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

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/m(2), 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/K(2)m 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 similar to 10(5) cm(-1) from visible to ultraviolet.