Electrocatalytic Hydrogen Evolution by Cobalt Complexes with a Redox Non-Innocent Polypyridine Ligand

Area of Science:

• Coordination Chemistry
• Electrocatalysis
• Sustainable Energy

Background:

• Transition metal complexes are crucial for catalysis.
• Redox-active ligands can modulate metal center reactivity.
• Efficient hydrogen evolution is key for renewable energy.

Purpose of the Study:

• Synthesize and characterize novel cobalt and zinc complexes with a tetradentate ppq ligand.
• Investigate the electrocatalytic hydrogen evolution activity of these complexes.
• Elucidate the mechanism of electrocatalytic hydrogen evolution.

Main Methods:

• Synthesis and full characterization of metal complexes.
• Electrochemical measurements (e.g., cyclic voltammetry) in DMF.
• Theoretical calculations (DFT) for electronic structure analysis.
• Mechanistic investigation of the electrocatalytic pathway.

Main Results:

• Novel cobalt and zinc complexes with the ppq ligand were successfully synthesized.
• The cobalt complex [Co(ppq)(PPh3)]+ exhibits two ligand-based electroreductions.
• The reduced cobalt complex acts as an efficient electrocatalyst for hydrogen evolution with high turnover frequencies.
• Theoretical calculations revealed a low-spin Co(II) center coupled with a triple-reduced ppq radical ligand in the active species.

Conclusions:

• The synthesized cobalt complex efficiently drives electrocatalytic hydrogen evolution.
• A proposed EECC mechanism highlights the role of ligand-based redox processes and proton transfer.
• This study provides insights into the function of redox-active ligands in transition metal-catalyzed hydrogen evolution.