Heterogeneous water oxidation: surface activity versus amorphization activation in cobalt phosphate catalysts

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Understanding the location of catalytic activity (surface vs. bulk) is crucial for designing efficient water oxidation catalysts.
• Cobalt-based materials are promising for water oxidation but their catalytic mechanisms require further elucidation.

Purpose of the Study:

• To investigate whether water oxidation is catalyzed at the surface or within the bulk of solid oxide materials.
• To differentiate the catalytic activity of crystalline pakhomovskyite (Pak) and amorphous cobalt oxide (CoCat).

Main Methods:

• X-ray spectroscopy to analyze material transformation under oxidizing potentials.
• Electrochemical analysis to determine catalytic activity and turnover frequency (TOF).

Main Results:

• Oxidizing potentials transform crystalline Pak into amorphous CoCat over 5-8 hours.
• Pak exhibits high surface activity, while the transformed CoCat shows dominant bulk activity.
• Directly deposited CoCat primarily shows bulk catalysis, with surface catalysis evident at low material loadings.

Conclusions:

• The catalytic site for water oxidation shifts from the surface in crystalline Pak to the bulk in amorphous CoCat.
• Material restructuring significantly influences catalytic pathways and efficiency.
• A comprehensive understanding of heterogeneous water oxidation necessitates considering surface, bulk, and restructuring dynamics.