Tantalum‐Based Perovskite Oxynitride Monolayers Derived From a Charge‐Balanced Nitridation Strategy for Photocatalytic Overall Water Splitting

ABSTRACT Sunlight‐driven photocatalytic overall water splitting is a promising means for a sustainable production of hydrogen with zero carbon footprint. For efficient solar energy conversions, this reaction should be conducted over narrow bandgap semiconductors with sufficient utilization of photo‐generated charge carriers. However, interference of charge carrier movement by defects often leads to poor access of charges to the reaction, accounting for substantial efficiency losses. In this work, a charge‐balanced nitridation strategy is applied to modulate the defect content in lanthanum‐tantalum perovskite oxynitride monolayers. Compared with conventional nitridation, which is charge‐imbalanced, the charge‐balanced one brings a desired combination of high nitrogen uptake for intense visible light absorption and low defect content for efficient charge carrier separation and migration. By depositing Pt nanoparticles and coating an amorphous layer of titanium oxyhydroxide, the modulated monolayers can photocatalyze overall water splitting with high stability, delivering an apparent quantum efficiency of 0.34% at 420 ± 20 nm and a solar‐to‐hydrogen efficiency of 0.018%. This work signifies the usefulness of charge‐balanced nitridation for defect control, which shall reinvigorate many other metal oxynitrides for photocatalytic overall water splitting.