Highly (211)‐Oriented CuBi2O4/TiO2 Heterojunction for Bifunctional Photoelectrochemical Water Splitting

Although p–n heterojunctions are fundamental components in photovoltaics and energy conversion devices, an internal electric field loss arising from interfacial defects obstructs the investigation of photoelectrochemical properties using p–n oxide heterojunction photoelectrode. Achieving a high‐quality p–n oxide heterojunction with a sharp interface provides an ideal platform for controlling internal electric fields without voltage loss due to structural defects. In this work, we fabricated highly (211)‐oriented p‐CuBi 2 O 4 thin films with sharp interface grown on (110) n‐TiO 2 single‐crystal substrate using pulsed laser deposition. The sharp heterointerface between (211) CuBi 2 O 4 and (110) Nb:TiO 2 resulted in the formation of a Schottky barrier with a height of 0.46 eV. This Schottky barrier suggests contributing to a bifunctional response resulting from a distinct bias‐dependent band structure transformation, where space charge region occurred. The CuBi 2 O 4 /Nb:TiO 2 heterostructure photoelectrode exhibited bifunctional (anodic/cathodic) photoelectrochemical properties, which show 47 and −77 µA cm −2 at a potential of 1.23 and 0 V RHE , respectively. These findings provide valuable insights into the development of high‐quality p–n heterojunction photoelectrodes for advanced bifunctional energy conversion technologies.