2D Nb 3 SBr 7 and Ta 3 SBr 7 : Experimentally Achievable Janus Photocatalysts with Robust Coexistence of Strong Optical Absorption, Intrinsic Charge Separation, and Ultrahigh Solar-to-Hydrogen Efficiency.

Recently, two-dimensional (2D) Janus semiconductors have attracted great attention in photocatalytic applications owing to their extraordinary properties, especially the intrinsic polarization-induced spontaneous carrier separation, strong optical absorption, and ultrahigh solar-to-hydrogen (STH) efficiency. However, experimental achievable candidates for 2D intrinsic Janus semiconductors are rarely reported. Herein, based on density functional theory (DFT) calculations, we uncovered two new 2D photocatalysts, namely, Janus Nb 3 SBr 7 and Ta 3 SBr 7 bilayers. We revealed that both structures are highly feasible to be obtained from their bulk counterparts. Excitingly, intrinsic charge separations emerge in both structures, which are beneficial to the repression of recombinations of their photoexcited carriers. Optical absorptions of both structures can be activated in the visible and even infrared regions. Most interestingly, Nb 3 SBr 7 and Ta 3 SBr 7 bilayers can exhibit ultrahigh STH efficiencies of 35% and 31%, respectively, which are larger than those of most 2D Janus structures. In addition, we further found that these distinguished photocatalytic properties are rather robust and are independent of their stacking modes. Experimental feasibilities and robust coexistences of intrinsic charge separations, ultrahigh STH efficiencies, and strong absorptions endow Nb 3 SBr 7 and Ta 3 SBr 7 bilayers as hopeful photocatalysts for water splitting.