Theory of proton-coupled electron transfer in energy conversion processes

Area of Science:

• Physical Chemistry
• Chemical Kinetics
• Electrochemistry

Background:

• Proton-coupled electron transfer (PCET) reactions are fundamental to biological energy processes like photosynthesis and respiration.
• PCET reactions are crucial for developing advanced energy technologies, including solar fuel cells and electrochemical devices.
• Predictive theoretical models are needed to optimize catalyst design for efficient energy conversion.

Purpose of the Study:

• To summarize theoretical predictions of how system properties influence PCET reaction rates.
• To explore strategies for tuning PCET reaction rates in various chemical systems.
• To provide insights into the physical principles governing PCET for catalyst development.

Main Methods:

• Development and application of a general theoretical formulation for PCET reactions based on nonadiabatic transitions.
• Derivation of nonadiabatic rate constant expressions for homogeneous and electrochemical PCET.
• Extension of theory to include solvent dynamics and ultrafast interfacial PCET.

Main Results:

• PCET rates increase with electronic coupling and temperature, and decrease with reorganization energy and donor-acceptor distance.
• Rate constants increase with more negative driving force due to accessible excited vibronic product states.
• pH dependence can arise from buffer protonation equilibria or competing reaction pathways; electrochemical PCET shows overpotential dependence.

Conclusions:

• Theoretical analysis provides a framework for understanding and predicting PCET rate dependencies on system properties.
• Tuning PCET rates is achievable through methods like pH adjustment, buffer selection, and chemical modifications.
• This theoretical understanding aids experimental efforts to enhance energy conversion processes via optimized catalysts.