Borocarbonitride Layers on Titanium Dioxide Nanoribbons for Efficient Photoelectrocatalytic Water Splitting

Heterostructures formed by ultrathin borocarbonitride (BCN) layers grown on TiO₂ nanoribbons were investigated as photoanodes for photoelectrochemical water splitting. TiO₂ nanoribbons were obtained by thermal oxidation of TiS₃ samples. Then, BCN layers were successfully grown by plasma enhanced chemical vapour deposition. The structure and the chemical composition of the starting TiS₃, the TiO₂ nanoribbons and the TiO₂-BCN heterostructures were investigated by Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Diffuse reflectance measurements showed a change in the gap from 0.94 eV (TiS₃) to 3.3 eV (TiO₂) after the thermal annealing of the starting material. Morphological characterizations, such as scanning electron microscopy and optical microscopy, show that the morphology of the samples was not affected by the change in the structure and composition. The obtained TiO₂-BCN heterostructures were measured in a photoelectrochemical cell, showing an enhanced density of current under dark conditions and higher photocurrents when compared with TiO₂. Finally, using electrochemical impedance spectroscopy, the flat band potential was determined to be equal in both TiO₂ and TiO₂-BCN samples, whereas the product of the dielectric constant and the density of donors was higher for TiO₂-BCN.