Confining Flat Ru Islands into TiO₂ Lattice with the Coexisting Ru–O–Ti and Ru–Ti Bonds for Ultra‐Stable Hydrogen Evolution at Amperometric Current Density and Hydrogen Oxidation at High Potential

Effective hydrogen evolution reaction (HER) under high current density and enhanced hydrogen oxidation reaction (HOR) over a wide potential range remain challenges for Ru-based electrocatalysts because its strong affinity to the adsorbed hydroxyl (OH_ad) inhibits the supply of the adsorbed hydrogen (H_ad). Herein, the coexisting Ru─O─Ti and Ru─Ti bonds are constructed by taking TiO₂ crystal confined flat-Ru clusters (F-Ru@TiO₂) to cope with above-mentioned obstacles. The different electronegativity (χ_Ti = 1.54 < χ_Ru = 2.20< χ_O = 3.44) can endow Ti in Ru─O─Ti bonds with more positive charge and stabilize Ru of Ru-Ti bonds with the low-valence. The strength of Ru─OH_ad is then weakened by the oxophilicity of positively charged Ti in Ru─O─Ti bonds and the stronger Ti─OH_ad bond could release active Ru, especially for low-valence Ru in Ru─Ti bonds, to serve as exclusive H_ad sites. As expected, F─TiRu@TiO₂ shows a low HER overpotential of 74 mV at 1000 mA cm^-2 and an ultrahigh mass activity (j_0,m) of 3155 A g_Ru ^-1 for HOR. More importantly, F─Ru@TiO₂ can tolerate the HER current density of 1000 mA cm^-2 for 100 h and the high anodic potential for HOR up to 0.5 V versus RHE.