Experimental and modelling studies on the photocatalytic generation of hydrogen during water-splitting over a commercial TiO2 photocatalyst P25. (1st October 2021)

• Record Type: Journal Article
• Authors: Edelmannová, Miroslava; de los Milagros Ballari, María; Přibyl, Michal; Kočí, Kamila
• Is Part Of: Energy conversion and management. Volume 245(2021)
• Publication Date: 2021-10-01
• Subjects: Photocatalysis -- Hydrogen generation -- Titanium dioxide -- Mathematical modelling -- LED irradiation; Direct energy conversion -- Periodicals; Energy storage -- Periodicals; Energy transfer -- Periodicals; Énergie -- Conversion directe -- Périodiques; Direct energy conversion; Periodicals; 621.3105
• DOI: 10.1016/j.enconman.2021.114582
• Languages: English
• ISSNs: 0196-8904

Abstract

Graphical abstract: Highlights: Experimental and modelling studies on photocatalytic generation of hydrogen. Photocatalytic reaction rate depending on TiO2 load and light intensity was proposed. Kinetics of hydrogen mass transfer from liquid to gas phase was involved in model. Polynomial function describing spatial distribution of irradiation was suggested. Optimal photocatalyst loading for maximal hydrogen generation was determined. Abstract: Hydrogen, generally perceived as an environmentally friendly fuel, possesses the potential to lower society's dependency on fossil energy sources whose utilization leads inherently to global warming problems. Its photocatalytic generation from aqueous solutions is a promising green technology competitive to traditionally employed methods such as steam reforming or water electrolysis. However, the limiting yet achievable efficiencies of this process remain unclear. To address the question of process efficiencies, we formulate a phenomenological model predicting the behavior of an experimental photocatalytic reactor. The model considers the polynomial light intensity distribution, the concentration of photocatalysts, and the finite rate of the mass transfer between liquid and gas phases. We validate the model against experimental data obtained from a study with a commercially available TiO2 P25 photocatalyst used as a gold standard in photocatalysis. The theoretical analysis shows that the mass transfer of hydrogen from the liquid to gas phase significantly affects the photoreactor dynamics. Initial accumulation of hydrogen in the liquid phase and its delayed transport to the gas phase result in a nonlinear time-dependence of the hydrogen concentration in the gas phase. The theoretical average reaction rate reaches a maximum for a photocatalyst concentration of 0.23 g/L, which is in good agreement with an experimentally obtained value of 0.25 g/L. The photonic efficiency, defined as a ratio of the average reaction rate to the average light intensity, also reaches a maximum at the same catalyst concentration and interestingly remains constant for any higher TiO2 loads. Finding the optimal photocatalyst concentration and identifying the critical role of mass transfer shall aid further research in developing and optimizing photocatalytic reactors for hydrogen production in the future.