Photocatalytic water splitting is a process that uses a semiconductor material to catalyze the splitting of water molecules into hydrogen and oxygen gas in the presence of light. This process has the potential to provide a clean and sustainable source of hydrogen fuel, which can be used for a variety of applications such as fuel cells and energy storage. The process of photocatalytic water splitting involves several steps, which can be divided into two main stages: light absorption and charge separation. The first stage involves the absorption of photons by the semiconductor material, which creates excited electrons and holes. The excited electrons and holes are then separated and can be used to drive the water splitting reaction. The second stage involves the transfer of the excited electrons and holes to the surface of the semiconductor material, where they can interact with water molecules. The excited electrons are used to reduce water molecules, producing hydrogen gas, while the holes are used to oxidize water molecules, producing oxygen gas. The overall reaction can be represented as follows:
2H2O + photons → 2H2 + O2
The efficiency of the photocatalytic water splitting process depends on several factors, including the choice of semiconductor material, the surface area and morphology of the catalyst, and the wavelength of light used. Some of the most commonly used semiconductor materials for photocatalytic water splitting include titanium dioxide (TiO2), zinc oxide (ZnO), and cadmium sulfide (CdS). One of the major challenges of photocatalytic water splitting is the limited efficiency of the process. The efficiency of the process is typically low due to a combination of factors, including the limited absorption of light by the semiconductor material, the rapid recombination of excited electrons and holes, and the inefficient transfer of charge to the surface of the catalyst. Researchers are actively working to overcome these challenges by developing new semiconductor materials, improving the morphology of the catalyst, and optimizing the reaction conditions.
Hydrogen produced from renewable energy sources can be used as fuels that do not contribute to CO2 emissions, and therefore is emerging as an important future power source.
In a new study led by Professor Gunther Andersson, who is Deputy Director of the Flinders University Institute for NanoScale Science and Technology at the College of Science and Engineering. first author in a new article outlining the method in the journal ACS Applied Materials & Interfaces. According to the authors, photocatalytic water splitting is a promising technique to split water into hydrogen and oxygen using semiconductor particles as photocatalysts. While researchers understand that the structural and electronic properties of photocatalyst semiconductors play a major role in determining photocatalytic activity, their goal is to find the best and most efficient material to assist this process which they have found to be chromium oxide. Cocatalysts can promote efficient photocatalytic water splitting by supporting the electron and hold separation and acts as active sites for the water splitting reaction, however, the cocatalyst requires a protective overlayer to suppress the H2 and O2 recombination which will result in a backward reaction that takes H2 and O2 back to H2O. We need to find the right overlayer material to ensure the most efficient photocatalytic water splitting and this led us to explore mixed transition metal oxides. The researchers found that chromium oxide overlayers protect the water splitting process in photocatalysis for solar light driven hydrogen production. Their work investigated the stability, oxidation state and the bulk and surface electronic structure of chromium-oxide photodeposited onto different particles as a function of the annealing process. Importantly, the international research team also found that the chromium oxide overlayers do not contribute to the water splitting reaction.
It is known that chromium oxide overlayers protect the water splitting process in photocatalysis for solar light driven hydrogen production. The researchers found that the thermal stability of the chromium oxide overlayer depends on the chemical nature of the underlying photocatalyst. Understanding the stability, oxidation state, and electronic structure of the chromium-oxide layer on photocatalyst particles under annealing is essential for overlayer applications in photocatalytic water splitting
In conclusion, photocatalytic water splitting is a promising technology for the production of hydrogen fuel from water using renewable energy sources. While the process is still in the early stages of development, ongoing research and development efforts are expected to lead to significant improvements in the efficiency and scalability of the technology in the coming years.
Alotabi AS, Small TD, Yin Y, Osborn DJ, Ozaki S, Kataoka Y, Negishi Y, Domen K, Metha GF, Andersson GG. Reduction and Diffusion of Cr-Oxide Layers into P25, BaLa4Ti4O15, and Al:SrTiO3 Particles upon High-Temperature Annealing. ACS Appl Mater Interfaces. 2023 Mar 12. doi: 10.1021/acsami.3c00250.