Enhanced Spatial Charge Separation in a Niobium and Tantalum Nitride Core-Shell Photoanode: In Situ Interface Bonding for Efficient Solar Water Splitting

Tantalum nitride (Ta3N5) has emerged as a promising photoanode material for photoelectrochemical (PEC) water splitting. However, the inefficient electron-hole separation remains a bottleneck that impedes its solar-to-hydrogen conversion efficiency. Herein, we demonstrate that a core-shell nanoarray photoanode of NbNx-nanorod@Ta3N5 ultrathin layer enhances light harvesting and forms a spatial charge-transfer channel, which leads to the efficient generation and extraction of charge carriers. Consequently, an impressive photocurrent density of 7 mA cm(-2) at 1.23 V-RHE is obtained with an ultrathin Ta3N5 shell thickness of less than 30 nm, accompanied by excellent stability and a low onset potential (0.46 V-RHE). Mechanistic studies reveal the enhanced performance is attributed to the high-conductivity NbNx core, high-crystalline Ta3N5 mono-grain shell, and the intimate Ta-N-Nb interface bonds, which accelerate the charge-separation capability of the core-shell photoanode. This study demonstrates the key roles of nanostructure design in improving the efficiency of PEC devices.