Constructing Ru/TiO₂ Heteronanostructures Toward Enhanced Photocatalytic Water Splitting via a RuO₂/TiO₂ Heterojunction and Ru/TiO₂ Schottky Junction

Photocatalysts based on metallic Ru and RuO₂ dual co-catalysts modified TiO₂ nanobelts (NBs) are constructed through a wet-impregnation reduction method with post thermal oxidation. The samples are characterized carefully and their photocatalytic activities for the half reactions of water splitting as well as full water splitting are evaluated systematically under solar light irradiation. The detailed characterizations and analyses clearly reveal the formation of a Schottky junction at the Ru-TiO₂ interface and of RuO₂/TiO₂ heterojunctions. The results of the photocatalytic tests show that both Ru and RuO₂ can improve the photocatalytic activity for H₂/O₂ evolution and water splitting. Moreover, the photocatalytic activity of the TiO₂ NBs can be further enhanced by co-modification with dual Ru and RuO₂ co-catalysts. The RuO₂/TiO₂ heterojunction improves the transfer of the photogenerated holes from the TiO₂ to the RuO₂, where water can be oxidized by the holes to evolve O₂, and the Ru/TiO₂ Schottky junction promotes the transfer of photogenerated electrons from the TiO₂ NBs to the metallic Ru for proton reduction into H₂. These two processes are involved in the overall water splitting. This work provides an important reference for designing highly efficient photocatalysts for water splitting through loading of dual co-catalysts containing the same element but with different valence structures. The coexistence of RuO₂ and Ru on TiO₂ NBs leads to double-junctions of Ru/TiO₂/RuO₂. Upon excitation of TiO₂, the built-in electric field in the double-junction region promotes the separate transport of the photogenerated electrons and holes across the Ru/TiO₂ Schottky junction and RuO₂/TiO₂ heterojunction to Ru and RuO₂ for proton reduction and water oxidation, respectively, thus achieving enhanced photocatalytic activities.