Alginate (ALG) is a natural polymer used in a wide range of applications. Cerium is a sustainable corrosion inhibitor for many metal substrates. In this study, ALG/Ce3+ hydrogel microparticles are presented as an innovative cerium(III) reservoir system for the smart release of cerium ions. The active corrosion inhibition capacity of the ALG/Ce3+ complex was investigated. Tests using ALG/Ce3+ macrogels (beads) and electrochemical experiments showed that, in saline media, ALG/Ce3+ hydrogel was

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... e to release Ce3+, which was subsequently exchanged with Al3+, Fe2+ and Fe3+ and, thus slowing the corrosion process of AA2024 (aluminum alloy) and AISI1020 (carbon steel) substrates, respectively. It is suggested that the presence of metal ions originated from the corrosion process triggers the cerium release. The corrosion protection of ALG/Ce3+ of the aluminum alloy was confirmed by polarization curves, electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET) and the protection of the carbon steel was demonstrated by EIS experiments. To the best of our knowledge, this is the first time that an alginate-based complex has been reported as an ion exchange corrosion-inhibiting system for metal substrates.