Homogeneous Electrochemical Water Oxidation at Neutral pH by Water-Soluble NiII Complexes Bearing Redox Non-innocent Tetraamido Macrocyclic Ligands

• Water oxidation is the bottleneck reaction in artificial photosynthesis. Exploring highly active and stable molecular water oxidation catalysts (WOCs) is still a great challenge. In this study, a water-soluble NiII complex bearing a redox non-innocent tetraamido macrocyclic ligand (TAML) is found to be an efficient electrocatalyst for water oxidation in neutral potassium phosphate buffer. Controlled-potential electrolysis experiments show that it can sustain at a steady current of approximately 0.2 mA cm−2 for >7 h at 1.75 V versus normal hydrogen electrode (NHE) without the formation of NiOx. Electrochemical and spectroelectrochemical tests show that the redox-active ligand, as well as HPO4 2− in the buffer, participate in the catalytic cycle. More importantly, catalytically active intermediate [NiIII(TAML2−)−O.] is formed via several proton-coupled electron transfer processes and reacts with H2O with the assistance of base to release molecular oxygen. Thus, the employment of redox non-innocent ligands is a useful strategy for designing effective molecular WOCs. 

Ämnesord

NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

Nyckelord

electrocatalysis

ligand effects

nickel

O−O bond formation

water oxidation

Artificial photosynthesis

Electrocatalysts

Ligands

Molecular oxygen

Oxidation

Potassium compounds

Redox reactions

Spectroelectrochemistry

Active intermediates

Controlled potential electrolysis

Macro-cyclic ligands

Non-innocent ligands

Normal hydrogen electrodes

Proton coupled electron transfers

Redox-active ligand

Spectroelectrochemical

Nickel compounds

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