Electrowinning for room-temperature ironmaking: Mapping the electrochemical aqueous iron interface

A promising route towards room-temperature ironmaking is electrowinning, where iron ore dissolution is coupled with cation electrodeposition to grow pure iron. However, poor faradaic efficiencies against the hydrogen evolution reaction (HER) is a major bottleneck. To develop a mechanistic picture of this technology, we conduct a first-principles thermodynamic analysis of the Fe110 aqueous electrochemical interface. Constructing a surface Pourbaix diagram, we predict that the iron surface will always drive towards adsorbate coverage. We calculate theoretical overpotentials for terrace and step sites and predict growth at the step sites are likely to dominate. Investigating the hydrogen surface phases we model several hydrogen absorption mechanisms, all of which are predicted to be endothermic. Additionally, for HER we identify step sites as being more reactive than on the terrace, and with competitive limiting potentials to iron plating. The results presented here further motivate electrolyte design towards HER suppression.