Alloying Effects on Iron Oxide Redox Pathways: Insights into Sustainable Hydrogen-Based Reduction

Hydrogen-based direct reduction of iron oxides, particularly using renewable hydrogen sources, presents a sustainable, zero-carbon footprint alternative for the steel industry. However, the influence of secondary metallic elements on reduction pathways and the redox behavior of iron oxide remains insufficiently understood. In this study, we investigate the reduction and oxidation behaviors of NiFe₂O₄ and pure Fe₃O₄ using environmental transmission electron microscopy (ETEM), revealing that Ni incorporation fundamentally modifies the reaction pathway, simplifying the reduction process from a two-step to a single-step mechanism. Additionally, by examining the reduction processes of Ni-, Co-, Cu-, and Al-Fe₃O₄ systems, we demonstrate that secondary metals with appropriate oxide Gibbs free energy (ΔG_oxide) and low mixing enthalpy (ΔH_mix), such as Ni and Co, significantly accelerate reduction by promoting alloy formation and inhibiting oxidation. This work advances the understanding of iron oxide redox mechanisms and lays the groundwork for designing next-generation alloys and sustainable metallurgical strategies.