Two-site H<sub>2</sub>O<sub>2</sub> photo-oxidation on haematite photoanodes.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 30301897.
- Also identified by DOI 10.1038/s41467-018-06141-0 and PMC identifier 6177486.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
H<sub>2</sub>O<sub>2</sub> is a sacrificial reductant that is often used as a hole scavenger to gain insight into photoanode properties. Here we show a distinct mechanism of H<sub>2</sub>O<sub>2</sub> photo-oxidation on haematite (α-Fe<sub>2</sub>O<sub>3</sub>) photoanodes. We found that the photocurrent voltammograms display non-monotonous behaviour upon varying the H<sub>2</sub>O<sub>2</sub> concentration, which is not in accord with a linear surface reaction mechanism that involves a single reaction site as in Eley-Rideal reactions. We postulate a nonlinear kinetic mechanism that involves concerted interaction between adions induced by H<sub>2</sub>O<sub>2</sub> deprotonation in the alkaline solution with adjacent intermediate species of the water photo-oxidation reaction, thereby involving two reaction sites as in Langmuir-Hinshelwood reactions. The devised kinetic model reproduces our main observations and predicts coexistence of two surface reaction paths (bi-stability) in a certain range of potentials and H<sub>2</sub>O<sub>2</sub> concentrations. This prediction is confirmed experimentally by observing a hysteresis loop in the photocurrent voltammogram measured in the predicted coexistence range.