Activating the Microsized Cubic Co ₃ O ₄ with Doping Y ₂ O ₃ Phase Inlaid on the Plasma‐Treated Soft Carbon Fiber for a Robust Electrocatalytic Alkalized‐Seawater Splitting

Abstract Engineering efficient bifunctional electrocatalysts for simultaneous hydrogen and oxygen evolution reactions (HER/OER) remains very crucial for practical anion exchange membrane water electrolyzers (AEMWEs). Herein, a yttrium oxide doped cubic Co ₃ O ₄ (Y ₂ O ₃ ‐Co ₃ O ₄ ) catalyst engineered on plasma‐treated carbon cloth (PCC) is reported which demonstrates exceptional performances for overall seawater splitting. Synthesized at an optimal crystallization temperature (250 °C), the obtained Y ₂ O ₃ ‐Co ₃ O ₄ /PCC features rich heterointerfaces which optimize active sites and enhance electron transfer, thereby, causing an outstanding HER activity with ultralow overpotentials of 301 mV (alkaline) and 346 mV (seawater) for transferring 1000 mA cm ⁻² ( j ₁₀₀₀ ). When the catalyst is integrated into AEMWE devices, low cell voltages of 2.11 V (alkaline) and 2.47 V (alkalized seawater) are achieved for generating j ₁₀₀₀ . Combined with the experimental and theoretical investigations, it reveals that the yttrium doping induces a favorable electron redistribution, where the electron delocalization of Y‐site stabilizes Co ³ ⁺ species and the electron accumulation of Co‐site optimizes H* adsorption. In addition, the formed heterointerface of Y ₂ O ₃ ‐Co ₃ O ₄ simultaneously enhances OER activity through optimizing the oxygen intermediate adsorption and strengthening the metal‐oxygen bonds. Furthermore, the heterostructure design additionally reduces the lattice strain and accelerates charge transfer kinetics for seawater splitting.