Enhanced corrosion resistance of equiatomic CoCrFeMnNi high-entropy alloy via chromium enrichment in the oxide layer induced by cathodic modification

Although CoCrFeMnNi requires enhanced corrosion resistance for application due to its weaker spontaneous passivation compared to stainless steel, altering its composition to improve corrosion resistance may undermine its inherent advantages such as excellent ductility and toughness. Herein, we propose a novel method to improve the corrosion resistance of CoCrFeMnNi without altering its composition by inducing spontaneous passivation through surface coating. By coating CoCrFeMnNi with Fe–N–C, a non-noble metal catalyst, we successfully induced spontaneous passivation in 0.5 M sulfuric acid solution. This was enabled by the increased oxygen reduction reaction (ORR) activity of Fe–N–C, which shifted the equilibrium potential and facilitated passive film formation. The resulting passive layer was enriched in Cr and remained stable during long-term immersion, as confirmed by ICP analysis, which showed a 72-fold reduction in metal dissolution. Furthermore, compared to conventional Pt-based cathodic modification strategies, the Fe–N–C coating, which is costing only 1/20,000 of Pt/C, offers a highly economical and scalable alternative for practical corrosion protection.