electrons from the external circuit to form a water molecule (H2O).

Fuel Cell Diagram

FUEL EFFICIENCY

If the fuel cell is powered with pure hydrogen, it has the potential to be up to 80% efficient. That is, it converts 80% of the energy content of the hydrogen into electrical energy. However, we still need to convert the electrical energy into mechanical work. This is accomplished by the electric motor and inverter. That gives an overall efficiency of about 64%. Honda's FCX concept vehicle reportedly has 60% energy efficiency.

COOL REAL LIFE FUEL CELL CONCEPT CARS

CHALLENGES

Cost

The biggest problem associated with fuel cells is how expensive they are. Fuel cells are costly. In order to be competitively priced compared to a gasoline-powered vehicle, fuel cell systems must cost $30 per kilowatt. Currently, the projected high-volume production price is $47 per kilowatt.

Durability

Fuel Cell EconomyPEMFC membranes must be durable and operate at temperatures greater than 100 degrees Celsius and still function at sub-zero temperatures. When you start and stop a car frequently, it is important for the membrane to remain stable under cycling conditions. Currently membranes tend to degrade while fuel cells cycle on and off, particularly as operating temperatures rise.

Hydration

PEMFC membranes must by hydrated in order to transfer hydrogen protons. Researchers must find a way to develop fuel cell systems that can continue to operate in sub-zero temperatures, low humidity environments, and high operating temperatures.

Storage

300 miles is a conventional driving range, the distance you can drive in a car with a full tank of gas. In order to create a comparable result with a fuel cell vehicle, researchers must overcome hydrogen storage considerations, vehicle weight and volume, cost, and safety. While PEMFC systems have become lighter and smaller as improvements are made, they still are too large and heavy for use in standard vehicles.

To sum up, fuel cell technologies are an attractive alternative to gasoline. Fuel cells give off no pollution and only produce heat and pure water as a byproduct. There is a lot of work to be done before fuel cells become a practical alternative to gasoline fueled vehicles. The goal to have a viable fuel cell based energy system may become a reality in a few decades.

SOURCES:

http://auto.howstuffworks.com/fuel-efficiency/alternative-fuels/fuel-cell.html
http://www.fueleconomy.gov/feg/fuelcell.shtml