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Accelerating Electrochemical Hydrogen Evolution by Introducing Local Proton Source in Non-Heme Iron (III) Complexes.

Bharath M1, Meenakshi Rana1, Santanu Pattanayak1

  • 1Department of Chemistry, Ashoka University, Rajiv Gandhi Education City, Sonipat, Haryana, 131029, India.

Chemistry, an Asian Journal
|September 23, 2025
PubMed
Summary

Researchers synthesized three non-heme iron(III) complexes to study their hydrogen evolution reaction (HER) catalysis. Complex 1, featuring hydroxy functional groups, exhibited superior electrocatalytic activity due to enhanced proton transfer mechanisms.

Keywords:
ElectrocatalysisHydrogen evolutionNon‐heme iron complexRedox active ligand

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Area of Science:

  • Inorganic Chemistry
  • Catalysis
  • Electrochemistry

Background:

  • Non-heme iron complexes are crucial in catalysis, but their efficiency in hydrogen evolution reactions (HER) requires optimization.
  • Ligand design plays a pivotal role in modulating the electronic and structural properties of metal complexes for enhanced catalytic performance.

Purpose of the Study:

  • To synthesize and characterize novel non-heme Fe(III) complexes with pyridine-2,6-dicarboxamide-based ligands.
  • To investigate the hydrogen evolution reaction (HER) catalytic activity of these complexes under acidic conditions.
  • To elucidate the structure-activity relationship, particularly the influence of ligand functional groups on HER performance.

Main Methods:

  • Synthesis and characterization of three Fe(III) complexes using elemental analysis, single crystal X-ray diffraction, EPR, Mössbauer, UV-Vis, and IR spectroscopy.
  • Electrocatalytic evaluation of HER activity in dimethylformamide (DMF) using various acidic media (acetic acid, triethylammonium chloride/tetrafluoroborate).
  • Kinetic analysis to determine catalytic turnover frequencies (kcat).

Main Results:

  • Three bis-chelated hexa-coordinated non-heme Fe(III) complexes, (FeIII[L1]2)− (1), (FeIII[L2]2)− (2), and (FeIII[L3]2)− (3), were successfully synthesized.
  • Complex 1, featuring a 4-hydroxy pyridine-2,6-dicarboxamide ligand, demonstrated significantly higher electrocatalytic activity for HER (kcat = 1.4 ± 0.07 × 10^5 M−1s−1) compared to complexes 2 and 3.
  • X-ray diffraction revealed differences in Fe-Npyridine bond distances between complexes 1 and 2, suggesting structural influences on activity.

Conclusions:

  • The presence of internal hydroxy functional groups in complex 1 enhances HER electrocatalytic activity by acting as a local proton source and facilitating intramolecular proton transfer.
  • Tuning ligand scaffolds in Fe(III) complexes is an effective strategy to modulate their catalytic performance for hydrogen evolution.
  • This study highlights the potential of specifically designed non-heme iron complexes for efficient hydrogen production.