Precise Electronic Structures of Amorphous Solids: Unraveling the Color Origin and Photocatalysis of Black Titania

Water splitting through efficient catalysts represents an ultimate solution for carbon neutrality within 40 years. To achieve this goal, amorphous photocatalysts are noted for their promising performances. Among them, the best known is black titania (amorphous TiOx, x = 2). However, despite a large number of studies on black titania, its color origin, structure-property relationship, and photocatalytic mechanism remain a topic of hot debate, largely due to the difficulty to calculate its precise electronic structure. Here, using ab initio molecular dynamics simulations, we report the precise electronic structures of black titania and further reveal the generic evolution pattern of the electronic structures of covalent compounds upon amorphization and reduction. An interesting disproportionation-like process resulting in metal clusters of Ti is discovered in heavily reduced amorphous titania, accompanied by oxygen vacancies in different energy states. This study elucidates the workings of amorphous catalysts and offers practical guidance for enhancing their performances.

Automated summary

Water splitting through efficient catalysts is the ultimate solution for achieving carbon neutrality within 40 years. Amorphous photocatalysts, such as black titania, show promising performances. However, the precise electronic structure and photocatalytic mechanism of black titania have been a topic of debate. In this study, the electronic structures of black titania are determined using ab initio molecular dynamics simulations, revealing the evolution pattern of electronic structures of covalent compounds upon amorphization and reduction. The study also discovers metal clusters of Ti and oxygen vacancies in heavily reduced amorphous titania, providing insights for enhancing the performance of amorphous catalysts.