Photoelectrochemical Hydride Generation with Oxide-Coated Silicon

Area of Science:

• Electrochemistry
• Materials Science
• Photochemistry

Background:

• Silicon photoelectrodes are crucial for electrochemical applications.
• Organic hydride donors are important in chemical synthesis and energy storage.
• Previous research has explored silicon-based photoelectrodes for various reductions.

Purpose of the Study:

• To demonstrate photoelectrochemical generation of a potent organic hydride donor using silicon photoelectrodes.
• To investigate the performance of oxide-coated p-type silicon photoelectrodes for reducing [PMBI][PF6].
• To analyze the reaction mechanisms and thermodynamics of hydride transfer.

Main Methods:

• Utilizing two types of oxide-coated p-type silicon photoelectrodes (Si|TiO2 and Si|SiO2).
• Performing photoelectrochemical reduction of 1,2,3,5,6-pentamethyl-1H-benzo[d]imidazol-3-ium hexafluorophosphate ([PMBI][PF6]) in acetonitrile with a DBN buffer.
• Measuring Faradaic efficiencies (FEs) and onset potentials under 1 sun illumination.
• Developing a thermochemical model to assess reaction thermodynamics.

Main Results:

• Both Si|TiO2 and Si|SiO2 photoelectrodes efficiently converted [PMBI]+ to PMBIH with high FEs (78% and 83%, respectively).
• Si|TiO2 catalyzed the reaction at milder potentials, while Si|SiO2 exhibited better selectivity for PMBIH generation over H2 evolution.
• The thermochemical model indicated that the hydride transfer reactions are thermodynamically favorable (downhill).
• High overpotentials were observed, highlighting the need for improved catalysts.

Conclusions:

• Oxide-coated silicon photoelectrodes are effective for generating organic hydride donors.
• The choice of oxide coating influences catalytic activity, selectivity, and reaction mechanism (outer-sphere ET vs. proton-coupled ET).
• The developed thermochemical model provides valuable insights into hydride transfer thermodynamics for electrochemical and photoelectrochemical processes.
• Further catalyst development is necessary to overcome overpotentials and enhance efficiency.