Gradient Self-Doped CuBi₂O₄ with Highly Improved Charge Separation Efficiency

Area of Science:

• Materials Science
• Electrochemistry
• Photocatalysis

Background:

• Improving charge separation efficiency is crucial for enhancing photoelectrochemical performance in metal oxide electrodes.
• Copper bismuth oxide (CuBi2O4) is a promising material for photocathodes, but its efficiency is often limited by charge recombination.

Purpose of the Study:

• To propose and investigate a novel strategy of forward gradient self-doping to improve charge separation efficiency in CuBi2O4 photocathodes.
• To understand the impact of copper vacancy gradients on the internal electric field and charge dynamics within CuBi2O4.

Main Methods:

• Preparation of CuBi2O4 photocathodes with controlled forward and reverse gradients in copper vacancies using a two-step, diffusion-assisted spray pyrolysis process.
• Characterization of photocathode properties, including carrier concentration, Fermi level, and flat band potential shifts.
• Photoelectrochemical measurements to evaluate charge separation efficiency and performance for reduction reactions and hydrogen evolution.

Main Results:

• Forward gradient self-doping significantly enhances charge separation efficiency and photoelectrochemical performance compared to homogeneous counterparts.
• CuBi2O4 photocathodes with a forward gradient achieved record photocurrent densities of -2.5 mA/cm² (AM 1.5) and 34% charge separation efficiency at 550 nm.
• Protected photocathodes with a CdS/TiO2 heterojunction and Pt catalyst demonstrated photocurrent densities of -1.0 mA/cm² at 0.0 V vs RHE and ~91% faradaic efficiency for hydrogen evolution.

Conclusions:

• Forward gradient self-doping is an effective strategy to create an internal electric field in CuBi2O4, facilitating charge separation and boosting photoelectrochemical performance.
• This method improves efficiency without compromising the material's crystal structure or carrier mobility, offering a promising route for advanced photocathode design.
• The developed gradient self-doped CuBi2O4 photocathodes show excellent potential for efficient solar energy conversion and hydrogen production.