Octahedral-coordinated Co₃O₄ for water electrolysis in acid

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Developing stable, non-noble metal oxide catalysts is critical for efficient acidic water electrolysis, aiming to replace iridium-based materials.
• Traditional spinel cobalt oxides exhibit performance limitations due to the presence of both inactive tetrahedral and active octahedral coordination sites.

Purpose of the Study:

• To synthesize and characterize a new trigonal-phase cobalt oxide (Tri-Co3O4) with enhanced catalytic properties for acidic water electrolysis.
• To investigate the structural and electronic properties of Tri-Co3O4 and elucidate its catalytic mechanism for the oxygen evolution reaction (OER).

Main Methods:

• A vacuum-mediated molten-alkali mechanochemical method was employed to produce the trigonal-phase Co3O4 (Tri-Co3O4).
• The catalyst's structure, coordination sites (edge-shared [CoO6] octahedral), and oxidation states (Co2+ and Co3+ in a 1:2 ratio) were analyzed.
• Electrochemical performance was evaluated for the acidic oxygen evolution reaction (OER) and in proton-exchange membrane water electrolysis (PEMWE) devices.

Main Results:

• Tri-Co3O4 demonstrated a significantly lower overpotential (269 mV at 10 mA cm-2) for the acidic OER compared to spinel Co3O4.
• The catalyst achieved high current densities (>1,800 mA cm-2 at 1.80 V) in proton-exchange membrane water electrolysis (PEMWE) devices.
• The 2D layered structure with edge-shared octahedral coordination improved intermediate adsorption and reduced cobalt dissolution, enhancing activity and stability.

Conclusions:

• The developed Tri-Co3O4 is a highly active and stable non-noble metal catalyst for acidic water electrolysis.
• Its unique trigonal structure and coordination environment offer a promising alternative to iridium-based catalysts for efficient hydrogen production.