Efficient TaN Photoanodes via Interface Engineering of Bixbyite-Type TaN Precursors.

Tantalum nitride (TaN) shows promising prospects for photoelectrochemical (PEC) water splitting due to its suitable band gap and band edge positions. However, high-performing TaN photoanodes typically require Ta foil substrates and film thicknesses of several hundred nanometers, leading to increased tantalum usage and fabrication costs. This study introduces bixbyite-type TaN as a superior precursor for synthesizing thin (≈100 nm) TaN films on silicon substrates, substantially reducing tantalum consumption while maintaining excellent PEC performance. The metastable TaN phase undergoes disproportionation into TaN and conductive Ta-subnitrides during ammonolysis, enabling efficient charge separation without relying on Ta foils. Optimization of ammonolysis conditions reveals a critical balance between TaN crystallinity, subnitride content, and surface Ta defect concentrations. Furthermore, degenerately doped silicon substrates enhance hole extraction by suppressing charge accumulation and leakage at the TaN/Si junction, as revealed by photoelectrochemical impedance spectroscopy. This synthesis strategy yields an anodic photocurrent density of 3.86 mA cm at 1.23 V for a 100 nm TaN film on n-Si(111), outperforming a 500 nm film derived from TaO precursor and achieving a 0.15 V cathodic shift in onset potential. These findings establish a scalable, low-Ta usage platform for advancing TaN-based PEC systems in solar fuel technologies.