What question did this study set out to answer?

To investigate the grain-size dependence of hydrogen and oxygen evolution reactions in a specific high-entropy alloy.

May 7, 2026Materials0 citationsOpen Access

Grain-Size-Dependent Hydrogen Evolution and Oxygen Evolution Reaction Behavior of a Non-Equiatomic Fe41Mn25Ni24Co8Cr2 High-Entropy Alloy

HJHee-Tae JeongHongik University WKW. Y. KimHongik University

Key Points

To investigate the grain-size dependence of hydrogen and oxygen evolution reactions in a specific high-entropy alloy.
Conducted experiments on six specimens with varying grain sizes produced via recrystallization.
Evaluated reactions in 1 M KOH using differential local Tafel-slope analysis.
Measured current density and overpotential to assess performance.
Utilized statistical analysis (R2 values) to interpret results.
HER demonstrated a clear correlation of local Tafel slope with grain size, especially in initial current density.
OER exhibited consistent behavior; overpotential increased with grain size while current density decreased.
Finer grain sizes showed more favorable performance for OER, indicating stronger dependency than HER.
Grain size acts as an important descriptor for electrocatalytic response in this high-entropy alloy.

Abstract

The grain-size dependence of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) behavior was systematically investigated in a non-equiatomic Fe41Mn25Ni24Co8Cr2 high-entropy alloy. Six fully recrystallized specimens spanning grain sizes from 5.1 to 197 μm, produced by high-ratio differential speed rolling (HRDSR) and controlled annealing, were tested in 1 M KOH. Differential local Tafel-slope analysis revealed distinct and asymmetric grain-size-dependent behavior for the two half-reactions. For HER, the local Tafel slope at −3 mA cm−2 showed the clearest correlation with log(d/μm) among the HER descriptors examined in the present dataset (R2 = 0.682), indicating that grain-size effects were most clearly expressed in the near-onset to intermediate current-density regime. For OER, finer-grained specimens consistently exhibited more favorable apparent performance: the overpotential at 10 mA cm−2 increased with log(d/μm) (R2 = 0.715; slope = 1.09 × 10−2 V dec−1), whereas the current density at an overpotential of 0.33 V decreased with grain size (j0.33; R2 = 0.787). Overall, OER showed stronger and more consistent grain-size dependence than HER. These results identify grain size as a useful empirical microstructural descriptor of apparent electrocatalytic response in this composition-fixed bulk HEA system and show that microstructural control provides a practical route for tuning alkaline HER and OER behavior.

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