Simultaneous high thermoelectric and photocatalytic performance towards single-layer ZnX2S4 (X = Al, Ga, In)

Abstract

Thermoelectric generation and photocatalytic water splitting to produce hydrogen are key measures to solve energy shortage and environmental pollution. In this work, we proposed three unexplored 2D materials, ZnAl₂S₄, ZnGa₂S₄ and ZnIn₂S₄, and further investigated their stability, thermoelectric and photocatalytic water splitting performance. We revealed the three single-layers possess low cleavage energies of 0.23–0.28 J/m², and simultaneously show high mechanical, thermal and dynamic stability. Besides, the single-layers are indirect semiconductors with band-gaps of 2.62/2.15/1.93 eV, and deliver thermoelectric power factors of 3.03/4.06/5.92 mW/K²m at 300 K. Also, due to the high nonlinear phonon dispersion and strong acoustic-optical interactions, they have high phonon scattering rates, as well as low lattice thermal conductivities of 1.11–3.06 W/mK. As a result, their thermoelectric figure of merit can reach 0.12/0.11/0.10 at 300 K, and increases to 0.77/0.69/0.66 at 700 K. Moreover, they also have suitable REDOX band-edges, which can drive photocatalytic water splitting to produce hydrogen and oxygen, and show high absorption coefficients of ∼ 10⁵ cm⁻¹ from visible to ultraviolet.