Unconventional High‐Entropy Oxide with Inner Metallic Coordination and Surface Medium‐Entropy Metal‐OH for Durable PEM Water Electrolysis at 2 A cm⁻²

The multicomponent synergistic effect has become increasingly important for electrocatalysis; however, there remain large unexplored compositional and structural spaces. Here, an unconventional high-entropy oxide (HEO) with inner metallic coordination interactions and surface medium-entropy metal-OH for durable proton exchange membrane water electrolyzers (PEMWEs) is presented. The metallic clusters inside the HEO particles generate the inner metallic coordination interactions that reserve electrons, with a multicomponent effect, to inhibit Ru/Ir overoxidation and switch reaction mechanisms toward an exclusive adsorbate evolution mechanism for acidic oxygen evolution reaction (OER). Surface medium-entropy metal-OH groups enable adaptive interfacial water networks to trap reactive water and promote proton transfer, reducing mass transport resistance at large current densities. Resultantly, this RuIrNiCoCrO2-incorporated PEMWEs achieve the ultralow voltages of 1.71 V@2.0 A cm-2 and 2.03 V@5.0 A cm-2 at 80 °C, and unprecedented durability >1500 h@2.0 A cm-2. Thus, the dual engineering of inner multicomponent coordination environments and surface functional groups overcomes the activity-stability dilemma in the PEMWEs.