Sub-50 nm perovskite-type tantalum-based oxynitride single crystals with enhanced photoactivity for water splitting

A long-standing trade-off exists between improving crystallinity and minimizing particle size in the synthesis of perovskite-type transition-metal oxynitride photocatalysts via the thermal nitridation of commonly used metal oxide and carbonate precursors. Here, we overcome this limitation to fabricate ATaO₂N (A = Sr, Ca, Ba) single nanocrystals with particle sizes of several tens of nanometers, excellent crystallinity and tunable long-wavelength response via thermal nitridation of mixtures of tantalum disulfide, metal hydroxides (A(OH)₂), and molten-salt fluxes (e.g., SrCl₂) as precursors. The SrTaO₂N nanocrystals modified with a tailored Ir-Pt alloy@Cr₂O₃ cocatalyst evolved H₂ around two orders of magnitude more efficiently than the previously reported SrTaO₂N photocatalysts, with a record solar-to-hydrogen energy conversion efficiency of 0.15% for SrTaO₂N in Z-scheme water splitting. Our findings enable the synthesis of perovskite-type transition-metal oxynitride nanocrystals by thermal nitridation and pave the way for manufacturing advanced long-wavelength-responsive particulate photocatalysts for efficient solar energy conversion.