Gradient Valence Engineering Synchronizes Charge-Carrier and Catalytic Dynamics for Efficient Solar Water Oxidation

Area of Science:

• Materials Science
• Electrochemistry
• Renewable Energy

Background:

• Photoelectrochemical (PEC) water splitting efficiency is limited by the kinetic gap between rapid charge separation and slow catalytic reactions.
• Mimicking the precise timing of natural photosystem II is crucial for advancing PEC technologies.

Purpose of the Study:

• To design and investigate a novel redox-engineered BiVO4/Fe-HOTP (BVO/R-Fe-HOTP) photoanode.
• To synchronize charge carrier dynamics with catalytic water oxidation for enhanced PEC performance.

Main Methods:

• Fabrication of a BVO/R-Fe-HOTP photoanode using sequential NaBH4 reduction and O2 oxidation treatment.
• Creation of a programmable valence gradient within the Fe-HOTP layer.
• Characterization of the photoanode's electronic and catalytic properties.

Main Results:

• The engineered photoanode exhibited a continuous valence transition from electron-rich Feδ+ to highly oxidized Fe3+ and Fe4+.
• Achieved a high turnover frequency (TOF) of 82 s-1 due to surface Fe4+ active sites.
• Reduced interfacial band offsets for efficient hole injection and extended carrier lifetime to 0.03 s.
• Delivered a photocurrent density of 6.1 mA cm-2 at 1.23 VRHE.

Conclusions:

• The BVO/R-Fe-HOTP photoanode demonstrates significant improvements in PEC water splitting efficiency.
• Gradient valence engineering effectively synchronizes charge carrier and catalytic dynamics.
• Achieved unbiased solar water splitting with a 4.58% solar-to-hydrogen efficiency when coupled with a Si solar cell.