Structure of the organic catalyst material for photocatalytic hydrogen evolution. Source: University of Liverpool

Inorganic materials are widely used as water-splitting photocatalysts for hydrogen production. Organic photocatalysts might be preferred because of their synthetic tunability but tend to offer low quantum efficiencies for water splitting.

An international team of researchers has now synthesized a highly active organic photocatalyst for this application. The crystalline covalent organic framework is based on a benzo-bis (benzothiophene sulfone) moiety that shows much higher activity for photochemical hydrogen evolution than its amorphous or semicrystalline counterparts.

The catalyst is stable under long-term visible irradiation and demonstrated steady photochemical hydrogen evolution with a sacrificial electron donor for at least 50 hours. The high quantum efficiency is attributed to the material’s crystallinity, strong visible light absorption and its wettable, hydrophilic 3.2 nm mesopores. The latter allows the framework to be dye-sensitized, leading to an additional 61% enhancement in the hydrogen evolution rate up to 16.3 mmol g^-1 h^-1.

Researchers from the University of Liverpool, University College London and East China University of Science and Technology contributed to this development.