Precise electronic structures of amorphous solids: unraveling the color origin and photocatalysis of black titania

TL;DR

This study uses ab initio simulations to precisely determine the electronic structures of black titania, revealing how amorphization and reduction influence its properties and photocatalytic activity, with implications for water splitting technologies.

Contribution

It provides the first detailed electronic structure analysis of black titania and explores surface co-catalyst adsorption, advancing understanding of amorphous photocatalysts.

Findings

Electronic structures evolve with amorphization and reduction.

Disordered surfaces facilitate co-catalyst atom accommodation.

Extended electronic states improve charge separation for hydrogen evolution.

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 the 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. Moreover, surface adsorption of the co-catalyst atoms (e.g., Pt) on amorphous substances is simulated for the first time: the disordered surface enables easy accommodation of the co-catalyst atoms, while the extended electronic states facilitate the separation of photo-induced electrons and holes, beneficial for hydrogen evolution. This study elucidates the workings of amorphous catalysts and offers practical guidance for enhancing their performances.