Anodic oxygen evolution reaction (OER) is recognized as kinetic bottleneck in water electrolysis. Transition metal sites with high valence states can accelerate the reaction kinetics to offer highly intrinsic activity, but suffer from thermodynamic formation barrier. Here, we show subtle engineering of highly oxidized Ni⁴⁺ species in surface reconstructed (oxy)hydroxides on multicomponent FeCoCrNi alloy film through interatomically electronic interplay. Our spectroscopic investigations with theoretical studies uncover that Fe component enables the formation of Ni⁴⁺ species, which is energetically favored by the multistep evolution of Ni²⁺→Ni³⁺→Ni⁴⁺. The dynamically constructed Ni⁴⁺ species drives holes into oxygen ligands to facilitate intramolecular oxygen coupling, triggering lattice oxygen activation to form Fe-Ni dual-sites as ultimate catalytic center with highly intrinsic activity. As a result, the surface reconstructed FeCoCrNi OER catalyst delivers outstanding mass activity and turnover frequency of 3601 A g_metal⁻¹ and 0.483 s⁻¹ at an overpotential of 300 mV in alkaline electrolyte, respectively.

Metastability engineering opens a new avenue to design high-entropy alloys (HEAs) originally proposed to benefit from phase stabilization. Meanwhile, boundary engineering via embedding planar defects such as stacking faults and nanotwins into the matrix of metals provides them with unique mechanical properties. In this work, for the first time, we combine the above two strategies to prepare Al_0.1CoCrFeNi HEA pillars populated with a high density of stacking faults and nanotwins. It is uncovered that the stacking faulted (SF) Al_0.1CoCrFeNi HEA pillars manifest ultrahigh strength exceeding 4.0 GPa and considerable compressive plasticity over 15%, much superior to their nanotwinned (NT) counterparts. Compared with the nanotwins undergoing detwinning during plastic deformation, the stacking faults in Al_0.1CoCrFeNi high-entropy alloy thin films (HEAFs) are quite stable to hinder dislocation motion. Our findings not only endow the Al_0.1CoCrFeNi HEAs with a predominant combination of strength and compression deformability, but also shed light on a new perspective for overcoming the strength and ductility trade-off in structural materials.