Light-Induced H₂ Evolution with a Macrocyclic Cobalt Diketo-Pyrphyrin as a Proton-Reducing Catalyst

Area of Science:

• Inorganic Chemistry
• Catalysis
• Photochemistry

Background:

• Cobalt complexes are effective catalysts for photocatalytic proton reduction.
• Macrocyclic tetrapyridyl ligands (pyrphyrins) and their Co(II) complexes are highly efficient H2 evolution catalysts.
• Developing stable and active water reduction catalysts (WRCs) is crucial for sustainable energy technologies.

Purpose of the Study:

• To synthesize and characterize a new macrocyclic cobalt complex with enhanced water reduction catalytic activity.
• To evaluate the performance of the novel Co(II) diketo-pyrphyrin complex as a water reduction catalyst.
• To assess the stability and limitations of the catalytic system.

Main Methods:

• Synthesis of a novel macrocyclic Co(II) diketo-pyrphyrin complex.
• Solubility testing in aqueous media.
• Photocatalytic water reduction experiments using [Ru(bpy)3]Cl2 as a photosensitizer and NaAscO as a sacrificial electron donor.
• Analysis of catalytic activity via turnover numbers (TONs).

Main Results:

• A new, water-soluble macrocyclic Co(II) diketo-pyrphyrin complex was successfully synthesized.
• The complex demonstrated high activity as a water reduction catalyst.
• Turnover numbers (TONs) of 2500 H2/Co were achieved in the photocatalytic system.
• The cobalt catalyst exhibited superior stability compared to the photosensitizer.

Conclusions:

• The novel Co diketo-pyrphyrin complex is a highly active and stable water reduction catalyst.
• The catalyst's stability is a key advantage, outlasting the photosensitizer in the tested system.
• This finding highlights the potential of diketo-pyrphyrin cobalt complexes for efficient hydrogen production.