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 NiFeO and pure FeO 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-FeO systems, we demonstrate that secondary metals with appropriate oxide Gibbs free energy (ΔG) and low mixing enthalpy (ΔH), 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.