For

chemical reaction A chemical reaction is a process that leads to the chemistry, chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an Gibbs free energy, ...

s, the zinc–zinc oxide cycle or Zn–ZnO cycle is a two step

thermochemical cycle In chemistry, thermochemical cycles combine solely heat sources (''thermo'') with ''chemical'' reactions to split water into its hydrogen and oxygen components. The term ''cycle'' is used because aside of water, hydrogen and oxygen, the chemical c ...

based on

zinc Zinc is a chemical element; it has symbol Zn and atomic number 30. It is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic tabl ...

and

zinc oxide Zinc oxide is an inorganic compound with the Chemical formula, formula . It is a white powder which is insoluble in water. ZnO is used as an additive in numerous materials and products including cosmetics, Zinc metabolism, food supplements, rubbe ...

for

hydrogen production Hydrogen gas is produced by several industrial methods. Nearly all of the world's current supply of hydrogen is created from fossil fuels. Article in press. Most hydrogen is ''gray hydrogen'' made through steam methane reforming. In this process, ...

with a typical efficiency around 40%.

Process description

The thermochemical two-step

water splitting Water splitting is the chemical reaction in which water is broken down into oxygen and hydrogen: Efficient and economical water splitting would be a technological breakthrough that could underpin a hydrogen economy. A version of water splitti ...

process uses

redox Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is t ...

systems:Solar thermal ZnO-decomposition
/ref> * Dissociation: ZnO → Zn + 1/2 O₂ *

Hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

: Zn + H₂O → ZnO + H₂ For the first

endothermic An endothermic process is a chemical or physical process that absorbs heat from its surroundings. In terms of thermodynamics, it is a thermodynamic process with an increase in the enthalpy (or internal energy ) of the system.Oxtoby, D. W; Gillis, ...

step

concentrating solar power Concentrated solar power (CSP, also known as concentrating solar power, concentrated solar thermal) systems generate solar power by using mirrors or lenses to concentrate a large area of sunlight into a receiver. Electricity is generated whe ...

is used in which zinc oxide is thermally dissociated at into zinc and oxygen. In the second non-solar

exothermic In thermodynamics, an exothermic process () is a thermodynamic process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), electricity (e ...

step zinc reacts at with water and produces

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

and zinc oxide. The temperature level is realized by using a

solar power tower A solar power tower, also known as 'central tower' power plant or 'heliostat' power plant, is a type of solar furnace using a tower to receive focused sunlight. It uses an array of flat, movable mirrors (called heliostats) to focus the sun's ra ...

and a set of

heliostat A heliostat () is a device that reflects sunlight toward a target, turning to compensate for the Sun's apparent motion. The reflector is usually a plane mirror. The target may be a physical object, distant from the heliostat, or a direct ...

s to collect the

solar thermal energy Solar thermal energy (STE) is a form of energy and a technology for harnessing solar energy to generate thermal energy for use in Industrial sector, industry, and in the residential and commercial sectors. Solar thermal collectors are classified ...

References

External links

H2 formation by zinc hydrolysis in a hot wall aerosol flow reactor
{{DEFAULTSORT:Zinc-zinc oxide cycle Inorganic reactions Hydrogen production Zinc Zinc oxide

Process description

See also

References

External links