The "sunbelt" regulations which included European, Australia and Sahara desert, and southern state of USA, receive about 1 KW m-² of solar power. These regions suitable sites for high - temperature solar H₂ production is using solar concentration systems that reflect and focus on the solar radiation into receiver furnace, producing temperature in excess of 1500⁰C. The intense heat, which is available in the mental surroundings a nuclear reactors, can be used to derive a turbines for generating electricity or to split water into H₂ and O₂ so producing a fuels.
The Direct, single step thermolysis of water required temperature in excess of 4000⁰C, which is well above the threshold readily attainable in a solar concentration or compatible with containment materials and engineering. By using a multi - step process, however it's possible to producing H₂ at much lower temperature. Many systems are undergoing investigations and development and which are two - stage processes involving metal oxides, such as the sequence,
Fe₃O₄(s) → 3FeO(s) + 1/2 O₂(ɡ) ∆H= +319. 5 kj mol-¹
H₂O(l) + 3FeO(s) →Fe₃O₄(s) + H₂(ɡ) ∆H =- 33.6 kj mol-¹
The Dihdrogen production by this way still requires temperature in excess of 2200⁰C. Water splitting at lower temperature have been achieved with hybrid processes that combine electrochemical and thermochemical reactions such as,
2Cu(s) +2HCl(g) →(425⁰C) H₂(ɡ) + 2CuCl(s)
4CuCl → (electrolysis) 2Cu(s) + 2CuCl₂(s)
2CuCl₂(s) + H₂O → (325⁰C) Cu₂OCl₂(s)+ 2HCl(ɡ)
CuOCI₂(S) →(550⁰C) 2CuCl (s) + 1/2 O₂(ɡ)
Solar photoelectrochemical H₂ production operate on principle and that used by plants photosynthesis. The splitting water electrochemically a cell potential greater than 1.23 Voltage is required which in principle could be provided by light with a wavelength below 1000 nanometer. The principle of a photochemical water splitting system based on the light sensitive particles. Which is represents water splitting in terms of two separate half reaction. The essential the (a) mechanism for generating excited electronic state by photon capture (b) efficient transfer for electron between the site of exitation catalytic Centre (c) H₂ production must be catalyst in order for this reaction occurs that short compared to the lifetime of the excited and oxidized states of P. For H₂ molecules the catalyst can be platinum, Although it's much cheaper alternative in order to achieve a feasible industrial scale system. The major challenge for photochemical water splitting is to achieve rapid and efficient production of O₂, and there are intense efforts to find substance that are mimic the Manganese catalyst used in plant photosynthesis.
Photochemical production of H₂ and O₂ molecule by catalyst attached to particles of conducting material such as depod TiO₂ to which a photosensitiser P is also attached. Excitation by visible light produces P*, a powerful reducing agent for producing H₂ molecules, Electron transfer from P* produces P⁺, a powerful oxidizing agent for producing O₂
Very nice
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