Highly nanotextured β-Bi₂O₃ pillars by electrostatic spray deposition as photoanodes for solar water splitting

We demonstrate fabrication of films of highly textured bismuth oxide (Bi₂O₃) pillars via electrostatic spray deposition and test the performance of these films as photoanodes in photoelectrochemical water splitting. The β-Bi₂O₃ and α-Bi₂O₃ phases were identified and distinguished using X-ray diffraction, Raman spectroscopy, and transmission electron microscopy. The β-Bi₂O₃ pillars of optimized thickness exhibited a photocurrent density of 0.97 mA⋅cm⁻² at 0.5 V vs Ag/AgCl. The tetragonal β-Bi₂O₃ pillars had enhanced visible light absorbance compared to α-Bi₂O₃ as well as other metal oxides like ZnO and TiO₂. Tauc plot analysis of film absorbance showed a decrease in the bandgap of the β-Bi₂O₃ phase to 2.5 eV. In Na₂SO₃ electrolyte, a hole scavenger, the onset voltage for the β-Bi₂O₃ phase was shifted to a more negative value (−0.4 V), which increased photocurrent density. The electron concentration reached its highest value of 9.1 × 10²⁰ cm⁻³ for the film with the highest photocurrent density.