Study of Al-Doped\nand Al₂O₃ Heterostructures\nfor Improving α‑Fe₂O₃ Catalysis\nfor the Oxygen Evolution Reaction

Abstract

As a photocatalytic anode material,\nhematite (α-Fe₂O₃) is the most promising\nof the three iron oxides. The\ntwo other oxides are FeO, which is seldom available, and Fe₃O₄, which is found naturally in magnetite. There are both\ntheoretical and experimental methods suggested for enhancing α-Fe₂O₃’s reactivity. First-principles calculations\nled to the design of two different doping concentrations of Al-doped\nα-Fe₂O₃(0001) structures and an Al₂O₃/Fe₂O₃ heterostructure\nin the (0001) plane. A detailed investigation of the state density\nand stability, band structure, local potentials, charge densities,\nand Bader charge analysis is presented in this paper. A reduction\nin energy was observed with the Al-doping of an α-Fe₂O₃(0001) surface slab. The increase in doping concentration\nfavors the formation of doped systems, and Al’s presence in\nα-Fe₂O₃(0001) is an energetically favorable\nprocess. The work function increases by increasing the Al concentration\non the surface compared to a pure α-Fe₂O₃(0001) slab. Based on Bader charge analysis and charge density difference\nstudies, it appears that chemical bonding becomes ionic in Al-doped\nregions. We additionally investigate Al₂O₃/Fe₂O₃ interfaces by using first-principles calculations,\naiming to shed light on their geometric structure and electronic properties.\nAl₂O₃/Fe₂O₃ interfaces\nare more thermodynamically favorable. The results of these studies\nsuggest that the Al₂O₃/Fe₂O₃ heterojunction is a type-III broken-gap heterojunction rather than\na staggered one. Additionally, oxygen evolution reaction (OER) electrocatalysts\nare discussed for Al-doped systems and the interface. As a result,\nthe most favorable rate-limiting step in high-performance electrocatalysts\nrelies on Al atom doping concentration to modulate the electronic\nand structural properties of Al-doped sites, while the concentration\nof active sites is increased and the OER rate is improved. Providing\na basic understanding of the OER process at these interfaces, the\ndiscussion will be useful for exploring and developing better catalysts\nand device units.