Catalyst self-assembly accelerates bimetallic light-driven electrocatalytic H₂ evolution in water

Area of Science:

• Catalysis
• Photochemistry
• Materials Science

Background:

• Hydrogen evolution is a key reaction for fuel generation, with ongoing debate regarding monometallic versus bimetallic pathways.
• Understanding the mechanisms of hydrogen-¡H₂!-evolution is crucial for developing efficient catalytic systems.
• Molecular iridium catalysts offer a platform to investigate these mechanistic pathways.

Purpose of the Study:

• To investigate the factors promoting bimetallic H-H coupling in molecular iridium catalysts.
• To understand the role of supramolecular self-assembly in photoelectrochemical hydrogen evolution.
• To compare the performance of diiridium and monometallic catalysts in neutral water splitting.

Main Methods:

• Synthesis of covalently tethered diiridium and monometallic iridium catalysts with varying substituents.
• Photoelectrochemical measurements to assess hydrogen evolution rates and overpotentials.
• Spectroscopic and microscopic techniques to characterize self-assembled nanoscale aggregates.

Main Results:

• Covalently tethered diiridium catalysts exhibited faster hydrogen evolution from neutral water than monometallic counterparts, even at lower overpotentials.
• Non-covalent supramolecular self-assembly into nanoscale aggregates was identified as the key factor for improved catalytic activity.
• Monometallic catalysts with long-chain alkane substituents also leveraged self-assembly to achieve high hydrogen evolution rates.
• The self-assembly process enhanced light harvesting and facilitated efficient H-H bond formation.

Conclusions:

• Supramolecular self-assembly of molecular catalysts is a powerful strategy to enhance photoelectrochemical hydrogen evolution.
• Bringing catalytic sites into close proximity via self-assembly improves bimolecular H-H coupling efficiency.
• Catalyst design should consider parameters for controlling proximity of catalytic sites and tuning microenvironments for optimal performance.
• This work provides insights into designing advanced catalysts for light-driven water splitting and sustainable hydrogen production.