Multistep Surface Trap State Finishing Based on in Situ One-Step MOF Modification over Hematite for Dramatically Enhanced Solar Water Oxidation.

Complex surface dynamics is the key to limit the photoelectrochemical performance of hematite, while its core content is the hole trapping and release by surface traps. Deep traps are accompanied by extremely fast capture rates and extremely slow release rates, which severely suppress the hole transport process. Herein, we proposed a unique method to progressively convert deep traps on the hematite surface for fast hole transfer via in situ one-step metal organic framework modification. This stepwise deep-trap passivation is achieved by hematite corrosion first on the surface and subsequent construction of a porous titanium layer. The gentle trap finishing helps prevent surface losses caused by excessively intense trap passivation. The hematite corrosion can initially passivate 80% of the surface deep traps, while the subsequent porous titanium layer can completely passivate the deep traps. In addition, the accurate optimization of the porous titanium layer can reconstruct the benign shallow traps on the surface, acting as superior oxygen evolution reaction active sites. This sophisticated surface-trap adjustment is accompanied by the rapid reduction of deep traps and the gradual increase of shallow traps, obtaining a superior surface state that is conducive to charge transport and interface catalysis. The obtained treated hematite yields a photocurrent density of 3.08 mA·cm-2 at 1.23 VRHE, increased by 570% compared to the pristine hematite.