# LaTiOxNy thin film model systems for photocatalytic water splitting: physicochemical evolution of the solid-liquid interface and the role of the crystallographic orientation

**Authors:** Markus Pichler, Wenping Si, Fatima Haydous, Helena Téllez, John Druce, Emiliana Fabbri, Mario El Kazzi, Max Döbeli, Silviya Ninova, Ulrich Aschauer, Alexander Wokaun, Daniele Pergolesi, Thomas Lippert  
**arXiv:** [1902.03832](https://arxiv.org/abs/1902.03832)  
**Date:** 2019-02-11  
**Summary page:** https://www.summarizepaper.com/en/paper/1902.03832v1/

## Key points

- Study focuses on physicochemical evolution of LaTiO2Ny thin film model systems for photocatalytic water splitting
- Oxynitride semiconductors have potential for efficient hydrogen and oxygen production under solar light illumination
- Compositional/structural surface modifications during operation affect photoelectrochemical performance
- Thin films provide more accurate representation compared to conventional powder samples
- Relation between electrochemical response and crystallographic surface orientation explored
- Epitaxial thin films exhibit higher absorbed photon-to-current conversion efficiency compared to polycrystalline samples
- Review of current techniques for fabricating and characterizing oxynitride thin films
- Analysis of initial physicochemical evolution of the surface reveals differences in photoelectrochemical performance based on crystallographic surface orientation
- Surface modifications and crystallographic orientation play a role in determining efficiency of oxynitride semiconductors for photocatalytic water splitting applications

## Summary

This study focuses on the physicochemical evolution of LaTiO2Ny thin film model systems for photocatalytic water splitting. Oxynitride semiconductors have shown promise for efficient hydrogen and oxygen production under solar light illumination due to their band gap size and energy position of the band edges. While intense research efforts have uncovered many important properties of oxynitride materials, two crucial aspects have received less attention. Firstly, the study addresses the issue of compositional/structural surface modifications that occur during operation and how they affect the photoelectrochemical performance. Understanding these surface changes is critical as it is at the surface where visible light-driven electrochemical reactions take place. Thin films are used as model systems for investigating these modifications, providing a more accurate representation compared to conventional powder samples. Secondly, the relation between the electrochemical response and the crystallographic surface orientation of oxynitride semiconductors is explored. The authors highlight that after stabilization, epitaxial thin films exhibit absorbed photon-to-current conversion efficiency that can differ by up to 50% for different crystallographic surface orientations and can be up to five times larger than that observed in polycrystalline samples. The study reviews current state-of-the-art techniques for fabricating and characterizing oxynitride thin films before focusing specifically on LaTiO2N as a representative photocatalyst. The investigation includes an analysis of the initial physicochemical evolution of the surface and highlights significant differences in photoelectrochemical performance based on crystallographic surface orientation. Overall, this research provides valuable insights into the role of surface modifications and crystallographic orientation in determining the efficiency of oxynitride semiconductors for photocatalytic water splitting applications. These findings contribute to advancing our understanding of this field and may inform future developments in renewable energy technologies.