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►Fuel Cells: Fuel Cell Components & Function A fuel cell is a device that uses hydrogen (or hydrogen-rich fuel) and oxygen to create electricity by an electrochemical process. A single fuel cell consists of an electrolyte sandwiched between two thin electrodes (a porous anode and cathode). While there are different fuel cell types, all work on the same principle: - Hydrogen, or a hydrogen-rich fuel, is fed to the anode where a catalyst separates hydrogen's negatively charged electrons from positively charged ions (protons). - At the cathode, oxygen combines with electrons and, in some cases, with species such as protons or water, resulting in water or hydroxide ions, respectively. - For polymer electrolyte membrane (PEM) and phosphoric acid fuel cells, protons move through the electrolyte to the cathode to combine with oxygen and electrons, producing water and heat. - For alkaline, molten carbonate, and solid oxide fuel cells, negative ions travel through the electrolyte to the anode where they combine with hydrogen to generate water and electrons. - The electrons from the anode side of the cell cannot pass through the membrane to the positively charged cathode; they must travel around it via an electrical circuit to reach the other side of the cell. This movement of electrons is an electrical current. The amount of power produced by a
fuel cell depends upon several factors, such as fuel cell type, cell
size, the temperature at which it operates, and the pressure at which
the gases are supplied to the cell. Still, a single fuel cell produces
enough electricity for only the smallest applications. Therefore,
individual fuel cells are typically combined in series into a fuel cell Direct hydrogen fuel cells produce pure water as the only emission. This water is typically released as water vapor. Fuel cells release less water vapor than internal combustion engines producing the same amount of power. Fuel Cells Types: Fuel cells are classified
primarily by the kind of electrolyte they employ. - Polymer Electrolyte Membrane (PEM) Polymer Electrolyte Membrane
Polymer electrolyte membrane (PEM)
fuel cells ,also called proton exchange membrane fuel cells, deliver
high power density and offer the advantages of low weight and volume,
compared to other fuel cells. PEM fuel cells use a solid polymer
as an electrolyte and porous carbon electrodes containing a platinum
catalyst. They need only hydrogen, oxygen from the air, and water to operate and do not require corrosive fluids like some fuel cells. They are typically fueled with pure hydrogen supplied from storage tanks or onboard reformers. Polymer electrolyte membrane fuel cells operate at relatively low temperatures, around 80°C (176°F). Low temperature operation allows them to start quickly (less warm-up time) and results in less wear on system components, resulting in better durability. However, it requires that a noble-metal catalyst (typically platinum) be used to separate the hydrogen's electrons and protons, adding to system cost. The platinum catalyst is also extremely sensitive to CO poisoning, making it necessary to employ an additional reactor to reduce CO in the fuel gas if the hydrogen is derived from an alcohol or hydrocarbon fuel. This also adds cost. Developers are currently exploring platinum/ruthenium catalysts that are more resistant to CO. PEM fuel cells are used primarily
for transportation applications and some stationary applications. Due to
their fast startup time, low sensitivity to orientation, and favorable
power-toweight ratio, PEM fuel cells are particularly suitable for use
in passenger vehicles, such as cars and buses. |
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