Photocatalytic reforming of formic acid for hydrogen production in aqueous solutions containing cupric ions and TiO2 suspended nanoparticles under UV-simulated solar radiation

Abstract

Hydrogen is the ideal candidate to fulfill the growing energy demand in a sustainable manner because of its high energy content and no emission of greenhouse gases from its combustion. Currently most of hydrogen generation techniques involve the employment of fossil fuels, with consequent production of toxic greenhouse gases. The possibility to produce hydrogen by means of photocatalytic processes using the solar radiation as energy source fits in perfectly with the switch to a more sustainable energy production. The solar photocatalytic hydrogen generation can be achieved by reforming organic substances contained in civil or industrial wastewaters. This could allow to combine water decontamination with production of an energy carrier starting from a renewable source, the solar radiation.Within this perspective, a novel nano-TiO2 photocatalytic system based on the solar reforming of formic acid in presence of cupric ions and chlorides has been investigated. The effect on hydrogen generation rate of the initial concentrations of formic acid, chloride and cupric ion, and pH values has been evaluated. For both formic acid and chloride ions, at least up to a starting concentration of 103mM, the higher the initial concentration, the higher the rate of hydrogen generation. Hydrogen production has turned out to be noticeably dependent on cupric ion concentration. An almost opposite behavior has been found varying the starting cupric ion concentration in the range 2.5–20mM, with the highest value of hydrogen production rate recorded for Cu(II) initial concentration equal to 5.0mM. The pH value has been identified to be a crucial parameter of the system. A decrease in hydrogen production has been also observed rising pH of the solution from 1.0 to 4.0. A characterization of the solid samples recovered at the end of the runs has been performed by X-ray Diffractometry. These experimental outcomes have been rationalized within a consistent reaction mechanism able to predict the system behavior under different operating conditions. This work opens the way to the development of new competitive processes able to use waste organic streams for hydrogen generation through photacatalytic system based on solar energy.