Studies of the pathways open to copper water oxidation catalysts containing proximal hydroxy groups during basic...

Area of Science:

• Inorganic Chemistry
• Electrochemistry
• Sustainable Energy

Background:

• Developing economical water oxidation catalysts is crucial for sustainable energy.
• Earth-abundant metals are preferred for catalyst affordability.
• Bipyridine ligands can stabilize metal complexes for catalytic applications.

Purpose of the Study:

• To synthesize and characterize 2:1 6,6'-dihydroxybipyridine (6,6'-dhbp)/copper complexes for electrocatalytic water oxidation.
• To investigate the influence of pH on precatalyst structure and stability.
• To determine the essential components for efficient water oxidation catalysis.

Main Methods:

• Synthesis of copper and zinc complexes with various dihydroxybipyridine ligands.
• X-ray crystallography to determine crystal structures.
• Spectroscopic techniques (CW-EPR, ENDOR, HYSCORE) to confirm ligand binding and study pH effects.
• Electrochemical studies to evaluate water oxidation activity and overpotential.

Main Results:

• Reported crystal structures of 2:1 6,6'-dhbp/copper(II) complexes in different protonation states.
• Demonstrated that 6,6'-dhbp ligand remains bound to copper across a wide pH range.
• Identified both copper and proximal hydroxyl groups as essential for low overpotential water oxidation.
• Achieved an overpotential of 477 mV for water oxidation with catalyst 1 at pH 12.6.

Conclusions:

• The synthesized 2:1 6,6'-dhbp/copper complexes are effective electrocatalysts for water oxidation in aqueous base.
• Catalyst activity is dependent on the presence of both copper and proximal hydroxyl groups.
• The study supports the role of hydrogen bonding and proton-coupled electron transfer in facilitating water oxidation.