A Co-tris coordination complex as a stable homogeneous electrocatalyst for aqueous water oxidation

Area of Science:

• Electrochemistry
• Catalysis
• Materials Science

Background:

• Developing molecular homogeneous catalysts for water oxidation without forming heterogeneous metal oxides is difficult.
• Cobalt salts (CoCl2·6H2O) typically act as pre-catalysts, generating inactive cobalt oxides (CoO_x) during water oxidation.
• A previously reported cobalt(II)-coordination complex (CoT) showed potential for homogeneous catalysis.

Purpose of the Study:

• To provide strong evidence that the Co(II)-coordination complex (CoT) functions as a true molecular homogeneous electrocatalyst for water oxidation.
• To demonstrate the suppression of cobalt oxide (CoO_x) formation during electrolysis.
• To evaluate the electrochemical stability and homogeneity of the CoT complex.

Main Methods:

• Electrochemical water oxidation experiments.
• Characterization using FESEM, EDX, XPS, PXRD, IR, Raman, and UV-visible diffuse reflectance spectroscopy to confirm the absence of CoO_x.
• Evaluation of stability and homogeneity using 1H NMR, 13C NMR, HRMS, and UV-visible spectroscopy.

Main Results:

• The CoT complex acted as a true molecular homogeneous electrocatalyst, suppressing CoO_x formation during electrolysis.
• Multiple characterization techniques confirmed the absence of electrodeposited CoO_x.
• The CoT complex exhibited excellent electrochemical stability and solution homogeneity.
• Achieved a low onset overpotential of 461 mV and a high faradaic efficiency of 94.3% for water oxidation.

Conclusions:

• The Co(II)-coordination complex (CoT) is a robust molecular homogeneous electrocatalyst for water oxidation.
• This finding overcomes the challenge of catalyst decomposition into heterogeneous oxides.
• CoT offers a promising alternative for efficient and stable electrochemical water splitting.