Monolayer SiP2S6: metal-free photocatalyst with spontaneous hydrogen and oxygen evolution half reactions

Abstract

Two-dimensional photocatalysts for water splitting with spontaneous hydrogen and oxygen evolution half reactions are long-desired materials for solving the environmental pollution and energy crisis. To date, several such photocatalysts have been reported, all based on metal-containing materials. Here, we propose a novel metal-free candidate, SiP2S6 monolayer, on the basis of first principles calculations. SiP2S6 monolayer holds a moderate band gap of 2.78 eV and suitable band edge positions for overall water splitting. Also, it harbors excellent optical absorption, even comparable to that of g-C3N4 monolayer. More remarkably, the photocatalytic hydrogen and oxygen evolution half reactions on the surface of SiP2S6 monolayer can occur spontaneously with only solar light irradiation, without needing sacrificial reagents or co-catalysts. This discovery not only reveals the great potential of SiP2S6 monolayer in photocatalytic applications but also broadens the scientific impact of two-dimensional photocatalysts.