Cobalt Carbonate as an Electrocatalyst for Water Oxidation

Area of Science:

• Electrochemistry
• Catalysis
• Inorganic Chemistry

Background:

• Aqueous cobalt(II) salts in the presence of bicarbonate/carbonate ions function as electrocatalysts for water oxidation.
• Understanding the redox processes and intermediate species is crucial for optimizing catalytic efficiency.

Purpose of the Study:

• To investigate the electrocatalytic mechanism of water oxidation by cobalt salts in bicarbonate solutions.
• To identify the active cobalt species and their role in the catalytic cycle.
• To explore the formation and catalytic activity of higher oxidation state cobalt-carbonate complexes.

Main Methods:

• Electrochemical techniques including cyclic voltammetry and chronoamperometry.
• Density Functional Theory (DFT) calculations to model cobalt species and reaction pathways.

Main Results:

• Observed distinct redox waves corresponding to Co(III/II), Co(IV), and Co(V) species.
• Identified catalytic oxidation of bicarbonate/carbonate to bicarbonate by Co(IV) and water/bicarbonate oxidation by Co(V).
• Chronoamperometry at 1.3 V resulted in a green deposit, indicating heterogeneous catalyst formation.
• DFT calculations confirmed the stability of Co(IV) and Co(V) carbonate complexes at experimentally relevant potentials.

Conclusions:

• Cobalt species in bicarbonate solutions act as effective electrocatalysts for water oxidation.
• The catalytic activity involves multiple oxidation states of cobalt, including Co(IV) and Co(V), which can oxidize both water and bicarbonate.
• The formation of a heterogeneous catalyst suggests potential for practical applications in water oxidation.