Metal–Organic Framework Derived Narrow Bandgap Cobalt Carbide Sensitized Titanium Dioxide Nanocage for Superior Photo‐Electrochemical Water Oxidation Performance

Abstract Despite recent progress in photo‐electrochemical (PEC) water oxidation systems for TiO 2 ‐based photoanodes, PEC performance improvement is still seriously hampered due to poor carrier transport efficiency and sluggish surface water oxidation kinetics of pristine TiO 2 . Herein, for the first time a brand new metal–organic framework (MOF)‐derived Co 3 C nanosheet with narrow bandgap energy is demonstrated, to effectively sensitize TiO 2 hollow cages as a heterostructure photoanode for PEC water oxidation. It is found that MOF‐derived Co 3 C nanosheet with narrow bandgap characteristic can simultaneously accelerate the surface water oxidation kinetics and extend the light harvesting range of pristine TiO 2 . Meanwhile, a uniquely matched type‐II heterojunction constructed between MOF‐derived Co 3 C and TiO 2 results in an evidently spontaneous e − /h + separation. MOF‐derived Co 3 C/TiO 2 heterostructure photoanodes bring about drastically improved PEC water oxidation performance. Specifically, MOF‐derived Co 3 C‐3/TiO 2 photoanode with an optimized content of Co 3 C achieves the highest photocurrent density and charge separation efficiency of 2.6 mA cm −2 and 92.6% at 1.23 V versus reversible hydrogen electrode, corresponding to 201% and 152% improvement compared with pristine TiO 2 nanocages. The ingeniously prepared MOF‐derived Co 3 C carbide with narrow bandgap energy as a cocatalyst paves new way to construct potentially high performance solar‐energy conversion system.