Solar electrolysis

Hydrogen can be produced from splitting of water through various processes ranging from water electrolysis, photo(solar)-electrolysis, photo-biological production to high-temperature water decomposition. 

The hybrid solar concentrator is a potential leap frog technology that may rapidly lower the cost of clean hydrogen in light of the following the imminent market entry of CPV systems for electricity production solar cell efficiencies above 40%, with clearer ideas for 50%-efficient solar cells and the opportunity to use wasted solar heat for augmenting solar electrolysis. 

Thermally assisted solar electrolysis consists of (i) light harvesting, (ii) spectral resolution of thermal (sub bandgap) and electronic (super-bandgap) radiation, the latter of which (iiia) drives photovoltaic or photoelectrochemical charge transfer V(iH2o) while the former (iiib) elevates water to temperature T, and pressure, p ... 

For solar driven charge transfer, this maximum power is described by the product of the insolation power, Psun, with r Phot, which is then applied to electrolysis, r photPsun = Pechem = /i i2o 14 i2o. Rearranging for imo, and substitution into Eq. 25, yields for heat balanced solar electrolysis at conditions of T and p, initiating with 25 °C, 1 bar water ... 

Next, we define an ideal semiconductor photoanode and photocathode for the solar electrolysis of water. We also briefly examine real world issues related to charge-transfer kinetics at semiconductor/electrolyte interfaces and the need for an external bias to drive the photolysis of water. 

Experimental data on photo or solar electrolysis efficiencies are contained in Table 4. Other compilations are available.313 76 In most of the instances, the attained laboratory efficiencies are well below the ideal limit (c.f., Table 3) although some of the numbers claimed (see entries 1, 9, 14, 15, for example, in Table 4) are indeed impressive. However, some of the values claimed have been questioned by others.214 Further independent verification is undoubtedly warranted, and the losses associated with process scale up are, as yet, unknown. 

Karanasios, K. A., Michailides, M. K., VasiUadou, I. A., Pavlou, S., Vayenas, D. V. (2011). Potable water hydrogenotrophic denitrification in packed-bed bioieactors coupled with a solar-electrolysis hydrogen production system. Desalination and Water Treatment, 55(1—3), 86-96. 

Brine Preparation. Rock salt and solar salt (see Chemicals frombrine) can be used for preparing sodium chloride solution for electrolysis. These salts contain Ca, Mg, and other impurities that must be removed prior to electrolysis. Otherwise these impurities are deposited on electrodes and increase the energy requirements. The raw brine can be treated by addition of sodium carbonate and hydroxide to reduce calcium and magnesium levels to below 10 ppm. If further reduction in hardness is required, an ion-exchange resin can be used. A typical brine specification for the Huron chlorate ceU design is given in Table 6. 

Wurster, R. Water Electrolysis and Solar Hydrogen Demonstration Projects 27... 

One suggested application of solar energy is to use the electrical current that can be generated for the electrolysis of water. What product of the electrolysis would be most valuable as an energy source Explain your choice. 

The same group, in a previous work, reported on the realization of a hybrid anode electrode [197]. An appreciable improvement in methanol oxidation activity was observed at the anode in direct methanol fuel cells containing Pt-Ru and Ti02 particles. Such an improvement was ascribed to a synergic effect of the two components (photocatalyst and metal catalyst). A similar behavior was also reported for a Pt-Ti02-based electrode [198]. Another recent study involved the electrolysis of aqueous solutions of alcohols performed on a Ti02 nanotube-based anode under solar irradiation [199]. 

CNTs can also be produced by diffusion flame synthesis, electrolysis, use of solar energy, heat treatment of a polymer, and low temperature solid pyrolysis. In flame synthesis, combustion of a portion of the hydrocarbon gas provides the elevated temperature required, with the remaining fuel conveniently serving as the required hydrocarbon reagent. Hence, the flame constitutes an efficient source of both energy and hydrocarbon raw material. Combustion synthesis has been shown to be scalable for a high volume commercial production. 

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