Hydrogen is the simplest element on Earth. A hydrogen atom consists of only one proton and one electron. At Earth surface temperatures and pressures, it is a colorless, odorless gas (H2). It is also the most plentiful element in the universe. But despite its simplicity and abundance, hydrogen doesn't 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, notably the "hydrocarbons" that make up fuels such as gasoline, natural gas, methanol, and propane. To generate electricity using hydrogen, pure hydrogen must first be extracted from a hydrogen-containing compound. Then it can be used in a fuel cell.
The energy in 2.2 lb (1 kg) of hydrogen gas is about the same as the energy in 1 gallon of gasoline. A light-duty fuel cell vehicle must store 11-29 lb (5-13 kg) of hydrogen to enable an adequate driving range of 300 miles or more. Because hydrogen has a low volumetric energy density (a small amount of energy by volume compared with fuels such as gasoline), storing this much hydrogen on a vehicle using currently available technology would require a very large tank-larger than the trunk of a typical car. Advanced technologies are needed to reduce the required storage space and weight.
Hydrogen is an excellent fuel for many reasons:
Zero to near-zero GHG emissions depending on method of production
Can be produced from fossil fuel-based feedstocks such as natural gas
Can be produced from off-peak electricity from nuclear, solar, wind, tidal energy sources
Waste stream hydrogen is available for capture from a variety of industrial processes
Safe to produce, store, transport and use in fuel cells and internal combustion engines
Can store off-peak energy produced by renewable energy technologies such as solar, wind and tidal generation
Hydrogen is not a source of energy, but an energy carrier. As a result, before it can be used as a fuel, hydrogen must be manufactured. There are a variety of ways to produce hydrogen, including from water through a process called electrolysis, or extracted from gases such as fossil fuels. It can also be produced using renewable hydro, wind, solar and nuclear power.
The ratio of hydrogen to carbon in the fuels we use has increased over the years. When we burn fossil fuels such as natural gas, the two primary products are carbon dioxide and water. The higher the percentage of hydrogen in a fuel, the less carbon dioxide and more water produced. As the hydrogen content of our fuels increases, they become cleaner. With supplies of many other fuels diminishing, hydrogen will play an important role in extending the life of fossil fuels and optimizing renewable energy sources.
HYDROGEN PRODUCTION
The following are some ways to produce hydrogen. Many are in the early stages of development.
Natural gas reforming-"synthesis gas" is created by reacting natural gas with high-temperature steam or by partial oxidation. The synthesis gas is then reacted with water to produce hydrogen
Renewable electrolysis-an electric current generated by renewable energy technologies, such as wind or solar, splits water into hydrogen and oxygen
Gasification-Coal or biomass is converted into gaseous components and then into synthesis gas, which is reacted with steam to produce hydrogen
Renewable liquid reforming-renewable liquid fuels such as ethanol are reacted with high-temperature steam to produce hydrogen near the point of end-use
Nuclear high-temperature electrolysis-heat from a nuclear reactor is used to improve the efficiency of water electrolysis to produce hydrogen
High-temperature thermochemical water-splitting-high temperatures generated by solar concentrators or nuclear reactors drive chemical reactions that split water to produce hydrogen
Photobiological-microbes such as green algae consume water in the presence of sunlight, producing hydrogen as a byproduct
Photoelectrochemical-photoelectrochemical systems produce hydrogen from water using special semiconductors and energy from sunlight
ABOUT FUEL CELL
A fuel cell is an electrochemical energy conversion device that uses hydrogen or other fuels to produce electricity, water, and heat. It operates much like a battery but does not require electrical recharging. It can generate power almost indefinitely, as long as fuel is supplied. A fuel cell can utilize a variety of fuels including hydrogen, natural gas, formira and methanol. A fuel cell consists of two electrodes-a negative electrode (or anode) and a positive electrode (or cathode)-sandwiched around an electrolyte. Hydrogen is fed to the anode, and oxygen is fed to the cathode. Activated by a catalyst, hydrogen atoms separate into protons and electrons, which take different paths to the cathode. The electrons go through an external circuit, creating a flow of electricity. The protons migrate through the electrolyte to the cathode, where they reunite with oxygen and the electrons to produce water and heat
Fuel cells are classified by their electrolyte, which can be in solid or liquid form.
