Hydrogen production by water photo-sonolysis: a modal approach to enhance the ultrasonic acoustic field in the solution

Abstract

Water photo-sonolysis is considered one of the most innovative ways of hydrogen production. Cited by the Italian strategy on hydrogen research as a promising field for innovation research, it consists of the coupling work of solar-light electromagnetic waves and mechanical ultrasonic waves to induce water splitting. Water photolysis requires catalysts to be performed and optimized, whereas ultrasound sonolysis acts independently. In the state of the art, it was experimentally demonstrated that the rates of hydrogen production by sonolysis rise according to resonance peaks of the solution in function of ultrasound wavelength. To enhance the effects of the ultrasound, the resonance of the solution can be geometrically achieved by acoustic modal analysis of a set of possible solution volumes. According to the geometry of the photo-sono reactor at the lab scale, the shape of the tested solution volumes is cylindrical. The modal analysis was led in a Matlab environment considering the cylindrical volume’s geometry and the fluid’s physical properties. To check the reliability of the simulated results, pressure measurements were led at the lab scale on the simulated water volumes by means of a hydrophone at a significant number of points.

Future perspectives in green hydrogen production by catalyzed sono-photolysis of water

“…In rectangular shaped reactors, Koch 81 found a correlation between the double layer cavitation structure and the acoustic power of ultrasound but there were no geometrical correlations, and comparing simulations and pressure measurements, eigenvalue influence was not proved, and symmetrical distribution of the sound pressure was discussed. 82…”

“…This is a factor which affects the spatial distribution of acoustic pressure into the vessel, rising differences between measurements and mechanical modal analysis. 82 Furthermore, efforts are underway to investigate the energy efficiency between the mechanical energy induced by ultrasonication in the solution and the subsequent extraction of hydrogen. Although an energy cavitation efficiency in the solution up to 44% has been reported in the literature, 66 direct measurements of acoustic amplitude in the solution and the optimization of impedance matching between the reactor and the ultrasonic transducer are required.…”