Water molecule switching heterogeneous proton-coupled electron transfer pathway

Area of Science:

• Photocatalysis
• Surface Chemistry
• Solar Energy Conversion

Background:

• Semiconductor-mediated proton-coupled electron transfer (PCET) is crucial for solar energy applications.
• Understanding the precise reaction pathway is essential for optimizing efficiency.

Purpose of the Study:

• To investigate the influence of adsorbed water molecules on the photo-induced PCET pathway on TiO2 surfaces.
• To elucidate the mechanism of water's role in modulating PCET reactions.

Main Methods:

• Systematic kinetic solvent isotope effect (KSIE) experiments.
• In situ Attenuated Total Reflectance Fourier-Transform Infrared (ATR-FTIR) spectroscopy.
• Density Functional Theory (DFT) calculations.

Main Results:

• Low water content (<1.7 wt%) resulted in a stepwise PT/ET pathway with inverse KSIE (H/D) ~0.5-1.
• High water content (>2 wt%) shifted the pathway to a concerted mechanism with normal KSIE (H/D) ≥ 2.
• Water molecules were found to significantly lower the proton/electron transfer energy barrier.

Conclusions:

• The amount of adsorbed water molecules is a critical determinant of the photo-induced PCET pathway on TiO2.
• Water facilitates a more efficient concerted PCET pathway by reducing the energy barrier, enhancing potential for solar energy conversion.