Thermodynamic Oxidation and Reduction Potentials of Photocatalytic Semiconductors in Aqueous Solution

TL;DR

This paper presents a new computational method combining ab initio calculations and electrochemical data to predict the stability of semiconductor photocatalysts in water, revealing stability trends for various compounds.

Contribution

A novel approach integrating ab initio calculations with experimental data to predict semiconductor stability in aqueous solutions, enabling comprehensive stability analysis of photocatalysts.

Findings

Only metal oxides are thermodynamically stable as n-type photoanodes.

Non-oxides are unstable due to easy oxidation but can resist reduction as p-type photocathodes.

A simplified Pourbaix diagram for 30 semiconductors was produced.

Abstract

We introduce an approach to calculate the thermodynamic oxidation and reduction potentials of semiconductors in aqueous solution. By combining a newly-developed ab initio calculation for compound formation energy and band alignment with electrochemistry experimental data, this approach can be used to predict the stability of almost any compound semiconductor in aqueous solution. 30 photocatalytic semiconductors have been studied, and a graph (a simplified Pourbaix diagram) showing their valence/conduction band levels and oxidation/reduction potentials is produced. Based on this graph, we have studied the stabilities and trends against the oxidative and reductive photocorrosion for compound semiconductors. We found that, only metal oxides can be thermodynamically stable when used as the n-type photoanodes. All the non-oxides are unstable due to easy oxidation by the photogenerated holes, but they can be resistant to the reduction by electrons, thus stable as the p-type photocathodes.