Photocatalytic Water Splitting Using Oxynitride Semiconductors

Photocatalytic water splitting harnesses solar energy to drive the decomposition of water into hydrogen and oxygen, offering a clean route to hydrogen fuel. Oxynitride semiconductors, formed by partial substitution of oxygen with nitrogen in oxide lattices, exhibit narrowed band gaps that extend light absorption into the visible region. The incorporation of nitrogen raises the valence band edge via enhanced anion covalency, while preserving suitable conduction band potentials for hydrogen evolution. Perovskite-type oxynitrides such as ATaO2N (A = Ca, Sr, Ba) have emerged as leading candidates, combining structural versatility with tunable optical and electronic properties. Advances in synthetic control—ranging from molten-salt flux methods to vapour-phase deposition—enable precise particle size and crystallinity. Concurrently, surface engineering through cocatalyst loading and facet modulation helps suppress charge recombination and promote interfacial redox reactions. Together, these developments are advancing the solar-to-hydrogen conversion efficiency of particulate and photoelectrochemical systems, bringing photocatalytic water splitting closer to practical application.

Research from Nature Portfolio

Recent studies have achieved a breakthrough in synthesising perovskite-type tantalum oxynitride nanocrystals with exceptional crystallinity and controllable dimensions below 50 nm. By employing a combination of tantalum disulfide, alkaline-earth hydroxides and molten salts during thermal nitridation, uniform ATaO2N single nanocrystals were produced. When modified with an Ir–Pt alloy@Cr2O3 cocatalyst, SrTaO2N exhibited a record solar-to-hydrogen conversion efficiency of 0.15 % in a Z-scheme system and H2 evolution rates two orders of magnitude higher than previous reports.

Another landmark effort improved the utilisation of photogenerated electrons in BaTaO2N photocatalysts via a sequential cocatalyst decoration strategy. Single-crystalline particulate BaTaO2N prepared with a flux-assisted route was first loaded with Pt by impregnation-reduction, followed by site-selective photodeposition. This dual loading approach yielded uniform Pt dispersion and intimate interfacial contact, driving an apparent quantum yield of 6.8 % at 420 nm and a solar-to-hydrogen efficiency of 0.24 % in a Z-scheme configuration.

An operando surface-sensitive investigation of LaTiOxNy thin films revealed unexpected oxidation of A-site cations during photoelectrocatalytic water splitting, while B-site cations underwent local disorder without valence change. This surface modification was shown to impede photocatalytic performance but could be largely suppressed by cocatalyst decoration, underlining the importance of protecting active sites for sustained hydrogen production.

Photocatalytic Water Splitting Using Oxynitride Semiconductors publication trend

The graph below shows the total number of articles in photocatalytic water splitting using oxynitride semiconductors across all publications each year (not limited to Nature Index journals).

Technical terms

Oxynitride semiconductor: A crystalline material in which nitrogen partially replaces oxygen in an oxide lattice, resulting in a reduced band gap and enhanced visible-light absorption.

Band gap: The energy difference between the valence band and conduction band of a semiconductor, dictating the spectrum of light it can absorb.

Cocatalyst: A secondary catalyst loaded onto a photocatalyst surface to facilitate charge separation and accelerate surface redox reactions.

Z-scheme water splitting: A two-step photocatalytic process that mimics natural photosynthesis, coupling two semiconductors to drive overall water splitting without external bias.

Apparent quantum yield: The ratio of reacted molecules to incident photons at a specific wavelength, measuring the efficiency of a photocatalytic process.

References

1. Sub-50 nm perovskite-type tantalum-based oxynitride single crystals with enhanced photoactivity for water splitting. Nature Communications (2023).
2. Sequential cocatalyst decoration on BaTaO2N towards highly-active Z-scheme water splitting. Nature Communications (2021).
3. Examining the surface evolution of LaTiOxNy an oxynitride solar water splitting photocatalyst. Nature Communications (2020).
4. Perovskite BaTaO2N: From Materials Synthesis to Solar Water Splitting. Advanced Science (2023).
5. Recent Developments in the Use of Heterogeneous Semiconductor Photocatalyst Based Materials for a Visible-Light-Induced Water-Splitting System—A Brief Review. Catalysts (2021).