Two novel easily exfoliated quaternary chalcogenides with high performance of photocatalytic hydrogen production

Based on density functional theory calculations, we have disclosed two novel monolayers Tl2SnAs2Q6 (Q = S, Se) with efficient photocatalytic ability. Both Tl2SnAs2S6 and Tl2SnAs2Se6 monolayers (referred to as TSAS and TSASe) show low cleavage energy comparable to that of graphene, which endorses they can be easily exfoliated from their bulk counterparts. Moderate band gaps are observed in TSAS (2.06 eV) and TSASe (1.81 eV) monolayers and both of their absorption peaks reach the order of 105 cm−1 in visible light region. Remarkably, the results of Gibbs free energy changes show that the hydrogen reaction can proceed efficiently without any extra voltage. Superior carrier mobilities with obvious anisotropy are also observed in TSAS and TSASe (∼103 cm2V-1s-1) monolayers, which are much larger than that of MoS2 (200 cm2V-1s-1). In addition, we also studied the adsorption energy of water molecules H2O and hydrogen atoms H on TSAS(Se) substrates, and the kinetic barriers in the process of hydrogen production, which is helpful to further understand the hydrogen evolution process of water splitting. This work demonstrates two novel easily exfoliated monolayers with significant hydrogen evolution performance, making them promising candidates for novel photocatalysts.