Hydrogen Production Via Photocatalytic Water Splitting Under Near-UV and Visible Light Using Doped Pd TiO2
Abstract
The present PhD thesis reports the modification of titanium dioxide (TiO2) with palladium (Pd), to enhance hydrogen production via water splitting, using 2.0v/v% ethanol as a scavenger. Titanium dioxide was used as photocatalyst, given its ability to absorb photons, producing e-/h+ pairs. Mesoporous TiO2 was synthesized using a soft template, following the sol-gel method, to modify its morphological properties. Palladium was used as co-catalyst doping TiO2 agent, narrowing the band gaps down to 2.51 eV, and creating additional active metal sites.
Water splitting experiments under near-UV and visible light irradiation were carried out in the Photo-CREC Water-II Reactor (PCW-II) unit. It allows precise irradiation measurements, for macroscopic irradiation energy balances.
Redox reactions in the PCW-II led to hydrogen production and by-product compounds formation such as methane, ethane, ethylene, acetaldehyde, carbon monoxide, carbon dioxide and hydrogen peroxide. It was found that this redox reaction followed an “in series-parallel” network, involving the organic scavenger ethanol. Carbon balances, OH• and H• radical balances were obtained to validate the proposed reaction network. Furthermore, a kinetic model for photocatalytic water splitting for hydrogen production was developed, with the proposed kinetics and the associated kinetic parameters, being validated with experimental data, obtained in PCW-II unit.
Regarding energy efficiencies (QY%), it was observed that the prepared TiO2-Pd photocatalyst presented a promising QY% based on H· produced of up to 69.4% under near-UV irradiation, and of 17.6% under visible light for hydrogen production.