Composition tuning of structural high entropy alloy (Fe-Co-Ni-Cu-Mn/Zn) nano-electrocatalysts for synergistic water splitting

Abstract

Structural high-entropy alloys (HEAs), composed of five or more earth-abundant, low-cost metals, offer a versatile platform for tailoring surface composition and active sites to develop efficient electrocatalysts. In this work, we compare Mn-HEA (Mn-Fe-Co-Ni-Cu) and Zn-HEA (Zn-Fe-Co-Ni-Cu) for the Oxygen Evolution Reaction (OER) and Hydrogen Evolution Reaction (HER) in alkaline media. Both HEAs show promising OER activity, with Zn-HEA exhibiting superior performance. Zn-HEA achieves overpotentials of 360 mV and 519 mV (vs. RHE) to reach 10 and 100 mA cm⁻², respectively, lower than the benchmark RuO₂. For HER in KOH, Zn-HEA reaches overpotentials of 414 mV and 631 mV at 10 and 100 mA cm⁻², respectively. The catalyst also demonstrates excellent stability, maintaining performance over 5000 cycles and 12 hours of operation. Post-electrocatalysis STEM mapping confirms compositional stability. Density Functional Theory (DFT) calculations reveal that substituting Mn with Zn lowers the Gibbs free energy for both OER and HER, further supporting Zn-HEA as a superior electrocatalyst. These findings establish Zn-HEA as a promising bifunctional catalyst for water splitting applications.