Crystal Facets-Activity Correlation for Oxygen Evolution Reaction in Compositional Complex Alloys.

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Compositional complex alloys, such as high- and medium-entropy alloys (HEAs/MEAs), are promising electrocatalysts for the oxygen evolution reaction (OER).
• The precise structure-activity relationship, particularly the role of crystal facets and surface reconstructions, remains poorly understood for these advanced materials.

Purpose of the Study:

• To elucidate the structure-activity relationship in FeCoNiCr medium-entropy alloys (MEAs) for oxygen evolution reaction (OER) electrocatalysis.
• To identify the most active crystal facets and understand the mechanism behind their enhanced performance, considering surface reconstruction effects.

Main Methods:

• Experimental validation using single crystal and polycrystal MEA samples.
• Density Functional Theory (DFT) calculations to investigate surface properties and reaction mechanisms.
• Electrochemical testing to assess OER activity.

Main Results:

• The {100} facets of FeCoNiCr MEAs demonstrate superior activity for the OER.
• A mechanism is proposed where the low in-plane density of {100} facets facilitates surface reconstruction, leading to the formation of amorphous structures with highly active species.
• Experimental and computational results consistently support the enhanced activity of the {100} facets.

Conclusions:

• The {100} facets are identified as the most active sites in FeCoNiCr MEAs for OER.
• Surface reconstruction on these facets is crucial for forming the true active species, advancing the fundamental understanding of MEA electrocatalysis.
• These findings provide physics-based insights for designing next-generation electrocatalysts with tailored facet properties.