Electrocatalytic Hydrogen Evolution of Bent Bis(dipyrrin) Ni(II) Complexes

Area of Science:

• Inorganic Chemistry
• Electrochemistry
• Catalysis

Background:

• Planar Ni(II) porphyrinoid complexes are established electrocatalysts for CO2 reduction, O2 reduction, and hydrogen evolution reactions (HER).
• Nonplanar Ni(II) tetra-pyrrolic complexes remain underexplored for catalytic applications.

Purpose of the Study:

• To synthesize and characterize novel bent bis(dipyrrin) Ni(II) complexes.
• To investigate their electronic properties and electrocatalytic activity for the hydrogen evolution reaction (HER).

Main Methods:

• Synthesis of three highly bent bis(dipyrrin) Ni(II) complexes.
• Cyclic voltammetry and thin-layer UV-visible spectroelectrochemistry.
• Density functional theory (DFT) calculations.

Main Results:

• The complexes exhibited four redox processes, leading to two reduced species.
• Phenyl- and pentafluorophenyl-bearing complexes showed high current ratios (i_c/i_p > 30) with trifluoroacetic acid.
• Faradaic efficiencies for H2 generation exceeded 93% for these complexes.
• DFT calculations indicated low endothermic energies for the HER in these bent complexes.

Conclusions:

• The synthesized bent bis(dipyrrin) Ni(II) complexes are efficient electrocatalysts for HER.
• Their nonplanar structure contributes to favorable energetics for hydrogen evolution.
• These findings highlight the potential of nonplanar Ni(II) complexes in catalysis.