Growth of bismuth oxyhalide nanoplates on self-standing TiO₂ nanowire film exhibiting enhanced photoelectrochemical performances

We report the sequential modification of the free-standing TiO₂ nanowires film with Ag nanoparticles and BiOX (X = Cl, Br, and I) nanoplates, for a purpose of achieving an efficient photoelectrochemical cells (PECs). In the resulting BiOX-Ag-TiO₂ film, Ag nanoparticles densely coated on the broad and flat surfaces of TiO₂ nanowires increase the conductivity of TiO₂ by 10⁷ and enable the film to propagate electrons rapidly. BiOX nanoplates obliquely grown on the Ag-coated TiO₂ nanowires can move the absorption edge of the film into the region of visible light and endow the film with the anti-reflection property. Especially, when the BiOCl-Ag-TiO₂, BiOBr-Ag-TiO₂, and BiOI-Ag-TiO₂ films are overlapped to form a laminated film, the anti-reflection response is further promoted. Besides the above optical and electronic metrics, the band alignment in the multi-component system favors the directed flow of photogenerated electrons from BiOX and TiO₂ to Ag, thus efficiently blocking the recombination of the e⁻–h⁺ pairs. Therefore, under the illumination of simulated solar light, the photoanode fabricated by the laminated BiOX-Ag-TiO₂ film could yield a small onset potential around 0.7 V vs RHE and a large photocurrent approaching 10 mA/cm² at 1.2 V vs RHE, which outperforms the state of the art photoanode based on IrO₂ modified hematite nanorod arrays.