ABSTRACT Seawater batteries (SWBs) that rely on the dissolved oxygen reduction reaction (ORR) on the cathode are a crucial choice for the long‐term power supply of underwater equipment. However, chloride ions (Cl − ) poisoning and the lean‐oxygen condition in seawater severely suppress the ORR kinetics, leading to rapid activity decay and poor durability of catalysts. Herein, we present a Cl − ‐resilient ORR catalyst of CoSn alloy anchored on nitrogen‐doped carbon substrate (CoSn@NC). The introd