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

Abstract

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.