Ferroelectric Control of Photoelectrochemical Ammonia Oxidation Reaction

Abstract Photoelectrochemical (PEC) technologies offer a sustainable approach for simultaneously producing clean fuels, such as hydrogen, and value‐added chemicals using renewable solar energy. Achieving high selectivity toward target oxidation reactions in aqueous environments, however, remains a challenge due to the competitive oxygen evolution reaction (OER). The current work demonstrates controllable selectivity tuning by manipulating the ferroelectric polarization state of a BiFeO ₃ /BiVO ₄ (BFO/BVO) heterostructure using ammonia as a model reactant. A suite of experimental techniques, including synchrotron‐based spectroscopy and density functional theory calculations, establishes that ammonia adsorption is significantly enhanced on the poled‐down BFO/BVO surface. This results in high selectivity toward the ammonia oxidation reaction, providing a 90.1% Faradaic efficiency for NO _x ^– products. In contrast, poled up BFO/BVO favors water adsorption, preferentially driving the competing OER. The polarization‐driven selectivity tuning is also applied to formic acid oxidation, showing that the phenomenon is general and effective for other reactions. The selectivity effect originates from the polarization‐dependent surface charge state, which governs electrostatic interactions between, and subsequent adsorption/desorption of, the reactants and products. The findings illustrate the potential of ferroelectric polarization as a powerful lever for controlling adsorption‐driven reaction selectivity in PEC applications and beyond.