Electrocatalytic water oxidation by a Ni(ii) salophen-type complex.

Area of Science:

• Inorganic Chemistry
• Electrochemistry
• Catalysis

Background:

• Water oxidation is crucial for renewable energy technologies.
• Developing efficient and stable electrocatalysts is essential for water splitting.
• Nickel-based complexes offer a promising avenue for water oxidation catalysis.

Purpose of the Study:

• Synthesize and characterize a new mononuclear Ni(ii) complex, NiL.
• Evaluate the electrocatalytic activity of NiL for water oxidation.
• Investigate the influence of pH on the catalytic performance and identify active species.

Main Methods:

• Synthesis of NiL complex using Ni(OAc)2·4H2O and a salophen-type ligand.
• Characterization by elemental analysis, spectroscopy, and single crystal X-ray diffraction.
• Electrochemical studies including linear sweep voltammetry, cyclic voltammetry, and amperometry in borate buffer at various pH values.
• Surface analysis using scanning electron microscopy and X-ray powder diffraction.

Main Results:

• NiL complex synthesized and characterized. Exhibits superior water oxidation activity at pH 11 with a low overpotential (21 mV) for 2.0 mA cm⁻² current density.
• Onset potential for water oxidation decreases significantly with increasing pH.
• Cyclic voltammetry and amperometry confirm efficient water oxidation with excellent stability at neutral and alkaline pH.
• SEM images suggest nickel oxide at pH 11 and nickel oxide/Ni-based compounds at pH 7 are the active catalysts, while no clear activity was observed at pH 3.

Conclusions:

• The synthesized NiL complex is an effective electrocatalyst for water oxidation.
• Catalytic performance is highly pH-dependent, with optimal activity in alkaline conditions.
• Nickel oxide species formed in situ are identified as the primary water oxidizing catalysts.
• This study highlights the potential of Ni(ii) complexes in developing efficient water oxidation systems.