Alternative/Renewable Energy Newsletter

Simply, fuel cells create electrical power through a chemical reaction between hydrogen and oxygen in the presence of a catalyst. The individual fuel cell creates less than a watt of electricity, but these fuel cells are connected or "stacked" to achieve higher voltage. There is no appreciable upper limit to this stacking. Emissions are only water. In the reaction process, the fuel cells also give off usable heat. Energy efficiencies of over 80% can be achieved by utilizing this heat. Even without utilizing the heat, energy efficiency is several times as high as the conventional combustion engine and emissions are effectively zero using pure hydrogen. Utility combustion generation and transmission of electric power usually achieves only about 20%-25% efficiencies with significant releases of carbon dioxide, carbon monoxide, nitrous oxides, sulfur oxide and particulate matter, all contributing to air pollution.

There are several types of fuel cells, but the type most home owners and auto owners will need to be familiar with is the Proton Exchange Membrane fuel cell, usually referred to as a PEM fuel cell. In the PEM fuel cell, hydrogen, or a hydrogen rich gas, enters the anode electrode side of the cell, passes through a gas diffusion layer (GDL) and encounters the outer surface of the membrane electrode assembly (MEA), which is coated with the catalyst, currently platinum, on both sides. The catalyst ionizes the hydrogen molecule (two atoms), releasing its two protons and two electrons; the membrane assembly allows the proton with a positive charge to pass through. The negatively charged electrons are forced to retreat to the anode and travel externally around the MEA to the positive electron pole (cathode), creating an electrical current. This electron is rejoined with the proton in the presence of the catalyst and air to form water. The chemistry on the anode side is H2 (hydrogen molecule), releasing 2 H- (electron) and 2H+ (protons). The cathode side chemistry is 2H+ + 2H- + 1/2 O2 (one oxygen molecule from the air) g H20 (water).

The electrical current created is of course a direct current (DC), which is transmitted through an inverter to create an alternating current (AC).

Basically the fuel cell has been around for over a hundred and fifty years. As usual, the "devil is in the details" of creating electricity. (The space program began using fuel cells for onboard electricity in the 1960s.) Details include the platinum catalyst, which is very sensitive to fuel contamination; water, air, heat and fuel must be provided and disposed of; the individual fuel cells must be combined or stacked to create significant electrical power; connecting the low voltage DC fuel cells to create high voltage DC and then AC. Size and weight are big problems for mobile applications. The average home needs 3 kilowatts to 10 kilowatts of power available, the automobile needs 75 kilowatts. Another problem is fuel; pure hydrogen is a problem, it is a liquid only at under a negative 200 degrees Centigrade, and as a gas, it creates volume and volatility problems. Other fuels that contain significant amounts of hydrogen (most of them) create contamination, emissions and infrastructure problems.

(from Fuel Cell Advocate)

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