Kinetic Modeling and Quantum Yields: Hydrogen Production via Pd-TiO2 Photocatalytic Water Splitting under Near-UV and Visible Light

Abstract

A palladium (Pd) doped mesoporous titanium dioxide (TiO2) photocatalyst was used to produce hydrogen (H2) via water splitting under both near-UV and visible light. Experiments were carried out in the Photo-CREC Water-II Reactor (PCW-II) using a 0.25 wt% Pd-TiO2 photocatalyst, initial pH = 4 and 2.0 v/v% ethanol, as an organic scavenger. After 6 h of near-UV irradiation, this photocatalyst yielded 113 cm3 STP of hydrogen (H2). Furthermore, after 1 h of near-UV photoreduction followed by 5 h of visible light, the 0.25 wt% Pd-TiO2 photocatalyst yielded 5.25 cm3 STP of H2. The same photocatalyst, photoreduced for 24 h under near-UV and subsequently exposed to 5 h of visible light, yielded 29 cm3 STP of H2. It was observed that the promoted redox reactions led to the production of hydrogen and by-products such as methane, ethane, ethylene, acetaldehyde, carbon monoxide, carbon dioxide and hydrogen peroxide. These redox reactions could be modeled using an “in series-parallel” reaction network and Langmuir Hinshelwood based kinetics. The proposed rate equations were validated using statistical analysis for the experimental data and calculated kinetic parameters. Furthermore, Quantum yields (QYH•%) based on the H• produced were also established at promising levels: (a) 34.8% under near-UV light and 1.00 g L−1 photocatalyst concentration; (b) 8.8% under visible light and 0.15 g L−1. photocatalyst concentration following 24 h of near-UV.

2023 roadmap on photocatalytic water splitting

“…To accomplish this, analytical instruments including GC-MS, HPLC, Raman spectroscopy should be adapted for the detection and quantification of organic scavenger derived chemical species. In addition, applicable reaction models are required for the establishment of reliable kinetics, consistent with postulated reaction mechanics [117,125]. These kinetic models should be studied and developed to lead to PC reactor operations with high QYs and PTEFs.…”

“…These advanced analytical techniques are essential for both the proper identification and quantification of products (i.e. hydrogen and organic scavenger derived chemical species (see figure 13(a))) [125]. Furthermore, the determination of irradiation densities at various reactor locations, requires high precision scanning photometric detectors that provide rapid and precise spectra analysis.…”