Sythesis And Photoelectrochemical Properties Of Vertically Aligned WO₃Nanoplate Arrays

Recently, highly ordered nanostructured tungsten trioxide (WO3) arrays have become hot topic in the field of photoelectric materials. Well-aligned nanostructured WO3arrays could be obtained by thermal-evaporation, chemical vapor deposition (CVD), template method and hydrothermal approach. Hydrothermal approach stands out to be a promising route because of its merits of low reaction temperature,simple equipment, low cost and easiness for scaling up. In this paper, we demonstrate a facial hydrothermal synthesis of vertically aligned hydrated WO3nanoplate arrays grown directly on FTO glass without the assistance of a WO3seed layer. The as-prepared films were calcined and applied in photoelectrochemical water splitting and dye-sensitised solar cells.The WO3·H2O nanoplate array film was hydrothermally grown directly on bare FTO substrate using sodium tungstate and hydrochloric acid as raw materials, and ammonium oxalate as capping agent. The hydrothermal process was conducted at120℃for12h. The average thickness of the platelets was260±30nm, all the platelets grew directly on the FTO substate with height of1.3μm. The as-grown hydrated WO3nanoplate arrays converted to monoclinic WO3after calcination at450℃and exhibited excellent photoelectrochemical activity. The anodic photocurrent density of the WO3nanoplate array film was4.22mA/cm2, which was superior to the WO3nanoplate arrays grown on the WO3seed layer coated FTO substrate with photocurrent density of3.05mA/cm2.The effects of hydrothermal synthesis conditions on the morphology and crystalline phase of the products were studied in detail. It was found that C2O42-played a key role in the controllable synthesis of vertically oriented WO3·H2O nanoplate array film. The possible formation mechanism of the WO3·H2O nanoplate arrays was then proposed.The WO3nanoplate array film with thickness of1.3μm was sensitized using N719dye and then assembled into dye-sensitized solar cell. The overall power conversion efficiency was0.0148%, and the highest IPCE value reached to13.3%. The properties of the DSSCs were improved after TiCl4treatment. The overall power conversion efficiency reached to0.169%, which is nearly10times higher than that of the untreated sample, while the highest IPCE value reached to29%.