Joule‐Heating‐Driven Encapsulation of FeCo Nanoparticles in Ion‐Selective Carbon Shell for Stable Seawater Electrolysis

Abstract The oxygen evolution reaction (OER) in seawater is notoriously hindered by slow kinetics and high overpotential, compounded by chloride‐induced corrosion, which impedes efficient hydrogen production via seawater electrolysis. A key challenge is to devise an OER catalyst that not only mitigates chlorine oxidation and corrosion but is also cost‐effective. In this work, the bimetallic iron‐cobalt (FeCo) nanoparticles are swiftly encapsulated within N‐doped carbon shells in mere seconds using the Joule‐heating technique, a process significantly faster than the several hours required by traditional furnace heating. Meanwhile, the high temperature could offer the necessary activation energy for Fe/Co atom redispersion on the carbon shell via forming abundant metal‐nitrogen (Co/Fe‐N−C) active sites. These Co/Fe‐N−C sites exhibit exceptional activity for OER catalysis. Consequently, the sample prepared by Joule‐heating at 800 °C for 5 seconds (FeCo@CN−J‐5) demonstrates superior OER performance, achieving a current density that is 35 times greater than that prepared without N doping and 6 times higher than that prepared via furnace heating. Moreover, FeCo@CN−J‐5 operates stably for 100 hours at 200 mA cm −2 with negligible degradation in the highly corrosive electrolyte of 0.1 M KOH + 0.6 M NaCl, demonstrating its promising potential for practical seawater splitting.