Grain-Boundary-Activity Correlation for Electrocatalytic Oxygen Evolution in High-Entropy Alloys

Abstract

High-entropy alloys (HEAs) have emerged as a promising platform for designing efficient electrocatalysts; however, the relationship between their structure and activity has not yet been clearly established. In particular, the influences of crystalline defects, such as grain boundaries (GBs), on activity and stability remain unclear. This study demonstrates the impacts of GBs on the oxygen evolution reaction (OER) activity in the FeCoCrNi HEA. We observe a logarithmic dependence of OER performance on mean grain size, spanning 3 orders of magnitude, as measured by evaluators like overpotential and Tafel slope. Spatially resolved microscopic imaging of activated samples indicates that the GBs undergo substantial reconstructions and they are enriched with the in situ formed metal oxides (M-O, M = Fe, Co, Ni) and the amorphous regions. By comparing with simple metals, we reveal a “high-entropy effect,” i.e., HEAs exhibit greater tolerance towards the grain refinements, which explains their activity both in bulk samples and nanoparticles. These findings offer physics-informed strategies for developing HEA electrocatalysis.