Orbital-Morphology-Based Oxygen Reduction in a Correlated Oxide

Orbital degree of freedom plays a crucial role in governing the physical and chemical properties of solid materials, and it is widely investigated in the fields of physics, material science, and chemistry. Typically, orbital-energy-related scenarios, such as d-band center or electron occupancy, have been discussed in the catalytic materials, since they can control the surface-adsorbate bonding strength to modulate the catalytic activity. However, the impact of orbital morphology, that is the "posture" of orbitals on catalysts' surfaces, has never been studied. Here the importance of 3d-orbital morphology on the activity of oxygen reduction reaction (ORR) in a strongly correlated oxide alpha-Ti2O3 is highlighted. Superior ORR performance is observed in alpha-Ti2O3 (Ti3+:3d(1)) than that of the anatase and rutile TiO2 (Ti4+:3d(0)), with higher Faradaic efficiency (87.3%) and H2O2 selectivity (93.2%). More importantly, a novel orbital-morphology-based mechanism is developed and the orbital morphology dominates the catalytic activity by determining the surface-adsorbates d-p orbital hybridization via orbitals' overlap, resulting in a crystal-plane-dependent ORR activity in alpha-Ti2O3. The work reveals the strong interplay between the orbital morphology, d-p hybridization, and ORR activity, which broadens the fundamental understanding of catalysts from a new view of the orbital degree of freedom.