MXene‐Derived Highly Oriented TiN Enables Ta 3 N 5 Photoanodes for Transmission‐Mode Bias‐Free Solar Water Splitting

ABSTRACT The incompatibility between optical transparency and photocarrier extraction in Ta 3 N 5 photoanodes, arising from the harsh ammonolysis process, has constrained their potential for bias‐free water splitting, despite intrinsically ideal band structures. Here, we report a transparent and nitridation‐compatible bottom electrode based on 2D MXene‐derived TiN thin films. The (111)‐preferred orientation of MXene‐derived TiN facilitates efficient electron extraction from Ta 3 N 5 , while maintaining high optical transmittance at an ultrathin thickness. By integrating with n ‐GaN, we design a heterostructured electron collector that further improves charge separation, corroborating the directional electron extraction in Ta 3 N 5 /TiN/ n ‐GaN via photoelectron spectroscopy and carrier dynamics studies. The transparent photoanode generates a photocurrent density of 9.2 mA cm −2 at 1.23 V…