Facile Fabrication of Sandwich Structured WO₃ Nanoplate Arrays for Efficient Photoelectrochemical Water Splitting

Herein, sandwich structured tungsten trioxide (WO₃) nanoplate arrays were first synthesized for photoelectrochemical (PEC) water splitting via a facile hydrothermal method followed by an annealing treatment. It was demonstrated that the annealing temperature played an important role in determining the morphology and crystal phase of the WO₃ film. Only when the hydrothermally prepared precursor was annealed at 500 °C could the sandwich structured WO₃ nanoplates be achieved, probably due to the crystalline phase transition and increased thermal stress during the annealing process. The sandwich structured WO₃ photoanode exhibited a photocurrent density of 1.88 mA cm^-2 and an incident photon-to-current conversion efficiency (IPCE) as high as 65% at 400 nm in neutral Na₂SO₄ solution under AM 1.5G illumination. To our knowledge, this value is one of the best PEC performances for WO₃ photoanodes. Meanwhile, simultaneous hydrogen and oxygen evolution was demonstrated for the PEC water splitting. It was concluded that the high PEC performance should be attributed to the large electrochemically active surface area and active monoclinic phase. The present study can provide guidance to develop highly efficient nanostructured photoelectrodes with the favorable morphology.