Single‐Atom Co‐Ultrafine RuO_x Clusters Codecorated TiO₂ Nanosheets Promote Photocatalytic Hydrogen Evolution: Modulating Charge Migration, H⁺ Adsorption, and H₂ Desorption of Active Sites

Abstract Ru as a cocatalyst has attracted wide attention as a substitute for Pt precious metal. However, the strong interaction between Ru and H atoms reduces the efficiency of hydrogen (H₂) desorption and slows the overall hydrogen evolution reaction (HER) efficiency. How to further improve the efficiency of Ru‐based cocatalyst is challenging. Herein, single‐atom Co‐ultrafine RuO_x clusters codecorated TiO₂ nanosheets for photocatalytic HER are synthesized using a simple hydrothermal–calcination method. Experiments and theoretical calculations demonstrate that Co atoms can serve as a specific electronic medium, promoting electron enrichment at RuO_x, thereby enhancing the adsorption of H⁺. Moreover, the electronic state of the interaction between adjacent Co atoms and RuO_x is conducive to the desorption of H₂. As a result, the proposed photocatalyst system gives a classy photocatalytic HER performance. The hydrogen production rate at stationary point reaches up to 20.20 mmol g⁻¹ h⁻¹, and the apparent quantum yield at 365 nm is 86.5%. It is worth noting that the hydrogen production rate in seawater is as high as 9.83 mmol g⁻¹ h⁻¹. This work offers precise guidance to design catalysts for efficient photocatalytic H₂ production from the in‐depth understanding of the electronic coupling effect of coupling active sites.