Substituent Effects in Iron Porphyrin Catalysts for the Hydrogen Evolution Reaction

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• A global hydrogen economy requires scalable, non-precious metal catalysts for water splitting.
• Metal-nitrogen-carbon (MNC) catalysts with MN4 active sites show promise but lack defined structures for optimization.
• Porphyrin model complexes offer insights into structure-property relationships for MNC catalysts.

Purpose of the Study:

• To investigate the impact of porphyrin substituents on the electronic and electrocatalytic properties of MN4 centers.
• To evaluate these properties for the hydrogen evolution reaction (HER) in aqueous electrolytes.
• To establish structure-property relationships for designing advanced MNC catalysts.

Main Methods:

• Combined experimental and theoretical approaches.
• Synthesis and characterization of porphyrin model complexes.
• Electrocatalytic evaluation of the hydrogen evolution reaction (HER).

Main Results:

• Porphyrin substituents significantly affect catalyst utilization on carbon supports.
• Substituents critically influence the electrocatalytic performance for the HER.
• A proposed HER mechanism involves a [FeII(P⋅)]− radical anion intermediate with an internal base.

Conclusions:

• Tailoring porphyrin substituents is key to optimizing MNC catalysts for the HER.
• The findings provide a foundation for designing highly efficient, non-precious metal electrocatalysts.
• The insights gained are potentially transferable to other catalytic applications beyond HER.