Why does NiOOH cocatalyst increase the oxygen evolution activity of α-Fe₂O₃?

Area of Science:

• Materials Science
• Electrochemistry
• Computational Chemistry

Background:

• Nickel oxyhydroxide (NiOOH) is recognized for improving oxygen evolution reaction (OER) in hematite (α-Fe2O3) photoanodes.
• Experimental studies suggest NiOOH activates the hematite surface rather than being active itself.

Purpose of the Study:

• Investigate the mechanistic origin of enhanced OER activity and low overpotentials in NiOOH-Fe2O3 photoanodes.
• Utilize first-principles calculations to explore catalytic site activity.

Main Methods:

• Density functional theory + U (DFT+U) calculations were employed.
• Studied NiOOH in cluster and continuous strip geometries on hematite (110) surfaces.
• Analyzed OER activity at various atomic sites within the simulated structures.

Main Results:

• A continuous strip geometry of NiOOH on hematite was found to be stable.
• Ni atoms at the edge sites of the NiOOH cocatalyst exhibited higher catalytic activity compared to those on the basal plane.
• Calculated overpotentials for the oxygen evolution reaction were as low as 0.39 V.

Conclusions:

• The enhanced OER performance of NiOOH-Fe2O3 photoanodes is attributed to the activation of the hematite surface by NiOOH.
• The specific arrangement of NiOOH as a continuous strip on hematite is crucial for stability and activity.
• Edge Ni sites on the NiOOH cocatalyst are identified as the primary active centers for the oxygen evolution reaction.