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

Abstract Tantalum nitride (Ta 3 N 5 ) 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 NbN x ‐nanorod@Ta 3 N 5 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 Ta 3 N 5 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 NbN x core, high‐crystalline Ta 3 N 5 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.