From Ecopedia

Overview

Fuel cells are electrochemical cells converting source fuels into electric power and water.

Fuel cells generate electricity inside cells through fuel-oxidant reactions triggered in the presence of water and such other electrolytes.

Leaving the electrolytes behind, chemical reactants flow into the cells and reaction products flow out of the cells. Fuel cells can thus become operational for virtually unlimited periods as long as the required flows are well maintained.

Fuel cells, unlike the traditional electrochemical cell batteries, consume reactants from external sources, which require replenishing. Fuel cells are therefore incorporate thermodynamic open systems. Batteries, on the other hand, represent thermodynamically closed systems, as batteries chemically store the electrical energy.

Moreover, unlike batteries, fuel cells cannot store energy. Rarely, in certain applications including stand-alone power plants that are based on discontinuous solar and wind power sources, fuel cells are combined with electrolyzers as well as storage systems, forming energy storage systems.

Fuel Cell Types

Fuels and oxidants are combined in different combinations resulting in varied fuel types such as: - Polymer Electrolyte Membrane (PEM) Fuel Cells - Direct Methanol Fuel Cells - Phosphoric Acid Fuel Cells - Molten Carbonate Fuel Cells - Solid Oxide Fuel Cells - Regenerative Fuel Cells

While hydrogen, hydrocarbons and alcohols are used as fuels, oxygen (usually from atmosphere), chlorine and chlorine oxide are used as oxidants.

Efficiency of Fuel Cells

Fuel cell efficiency largely depends on the amount of power drawn from the cells. In general, drawing more power (current) lowers the efficiency of fuel cells. As most such efficiency losses are manifested as voltage drop in the cells, fuel cell efficiency is almost directly proportional to the cells’ voltage.

Fuel cell Vehicles

A Fuel cell vehicle is a hydrogen vehicle, which utilizes fuel cells to produce on-board vehicular power. Fuel cells generate electricity for powering the electric motors by utilizing either hydrogen or reformed hydrocarbon fuels and atmospheric oxygen.

In 1807, François Isaac de Rivaz built the first hydrogen vehicle.

In 1996, the first “road worthy” (with the exception of the Allis-Chalmers Fuel-Cell Tractor) fuel cell vehicle was introduced by General Motors.

Fuel Cells and Environment

Environmental Advantages

As oxidation of molecular hydrogen produces only water as a direct by-product, hydrogen fuel cells aid insignificant reduction of air contaminants including the global warming-causing greenhouse gases (GHGs).

Fuel cells are potentially clean and environment-friendly sources of energy due to extremely high fuel efficiencies for both heat and electricity. In spite of the fact that most fuel cells primarily depend on natural gas, an environmentally-hazardous fossil fuel, for producing hydrogen, the efficient use of the fuel makes the fuel cell technology a clean energy technology. Moreover, current ongoing research into the utilization of wind, solar and water power for hydrogen production might eventually make the fuel cell technology a completely renewable technology.

As no combustion occurs in fuel cells, no harmful emissions are released into the atmosphere. Due to minimal or no harmful emissions, permits and certificates are rarely required for deploying commercial purpose fuel cell systems.

Environmental drawbacks

Although fuel cells are potentially clean energy sources, hydrogen production using fossil fuels leads to the production of greenhouse gases (GHG) including carbon dioxide. Unless and until increased reliance on renewable fuel sources could be implemented, environmental benefits could be hard to accomplish.

Hydrogen storage and transportation issue is another cause for concern for the environmentalists. Large-scale hydrogen economy and related technologies in manufacturing, storing as well as transporting hydrogen would produce leaks, which when accumulated in the upper atmosphere in large amounts might cause potential danger to the ozone layer. Thus, most environmentalists opine that hydrogen leaks, which are inevitable, cause atmospheric ozone depletion.

References

http://en.wikipedia.org/wiki/Fuel_cell http://en.wikipedia.org/wiki/Fuel_cell_vehicle http://physicsworld.com/cws/article/news/17694 http://www.masstech.org/cleanenergy/fuelcell/impactenv.htm