Anion-Directed Engineering of High-Entropy Layered Double Hydroxides for Oxygen Evolution Catalysis

The development of highly active and durable oxygen evolution reaction (OER) electrocatalysts is crucial for efficient hydrogen production via anion exchange membrane water electrolysis (AEMWE). High-entropy materials have emerged as a versatile platform for electrocatalysis due to their tunable compositions and synergistic effects among multiple elements. Herein, we systematically investigate the influence of different anions, specifically sulfate (SO₄^2-), nitrate (NO₃^-), and chloride (Cl^-), on the morphology, surface structure, and OER performance of high-entropy layered double hydroxides (HELDHs) composed of Fe, Co, Ni, Mn, and Zn. Since anions change the microenvironment during the synthesis process, the structures of the prepared nanomaterials vary significantly, from nanosheets and nanowires to porous flower-like structures. These morphological differences directly impact the electrochemically active surface area, oxygen species adsorption, and charge transfer kinetics. Among the evaluated systems, sulfate-based HELDHs (HELDH-SO₄^2-) feature a highly porous, interconnected nanosheet architecture and deliver outstanding OER activity and stability in alkaline media, achieving an overpotential of 282 mV at 100 mA cm^-2 with a low Tafel slope of 45.53 mV dec^-1. They also demonstrate exceptional performance as anode catalysts in AEMWE. Density functional theory calculations reveal that cation vacancies combined with adsorbed sulfate ions reduce the reaction energy barrier, accounting for the superior activity. These results underscore the pivotal role of anions in tuning the structure-function relationship of high-entropy catalysts and provide a efficient strategy for designing high-performance water oxidation electrocatalysts.