Tunable Photocatalytic Water Splitting by the Ferroelectric Switch in a 2D AgBiP₂Se₆ Monolayer

Photocatalytic water splitting is a promising technology to solve the energy crisis and provide renewable and clean energies. Recently, although numerous 2D materials have been proposed as the photocatalytic candidates, the strategies to effectively modulate photocatalytic reactions and conversion efficiency are still lacking. Herein, based on first-principles calculations, we show that the photocatalytic activities and energy conversion efficiency can be well tuned by ferroelectric-paraelectric phase transition of a AgBiP₂Se₆ monolayer. It is found that the AgBiP₂Se₆ monolayer has a higher potential and driving forces of photogenerated holes for water oxidation in the ferroelectric phase, but higher corresponding values of photogenerated electrons for the hydrogen reduction reaction in the paraelectric phase. Besides, the solar-to-hydrogen energy conversion efficiency is also tunable with the phase transition; it is up to 10.04% at the ferroelectric phase due to the better carrier utilization, but only 6.66% at the paraelectric phase. Moreover, the exciton binding energy is always smaller in the paraelectric state than that in the ferroelectric state, indicating that the ferroelectric switch could also make a directional adjustment to the photoexcited carrier separation. Our theoretical investigation not only reveals the importance of ferroelectric polarization on water splitting, but also opens an avenue to modify the photocatalytic properties of 2D ferroelectric materials via a ferroelectric switch.