Hydrogen is the simplest element on Earth. A hydrogen atom consists of only one proton and one electron. It is also the most abundant element in the universe.
But despite its simplicity and abundance, hydrogen does not occur naturally as a gas on Earth. It is always combined with other elements. Water, for example, is a combination of hydrogen and oxygen. Hydrogen is also found in many organic compounds, especially " hydrocarbons" that make up fuels such as gasoline, natural gas, methanol and propane.
To generate electricity based on hydrogen, pure hydrogen must first be extracted from a compound of hydrogen. Then it can be used in a fuel cell.
Hydrogen is a clean fuel that, when consumed, produces only water. Hydrogen can be produced from a variety of internal sources, such as coal, natural gas, nuclear power and renewable energy. These qualities presents him as an attractive option of fuel for transport and electricity producing applications.
Hydrogen is an energy carrier that can be used to store, move and deliver energy produced from other sources. The energy from the hydrogen fuel is derived from fuels and processes used to produce hydrogen.
Today, hydrogen fuels can be produced by several methods. The most common are thermal processes, electrolytic and photolytic.
Thermal hydrogen production processes typically involve steam reforming, a high temperature process in which steam reacts with a fuel containing hydrocarbons to produce hydrogen.
Many hydrocarbon based fuels can be reformed to produce hydrogen, including natural gas, oil, renewable liquid fuels, gasificated coal, or gasificated biomass. Today, about 95% of all hydrogen is produced by steam reforming of natural gas.
Water can be separated into hydrogen and oxygen through a process called electrolysis. The electrolytic processes are taking place in an electrolysis device that works more like a fuel cell in reverse.
The photolytic processes are using light as an agent for the production of hydrogen. The photobiological processes are using natural photosynthetic activity of a bacteria and green algae to produce hydrogen.
The photoelectrochemical processes are using specialized semiconductors to separate water into hydrogen and oxygen.
Fuel cells represent an emerging technology that can provide electricity and heat for buildings and power vehicles and electronic devices.
How do fuel cells work
Fuel cells work like batteries, but they do not consume or need recharging. They produce electricity and heat as long as fuel is supplied. A fuel cell consists of two electrodes – a negative electrode (or anode) and a positive electrode (or cathode) – placed one over another around an electrolyte.
A fuel such as hydrogen, is powered to the anode and air is powered to the cathode. Activated by a catalyst, hydrogen atoms separate into protons and electrons, which take different paths to the cathode. Electrons pass through an external circuit, creating a flow of electricity. The protons migrate through the electrolyte to the cathode, where they reunite with oxygen and electrons to produce water and heat.
Types of Fuel Cells
Although the basic operations of all fuel cells are the same, many types have been developed to take advantage of different electrolytes to serve different application needs.
Electrolyte polymer fuel cells membrane
Electrolyte polymer fuel cells membrane, also called exchange proton fuel cell membrane, is using a polymer membrane as electrolyte.
These cells operate at relatively low temperatures and can vary quickly their output to meet changing power demands. These fuel cells are the best candidates for powering automobiles. They can also be used for stationary power production.
Fuel cell based on Direct Methanol
Fuel cell based on Direct Methanol are similar to PEM cell in that they use a polymer membrane as an electrolyte. However, the fuel cells presented here are using methanol direct on the anode, eliminating the need for a fuel reformer. These cells are of interest to power portable electronic devices such as computers, laptops and rechargeable battery.
Alkaline Fuel Cells
They use an alkaline electrolyte such as potassium hydroxide or an alkaline membrane. Originally used by NASA in space missions, alkaline fuel cells have now found new applications such as portable power.
Fuel cells based on phosphoric acid
They use a phosphoric acid electrolyte held within a porous matrix and operates at about 200 ° C. They are usually used in modules of 400 kW or greater and are used for stationary power generation in hotels, hospitals, grocery stores and office buildings, where waste heat can also be used.
Phosphoric acid also can be immobilized in polymer membrane. Fuel cells that use these membranes are of interest for a variety of stationary power applications.
Fuel cells based on molten carbonate
They use a molten salt carbonate immobilized in a porous matrix as electrolyte. They are already used in a variety of stationary medium- large scale applications in which their high efficiency produce net energy savings. High operating temperature (about 600 ° C) allows them to internally reform fuels such as natural gas and biogas.
Fuel cells based on solid oxide
They use a thin layer of ceramic as a solid electrolyte. They are being developed for use in a variety of stationary power applications, such as in auxiliary power for heavy trucks.
Operating at 700 – 1000 ° C with electrolytes based on zirconia, and as low as 500 ° C with electrolytes based on “ ceria”, these fuel cells can internally reform natural gas and biogas and can be combined with a turbine gas to produce high efficiency up to 75%.
Thermal and electrical cogeneration
In addition to electricity, fuel cells produce heat. This heat can be used to meet heating needs, including hot water and space heating. Fuel cells that use cogeneration heat and electricity are of interest to power homes and buildings, where shows an efficiency of 90%.
This high efficiency operation saves money, saves energy and reduces emissions of greenhouse gases.
Reversible and renewable fuel cells
This special class of fuel cells produce electricity from hydrogen and oxygen, but can be reversed and powered with electricity to produce hydrogen and oxygen. This emerging technology could provide storage for excess of energy from intermittent renewable energy sources such as wind and solar energy, releasing this energy during periods of low energy production.
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