A 3d‐4d‐5d High Entropy Alloy as a Bifunctional Oxygen Catalyst for Robust Aqueous Zinc–Air Batteries

High entropy alloys (HEAs) are highly suitable candidate catalysts for oxygen evolution and reduction reactions (OER/ORR) as they offer numerous parameters for optimizing the electronic structure and catalytic sites. Herein, FeCoNiMoW HEA nanoparticles are synthesized using a solution‐based low‐temperature approach. Such FeCoNiMoW nanoparticles show high entropy properties, subtle lattice distortions, and modulated electronic structure, leading to superior OER performance with an overpotential of 233 mV at 10 mA cm−2 and 276 mV at 100 mA cm−2. Density functional theory calculations reveal the electronic structures of the FeCoNiMoW active sites with an optimized d‐band center position that enables suitable adsorption of OOH* intermediates and reduces the Gibbs free energy barrier in the OER process. Aqueous zinc–air batteries (ZABs) based on this HEA demonstrate a high open circuit potential of 1.59 V, a peak power density of 116.9 mW cm−2, a specific capacity of 857 mAh gZn−1, and excellent stability for over 660 h of continuous charge–discharge cycles. Flexible and solid ZABs are also assembled and tested, displaying excellent charge–discharge performance at different bending angles. This work shows the significance of 4d/5d metal‐modulated electronic structure and optimized adsorption ability to improve the performance of OER/ORR, ZABs, and beyond. The noble metal‐free 3d‐4d‐5d high entropy alloy, FeCoNiMoW, with high configurational entropy, subtle lattice distortions, and modulated electronic structure is an efficient bifunctional oxygen catalyst for robust aqueous, solid, and flexible zinc–air batteries.