Thermodynamic and kinetics of hydrogen photoproduction enhancement by concentrated sunlight with CO2 photoreduction by heterojunction photocatalysts

Abstract

For achieving water splitting into hydrogen under sunlight for practical applications, the high efficiencies of the photoreduction of CO2 over TiO2/Fe3O4 photocatalysts combined with hydrogenation of water splitting over Pt/TiO2 were investigated by practical concentrated solar energy compared with Hg lamp and Xe lamp. Based on AI analysis on the influence factors, the key parameters for TOC concentration were photocatalysts, Na2CO3 concentration and radiation intensity while the key parameters for hydrogen production were photocatalysts, radiation intensity, and TOC concentration. Accordingly, the mechanism of concentrated sunlight effects has been discussed from the view of thermodynamics and kinetics. The concentrated sunlight provides a simultaneous supply of sufficient electron–hole pairs and thermal energy. Water to hydrogen and CO2 reduction are both enhanced in concentrated sunlight due to endothermal reactions. Doping changes the internal electric field of p-n junction of in different possible ways, and thus composite photocatalysts with favorable formation of p-n junctions would enhance the charge separation by internal electric field. Moreover, photocatalysts are beneficial for providing more excited electrons at a time for achieving CO2 photoreduction at the surface region of the particles with higher density of radiation by concentrated solar energy. Subsequently, products from CO2 photoreduction, acting as sacrificial electron donors, improved hydrogen evolution in solar-mediated water splitting for prohibiting reverse reactions.

Keywords

• Concentrated sunlight
• Hydrogen evolution
• CO2 photoreduction
• p-n junction
• Thermodynamics and kinetics