Synthesizing Zr-based oxynitride with low defect by CaH2-assisted nitridation for photocatalytic Z-scheme overall water splitting

Abstract

Metal oxynitrides represent a promising class of semiconductor materials demonstrating broad visible-light spectrum absorption and considerable potential for photocatalytic overall water splitting (OWS). Nevertheless, the development of efficient synthesis methods combined with effective defect-density control in these materials remains a substantial challenge. Herein, we employ calcium hydride (CaH2) as an innovative nitridation agent, enabling the synthesis of zirconium oxynitride (Zr2ON2) powder at a reaction temperature 300 K lower than conventional approaches, with reduced defect concentration and a shortened processing time of 5 hours. The CaH2 additive not only enhances nitridation kinetics but also promotes Ca2+ incorporation into the Zr2ON2 lattice, effectively inhibiting defect formation. The optimized Zr2ON2 photocatalyst exhibits remarkable hydrogen evolution performance when coupled with a platinum (Pt) cocatalyst. Moreover, successful photocatalytic OWS is achieved through integration with an oxygen-evolving photocatalyst (WO3). This CaH2-assisted nitridation strategy demonstrates broad applicability, enabling the efficient synthesis of diverse low-defect metal oxynitrides including tantalum nitride (Ta3N5), strontium tantalum oxynitride (SrTaO2N), and hafnium oxynitride (Hf2ON2). The developed synthetic methodology and high-performance Zr2ON2 photocatalyst offer significant advancements toward more efficient hydrogen production through photocatalytic water splitting.