Fast Interfacial Hole Consumption Suppresses Space-Charge Layer Trap Filling in BiVO₄ Photoanodes

Area of Science:

• Electrochemistry
• Materials Science
• Photocatalysis

Background:

• Photoelectrochemical (PEC) oxidation of biomass-derived organics offers advantages over water oxidation, producing valuable chemicals.
• Understanding the kinetics, particularly hole consumption and space-charge-layer (SCL) trap dynamics, is crucial for optimizing PEC performance.
• BiVO4 serves as a model photoanode for investigating these complex processes.

Purpose of the Study:

• To elucidate the kinetic basis of enhanced PEC oxidation of glycerol compared to water oxidation.
• To investigate the influence of glycerol on charge-carrier dynamics, SCL trap filling, and recombination.
• To identify key design principles for efficient PEC oxidation of renewable organics.

Main Methods:

• Utilized operando optical and photocurrent spectroscopies, including trap-selective pump-push photocurrent (PPPC) mapping.
• Tracked bulk and interfacial charge-carrier dynamics across femtosecond-to-second timescales.
• Employed spatially resolved PPPC mapping to analyze charge dynamics over a 20 mm² area.

Main Results:

• Glycerol oxidation significantly accelerates interfacial hole consumption, reducing surface-hole density requirements.
• This acceleration suppresses SCL trap filling and trap-mediated recombination, increasing turnover frequency 32-fold.
• Photocurrent density at 1.23 V_RHE increased from ~0.5 to ~1.3 mA cm^-2, with formic acid and dihydroxyacetone as major products.
• Glycerol suppressed localized trap-filled hot spots and microsecond-scale buildup of trapped electrons in the SCL.

Conclusions:

• The kinetic competition between interfacial hole consumption and SCL trap filling at the microsecond timescale is a critical factor in PEC oxidation of renewables.
• Optimizing interfacial hole consumption is a key strategy for enhancing PEC performance and suppressing recombination.
• This study provides fundamental insights for designing efficient photoanodes for biomass-derived organic oxidation.