FUEL CELLS and FUEL CELL SYSTEMS: How They Work


An individual fuel cell element produces electricity by means of an electrochemical reaction. As depicted in Figure 1, each fuel cell element consists of an anode layer, an electrolyte matrix layer, and a cathode layer.

 In many cases (notably the low-temperature fuel cells), pure hydrogen is fed into the anode, where electrons are stripped from the hydrogen atoms, forming protons. The protons proceed through the electrolyte matrix layer to the cathode. The "borrowed" electrons are sent out to perform work, and are then returned to the cathode, where they combine with oxygen atoms to form ionized oxygen.  The ionized oxygen then combines with the protons to form water.  


The exhausts from this type of fuel cell are water, nitrogen and heat.  Some fuel cells (notably the high-temperature types) can also handle direct feed of methane, coal gas, natural gas, or other hydrocarbon fuel. Here, the exhaust consists of carbon dioxide, water, nitrogen, and heat. Also, the ion that moves through the electrolyte in these higher temperature fuel cells is usually a negatively charged ion, such as oxygen or a carbonate ion. In all cases, catalytic materials are applied to the anode and cathode electrodes, to enhance the speed of the various reactions.


For all of the fuel cell types included in this report, the fuel is either hydrogen or a hydrogen-containing, energy-rich fuel.  The oxidant is oxygen in all cases, usually brought in as air.  The ions that traverse the electrolyte matrix will vary with fuel cell type.

 

A complete fuel cell power generation system as depicted in the figure below, will usually include three major sub-systems.  These are


For systems that use hydrogen as a fuel, the fuel processor is not needed.  Also, some systems incorporate the fuel processor into the fuel cell.  Finally, for those systems that can use DC electrical power, some elements of the power conditioner are not needed.


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