Dynamic Carboxylic Acid Arms Enable Proton Shuttling in Iron-Based Hydrogen Catalysis

Area of Science:

• Inorganic Chemistry
• Electrocatalysis
• Bioinorganic Chemistry

Background:

• Mimicking natural hydrogenase enzymes with artificial electrocatalysts is a key strategy for efficient hydrogen production.
• Proton relay motifs near the active center facilitate hydrogen generation through proton-coupling steps.

Purpose of the Study:

• To investigate iron (III) complexes with tunable proton relay functionalities for electrocatalytic hydrogen evolution.
• To elucidate the mechanism of hydrogen evolution enabled by pendant carboxylic acid arms.

Main Methods:

• Synthesis and characterization of Fe(III) picolinate complexes.
• Electrochemical studies to evaluate hydrogen evolution reaction (HER) activity.
• Mechanistic investigations including kinetic analysis and intermediate identification.

Main Results:

• Fe(III) complexes with reversible dechelation/chelation exhibited proton-relay capabilities in acidic media.
• The pendant carboxylic acid arms were crucial for facilitating sequential reductions and hydride formation.
• Achieved high turnover frequency (TOFmax) of 10,000 s⁻¹ and >90% faradaic efficiency for HER.

Conclusions:

• Tailored secondary-sphere interactions are vital for designing efficient, earth-abundant electrocatalysts.
• The developed iron complexes demonstrate a promising pathway for sustainable hydrogen production.
• Insights gained can inform future catalyst design for small molecule activation reactions.