Fuel Cells

Fuel cell vehicles, powered by hydrogen, have the potential to revolutionize our transportation system. They are more efficient than conventional internal combustion engine vehicles and produce no harmful tailpipe exhaust—their only emission is water. Fuel cell vehicles and the hydrogen infrastructure to fuel them are in an early stage of development. The U.S. Department of Energy is leading government and industry efforts to make hydrogen-powered vehicles an affordable, environmentally friendly, and safe transportation option. Hydrogen is considered an alternative fuel under the Energy Policy Act of 1992 and qualifies for alternative fuel vehicle tax credits.

http://www.afdc.energy.gov/vehicles/fuel_cell.htmlSource US Dept of Energy

 

What is a fuel cell vehicle?

Fuel cell vehicles use a completely different propulsion system than conventional vehicles, which can be two to three times more efficient. Unlike conventional vehicles, they produce no harmful exhaust emissions. Other benefits include increasing U.S. energy security and strengthening the economy.

Fuel cell vehicles can be fueled with pure hydrogen gas stored directly on the vehicle or extracted from a secondary fuel—such as methanol, ethanol, or natural gas—that carries hydrogen. These secondary fuels must first be converted into hydrogen gas by an onboard device called a reformer. Fuel cell vehicles fueled with pure hydrogen emit no pollutants, only water and heat. Vehicles that use secondary fuels and a reformer produce only small amounts of air pollutants.

Fuel cell vehicles can be equipped with other advanced technologies to increase efficiency, such as regenerative braking systems, which capture the energy lost during braking and store it in a large battery. These vehicles are still at an early stage of development.Research and development efforts are bringing them closer to commercialization.

 

How Fuel Cell Vehicles Work

Like all-electric vehicles, fuel cell vehicles use electricity to power motors located near the vehicle's wheels. In contrast to electric vehicles, fuel cell vehicles produce their primary electricity using a fuel cell powered by hydrogen.

The most common type of fuel cell for vehicle applications is the polymer electrolyte membrane (PEM) fuel cell. In a PEM fuel cell, an electrolyte membrane is sandwiched between a positive electrode (cathode) and a negative electrode (anode). Hydrogen is introduced to the anode and oxygen to the cathode. The hydrogen molecules travel through the membrane to the cathode but not before the membrane strips the electrons off the hydrogen molecules.

The electrons are forced to travel through an external circuit to recombine with the hydrogen ions on the cathode side, where the hydrogen ions, electrons, and oxygen molecules combine to form water. The flow of electrons through the external circuit forms the electrical current needed to power a vehicle. See the fuel cell animation to learn more about the process.

Stationary distributed energy

All fuel cells can run on hydrogen. 

Some can run on hydrocarbons such as methane or towns gas.

Ceramic fuel cells

One company, Ceramic Fuel Cells, is making solid oxide fuel cells to produce electricity and heat in buildings from gas. By using the waste heat, the efficiency increases.  http://www.cfcl.com.au

Efficiency of solid oxide fuel cell  - SOFC - 33%

12% losses between oil well and filling station: factor 0.88
50% HHV efficiency of SOFC with internal reforming and Diesel fuel: factor 0.50
  5% parasitic losses for the SOFC system: factor 0.95
10% electric losses in the drive-train between battery and wheels: factor 0.90
20% losses for battery charging and discharging: factor 0.80
10% bonus for regenerative braking: factor 1.10

With these numbers the well-to-wheel efficiency of a hybrid electric car with SOFC
range extender operated on Diesel fuel becomes 33%

Source: http://www.efcf.com/reports/E04.pdf

...
   

Direct Carbon Fuel Cells (DCFC) 

Another technology in the early stage of development is the Direct Carbon Fuel Cell (DCFC) that could offer conversion efficiencies of up to 80%. 
 
Power is generated by elemental carbon particles (immersed in molten electrolyte) and atmospheric 
oxygen. Fuel is made by thermally decomposing coal at low temperatures yielding very reactive carbon 
and gas rich in hydrogen and simple hydrocarbons. Flue gas from the fuel cell itself is near pure 
CO2, thus avoiding the need for capture. 
 
DCFC technology is unlikely to be available for large scale power production for several decades. 

Energy dense sugar battery

Virginia Tech

Researcher Zhang is using a series of enzymes mixed together in combinations not found in nature. In this newest development, Zhang and his colleagues constructed a non-natural synthetic enzymatic pathway that strip all charge potentials from the sugar to generate electricity in an enzymatic fuel cell. Then, low-cost biocatalyst enzymes are used as catalyst instead of costly platinum, which is typically used in conventional batteries.

Like all fuel cells, the sugar battery combines fuel — in this case, maltodextrin, a polysaccharide made from partial hydrolysis of starch — with air to generate electricity and water as the main byproducts.

While other sugar batteries have been developed, this one has an energy density an order of magnitude higher than others, allowing it to run longer before needing to be refueled, Zhang said.

 

Other pages on this site

Hydrogen economy                        

Hydrogen production                 

Hydrogen powered transport   

Fuel cells                  

Fuel cell aircraft                    

Hydrogen for steelmaking        

Hydrogen storage                 

Hydrogen distribution