Enhanced Charge Separation in Nanoporous BiVO4 by External Electron Transport Layer Boosts Solar Water Splitting

Area of Science:

• Materials Science
• Electrochemistry
• Renewable Energy

Background:

• Artificial photosynthesis requires efficient charge transport and separation for redox reactions.
• Bismuth vanadate (BiVO4) is a promising photoanode material but suffers from poor charge separation and transport.
• Overcoming charge recombination is key to improving solar water splitting efficiency.

Purpose of the Study:

• To introduce and validate an external electron transport layer (ETL) concept for enhancing bismuth vanadate photoanodes.
• To improve charge separation and suppress recombination in BiVO4 for solar water splitting.
• To achieve a new record in activity-stability trade-off for single BiVO4 light absorbers.

Main Methods:

• Conformal carbon encapsulation was applied to BiVO4 photoanodes.
• The carbon layer acted as an external electron transport layer (ETL) to passivate surface traps and enhance conductivity.
• An oxygen evolution catalyst was used to accelerate surface charge transfer.

Main Results:

• Carbon encapsulation significantly improved charge separation efficiency in BiVO4.
• The carbon-encased BiVO4 (BVO@C) photoanode demonstrated stable water splitting for over 120 hours.
• A high current density of 5.9 mA cm⁻² at 1.23 V vs RHE was achieved under 1 sun irradiation.
• This represents a record activity-stability trade-off for single BiVO4 light absorbers.

Conclusions:

• External electron transport layers, like carbon encapsulation, are effective in suppressing charge recombination in photoanodes.
• Carbon encapsulation enhances BiVO4 performance by passivating surface states and providing external conductance pathways.
• This approach offers a new strategy for optimizing charge separation in materials for solar fuel conversion.