As a well-known semiconductor that can catalyse the oxygen evolution reaction, TiO 2 has been extensively investigated for its solar photoelectrochemical water properties. Unmodified TiO 2 shows some issues, particularly with respect to its photoelectrochemical performance. In this paper, we present a strategy for the controlled deposition of controlled amounts of GaO xN y cocatalysts on TiO 2 1D nanowires (TiO 2@GaO xN y core-shell) using atomic layer deposition. We show that this modification significantly enhances the photoelectrochemical performance compared to pure TiO 2 NW photoanodes. For our most active TiO 2@GaO xN y core-shell nanowires with a GaO xN y thickness of 20 nm, a photocurrent density up to 1.10 mA cm -2 (at 1.23 V vs. RHE) under AM 1.5 G irradiation (100 mW cm -2) has been achieved, which is 14 times higher than that of unmodified TiO 2 NWs. Furthermore, the band gap matching with TiO 2 enhances the absorption of visible light over unmodified TiO 2 and the facile oxygen vacancy formation after the deposition of GaO xN y also provides active sites for water activation. Density functional theory studies of model systems of GaO xN y-modified TiO 2 confirm the band gap reduction, high reducibility and ability to activate water. The highly efficient and stable systems of TiO 2@GaO xN y core-shell nanowires with ALD deposited GaO xN y demonstrate a good strategy for the fabrication of core-shell structures that enhance the photoelectrochemical performance of readily available photoanodes.