Concerning the eco problem and energy crisis we are facing now, the energy harvested from sunlight offers a desirable approach [1]. Photoelectrochemical (PEC) hydrogen production from water provides a way to directly convert the solar energy into a storable clean fuel [2]. GaAs nanowire (NW) configuration is preferred for the high specific surface area as well as the good light absorption [3]. It can serve as a model system to demonstrate the quality of NW-array light absorber. However GaAs suffers the photo-corrosion in aqueous electrolytes [4]. TiO 2 is mainly used to passivate semiconductor electrodes for its remarkable stability [4, 5], which may well enhance the stability of GaAs based electrodes. Self-catalyzed GaAs NWs were grown on Si(111) substrate by molecular beam epitaxy (MBE). Then, a 5 nm-thick TiO 2 layer was also deposited via MBE on the GaAs NWs (Figure 1 a). For the bare GaAs NW array, the current desnstiy is about-0.135 mA/cm 2 at 0.033 V vs RHE, and the V onset is-0.47 V. After passivated by the amorphous TiO 2 layer, only a small transient current is detected (Figure 1 b). However, the photocurrent also decreases due to the poor conductivity of TiO 2. The optimization of the PEC performances of TiO 2 passivated GaAs NW array is being worked on. Figure 1: a) SEM image of the GaAs / TiO 2 NW array, b) PEC responses (on-off curve) of the GaAs NWs array and GaAs / TiO 2 NW array in NaOH solution (pH=13). Références: [1] J. Gu et al, Nat. Mater. 2016, 15, 456-460. [2] M. G. Walter et al, Chem. Rev.