Site Engineering of MIL‐100(Fe) via Atomic Layer Deposition of TiO ₂ for Photocatalytic Water Splitting

ABSTRACT Photocatalysis, particularly for water splitting, represents a promising pathway toward sustainable energy production. However, this field faces significant challenges, especially in achieving efficient charge separation and transfer. In this study, atomic layer deposition (ALD) was employed as a precise and controllable method to engineer hybrid photocatalysts by depositing photoactive TiO 2 species onto the high‐surface‐area metal–organic framework MIL‐100(Fe). X‐ray photoelectron spectroscopy (XPS) was used to investigate the spatial distribution and electronic interaction of Ti in relation to the Fe clusters within the MOF. The effects of TiO 2 incorporation on the photocatalytic properties were further examined using a suite of characterization techniques, including UV‐vis diffuse reflectance spectroscopy (UV‐Vis DRS), electrochemical impedance spectroscopy (EIS), photocurrent measurements, Nyquist plots, and Mott–Schottky analysis. Although Ti deposition partially blocked MOF pores, reducing the surface area from 1600 m 2 g − 1 for MIL‐100(Fe) to 830 and 155 m 2 g − 1 for Ti@MIL (1 ALD cycle) and 3Ti@MIL (3 ALD cycle), respectively, the water splitting activity per area increased from 0.08 to 0.12 and 0.35 µmol m −2 h − 1 . These results demonstrate the potential of ALD as an advanced and powerful tool for controlled and rational design and surface modification of MOF‐based photocatalysts.