Bismuth oxyhalides: synthesis, structure and photoelectrochemical activity

Area of Science:

• Materials Science
• Photochemistry
• Nanotechnology

Background:

• Bismuth oxyhalides (BiOX) are promising photocatalysts for solar energy applications.
• Controlling film morphology and crystal orientation is crucial for enhancing photoelectrochemical performance.
• Understanding the relationship between halide composition and electronic structure is key to designing efficient materials.

Purpose of the Study:

• To synthesize phase-pure tetragonal matlockite BiOX (X = Cl, Br, I) films.
• To investigate the photoelectrochemical properties and stability of these films for solar fuel production.
• To correlate material properties with performance using experimental and computational methods.

Main Methods:

• Aerosol-assisted chemical vapor deposition (AACVD) for film synthesis.
• UV-Vis spectroscopy and density functional theory (DFT) calculations for bandgap analysis.
• Photoelectrochemical measurements (including photocurrent and onset potential) and X-ray diffraction (XRD) for structural analysis.

Main Results:

• Synthesized phase-pure tetragonal matlockite BiOX films with tunable bandgaps.
• Observed a red shift in optical bandgaps with increasing halide size, consistent with DFT calculations.
• Achieved a record photocurrent density of 0.3 mA cm⁻² at 1.23 V vs. RHE for BiOBr, with a low onset potential of 0.2 V vs. RHE.
• Identified preferred [011] growth direction in BiOBr films, leading to enhanced charge carrier separation.

Conclusions:

• BiOX films, particularly BiOBr, are highly promising for solar fuel production.
• The [011] crystal orientation in BiOBr films significantly enhances photoelectrochemical performance by minimizing charge recombination.
• The synthesis and characterization approach provides a pathway for designing advanced photocatalytic materials.