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

Abstract

. Development of a true molecular homogeneous catalyst for electrochemical water oxidation without its decomposition into a metal-oxide-based heterogeneous catalyst is truly challenging. The commercially available, low-cost, and non-noble metal salt, i.e., CoCl2∙6H2O, is well-known for electrochemical water oxidation for a limited time by generating CoOx in situ; it acts as a pre-catalyst and not a true molecular catalyst for electrocatalytic water oxidation. Recently, we have reported a preliminary result of effective complexation of TrisH3 (tris(hydroxymethyl)aminomethane) ligand with Co(II) in an aqueous solution of CoCl2∙6H2O and NaOAc at pH value of 8.6, leading to the formation of a Co(II)-coordination complex, [CoII(TrisH2)(TrisH3)(CH3COO)(H2O)] (CoT). In the present report, we provide strong evidence that Co(II)-coordination complex (CoT) acts as a true molecular homogeneous electrocatalyst for water oxidation, by suppressing the formation of CoOx during the electrolysis. The absence of electrodeposited material (i.e., CoOx) during electrolysis was confirmed by using multiple characterization techniques, including FESEM, EDX, XPS, PXRD, IR, Raman, and UV–visible diffuse reflectance spectroscopy. The electrochemical stability and solution homogeneity of the CoT complex were evaluated using a combination of electrochemical, spectroscopic, and microscopic techniques, including 1H NMR, 13C NMR, HRMS, and UV–visible spectroscopy. The electrocatalytic water oxidation performance of CoT complex attains a low onset overpotential value of 461 mV with a Faradaic efficiency value of 94.3% (± 4.7%).