A Cubane-Like Cobalt Complex in Water Oxidation: Synthesis, True Catalyst, and Catalytic Mechanism

Area of Science:

• Electrochemistry and Materials Science
• Catalysis research focusing on energy conversion

Background:

• Multinuclear cobalt complexes are investigated for their catalytic potential.
• Understanding the in-situ formation of active species during oxygen evolution reaction (OER) is crucial.

Purpose of the Study:

• To evaluate the OER performance of a specific cuboidal cobalt complex ([Co4(dpyOHO)4(OAc)3(H2O)](ClO4)(1.7H2O), complex 1).
• To identify the true catalytic species formed during OER from the cobalt complex precursor.

Main Methods:

• Electrochemical methods were employed to study OER performance at pH 11.
• In-situ nanoparticle formation was analyzed using a suite of techniques: EDX, SEM, XAS, XPS, XRD, FTIR, ERDA, UV-vis, and Raman spectroscopy.
• X-ray absorption spectroscopy (XAS) and elastic recoil detection analysis (ERDA) were key for characterizing the active catalyst and complex decomposition.

Main Results:

• Complex 1 serves as a precursor, generating nanoparticles on the electrode surface during OER.
• XAS confirmed the formation of cobalt oxyhydroxide (CoO(OH)) as the active OER catalyst.
• ERDA indicated ligand removal and complex decomposition, with Fe impurities potentially enhancing catalytic activity.

Conclusions:

• The study proposes CoO(OH) nanoparticles, formed from the cobalt complex precursor, as the true OER catalysts.
• The presence of Fe impurities may play a significant role in the observed catalytic efficiency.
• This work provides insights into the formation and role of metal (hydr)oxide nanoparticles in cobalt-catalyzed OER.