A molecular-level mechanistic framework for interfacial proton-coupled electron transfer kinetics

Area of Science:

• Electrochemistry
• Surface Science
• Chemical Kinetics

Background:

• Proton-coupled electron transfer (PCET) is crucial for energy conversion and catalysis.
• Outer-sphere PCET (OS-PCET) is well-understood, but inner-sphere PCET (I-PCET) is challenging due to surface heterogeneity.
• Molecular-level understanding of I-PCET is needed to optimize catalytic processes.

Purpose of the Study:

• To isolate and understand the intrinsic kinetics of I-PCET.
• To investigate the pH-dependence of I-PCET at a molecular level.
• To differentiate I-PCET mechanisms from OS-PCET.

Main Methods:

• Utilized graphite-conjugated carboxylic acids (GC-COOH) as model systems for I-PCET.
• Measured I-PCET reaction rates across a wide pH range.
• Developed a mechanistic model to interpret the observed pH-dependence.

Main Results:

• Discovered a V-shaped pH-dependence for I-PCET, unlike the pH-independent regions in OS-PCET.
• The mechanistic model accurately captured the experimental data with minimal parameters.
• I-PCET with hydronium/water donors is four times faster than with water/hydroxide.

Conclusions:

• I-PCET exhibits distinct mechanistic features compared to OS-PCET.
• The study provides a framework for understanding complex I-PCET reactions.
• Findings are critical for designing efficient catalysts for energy conversion and chemical synthesis.