Cerium driven active site relocation in spinel Co₃O₄ enables stable chlorine evolution in acidic media

The chlorine evolution reaction underpins the chlor-alkali industry, yet its harsh acidic oxidative environment severely limits the stability of non-noble catalysts. Here we show that atomically dispersed Ce in spinel Co₃O₄ with a three-dimensional ordered macroporous nanostructure triggers active site relocation from lattice oxygen to cobalt, simultaneously enhancing activity and inhibiting lattice oxygen corrosion. Ce occupies octahedral Co sites, inducing polyhedral distortion and creating unsaturated Co Centers that directly adsorb Cl⁻. In 4 M NaCl at pH = 2, the catalyst achieves overpotentials of 44 and 218 mV at 10 and 1000 mA cm^-2, respectively, with ~99.1% chlorine selectivity and robust durability over 550 h in a chlor-alkali cell at 2.5 kA m^-2. In situ Raman, attenuated total reflection surface-enhanced infrared absorption spectroscopy and differential electrochemical mass spectrometry confirm the active-site transformation, while density functional theory calculations reveal optimized Cl adsorption free energy, suppressed oxygen-mediated degradation, and preserved structural integrity. This active-site engineering strategy offers a route to designing stable, high-current-density catalysts for chlorine production beyond noble metals.