Probing Intra‐Gap States Mediated Charge Dynamics of Rh‐Doped Rutile TiO2 Photocatalyst by Light‐Modulated Photocurrent Spectroscopies

Abstract The intra‐gap states that are introduced into a semiconducting photocatalyst via dopants and other defects have significant implications on the transport dynamics of photoexcited electrons and holes during an aqueous light‐driven reaction. In this work, mechanistic understanding of Rh‐doped rutile, a promising photocatalyst for hydrogen production from water, is gained by systematic assessment combining intensity‐modulated photocurrent spectroscopy with sub‐gap excitations and alternating‐current photocurrent spectroscopy. These operando techniques not only help in discovering a new electronic transport path in Rh‐rutile via surface Rh 4+ species and elucidating complex interaction between electrolyte molecules and semiconductors, but also underscore the potential of utilizing multiple sub‐gap excitations synergistically. This combination offers a powerful tool for acquiring insight into photo‐physical and photo‐chemical behaviors of photo(electro)catalysts with intra‐gap states.