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Other bacteria may then consume free H2, which may also be oxidised photochemically in the atmosphere or lost to space. Hydrogen is also thought to be an important reactant in pre-biotic chemistry and the early evolution of life on Earth, and potentially elsewhere in the Solar System .
Hydrogen can be purified by passing through a membrane composed of palladium and silver. Permeability of the former to hydrogen was discovered back in the 1860s. [2] An alloy with a ca. 3:1 ratio for Pd:Ag is more structural robust than pure Pd, which is the active component that allows the selective diffusion of H 2 through it.
Hydrogen can be used in fuel cells to produce electricity, or burned to generate heat. [153] When hydrogen is consumed in fuel cells, the only emission at the point of use is water vapour. [153] When burned, hydrogen produces relatively little pollution at the point of combustion, but can lead to thermal formation of harmful nitrogen oxides. [153]
High pressure electrolysis is the electrolysis of water by decomposition of water (H 2 O) into oxygen (O 2) and hydrogen gas (H 2) by means of an electric current being passed through the water. The difference with a standard electrolyzer is the compressed hydrogen output around 120–200 bar (1740–2900 psi , 12–20 MPa ). [ 146 ]
It should not be confused with green chemistry, which seeks to reduce potential pollution at its source. It can be defined as the study of the sources, reactions, transport, effects, and fates of chemical species in the air , soil , and water environments; and the effect of human activity and biological activity on these.
Water molecules have two hydrogen atoms and one oxygen atom. While H 2 is not very reactive under standard conditions, it does form compounds with most elements. Hydrogen can form compounds with elements that are more electronegative, such as halogens (F, Cl, Br, I), or oxygen; in these compounds hydrogen takes on a partial positive charge. [1]
Modelling suggests that enough natural hydrogen exists to meet humanity's demand for hydrogen for thousands of years, however most of this cannot be extracted economically. [ 5 ] [ 6 ] Natural hydrogen has been identified in many source rocks in areas beyond the sedimentary basins where oil companies typically operate.
Hydrogen can be produced using aluminium by reacting it with water. [26] It was previously believed that, to react with water, aluminium must be stripped of its natural oxide layer using caustic substances, alloys, [ 27 ] or mixing with gallium (which produces aluminium nanoparticles that allow 90% of the aluminium to react). [ 28 ]