Green steel at atomistic scale: Ab initio simulation of surface reduction mechanism of Wüstite (FeO) by hydrogen

The reduction of FeO (wüstite) to Fe represents the final and slowest step in the hydrogen-based direct reduction of iron ores for sustainable ironmaking. However, the atomistic-scale mechanisms and kinetics of this process remain poorly understood. Here, we employ ab initio meta-dynamics simulations to investigate reaction pathways and energy barriers for this redox process on FeO(1 0 0) and FeO(1 1 1) surfaces. Differences in surface configurations lead to variations in the number of H molecules required, reaction pathways, and energy barriers. The FeO surface exhibits an autocatalytic effect, facilitating H dissociation and reducing the energy barrier for breaking H molecular bonds. Nevertheless, hydrogen dissociation and adsorption, forming O–H bonds, constitute the primary rate-limiting step. Following this, the Fe-O bond spontaneously breaks in the presence of individual H atoms. Increasing H partial pressure enhances reaction efficiency by raising the density of reactive H molecules, consistent with macroscopic observations. These insights advance the atomistic-scale understanding of hydrogen-based direct reduction, highlighting the influence of pressure and rate-limiting factors.