High-Density Ruthenium Single Atoms Anchored on Oxygen-Vacancy-Rich g‑C₃N₄‑C-TiO₂ Heterostructural Nanosphere for Efficient Electrocatalytic Hydrogen Evolution Reaction

Designing and constructing high-density single-atom catalysts (SACs) is vital for electrochemical hydrogen evolution to meet the demand for fundamental research and practical applications of electrocatalysis. However, it is challenging to synthesize atomically dispersed electrocatalysts with high density and high performance. Herein, an integrated g-C₃N₄-C-TiO₂ heterostructural nanosphere with oxygen-rich vacancies is constructed by a multicomponent assembly-calcination strategy. Abundant single Ru atoms (12.4 wt %) are then anchored via the occupation of partial oxygen vacancies, forming a unique Ru/g-C₃N₄-C-TiO₂ heterostructure. A reasonable configuration is developed including single Ru atoms bonded with two oxygens and two nitrogens and coupled with jacent oxygen vacancies on the g-C₃N₄-C-TiO₂ nanosphere. Density functional theory calculations reveal that the remaining oxygen vacancies are beneficial for water dissociation, while single Ru atoms facilitate hydrogen adsorption. As expected, the result exhibits high electrocatalytic activity, delivering overpotentials of 112 and 107 mV at 10 mA cm^–2, Tafel slopes of 83 and 65 mV dec^–1 in H₂SO₄ and KOH, and a turnover frequency of 0.28 H₂ s^–1 at −100 mV toward the hydrogen evolution reaction (HER). Benefiting from the outstanding electrocatalytic performance, such a unique heterostructure with dense single Ru sites and oxygen vacancies could serve as a prominent alternative HER catalyst for renewable energy applications.