Black TiO₂: What are exact functions of disorder layer

Abstract Among the substantial amount of photocatalyst materials, TiO₂ has been enthusiastically studied for a few decades due to its outstanding photocatalytic activity and stability. Recently, black TiO₂ consisting of approximately 2 nm of thin disorder layer around the surface showed surprisingly high solar hydrogen generation ability. The disorder layer of TiO₂ can enhance its light absorption, charge separation, and surface reaction abilities, however exact fundamentals of photocatalytic water‐splitting pathways are still ambiguous. Herein, recent progress and investigations on exact functions of disorder layer and its application in photocatalytic CO₂ reduction will be discussed. Throughout the comprehensive studies on disorder layer of TiO₂, disorder engineering on photocatalyst materials will suggest the further extension of developing solar‐fuel production technologies.