Ab initio simulations of water splitting on hematite

Area of Science:

• Materials Science
• Photocatalysis
• Computational Chemistry

Background:

• Hematite is a promising photocatalyst for water splitting.
• Understanding its atomistic properties is crucial for optimizing performance.
• Key mechanisms and limiting factors require further investigation.

Purpose of the Study:

• To elucidate the optical, electronic, and chemical properties of hematite using density functional theory.
• To investigate the effects of bulk doping on band gap, photoabsorption, and charge mobility.
• To analyze surface terminations and their roles in water splitting.

Main Methods:

• Density functional theory (DFT) calculations.
• Atomistic simulations of bulk and surface properties.
• Analysis of charge transport mechanisms (adiabatic polaron hopping).

Main Results:

• Bulk doping reduces the band gap and enhances photoabsorption and charge mobility.
• The (0001) surface exhibits different terminations (stoichiometric, hydroxylated, oxygen-rich) depending on the environment.
• Surface states on oxygen-rich terminations can act as recombination centers, while gallium oxide overlayers passivate these states.

Conclusions:

• DFT provides atomistic insights into hematite's photocatalytic behavior.
• Surface termination significantly influences charge recombination.
• The water oxidation mechanism involves proton-coupled electron transfers with calculated overpotentials of 0.5-0.6 V.