Symmetry Breaking and Polarization Regulation in AgFeO2‐Based Photocathodes Through Oxygen Defect Engineering.

Polar materials, with intrinsic polarization effects, present significant potential for photo(electro)catalysis. However, the available natural polar materials in this field are quite scarce, due to the requisite structural non‐centrosymmetry. Defect engineering emerges as a promising avenue for tuning material symmetry, yet achieving the transition from centrosymmetric to non‐centrosymmetric structures and optimizing associated polarization effects remains challenging. This study demonstrates symmetry breaking in centrosymmetric 3R‐delafossite AgFeO2 through ordered oxygen defects introduction, yielding substantial macroscopic polarization. The transition is achieved via annealing post‐treatment of co‐precipitation‐hydrothermal AgFeO2 samples, with precision in oxygen defects control by tailoring annealing conditions. Experimental characterizations reveal ordered interstitial oxygen and disordered oxygen vacancies. Density functional theory calculations indicate a higher propensity for the formation of disordered oxygen vacancies compared to ordered ones, while ordered interstitial oxygen is more easily formed than its disordered counterpart. Resultant macroscopic polarization enhances photoelectrochemical performance, with photocurrent density increasing from 0.79 to 2.95 µA cm−2. Coupling macroscopic and spin polarization via external electric and magnetic fields further enhances photocurrent density (≈18.44 µA cm−2). These findings provide reference cases and strategies for applying polarization effects in photo(electro)catalytic technology. [ABSTRACT FROM AUTHOR]