Hydrogen
Element 1 · chemical symbol: H
These Vrulum profiles mention Hydrogen by name. Read each profile for its specific context; a mention alone does not establish composition, performance or use of the pure element.
For periodic-table data and other properties, consult the Royal Society of Chemistry periodic table.
Related technology profiles
Artificial photosynthesis
Artificial leaves are devices that use sunlight to split water into hydrogen and oxygen in one integrated unit. Laboratory modules have reached about 11% solar-to-hydrogen efficiency under one-sun illumination, but durability and outdoor performance at useful scale have not yet been shown.
Electric aircraft
Electric aircraft drive their propellers or fans with electric motors, powered either by batteries alone or by batteries combined with a fuel-burning engine. A two-seat electric trainer is type-certified, and larger hybrid-electric demonstrators have flown, but the sources reviewed here show no airline service on regional or longer routes.
Electrolysers for low-carbon hydrogen
Electrolysers use electricity to split water into hydrogen and oxygen. Alkaline and proton-exchange-membrane systems are commercially available, while solid-oxide and anion-exchange-membrane designs offer different trade-offs and maturity levels. Hydrogen is only low emissions when the electricity and wider supply chain are low emissions; project announcements and electrolyser capacity do not by themselves establish climate benefit or delivered hydrogen output.
Fusion energy
Fusion energy joins light atoms to release energy, the process that powers the Sun. Laser experiments at the US National Ignition Facility have produced more fusion energy than the laser energy delivered to the target, and magnetic machines have set energy records. No fusion plant yet supplies net electricity to a grid.
Hydrogen aircraft
Hydrogen aircraft would use hydrogen either in a fuel cell that drives electric propellers or in a modified gas turbine. Engine and fuel-cell tests, an uncrewed drone flight and airport ground trials have taken place, but no hydrogen passenger aircraft has entered service and the climate benefit depends on how the hydrogen is made.
Industrial steelmaking
Industrial steelmaking turns molten iron into steel by removing carbon and other impurities. The main methods date from the Bessemer process of 1856 and the open-hearth furnace, and today's routes are the basic oxygen furnace and the electric arc furnace.
Making oxygen and fuel on Mars
NASA's MOXIE instrument on the Perseverance rover made oxygen from the Martian atmosphere over 16 runs, reaching 12 grams per hour at its most efficient. Making methane fuel and extracting water on Mars, and scaling oxygen production for crewed missions, remain at model, proposal or concept stage.
Nuclear space propulsion and power
Nuclear energy already supplies electricity on some spacecraft through radioisotope generators, and one fission reactor flew in Earth orbit in 1965. Nuclear thermal and nuclear electric propulsion have been tested on the ground or planned, but have not yet flown, and NASA's planned SR-1 Freedom mission targets a launch in late 2028.
Petroleum refining
Petroleum refining separates crude oil into fractions and changes their molecules to make petrol, diesel, jet fuel and lubricating oils. Its key steps ran from early kerosene stills to catalytic cracking in the 1930s. EPA reports that refinery sulphur dioxide and nitrogen oxide emissions have fallen since 2000.
Protein made from air and electricity
Gas fermentation grows microbes on hydrogen, carbon dioxide and oxygen, then dries the cells into a protein powder for food or feed. One producer reports a food approval in Singapore and a self-affirmed GRAS conclusion in the United States, but published cost and life-cycle studies depend heavily on low-carbon electricity and are mostly modelled rather than measured at scale.
Seawater electrolysis
Seawater electrolysis uses electricity to split seawater directly into hydrogen and oxygen, without first removing the salt. Laboratory and small-device studies report long test runs, but no complete system has yet been shown to be cheaper, cleaner or more reliable than purifying water first.
Self-healing polymers
Self-healing polymers are plastics, rubbers and composites that can repair cracks or cuts, either on their own or with a trigger such as heat. Laboratory work since 2001 has shown partial to full recovery of strength in several material families. Bacteria-based concrete has reached full-scale pilots, but most systems remain at the research and prototype stage.
Transparent wood
Transparent wood is wood in which the light-absorbing lignin has been removed or chemically modified and the open porous structure is filled with a clear polymer, so that light can pass through. Laboratory samples reach up to about 90% total transmittance, but high haze, limits on thickness and unproven outdoor durability keep it at research and prototype stage.