Photoelectrocatalytic C-H halogenation over an oxygen vacancy-rich TiO₂ photoanode

Photoelectrochemical cells are emerging as powerful tools for organic synthesis. However, they have rarely been explored for C-H halogenation to produce organic halides of industrial and medicinal importance. Here we report a photoelectrocatalytic strategy for C-H halogenation using an oxygen-vacancy-rich TiO₂ photoanode with NaX (X=Cl^-, Br^-, I^-). Under illumination, the photogenerated holes in TiO₂ oxidize the halide ions to corresponding radicals or X₂, which then react with the substrates to yield organic halides. The PEC C-H halogenation strategy exhibits broad substrate scope, including arenes, heteroarenes, nonpolar cycloalkanes, and aliphatic hydrocarbons. Experimental and theoretical data reveal that the oxygen vacancy on TiO₂ facilitates the photo-induced carriers separation efficiency and more importantly, promotes halide ions adsorption with intermediary strength and hence increases the activity. Moreover, we designed a self-powered PEC system and directly utilised seawater as both the electrolyte and chloride ions source, attaining chlorocyclohexane productivity of 412 µmol h^-1 coupled with H₂ productivity of 9.2 mL h^-1, thus achieving a promising way to use solar for upcycling halogen in ocean resource into valuable organic halides.