Iron-Based Layered Perovskite Oxyfluoride Electrocatalyst for Oxygen Evolution: Insights from Crystal Facets with Heteroanionic Coordination

Mixed-anion compounds have recently attracted attention as solid-state materials that exhibit properties unattainable with those of their single-anion counterparts. However, the use of mixed-anion compounds to control the morphology and engineer the crystal facets of electrocatalysts has been limited because their synthesis method is still immature. This study explored the electrocatalytic properties of a Pb-Fe oxyfluoride, Pb₃Fe₂O₅F₂, with a layered perovskite structure for oxygen evolution reaction (OER) and compared its properties in detail with those of a bulk-type cubic three-dimensional (3D) perovskite, PbFeO₂F. A Pb₃Fe₂O₅F₂ electrode prepared with carbon nanotubes and a graphite sheet as a conductive support and a substrate, respectively, demonstrated better OER performance than a PbFeO₂F electrode. The role of specific crystal facets of Pb₃Fe₂O₅F₂ in enhancing the OER activity was elucidated through electrochemical analysis. Density functional theory calculations indicated that the Pb₃Fe₂O₅F₂ (060) facet with Fe sites exhibited a lower theoretical overpotential for the OER, which was attributed to a moderately strong interaction between the active sites and the reaction intermediates; this interaction was reinforced by the strong electron-withdrawing behavior of fluoride ions. This finding offers new insights for developing efficient electrocatalysts based on oxyfluorides, leveraging the high electronegativity of fluorine to optimize the electronic states at active sites for the OER, without relying on precious metals.