The universal emergence of atomic hydrogen first occurred during the recombination epoch. At standard temperature and pressure, hydrogen is a colorless, odorless, tasteless, non-toxic, nonmetallic, highly combustible diatomic gas with the molecular formula H2. Since hydrogen readily forms covalent compounds with most non-metallic elements, most of the hydrogen on Earth exists in molecular forms such as in the form of water or organic compounds.
In 1671, Robert Boyle discovered and described the reaction between iron filings and dilute acids, which results in the production of hydrogen gas
Hydrogen gas was first artificially produced in the early 16th century, via the mixing of metals with acids. In 1766–81, Henry Cavendish was the first to recognize that hydrogen gas was a discrete substance, and that it produces water when burned, a property which later gave it its name: in Greek, hydrogen means “water-former”.
In 1783, Antoine Lavoisier gave the element the name hydrogen (from the Greek ὑδρο- hydro meaning “water” and -γενής genes meaning “creator”) when he and Laplace reproduced Cavendish’s finding that water is produced when hydrogen is burned
Hydrogen Characteristics
Hydrogen can be an environmentally cleaner source of energy to end-users, particularly in transportation applications, without release of pollutants (such as particulate matter) or carbon dioxide at the point of end use. A 2004 analysis asserted that “most of the hydrogen supply chain pathways would release significantly less carbon dioxide into the atmosphere than would gasoline used in hybrid electric vehicles” and that significant reductions in carbon dioxide emissions would be possible if carbon capture or carbon sequestration methods were utilized at the site of energy or hydrogen production
Hydrogen has a high energy density by weight but has a low energy density by volume when not highly compressed or liquified. An Otto cycle internal-combustion engine running on hydrogen is said to have a maximum efficiency of about 38%, 8% higher than a gasoline internal-combustion engine.
The combination of the fuel cell and electric motor is 2-3 times more efficient than an internal-combustion engine. However, the high capital costs of fuel cells, about $5,500/kW in 2002, are one of the major obstacles of its development, meaning that the fuel cell is only technically, but not economically, more efficient than an internal-combustion engine.
Other technical obstacles include hydrogen storage issues and the purity requirement of hydrogen used in fuel cells – with current technology, an operating fuel cell requires the purity of hydrogen to be as high as 99.999%. On the other hand, hydrogen engine conversion technology is more economical than fuel cells.
Hydrogen production is a large and growing industry. Globally, some 57 million metric tons of hydrogen, equal to about 170 million tons of oil equivalent, were produced in 2004. The growth rate is around 10% per year. Within the United States, 2004 production was about 11 million metric tons (Mt), an average power flow of 48 gigawatts. (For comparison, the average electric production in 2003 was some 442 GW.) As of 2005, the economic value of all hydrogen produced worldwide is about $135 billion per year.
