Cascaded photo-potential in a carbon dot-hematite system driving overall water splitting under visible light.

Hematite is an earth-abundant and ubiquitous semiconductor with a suitable bandgap of 2.1 eV for solar water splitting. Unfortunately, it suffers from a low conduction band position compared to the H+/H2 potential and typically an external bias has to be applied. Here, we demonstrate carbon dot-hematite (CD-Fe2O3) nanocomposites as photocatalysts for visible-light-driven overall water splitting without any external bias or scavenger. Notably, the CD-Fe2O3 nanocomposites (carbon dots, 5 wt%) show a hydrogen evolution rate of 0.390 μmol h-1 and an oxygen evolution rate of 0.225 μmol h-1 under visible light illumination. In our system, carbon dots have been well coupled with hematite and are detected to generate a photo-induced potential. This photo-potential can be combined with hematite to meet the requirement for overall water splitting. In addition, carbon dots can significantly improve the charge separation efficiency. Our finding may greatly enhance the practical application of hematite for solar water splitting.