Employing seawater splitting systems to generate hydrogen can be economically advantageous but still remains challenging, particularly for designing efficient and high Cl−‐corrosion resistant trifunctional catalysts toward the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). Herein, single CoNC catalysts with well‐defined symmetric CoN4 sites are selected as atomic platforms for electronic structure tailoring. Density function theory reveals that P‐doping into CoNC can lead to the formation of asymmetric CoN3P1 sites with symmetry‐breaking electronic structures, enabling the affinity of strong oxygen‐containing intermediates, moderate H adsorption, and weak Cl− adsorption. Thus, ORR/OER/HER activities and stability are optimized simultaneously with high Cl−‐corrosion resistance. The asymmetric CoN3P1 structure based catalyst with boosted ORR/OER/HER performance endows seawater‐based Zn–air batteries (S‐ZABs) with superior long‐term stability over 750 h and allows seawater splitting to operate continuously for 1000 h. A self‐driven seawater splitting powered by S‐ZABs gives ultrahigh H2 production rates of 497 μmol h−1. This work is the first to advance the scientific understanding of the competitive adsorption mechanism between Cl− and reaction intermediates from the perspective of electronic structure, paving the way for synthesis of efficient trifunctional catalysts with high Cl−‐corrosion resistance.

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