Identification of Facet‐Governing Reactivity in Hematite for Oxygen Evolution

Unveiling the impact of a single parameter on the catalytic descriptor is fundamental to guide rational design principles for high-activity catalysts. Facets with distinct surface coordination that exhibit a central role in the kinetics modulation (reactivity) of surface electrochemistry, have remained elusive in oxygen evolution reactions (OERs). Here, the relationship between the predominant facets and catalytic reactivity is revealed, and it is recognized that facets decisively govern the oxygen evolution activity descriptor in hematite nanocrystals. Specifically, the hematite shows facet-dependent activity that follows the computed binding energy of surface-oxygenated intermediates. Moreover, a lower kinetics energy barrier is observed on a highly coordinated surface, both experimentally and computationally, in the light of molecular orbital principles. Consequently, a record-low overpotential and Tafel slope in iron oxides toward OER are manifested, competing against the benchmark binary transition metal oxide electrocatalysts and expelling the stereotype of the passive oxygen evolution activity of iron oxides. Significantly, the identification of facet-governing reactivity, construction of favorable facets, and strategic regulation of surface covalency enlighten design strategies for highly active catalysts.