Illustrating the potential of oxynitrides: harnessing solar power for efficient water splitting

Photocatalytic water splitting using solar energy presents an ideal approach for clean hydrogen production. Efforts to develop efficient photocatalysts have gained momentum since the discovery of the Honda–Fujishima effect. However, achieving large-scale solar hydrogen production remains a challenge, despite significant progress in catalyst development. Key characteristics of an ideal photocatalyst include photoactivity, narrow band gap, hydrophilicity, suitable band edge potentials, enhanced charge separation, and minimal recombination. Band structure engineering, altering catalyst size or doping, is pivotal in optimizing photocatalyst performance. Metal oxides, though successful, lack visible light activity due to their broad band-gap. Nitrides, with narrower band gap, are promising but suffer from poor water stability. Oxynitrides, formed by anionic substitutions in oxides, exhibit both visible light activity and water stability, making them ideal for solar-driven water splitting. Oxynitrides' properties such as visible light absorption, charge carrier conductivity, and corrosion resistance, make them suitable for solar energy conversion. With most solar energy falling within the visible spectrum, oxynitrides offer a practical solution for efficient water splitting. The inquiry into how to enhance the design of these materials to further improve their ability for water splitting is both intriguing and significant. This review outlines the development and properties of oxynitride photocatalysts for solar-driven water splitting. It discusses synthesis protocols, optical properties, and structural variations, which are crucial for enhancing photocatalytic performance. Oxynitrides hold immense potential in advancing solar energy conversion technologies, paving the way towards a sustainable energy future.