Correlating activity and defects in (photo)electrocatalysts using in-situ transient optical microscopy

TL;DR

This study employs in-situ optical microscopy and X-ray techniques to map local electrochemical activity and defects in hematite photoanodes, revealing how microstructure and vacancies influence photoelectrochemical performance.

Contribution

It introduces a combined in-situ optical microscopy and X-ray approach to correlate microstructural defects with activity in photoelectrodes, advancing understanding of structure-function relationships.

Findings

Regions near cracks show improved photoresponse.

Optimal oxide vacancy concentration reduces recombination.

Film thickness and impurities significantly affect activity.

Abstract

(Photo)electrocatalysts capture sunlight and use it to drive chemical reactions such as water splitting to produce H2. A major factor limiting photocatalyst development is their large heterogeneity which spatially modulates reactivity and precludes establishing robust structure-function relationships. To make such links requires simultaneously probing of the electrochemical environment at microscopic length scales (nm to um) and broad timescales (ns to s). Here, we address this challenge by developing and applying in-situ steady-state and transient optical microscopies to directly map and correlate local electrochemical activity with hole lifetimes, oxygen vacancy concentration and the photoelectrodes crystal structure. Using this combined approach alongside spatially resolved X-Ray absorption measurements, we study microstructural and point defects in prototypical hematite (Fe2O3) photoanodes. We demonstrate that regions of Fe2O3, adjacent to microstructural cracks have a better photoelectrochemical response and reduced back electron recombination due to an optimal oxide vacancy concentration, with the film thickness and carbon impurities also dramatically influencing activity in a complex manner. Our work highlights the importance of microscopic mapping to understand activity and the impact of defects in even, seemingly, homogeneous solid-state metal oxide photoelectrodes.