What does a fuel cell look like

The date was chosen in recognition of the atomic weight of hydrogen 1. Fuel cells come in many varieties; however, they all work in the same general manner. They are made up of three adjacent segments: the anode , the electrolyte , and the cathode. Two chemical reactions occur at the interfaces of the three different segments.

The net result of the two reactions is that fuel is consumed, water or carbon dioxide is created, and an electric current is created, which can be used to power electrical devices, normally referred to as the load. At the anode a catalyst oxidizes the fuel, usually hydrogen, turning the fuel into a positively charged ion and a negatively charged electron. The electrolyte is a substance specifically designed so ions can pass through it, but the electrons cannot. The freed electrons travel through a wire creating the electric current. The ions travel through the electrolyte to the cathode.

Once reaching the cathode, the ions are reunited with the electrons and the two react with a third chemical, usually oxygen, to create water or carbon dioxide. A typical fuel cell produces a voltage from 0.

Voltage decreases as current increases, due to several factors:. To deliver the desired amount of energy, the fuel cells can be combined in series to yield higher voltage , and in parallel to allow a higher current to be supplied. Such a design is called a fuel cell stack. The cell surface area can also be increased, to allow higher current from each cell. Within the stack, reactant gases must be distributed uniformly over each of the cells to maximize the power output. In the archetypical hydrogen—oxide proton-exchange membrane fuel cell design, a proton-conducting polymer membrane typically nafion contains the electrolyte solution that separates the anode and cathode sides.

Notice that the synonyms "polymer electrolyte membrane" and "proton exchange mechanism" result in the same acronym. On the anode side, hydrogen diffuses to the anode catalyst where it later dissociates into protons and electrons. These protons often react with oxidants causing them to become what are commonly referred to as multi-facilitated proton membranes.

The protons are conducted through the membrane to the cathode, but the electrons are forced to travel in an external circuit supplying power because the membrane is electrically insulating. On the cathode catalyst, oxygen molecules react with the electrons which have traveled through the external circuit and protons to form water.


Hydrogen fuel is back in the picture

In addition to this pure hydrogen type, there are hydrocarbon fuels for fuel cells, including diesel , methanol see: direct-methanol fuel cells and indirect methanol fuel cells and chemical hydrides. The waste products with these types of fuel are carbon dioxide and water. When hydrogen is used, the CO2 is released when methane from natural gas is combined with steam, in a process called steam methane reforming , to produce the hydrogen. This can take place in a different location to the fuel cell, potentially allowing the hydrogen fuel cell to be used indoors—for example, in fork lifts.

The materials used for different parts of the fuel cells differ by type. The bipolar plates may be made of different types of materials, such as, metal, coated metal, graphite , flexible graphite, C—C composite , carbon — polymer composites etc. The electrolyte could be a polymer membrane. Elmore and H. In these cells phosphoric acid is used as a non-conductive electrolyte to pass positive hydrogen ions from the anode to the cathode.

Fuel cells

These cells commonly work in temperatures of to degrees Celsius. This high temperature will cause heat and energy loss if the heat is not removed and used properly. This heat can be used to produce steam for air conditioning systems or any other thermal energy consuming system.

Since the hydrogen ion production rate on the anode is small, platinum is used as catalyst to increase this ionization rate. A key disadvantage of these cells is the use of an acidic electrolyte. This increases the corrosion or oxidation of components exposed to phosphoric acid.

Solid acid fuel cells SAFCs are characterized by the use of a solid acid material as the electrolyte. At low temperatures, solid acids have an ordered molecular structure like most salts. At warmer temperatures between and degrees Celsius for CsHSO 4 , some solid acids undergo a phase transition to become highly disordered "superprotonic" structures, which increases conductivity by several orders of magnitude.

The alkaline fuel cell or hydrogen-oxygen fuel cell was designed and first demonstrated publicly by Francis Thomas Bacon in It was used as a primary source of electrical energy in the Apollo space program. The space between the two electrodes is filled with a concentrated solution of KOH or NaOH which serves as an electrolyte.

Proton Exchange Membrane Fuel Cell(PEMFC)

H 2 gas and O 2 gas are bubbled into the electrolyte through the porous carbon electrodes. Thus the overall reaction involves the combination of hydrogen gas and oxygen gas to form water. The cell runs continuously until the reactant's supply is exhausted. This type of cell operates efficiently in the temperature range K to K and provides a potential of about 0. Solid oxide fuel cells SOFCs use a solid material, most commonly a ceramic material called yttria-stabilized zirconia YSZ , as the electrolyte.

Because SOFCs are made entirely of solid materials, they are not limited to the flat plane configuration of other types of fuel cells and are often designed as rolled tubes. SOFCs are unique since in those, negatively charged oxygen ions travel from the cathode positive side of the fuel cell to the anode negative side of the fuel cell instead of positively charged hydrogen ions travelling from the anode to the cathode, as is the case in all other types of fuel cells. Oxygen gas is fed through the cathode, where it absorbs electrons to create oxygen ions.

The oxygen ions then travel through the electrolyte to react with hydrogen gas at the anode. The reaction at the anode produces electricity and water as by-products. Carbon dioxide may also be a by-product depending on the fuel, but the carbon emissions from an SOFC system are less than those from a fossil fuel combustion plant. SOFC systems can run on fuels other than pure hydrogen gas.

However, since hydrogen is necessary for the reactions listed above, the fuel selected must contain hydrogen atoms.

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For the fuel cell to operate, the fuel must be converted into pure hydrogen gas. SOFCs are capable of internally reforming light hydrocarbons such as methane natural gas , [49] propane and butane. Challenges exist in SOFC systems due to their high operating temperatures. One such challenge is the potential for carbon dust to build up on the anode, which slows down the internal reforming process. Research to address this "carbon coking" issue at the University of Pennsylvania has shown that the use of copper-based cermet heat-resistant materials made of ceramic and metal can reduce coking and the loss of performance.

Despite these disadvantages, a high operating temperature provides an advantage by removing the need for a precious metal catalyst like platinum, thereby reducing cost. The high operating temperature is largely due to the physical properties of the YSZ electrolyte.

As temperature decreases, so does the ionic conductivity of YSZ. Therefore, to obtain optimum performance of the fuel cell, a high operating temperature is required. The lower operating temperature allows them to use stainless steel instead of ceramic as the cell substrate, which reduces cost and start-up time of the system.

MCFCs use lithium potassium carbonate salt as an electrolyte, and this salt liquefies at high temperatures, allowing for the movement of charge within the cell — in this case, negative carbonate ions. The reforming process creates CO 2 emissions.

How Do Hydrogen Fuel Cell Vehicles Work? | Union of Concerned Scientists

MCFC-compatible fuels include natural gas, biogas and gas produced from coal. The hydrogen in the gas reacts with carbonate ions from the electrolyte to produce water, carbon dioxide, electrons and small amounts of other chemicals. The electrons travel through an external circuit creating electricity and return to the cathode.

There, oxygen from the air and carbon dioxide recycled from the anode react with the electrons to form carbonate ions that replenish the electrolyte, completing the circuit. This makes MCFC systems not suitable for mobile applications, and this technology will most likely be used for stationary fuel cell purposes. The main challenge of MCFC technology is the cells' short life span.