Ferroelectric Control of Photoelectrochemical Ammonia Oxidation Reaction

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 BiFeO₃/BiVO₄ (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.